Andromeda Galaxy

Last updated

Andromeda Galaxy
M31 09-01-2011 (cropped).jpg
A visible light image of the Andromeda Galaxy. Messier 32 is to the left of the galactic nucleus and Messier 110 is at the bottom right.
Observation data (J2000 epoch)
Pronunciation /ænˈdrɒmɪdə/
Constellation Andromeda
Right ascension 00h 42m 44.3s [1]
Declination +41° 16′ 9″ [1]
Redshift z = −0.001004 (minus sign indicates blueshift) [1]
Heliocentric radial velocity −301 ± 1 km/s [2]
Distance 765  kpc (2.50  Mly) [3]
Apparent magnitude  (V)3.44 [4] [5]
Absolute magnitude  (V)−21.5 [lower-alpha 1] [6]
Characteristics
Type SA(s)b [1]
Mass (1.5±0.5)×1012 [7]   M☉
Number of stars~1 trillion (1012) [8]
Size46.56  kpc (152,000  ly)
(diameter; D25 isophote) [1] [9] [lower-alpha 2]
Apparent size  (V)3.167° × 1° [1]
Other designations
M31, NGC 224, UGC 454, PGC 2557, 2C 56 (Core), [1] CGCG 535-17, MCG +07-02-016, IRAS 00400+4059, 2MASX J00424433+4116074, GC 116, h 50, Bode 3, Flamsteed 58, Hevelius 32, Ha 3.3, IRC +40013

The Andromeda Galaxy is a barred spiral galaxy and is the nearest major galaxy to the Milky Way. It was originally named the Andromeda Nebula and is cataloged as Messier 31, M31, and NGC 224. Andromeda has a D25 isophotal diameter of about 46.56 kiloparsecs (152,000 light-years ) [9] and is approximately 765 kpc (2.5 million light-years) from Earth. The galaxy's name stems from the area of Earth's sky in which it appears, the constellation of Andromeda, which itself is named after the princess who was the wife of Perseus in Greek mythology. [9]

Contents

The virial mass of the Andromeda Galaxy is of the same order of magnitude as that of the Milky Way, at 1  trillion solar masses (2.0×1042 kilograms ). The mass of either galaxy is difficult to estimate with any accuracy, but it was long thought that the Andromeda Galaxy was more massive than the Milky Way by a margin of some 25% to 50%. [11] This has been called into question by early 21st-century studies indicating a possibly lower mass for the Andromeda Galaxy [11] and a higher mass for the Milky Way. [12] [13] The Andromeda Galaxy has a diameter of about 46.56 kpc (152,000 ly), making it the largest member of the Local Group of galaxies in terms of extension. [13]

The Milky Way and Andromeda galaxies are expected to collide in around 4–5 billion years, [14] merging to potentially form a giant elliptical galaxy [15] or a large lenticular galaxy. [16]

With an apparent magnitude of 3.4, the Andromeda Galaxy is among the brightest of the Messier objects, [17] and is visible to the naked eye from Earth on moonless nights, [18] even when viewed from areas with moderate light pollution. [9]

Observation history

The Andromeda Galaxy is visible to the naked eye in dark skies. Around the year 964 CE, the Persian astronomer Abd al-Rahman al-Sufi was the first to formally describe the Andromeda Galaxy. He referred to it in his Book of Fixed Stars as a "nebulous smear" or "small cloud". [19] [20]

Star charts of that period labeled it as the Little Cloud. [21] In 1612, the German astronomer Simon Marius gave an early description of the Andromeda Galaxy based on telescopic observations. [22] Pierre Louis Maupertuis conjectured in 1745 that the blurry spot was an island universe. [23] In 1764, Charles Messier cataloged Andromeda as object M31 and incorrectly credited Marius as the discoverer despite its being visible to the naked eye. In 1785, the astronomer William Herschel noted a faint reddish hue in the core region of Andromeda. [18] He believed Andromeda to be the nearest of all the "great nebulae", and based on the color and magnitude of the nebula, he incorrectly guessed that it was no more than 2,000 times the distance of Sirius, or roughly 18,000  ly (5.5  kpc ). [24]

In 1850, William Parsons, 3rd Earl of Rosse made the first drawing of Andromeda's spiral structure. [25] [ better source needed ]

In 1864, William Huggins noted that the spectrum of Andromeda differed from that of a gaseous nebula. [26] The spectrum of Andromeda displays a continuum of frequencies, superimposed with dark absorption lines that help identify the chemical composition of an object. Andromeda's spectrum is very similar to the spectra of individual stars, and from this, it was deduced that Andromeda has a stellar nature. In 1885, a supernova (known as S Andromedae) was seen in Andromeda, the first and so far only one observed in that galaxy. [27] At the time it was called "Nova 1885" [28] —the difference between "novae" in the modern sense and supernovae was not yet known. Andromeda was considered to be a nearby object, and it was not realized that the "nova" was much brighter than ordinary novae.[ citation needed ]

The earliest known photograph of the Great Andromeda "Nebula" (with M110 to the upper right), by Isaac Roberts (29 December 1888) Andromeda Nebula - Isaac Roberts, 29 December 1888.jpg
The earliest known photograph of the Great Andromeda "Nebula" (with M110 to the upper right), by Isaac Roberts (29 December 1888)

In 1888, Isaac Roberts took one of the first photographs of Andromeda, which was still commonly thought to be a nebula within our galaxy. Roberts mistook Andromeda and similar "spiral nebulae" as star systems being formed. [29] [30]

In 1912, Vesto Slipher used spectroscopy to measure the radial velocity of Andromeda with respect to the Solar System—the largest velocity yet measured, at 300 km/s (190 mi/s). [31]

"Island universes" hypothesis

Location of the Andromeda Galaxy (M31) in the Andromeda constellation Andromeda constellation map.svg
Location of the Andromeda Galaxy (M31) in the Andromeda constellation

As early as 1755 the German philosopher Immanuel Kant proposed the hypothesis that the Milky Way is only one of many galaxies, in his book Universal Natural History and Theory of the Heavens . Arguing that a structure like the Milky Way would look like a circular nebula viewed from above and like an elliptical if viewed from an angle, he concluded that the observed elliptical nebulae like Andromeda, which could not be explained otherwise at the time, were indeed galaxies similar to the Milky Way, not a nebula, like how Andromeda was commonly thought of. [32]

In 1917, Heber Curtis observed a nova within Andromeda. Searching the photographic record, 11 more novae were discovered. Curtis noticed that these novae were, on average, 10 magnitudes fainter than those that occurred elsewhere in the sky. As a result, he was able to come up with a distance estimate of 500,000 ly (3.2×1010 AU). Although this estimate is about fivefold lower than the best estimates now available, it was the first known estimate of the distance to Andromeda that was correct to the order of magnitude (i.e. which was correct to within a factor of ten of current high-accuracy estimates, which place the distance around 2.5 million light-years [2] [33] [6] [34] ). Curtis became a proponent of the so-called "island universes" hypothesis: that spiral nebulae were actually independent galaxies. [35]

In 1920, the Great Debate between Harlow Shapley and Curtis took place concerning the nature of the Milky Way, spiral nebulae, and the dimensions of the universe. [36] To support his claim of the Great Andromeda Nebula being, in fact, an external galaxy, Curtis also noted the appearance of dark lanes within Andromeda which resembled the dust clouds in our own galaxy, as well as historical observations of Andromeda Galaxy's significant Doppler shift. In 1922 Ernst Öpik presented a method to estimate the distance of Andromeda using the measured velocities of its stars. His result placed the Andromeda Nebula far outside our galaxy at a distance of about 450 kpc (1,500 kly). [27] Edwin Hubble settled the debate in 1925 when he identified extragalactic Cepheid variable stars for the first time on astronomical photos of Andromeda. These were made using the 100-inch (2.5 m) Hooker telescope, and they enabled the distance of the Great Andromeda Nebula to be determined. His measurement demonstrated conclusively that this feature was not a cluster of stars and gas within our own galaxy, but an entirely separate galaxy located a significant distance from the Milky Way. [36]

In 1943, Walter Baade was the first person to resolve stars in the central region of the Andromeda Galaxy. Baade identified two distinct populations of stars based on their metallicity, naming the young, high-velocity stars in the disk Type I and the older, red stars in the bulge Type II. [37] This nomenclature was subsequently adopted for stars within the Milky Way, and elsewhere. (The existence of two distinct populations had been noted earlier by Jan Oort.) [37] Baade also discovered that there were two types of Cepheid variable stars, which resulted in a doubling of the distance estimate to Andromeda, as well as the remainder of the universe. [38]

In 1950, radio emission from the Andromeda Galaxy was detected by Hanbury Brown and Cyril Hazard at Jodrell Bank Observatory. [39] [40] The first radio maps of the galaxy were made in the 1950s by John Baldwin and collaborators at the Cambridge Radio Astronomy Group. [41] The core of the Andromeda Galaxy is called 2C 56 in the 2C radio astronomy catalog. In 2009, an occurrence of microlensing—a phenomenon caused by the deflection of light by a massive object—may have led to the first discovery of a planet in the Andromeda Galaxy. [42]

Observations of linearly polarized radio emission with the Westerbork Synthesis Radio Telescope, the Effelsberg 100-m Radio Telescope, and the Very Large Array revealed ordered magnetic fields aligned along the "10-kpc ring" of gas and star formation. [43]

General

The estimated distance of the Andromeda Galaxy from our own was doubled in 1953 when it was discovered that there is another, dimmer type of Cepheid variable star. In the 1990s, measurements of both standard red giants as well as red clump stars from the Hipparcos satellite measurements were used to calibrate the Cepheid distances. [44] [45]

Formation and history

Processed image of the Andromeda Galaxy, with enhancement of H-alpha to highlight its star-forming regions Andromeda Galaxy 560mm FL.jpg
Processed image of the Andromeda Galaxy, with enhancement of H-alpha to highlight its star-forming regions

A major merger occurred 2 to 3 billion years ago at the Andromeda location, involving two galaxies with a mass ratio of approximately 4. [46] [47]

Discovery of a recent merger in the Andromeda galaxy was firstly based on interpreting its anomalous age-velocity dispersion relation, [48] as well as the fact that 2 billion years ago, star formation throughout Andromeda's disk was much more active than today. [49]

Modeling [46] of this violent collision shows that it has formed most of the galaxy's (metal-rich) galactic halo, including the Giant Stream, [50] and also the extended thick disk, the young age thin disk, including the static 10 kpc ring. During this epoch, its rate of star formation would have been very high, to the point of becoming a luminous infrared galaxy for roughly 100 million years. Modeling also recovers the bulge profile, the large bar, and the overall halo density profile.

Andromeda and the Triangulum Galaxy (M33) might have had a very close passage 2–4 billion years ago, but it seems unlikely from the last measurements from the Hubble Space Telescope. [51]

Distance estimate

Illustration showing both the size of each galaxy and the distance between the two galaxies, to scale Milky Way and Andromeda in space, to scale.jpg
Illustration showing both the size of each galaxy and the distance between the two galaxies, to scale

At least four distinct techniques have been used to estimate distances from Earth to the Andromeda Galaxy. In 2003, using the infrared surface brightness fluctuations (I-SBF) and adjusting for the new period-luminosity value and a metallicity correction of −0.2 mag dex−1 in (O/H), an estimate of 2.57 ± 0.06 million light-years (1.625×1011 ± 3.8×109 astronomical units ) was derived. A 2004 Cepheid variable method estimated the distance to be 2.51 ± 0.13 million light-years (770 ± 40 kpc). [2] [33]

In 2005, an eclipsing binary star was discovered in the Andromeda Galaxy. The binary [lower-alpha 3] is two hot blue stars of types O and B. By studying the eclipses of the stars, astronomers were able to measure their sizes. Knowing the sizes and temperatures of the stars, they were able to measure their absolute magnitude. When the visual and absolute magnitudes are known, the distance to the star can be calculated. The stars lie at a distance of 2.52×10^6 ± 0.14×10^6 ly (1.594×1011 ± 8.9×109 AU) and the whole Andromeda Galaxy at about 2.5×10^6 ly (1.6×1011 AU). [6] This new value is in excellent agreement with the previous, independent Cepheid-based distance value. The TRGB method was also used in 2005 giving a distance of 2.56×10^6 ± 0.08×10^6 ly (1.619×1011 ± 5.1×109 AU). [34] Averaged together, these distance estimates give a value of 2.54×10^6 ± 0.11×10^6 ly (1.606×1011 ± 7.0×109 AU). [lower-alpha 4]

Mass estimates

Giant halo around Andromeda Galaxy Hubble Finds Giant Halo Around the Andromeda Galaxy.jpg
Giant halo around Andromeda Galaxy

Until 2018, mass estimates for the Andromeda Galaxy's halo (including dark matter) gave a value of approximately 1.5×1012  M☉, [53] compared to 8×1011 M☉ for the Milky Way. This contradicted even earlier measurements that seemed to indicate that the Andromeda Galaxy and Milky Way are almost equal in mass. In 2018, the earlier measurements for equality of mass was re-established by radio results as approximately 8×1011 M☉. [54] [55] [56] [57] In 2006, the Andromeda Galaxy's spheroid was determined to have a higher stellar density than that of the Milky Way, [58] and its galactic stellar disk was estimated at twice the diameter of that of the Milky Way. [10] The total mass of the Andromeda Galaxy is estimated to be between 8×1011 M☉ [54] and 1.1×1012 M☉. [59] [60] The stellar mass of M31 is 10–15×1010 M☉, with 30% of that mass in the central bulge, 56% in the disk, and the remaining 14% in the stellar halo. [61] The radio results (similar mass to the Milky Way Galaxy) should be taken as likeliest as of 2018, although clearly, this matter is still under active investigation by several research groups worldwide.

As of 2019, current calculations based on escape velocity and dynamical mass measurements put the Andromeda Galaxy at 0.8×1012 M☉, [62] which is only half of the Milky Way's newer mass, calculated in 2019 at 1.5×1012 M☉. [63] [64] [65]

In addition to stars, the Andromeda Galaxy's interstellar medium contains at least 7.2×109 M☉ [66] in the form of neutral hydrogen, at least 3.4×108 M☉ as molecular hydrogen (within its innermost 10 kiloparsecs), and 5.4×107 M☉ of dust. [67]

The Andromeda Galaxy is surrounded by a massive halo of hot gas that is estimated to contain half the mass of the stars in the galaxy. The nearly invisible halo stretches about a million light-years from its host galaxy, halfway to our Milky Way Galaxy. Simulations of galaxies indicate the halo formed at the same time as the Andromeda Galaxy. The halo is enriched in elements heavier than hydrogen and helium, formed from supernovae, and its properties are those expected for a galaxy that lies in the "green valley" of the Galaxy color–magnitude diagram (see below). Supernovae erupt in the Andromeda Galaxy's star-filled disk and eject these heavier elements into space. Over the Andromeda Galaxy's lifetime, nearly half of the heavy elements made by its stars have been ejected far beyond the galaxy's 200,000-light-year-diameter stellar disk. [68] [69] [70] [71]

Luminosity estimates

Compared to the Milky Way, the Andromeda Galaxy appears to have predominantly older stars with ages >7×109 years. [61] [ clarification needed ] The estimated luminosity of the Andromeda Galaxy, ~2.6×1010  L☉, is about 25% higher than that of our own galaxy. [72] [73] However, the galaxy has a high inclination as seen from Earth, and its interstellar dust absorbs an unknown amount of light, so it is difficult to estimate its actual brightness and other authors have given other values for the luminosity of the Andromeda Galaxy (some authors even propose it is the second-brightest galaxy within a radius of 10 megaparsecs of the Milky Way, after the Sombrero Galaxy, [74] with an absolute magnitude of around −22.21 [lower-alpha 5] or close [75] ).

An estimation done with the help of Spitzer Space Telescope published in 2010 suggests an absolute magnitude (in the blue) of −20.89 (that with a color index of +0.63 translates to an absolute visual magnitude of −21.52, [lower-alpha 1] compared to −20.9 for the Milky Way), and a total luminosity in that wavelength of 3.64×1010 L☉. [76]

The rate of star formation in the Milky Way is much higher, with the Andromeda Galaxy producing only about one solar mass per year compared to 3–5 solar masses for the Milky Way. The rate of novae in the Milky Way is also double that of the Andromeda Galaxy. [77] This suggests that the latter once experienced a great star formation phase, but is now in a relative state of quiescence, whereas the Milky Way is experiencing more active star formation. [72] Should this continue, the luminosity of the Milky Way may eventually overtake that of the Andromeda Galaxy.

According to recent studies, the Andromeda Galaxy lies in what is known in the galaxy color–magnitude diagram as the "green valley", a region populated by galaxies like the Milky Way in transition from the "blue cloud" (galaxies actively forming new stars) to the "red sequence" (galaxies that lack star formation). Star formation activity in green valley galaxies is slowing as they run out of star-forming gas in the interstellar medium. In simulated galaxies with similar properties to the Andromeda Galaxy, star formation is expected to extinguish within about five billion years, even accounting for the expected, short-term increase in the rate of star formation due to the collision between the Andromeda Galaxy and the Milky Way. [78]

Structure

Andromeda Galaxy M31 - Heic1502a 10k.jpg
A panorama of foreground stars and the Andromeda Galaxy's nucleus
A narrated tour of the Andromeda Galaxy, made by NASA's Swift satellite team

Based on its appearance in visible light, the Andromeda Galaxy is classified as an SA(s)b galaxy in the de Vaucouleurs–Sandage extended classification system of spiral galaxies. [1] However, infrared data from the 2MASS survey and the Spitzer Space Telescope showed that Andromeda is actually a barred spiral galaxy, like the Milky Way, with Andromeda's bar major axis oriented 55 degrees anti-clockwise from the disc major axis. [79]

There are various methods used in astronomy in defining the size of a galaxy, and each method can yield different results concerning one another. The most commonly employed is the D25 standard, the isophote where the photometric brightness of a galaxy in the B-band (445 nm wavelength of light, in the blue part of the visible spectrum) reaches 25 mag/arcsec2. [80] The Third Reference Catalogue of Bright Galaxies (RC3) used this standard for Andromeda in 1991, yielding an isophotal diameter of 46.56 kiloparsecs (152,000 light-years) at a distance of 2.5 million light-years. [9] An earlier estimate from 1981 gave a diameter for Andromeda at 54 kiloparsecs (176,000 light-years). [81]

A study in 2005 by the Keck telescopes shows the existence of a tenuous sprinkle of stars, or galactic halo, extending outward from the galaxy. [10] The stars in this halo behave differently from the ones in Andromeda's main galactic disc, where they show rather disorganized orbital motions as opposed to the stars in the main disc having more orderly orbits and uniform velocities of 200 km/s. [10] This diffuse halo extends outwards away from Andromeda's main disc with the diameter of 67.45 kiloparsecs (220,000 light-years). [10]

The galaxy is inclined an estimated 77° relative to Earth (where an angle of 90° would be edge-on). Analysis of the cross-sectional shape of the galaxy appears to demonstrate a pronounced, S-shaped warp, rather than just a flat disk. [82] A possible cause of such a warp could be gravitational interaction with the satellite galaxies near the Andromeda Galaxy. The Galaxy M33 could be responsible for some warp in Andromeda's arms, though more precise distances and radial velocities are required.

Spectroscopic studies have provided detailed measurements of the rotational velocity of the Andromeda Galaxy as a function of radial distance from the core. The rotational velocity has a maximum value of 225 km/s (140 mi/s) at 1,300  ly (82,000,000  AU ) from the core, and it has its minimum possibly as low as 50 km/s (31 mi/s) at 7,000 ly (440,000,000 AU) from the core. Further out, rotational velocity rises out to a radius of 33,000 ly (2.1×109 AU), where it reaches a peak of 250 km/s (160 mi/s). The velocities slowly decline beyond that distance, dropping to around 200 km/s (120 mi/s) at 80,000 ly (5.1×109 AU). These velocity measurements imply a concentrated mass of about 6×109  M☉ in the nucleus. The total mass of the galaxy increases linearly out to 45,000 ly (2.8×109 AU), then more slowly beyond that radius. [83]

The spiral arms of the Andromeda Galaxy are outlined by a series of HII regions, first studied in great detail by Walter Baade and described by him as resembling "beads on a string". His studies show two spiral arms that appear to be tightly wound, although they are more widely spaced than in our galaxy. [84] His descriptions of the spiral structure, as each arm crosses the major axis of the Andromeda Galaxy, are as follows [85] §pp1062 [86] §pp92:

Baade's spiral arms of M31
Arms (N=cross M31's major axis at north, S=cross M31's major axis at south)Distance from center (arcminutes) (N*/S*)Distance from the center (kpc) (N*/S*)Notes
N1/S13.4/1.70.7/0.4Dust arms with no OB associations of HII regions.
N2/S28.0/10.01.7/2.1Dust arms with some OB associations.
N3/S325/305.3/6.3As per N2/S2, but with some HII regions too.
N4/S450/4711/9.9Large numbers of OB associations, HII regions, and little dust.
N5/S570/6615/14As per N4/S4 but much fainter.
N6/S691/9519/20Loose OB associations. No dust is visible.
N7/S7110/11623/24As per N6/S6 but fainter and inconspicuous.
Image of the Andromeda Galaxy taken by Spitzer in infrared, 24 micrometres (Credit: NASA/JPL-Caltech/Karl D. Gordon, University of Arizona) Andromeda galaxy Ssc2005-20a1.jpg
Image of the Andromeda Galaxy taken by Spitzer in infrared, 24 micrometres (Credit: NASA/JPL–Caltech/Karl D. Gordon, University of Arizona)

Since the Andromeda Galaxy is seen close to edge-on, it is difficult to study its spiral structure. Rectified images of the galaxy seem to show a fairly normal spiral galaxy, exhibiting two continuous trailing arms that are separated from each other by a minimum of about 13,000  ly (820,000,000  AU ) and that can be followed outward from a distance of roughly 1,600 ly (100,000,000 AU) from the core. Alternative spiral structures have been proposed such as a single spiral arm [87] or a flocculent [88] pattern of long, filamentary, and thick spiral arms. [1] [89]

The most likely cause of the distortions of the spiral pattern is thought to be interaction with galaxy satellites M32 and M110. [90] This can be seen by the displacement of the neutral hydrogen clouds from the stars. [91]

In 1998, images from the European Space Agency's Infrared Space Observatory demonstrated that the overall form of the Andromeda Galaxy may be transitioning into a ring galaxy. The gas and dust within the galaxy are generally formed into several overlapping rings, with a particularly prominent ring formed at a radius of 32,000 ly (9.8 kpc) from the core, [92] nicknamed by some astronomers the ring of fire. [93] This ring is hidden from visible light images of the galaxy because it is composed primarily of cold dust, and most of the star formation that is taking place in the Andromeda Galaxy is concentrated there. [94]

Later studies with the help of the Spitzer Space Telescope showed how the Andromeda Galaxy's spiral structure in the infrared appears to be composed of two spiral arms that emerge from a central bar and continue beyond the large ring mentioned above. Those arms, however, are not continuous and have a segmented structure. [90]

Close examination of the inner region of the Andromeda Galaxy with the same telescope also showed a smaller dust ring that is believed to have been caused by the interaction with M32 more than 200 million years ago. Simulations show that the smaller galaxy passed through the disk of the Andromeda Galaxy along the latter's polar axis. This collision stripped more than half the mass from the smaller M32 and created the ring structures in Andromeda. [95] It is the co-existence of the long-known large ring-like feature in the gas of Messier 31, together with this newly discovered inner ring-like structure, offset from the barycenter, that suggested a nearly head-on collision with the satellite M32, a milder version of the Cartwheel encounter. [96]

Studies of the extended halo of the Andromeda Galaxy show that it is roughly comparable to that of the Milky Way, with stars in the halo being generally "metal-poor", and increasingly so with greater distance. [58] This evidence indicates that the two galaxies have followed similar evolutionary paths. They are likely to have accreted and assimilated about 100–200 low-mass galaxies during the past 12 billion years. [97] The stars in the extended halos of the Andromeda Galaxy and the Milky Way may extend nearly one-third the distance separating the two galaxies.

Nucleus

Hubble image of the Andromeda Galaxy core showing possible double structure. NASA/ESA photo Double Nucleus of the Andromeda Galaxy (M31).tif
Hubble image of the Andromeda Galaxy core showing possible double structure. NASA/ESA photo

The Andromeda Galaxy is known to harbor a dense and compact star cluster at its very center, similar to our own galaxy. A large telescope creates a visual impression of a star embedded in the more diffuse surrounding bulge. In 1991, the Hubble Space Telescope was used to image the Andromeda Galaxy's inner nucleus. The nucleus consists of two concentrations separated by 1.5  pc (4.9  ly ). The brighter concentration, designated as P1, is offset from the center of the galaxy. The dimmer concentration, P2, falls at the true center of the galaxy and contains a black hole measured at 3–5 × 107M☉ in 1993, [98] and at 1.1–2.3 × 108M☉ in 2005. [99] The velocity dispersion of material around it is measured to be ≈ 160  km/s (100  mi/s ). [100]

It has been proposed that the observed double nucleus could be explained if P1 is the projection of a disk of stars in an eccentric orbit around the central black hole. [101] The eccentricity is such that stars linger at the orbital apocenter, creating a concentration of stars. It has been postulated that such an eccentric disk could have been formed from the result of a previous black hole merger, where the release of gravitational waves could have "kicked" the stars into their current eccentric distribution. [102] P2 also contains a compact disk of hot, spectral-class A stars. The A stars are not evident in redder filters, but in blue and ultraviolet light they dominate the nucleus, causing P2 to appear more prominent than P1. [103]

While at the initial time of its discovery it was hypothesized that the brighter portion of the double nucleus is the remnant of a small galaxy "cannibalized" by the Andromeda Galaxy, [104] this is no longer considered a viable explanation, largely because such a nucleus would have an exceedingly short lifetime due to tidal disruption by the central black hole. While this could be partially resolved if P1 had its own black hole to stabilize it, the distribution of stars in P1 does not suggest that there is a black hole at its center. [101]

Discrete sources

The Andromeda Galaxy in high-energy X-ray and ultraviolet light (released 5 January 2016) PIA20061 - Andromeda in High-Energy X-rays, Figure 1.jpg
The Andromeda Galaxy in high-energy X-ray and ultraviolet light (released 5 January 2016)

Apparently, by late 1968, no X-rays had been detected from the Andromeda Galaxy. [105] A balloon flight on 20 October 1970, set an upper limit for detectable hard X-rays from the Andromeda Galaxy. [106] The Swift BAT all-sky survey successfully detected hard X-rays coming from a region centered 6 arcseconds away from the galaxy center. The emission above 25 keV was later found to be originating from a single source named 3XMM J004232.1+411314, and identified as a binary system where a compact object (a neutron star or a black hole) accretes matter from a star. [107]

Multiple X-ray sources have since been detected in the Andromeda Galaxy, using observations from the European Space Agency's (ESA) XMM-Newton orbiting observatory. Robin Barnard et al. hypothesized that these are candidate black holes or neutron stars, which are heating the incoming gas to millions of kelvins and emitting X-rays. Neutron stars and black holes can be distinguished mainly by measuring their masses. [108] An observation campaign of NuSTAR space mission identified 40 objects of this kind in the galaxy. [109] In 2012, a microquasar, a radio burst emanating from a smaller black hole was detected in the Andromeda Galaxy. The progenitor black hole is located near the galactic center and has about 10 M☉. It was discovered through data collected by the European Space Agency's XMM-Newton probe and was subsequently observed by NASA's Swift Gamma-Ray Burst Mission and Chandra X-Ray Observatory, the Very Large Array, and the Very Long Baseline Array. The microquasar was the first observed within the Andromeda Galaxy and the first outside of the Milky Way Galaxy. [110]

Globular clusters

Star clusters in the Andromeda Galaxy Star cluster in the Andromeda galaxy.jpg
Star clusters in the Andromeda Galaxy

There are approximately 460 globular clusters associated with the Andromeda Galaxy. [112] The most massive of these clusters, identified as Mayall II, nicknamed Globular One, has a greater luminosity than any other known globular cluster in the Local Group of galaxies. [113] It contains several million stars and is about twice as luminous as Omega Centauri, the brightest known globular cluster in the Milky Way. Globular One (or G1) has several stellar populations and a structure too massive for an ordinary globular. As a result, some consider G1 to be the remnant core of a dwarf galaxy that was consumed by Andromeda in the distant past. [114] The globular with the greatest apparent brightness is G76 which is located in the southwest arm's eastern half. [21] Another massive globular cluster, named 037-B327 and discovered in 2006 as is heavily reddened by the Andromeda Galaxy's interstellar dust, was thought to be more massive than G1 and the largest cluster of the Local Group; [115] however, other studies have shown it is actually similar in properties to G1. [116]

Unlike the globular clusters of the Milky Way, which show a relatively low age dispersion, Andromeda Galaxy's globular clusters have a much larger range of ages: from systems as old as the galaxy itself to much younger systems, with ages between a few hundred million years to five billion years. [117]

In 2005, astronomers discovered a completely new type of star cluster in the Andromeda Galaxy. The new-found clusters contain hundreds of thousands of stars, a similar number of stars that can be found in globular clusters. What distinguishes them from the globular clusters is that they are much larger—several hundred light-years across—and hundreds of times less dense. The distances between the stars are, therefore, much greater within the newly discovered extended clusters. [118]

The most massive globular cluster in the Andromeda Galaxy, B023-G078, likely has a central intermediate black hole of almost 100,000 solar masses. [119]

PA-99-N2 event and possible exoplanet in galaxy

PA-99-N2 was a microlensing event detected in the Andromeda Galaxy in 1999. One of the explanations for this is the gravitational lensing of a red giant by a star with a mass between 0.02 and 3.6 times that of the Sun, which suggested that the star is likely orbited by a planet. This possible exoplanet would have a mass 6.34 times that of Jupiter. If finally confirmed, it would be the first ever found extragalactic planet. However, anomalies in the event were later found. [120]

Nearby and satellite galaxies

The Andromeda Galaxy with satellite galaxies M32 (center left above the galactic nucleus) and M110 (center right below the galaxy) M31, the Andromeda Galaxy, Killarney Provincial Park Observatory.jpg
The Andromeda Galaxy with satellite galaxies M32 (center left above the galactic nucleus) and M110 (center right below the galaxy)

Like the Milky Way, the Andromeda Galaxy has smaller satellite galaxies, consisting of over 20 known dwarf galaxies. The Andromeda Galaxy's dwarf galaxy population is very similar to the Milky Way's, but the galaxies are much more numerous. [121] The best-known and most readily observed satellite galaxies are M32 and M110. Based on current evidence, it appears that M32 underwent a close encounter with the Andromeda Galaxy in the past. M32 may once have been a larger galaxy that had its stellar disk removed by M31 and underwent a sharp increase of star formation in the core region, which lasted until the relatively recent past. [122]

M110 also appears to be interacting with the Andromeda Galaxy, and astronomers have found in the halo of the latter a stream of metal-rich stars that appear to have been stripped from these satellite galaxies. [123] M110 does contain a dusty lane, which may indicate recent or ongoing star formation. [124] M32 has a young stellar population as well. [125]

The Triangulum Galaxy is a non-dwarf galaxy that lies 750,000 light years from Andromeda. It is currently unknown whether it is a satellite of Andromeda. [126]

In 2006, it was discovered that nine of the satellite galaxies lie in a plane that intersects the core of the Andromeda Galaxy; they are not randomly arranged as would be expected from independent interactions. This may indicate a common tidal origin for the satellites. [127]

Collision with the Milky Way

Illustration of the collision path between the Milky Way and Andromeda galaxy Collision paths of our Milky Way galaxy and the Andromeda galaxy.jpg
Illustration of the collision path between the Milky Way and Andromeda galaxy

The Andromeda Galaxy is approaching the Milky Way at about 110 kilometres (68 miles) per second. [128] It has been measured approaching relative to the Sun at around 300 km/s (190 mi/s) [1] as the Sun orbits around the center of the galaxy at a speed of approximately 225 km/s (140 mi/s). This makes the Andromeda Galaxy one of about 100 observable blueshifted galaxies. [129] Andromeda Galaxy's tangential or sideways velocity concerning the Milky Way is relatively much smaller than the approaching velocity and therefore it is expected to collide directly with the Milky Way in about 2.5–4 billion years. A likely outcome of the collision is that the galaxies will merge to form a giant elliptical galaxy [130] or possibly large disc galaxy. [16] Such events are frequent among the galaxies in galaxy groups. The fate of Earth and the Solar System in the event of a collision is currently unknown. Before the galaxies merge, there is a small chance that the Solar System could be ejected from the Milky Way or join the Andromeda Galaxy. [131]

Amateur observation

Superimposing picture showing sizes of the Moon and the Andromeda Galaxy as observed from Earth. Because the galaxy is not very bright from an amateur's point of view, its size is not evident. Moon over Andromeda (rotated).jpg
Superimposing picture showing sizes of the Moon and the Andromeda Galaxy as observed from Earth. Because the galaxy is not very bright from an amateur's point of view, its size is not evident.

Under most viewing conditions, the Andromeda Galaxy is one of the most distant objects that can be seen with the naked eye (M33 and M81 can be seen under very dark skies), due to its sheer size. [134] [135] [136] [137] The galaxy is commonly located in the sky about the constellations Cassiopeia and Pegasus. Andromeda is best seen during autumn nights in the Northern Hemisphere when it passes high overhead, reaching its highest point around midnight in October, and two hours earlier each successive month. In the early evening, it rises in the east in September and sets in the west in February. [138] From the Southern Hemisphere the Andromeda Galaxy is visible between October and December, best viewed from as far north as possible. Binoculars can reveal some larger structures of the galaxy and its two brightest satellite galaxies, M32 and M110. [139] An amateur telescope can reveal Andromeda's disk, some of its brightest globular clusters, dark dust lanes, and the large star cloud NGC 206. [140] [141]

See also

Notes

  1. 1 2 Blue absolute magnitude of −20.89 – Color index of 0.63 = −21.52
  2. ↑ This is the diameter as measured through the D25 standard. The halo extends up to a distance of 67.45 kiloparsecs (220×103 ly). [10]
  3. ↑ J00443799+4129236 is at celestial coordinates R.A. 00h 44m 37.99s, Dec. +41° 29′ 23.6″.
  4. ↑ average(787 ± 18, 770 ± 40, 772 ± 44, 783 ± 25) = ((787 + 770 + 772 + 783) / 4) ± (182 + 402 + 442 + 252)0.5 / 2 = 778 ± 33.
  5. ↑ Blue absolute magnitude of −21.58 (see reference) – Color index of 0.63 = absolute visual magnitude of −22.21

Related Research Articles

<span class="mw-page-title-main">Galaxy</span> Large gravitationally bound system of stars and interstellar matter

A galaxy is a system of stars, stellar remnants, interstellar gas, dust, and dark matter bound together by gravity. The word is derived from the Greek galaxias (γαλαξίας), literally 'milky', a reference to the Milky Way galaxy that contains the Solar System. Galaxies, averaging an estimated 100 million stars, range in size from dwarfs with less than a thousand stars, to the largest galaxies known – supergiants with one hundred trillion stars, each orbiting its galaxy's center of mass. Most of the mass in a typical galaxy is in the form of dark matter, with only a few percent of that mass visible in the form of stars and nebulae. Supermassive black holes are a common feature at the centres of galaxies.

<span class="mw-page-title-main">Globular cluster</span> Spherical collection of stars

A globular cluster is a spheroidal conglomeration of stars that is bound together by gravity, with a higher concentration of stars towards their centers. They can contain anywhere from tens of thousands to many millions of member stars, all orbiting in a stable, compact formation. Globular clusters are similar in form to dwarf spheroidal galaxies, and the distinction between the two is not always clear. Their name is derived from Latin globulus. Globular clusters are occasionally known simply as "globulars".

<span class="mw-page-title-main">Local Group</span> Group of galaxies that includes the Milky Way

The Local Group is the galaxy group that includes the Milky Way, where Earth is located. It has a total diameter of roughly 3 megaparsecs (10 million light-years; 9×1019 kilometres), and a total mass of the order of 2×1012 solar masses (4×1042 kg). It consists of two collections of galaxies in a "dumbbell" shape; the Milky Way and its satellites form one lobe, and the Andromeda Galaxy and its satellites constitute the other. The two collections are separated by about 800 kiloparsecs (3×10^6 ly; 2×1019 km) and are moving toward one another with a velocity of 123 km/s. The group itself is a part of the larger Virgo Supercluster, which may be a part of the Laniakea Supercluster. The exact number of galaxies in the Local Group is unknown as some are occluded by the Milky Way; however, at least 80 members are known, most of which are dwarf galaxies.

<span class="mw-page-title-main">Star cluster</span> Group of stars

Star clusters are large groups of stars held together by self-gravitation. Two main types of star clusters can be distinguished: globular clusters are tight groups of ten thousand to millions of old stars which are gravitationally bound, while open clusters are more loosely clustered groups of stars, generally containing fewer than a few hundred members, and are often very young. Open clusters become disrupted over time by the gravitational influence of giant molecular clouds as they move through the galaxy, but cluster members will continue to move in broadly the same direction through space even though they are no longer gravitationally bound; they are then known as a stellar association, sometimes also referred to as a moving group.

<span class="mw-page-title-main">Triangulum Galaxy</span> Spiral galaxy in the constellation Triangulum

The Triangulum Galaxy is a spiral galaxy 2.73 million light-years (ly) from Earth in the constellation Triangulum. It is catalogued as Messier 33 or NGC (New General Catalogue) 598. With the D25 isophotal diameter of 18.74 kiloparsecs (61,100 light-years), the Triangulum Galaxy is the third-largest member of the Local Group of galaxies, behind the Andromeda Galaxy and the Milky Way.

<span class="mw-page-title-main">Spiral galaxy</span> Class of galaxy that has spiral structures extending from their cores.

Spiral galaxies form a class of galaxy originally described by Edwin Hubble in his 1936 work The Realm of the Nebulae and, as such, form part of the Hubble sequence. Most spiral galaxies consist of a flat, rotating disk containing stars, gas and dust, and a central concentration of stars known as the bulge. These are often surrounded by a much fainter halo of stars, many of which reside in globular clusters.

<span class="mw-page-title-main">Messier 87</span> Elliptical galaxy in the Virgo Galaxy Cluster

Messier 87 is a supergiant elliptical galaxy in the constellation Virgo that contains several trillion stars. One of the largest and most massive galaxies in the local universe, it has a large population of globular clusters—about 15,000 compared with the 150–200 orbiting the Milky Way—and a jet of energetic plasma that originates at the core and extends at least 1,500 parsecs, traveling at a relativistic speed. It is one of the brightest radio sources in the sky and a popular target for both amateur and professional astronomers.

<span class="mw-page-title-main">RR Lyrae variable</span> Type of variable star

RR Lyrae variables are periodic variable stars, commonly found in globular clusters. They are used as standard candles to measure (extra) galactic distances, assisting with the cosmic distance ladder. This class is named after the prototype and brightest example, RR Lyrae.

<span class="mw-page-title-main">Sombrero Galaxy</span> Galaxy in the constellation Virgo

The Sombrero Galaxy is a peculiar galaxy of unclear classification in the constellation borders of Virgo and Corvus, being about 9.55 megaparsecs from the Milky Way galaxy. It is a member of the Virgo II Groups, a series of galaxies and galaxy clusters strung out from the southern edge of the Virgo Supercluster. It has an isophotal diameter of approximately 29.09 to 32.32 kiloparsecs, making it slightly bigger in size than the Milky Way.

<span class="mw-page-title-main">Messier 32</span> Dwarf elliptical galaxy in the constellation Andromeda

Messier 32 is a dwarf "early-type" galaxy about 2,650,000 light-years (810,000 pc) from the Solar System, appearing in the constellation Andromeda. M32 is a satellite galaxy of the Andromeda Galaxy (M31) and was discovered by Guillaume Le Gentil in 1749.

<span class="mw-page-title-main">Dwarf galaxy</span> Small galaxy composed of up to several billion stars

A dwarf galaxy is a small galaxy composed of about 1000 up to several billion stars, as compared to the Milky Way's 200–400 billion stars. The Large Magellanic Cloud, which closely orbits the Milky Way and contains over 30 billion stars, is sometimes classified as a dwarf galaxy; others consider it a full-fledged galaxy. Dwarf galaxies' formation and activity are thought to be heavily influenced by interactions with larger galaxies. Astronomers identify numerous types of dwarf galaxies, based on their shape and composition.

<span class="mw-page-title-main">Dwarf spheroidal galaxy</span> Small, low-luminosity galaxy with an old stellar population and little dust

A dwarf spheroidal galaxy (dSph) is a term in astronomy applied to small, low-luminosity galaxies with very little dust and an older stellar population. They are found in the Local Group as companions to the Milky Way and as systems that are companions to the Andromeda Galaxy (M31). While similar to dwarf elliptical galaxies in appearance and properties such as little to no gas or dust or recent star formation, they are approximately spheroidal in shape and generally have lower luminosity.

<span class="mw-page-title-main">NGC 2419</span> Globular cluster in the constellation Lynx

NGC 2419 is a globular cluster in the constellation Lynx. It was discovered by William Herschel on December 31, 1788. NGC 2419 is at a distance of about 300,000 light years from the Solar System and at the same distance from the Galactic Center.

<span class="mw-page-title-main">Andromeda I</span> Dwarf galaxy in the constellation Andromeda

Andromeda I is a dwarf spheroidal galaxy (dSph) about 2.40 million light-years away in the constellation Andromeda. Andromeda I is part of the local group of galaxies and a satellite galaxy of the Andromeda Galaxy (M31). It is roughly 3.5 degrees south and slightly east of M31. As of 2005, it is the closest known dSph companion to M31 at an estimated projected distance of ~40 kpc or ~150,000 light-years.

<span class="mw-page-title-main">Milky Way</span> Galaxy containing the Solar System

The Milky Way is the galaxy that includes the Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye. The term Milky Way is a translation of the Latin via lactea, from the Greek γαλαξίας κύκλος, meaning "milky circle". From Earth, the Milky Way appears as a band because its disk-shaped structure is viewed from within. Galileo Galilei first resolved the band of light into individual stars with his telescope in 1610. Until the early 1920s, most astronomers thought that the Milky Way contained all the stars in the Universe. Following the 1920 Great Debate between the astronomers Harlow Shapley and Heber Doust Curtis, observations by Edwin Hubble showed that the Milky Way is just one of many galaxies.

Andromeda III is a dwarf spheroidal galaxy about 2.44 million light-years away in the constellation Andromeda. It is part of the Local Group and is a satellite galaxy of the Andromeda Galaxy (M31). The galaxy was discovered by Sidney van den Bergh on photographic plates taken in 1970 and 1971.

A super star cluster (SSC) is a very massive young open cluster that is thought to be the precursor of a globular cluster. These clusters called "super" because they are relatively more luminous and contain more mass than other young star clusters. The SSC, however, does not have to physically be larger than other clusters of lower mass and luminosity. They typically contain a very large number of young, massive stars that ionize a surrounding HII region or a so-called "Ultra dense HII region (UDHII)" in the Milky Way Galaxy or in other galaxies. An SSC's HII region is in turn surrounded by a cocoon of dust. In many cases, the stars and the HII regions will be invisible to observations in certain wavelengths of light, such as the visible spectrum, due to high levels of extinction. As a result, the youngest SSCs are best observed and photographed in radio and infrared. SSCs, such as Westerlund 1 (Wd1), have been found in the Milky Way Galaxy. However, most have been observed in farther regions of the universe. In the galaxy M82 alone, 197 young SSCs have been observed and identified using the Hubble Space Telescope.

<span class="mw-page-title-main">Andromeda–Milky Way collision</span> Predicted galactic collision

The Andromeda–Milky Way collision is a galactic collision predicted to occur in about 4.5 billion years between the two largest galaxies in the Local Group—the Milky Way and the Andromeda Galaxy. The stars involved are sufficiently far apart that it is improbable that any of them will individually collide, though some stars will be ejected.

<span class="mw-page-title-main">Maffei 1</span> Galaxy in the constellation Cassiopeia

Maffei 1 is a massive elliptical galaxy in the constellation Cassiopeia. Once believed to be a member of the Local Group of galaxies, it is now known to belong to a separate group, the IC 342/Maffei Group. It was named after Paolo Maffei, who discovered it and the neighboring Maffei 2 in 1967 via their infrared emissions.

<span class="mw-page-title-main">Gaia Sausage</span> Remains galaxy merger in the Milky Way

The Gaia Sausage or Gaia Enceladus is the remains of a dwarf galaxy that merged with the Milky Way about 8–11 billion years ago. At least eight globular clusters were added to the Milky Way along with 50 billion solar masses of stars, gas and dark matter. It represents the last major merger of the Milky Way.

References

  1. 1 2 3 4 5 6 7 8 9 10 "Results for Messier 31". NASA/IPAC Extragalactic Database. NASA/IPAC . Retrieved 28 February 2019.
  2. 1 2 3 Karachentsev, Igor D.; Kashibadze, Olga G. (2006). "Masses of the Local Group and of the M81 group estimated from distortions in the local velocity field". Astrophysics . 49 (1): 3–18. Bibcode:2006Ap.....49....3K. doi:10.1007/s10511-006-0002-6. S2CID   120973010.
  3. ↑ Riess, Adam G.; Fliri, Jürgen; Valls-Gabaud, David (2012). "Cepheid Period-Luminosity Relations in the Near-Infrared and the Distance to M31 from Thehubble Space Telescopewide Field Camera 3". The Astrophysical Journal. 745 (2): 156. arXiv: 1110.3769 . Bibcode:2012ApJ...745..156R. doi:10.1088/0004-637X/745/2/156. S2CID   119113794.
  4. ↑ "M 31" . Retrieved 30 September 2018.
  5. ↑ Gil de Paz, Armando; Boissier, Samuel; Madore, Barry F.; et al. (2007). "The GALEX Ultraviolet Atlas of Nearby Galaxies". Astrophysical Journal . 173 (2): 185–255. arXiv: astro-ph/0606440 . Bibcode:2007ApJS..173..185G. doi:10.1086/516636. S2CID   119085482.
  6. 1 2 3 Ribas, Ignasi; Jordi, Carme; Vilardell, Francesc; et al. (2005). "First Determination of the Distance and Fundamental Properties of an Eclipsing Binary in the Andromeda Galaxy". Astrophysical Journal Letters . 635 (1): L37–L40. arXiv: astro-ph/0511045 . Bibcode:2005ApJ...635L..37R. doi:10.1086/499161. S2CID   119522151.
  7. ↑ "The median values of the Milky Way and Andromeda masses are MG = 0.8+0.4
    −0.3    ×1012 M☉     and MA = 1.5+0.5
    −0.4    ×1012 M☉     at a 68% level" Peñarrubia, Jorge; Ma, Yin-Zhe; Walker, Matthew G.; McConnachie, Alan W. (29 July 2014). "A dynamical model of the local cosmic expansion". Monthly Notices of the Royal Astronomical Society. 433 (3): 2204–2222. arXiv: 1405.0306 . Bibcode:2014MNRAS.443.2204P. doi:10.1093/mnras/stu879. S2CID   119295582., but compare "[we estimate] the virial mass and radius of the galaxy to be 0.8×1012 ± 0.1×1012  M☉ (1.59×1042 ± 2.0×1041  kg)" Kafle, Prajwal R.; Sharma, Sanjib; Lewis, Geraint F.; et al. (1 February 2018). "The Need for Speed: Escape velocity and dynamical mass measurements of the Andromeda Galaxy". Monthly Notices of the Royal Astronomical Society. 475 (3): 4043–4054. arXiv: 1801.03949 . Bibcode:2018MNRAS.475.4043K. doi:10.1093/mnras/sty082. ISSN   0035-8711. S2CID   54039546.
  8. ↑ Young, Kelly (6 June 2006). "The Andromeda galaxy hosts a trillion stars". New Scientist . Retrieved 6 October 2014.
  9. 1 2 3 4 5 De Vaucouleurs, Gerard; De Vaucouleurs, Antoinette; Corwin, Herold G.; Buta, Ronald J.; Paturel, Georges; Fouque, Pascal (1991). Third Reference Catalogue of Bright Galaxies. Bibcode:1991rc3..book.....D.
  10. 1 2 3 4 5 Chapman, Scott C.; Ibata, Rodrigo A.; Lewis, Geraint F.; et al. (2006). "A kinematically selected, metal-poor spheroid in the outskirts of M31". Astrophysical Journal . 653 (1): 255–266. arXiv: astro-ph/0602604 . Bibcode:2006ApJ...653..255C. doi:10.1086/508599. S2CID   14774482. Also see the press release, "Andromeda's Stellar Halo Shows Galaxy's Origin to Be Similar to That of Milky Way" (Press release). Caltech Media Relations. 27 February 2006. Archived from the original on 9 May 2006. Retrieved 24 May 2006.
  11. 1 2 Kafle, Prajwal R.; Sharma, Sanjib; Lewis, Geraint F.; et al. (1 February 2018). "The Need for Speed: Escape velocity and dynamical mass measurements of the Andromeda Galaxy". Monthly Notices of the Royal Astronomical Society. 475 (3): 4043–4054. arXiv: 1801.03949 . Bibcode:2018MNRAS.475.4043K. doi:10.1093/mnras/sty082. ISSN   0035-8711. S2CID   54039546.
  12. ↑ López-Corredoira, M.; Prieto, C. Allende; Garzón, F.; Wang, H.; Liu, C.; Deng, L. (1 April 2018). "Disk stars in the Milky Way detected beyond 25 kpc from its center". Astronomy & Astrophysics. 612: L8. arXiv: 1804.03064 . Bibcode:2018A&A...612L...8L. doi:10.1051/0004-6361/201832880 – via www.aanda.org.
  13. 1 2 "Milky Way tips the scales at 1.5 trillion solar masses" (11 March 2019). AstronomyNow.com. Retrieved 13 July 2019.
  14. ↑ Schiavi, Riccardo; Capuzzo-Dolcetta, Roberto; Arca-Sedda, Manuel; Spera, Mario (October 2020). "Future merger of the Milky Way with the Andromeda galaxy and the fate of their supermassive black holes". Astronomy & Astrophysics. 642: A30. arXiv: 2102.10938 . Bibcode:2020A&A...642A..30S. doi:10.1051/0004-6361/202038674. S2CID   224991193.
  15. ↑ "NASA's Hubble Shows Milky Way is Destined for Head-On Collision". NASA. 31 May 2012. Archived from the original on 4 June 2014. Retrieved 12 July 2012.
  16. 1 2 Ueda, Junko; Iono, Daisuke; Yun, Min S.; et al. (2014). "Cold molecular gas in merger remnants. I. Formation of molecular gas disks". The Astrophysical Journal Supplement Series. 214 (1): 1. arXiv: 1407.6873 . Bibcode:2014ApJS..214....1U. doi:10.1088/0067-0049/214/1/1. S2CID   716993.
  17. ↑ Frommert, Hartmut; Kronberg, Christine (22 August 2007). "Messier Object Data, sorted by Apparent Visual Magnitude". SEDS. Archived from the original on 12 July 2007. Retrieved 27 August 2007.
  18. 1 2 "M 31, M 32 & M 110". 15 October 2016.
  19. ↑ Hafez, Ihsan (2010). Abd al-Rahman al-Sufi and his book of the fixed stars: a journey of re-discovery (PhD Thesis). James Cook University. Bibcode:2010PhDT.......295H . Retrieved 23 June 2016.
  20. ↑ "The Andromeda Galaxy (M31): Location, Characteristics & Images". Space.com . 10 January 2018.
  21. 1 2 Kepple, George Robert; Sanner, Glen W. (1998). The Night Sky Observer's Guide. Vol. 1. Willmann-Bell. p. 18. ISBN   978-0-943396-58-3.
  22. ↑ Davidson, Norman (1985). Astronomy and the imagination: a new approach to man's experience of the stars. Routledge Kegan & Paul. p. 203. ISBN   978-0-7102-0371-7.
  23. ↑ Kant, Immanuel, Universal Natural History and Theory of the Heavens (1755)
  24. ↑ Herschel, William (1785). "On the Construction of the Heavens". Philosophical Transactions of the Royal Society of London . 75: 213–266. doi:10.1098/rstl.1785.0012. S2CID   186213203.
  25. ↑ Payne-Gaposchkin, Cecilia H. (1953). "Why Do Galaxies Have a Spiral Form?". Scientific American. 189 (3): 89–99. Bibcode:1953SciAm.189c..89P. doi:10.1038/scientificamerican0953-89. JSTOR   24944338 – via JSTOR.
  26. ↑ Huggins, William (1864). "On the Spectra of Some of the Nebulae". Philosophical Transactions of the Royal Society of London . 154: 437–444. Bibcode:1864RSPT..154..437H. doi: 10.1098/rstl.1864.0013 .
  27. 1 2 Öpik, Ernst (1922). "An estimate of the distance of the Andromeda Nebula". Astrophysical Journal . 55: 406–410. Bibcode:1922ApJ....55..406O. doi:10.1086/142680.
  28. ↑ Backhouse, Thomas W. (1888). "Nebula in Andromeda and Nova, 1885". Monthly Notices of the Royal Astronomical Society . 48 (3): 108–110. Bibcode:1888MNRAS..48..108B. doi: 10.1093/mnras/48.3.108 .
  29. ↑ Roberts, I. (1888). "photographs of the nebulæ M 31, h 44, and h 51 Andromedæ, and M 27 Vulpeculæ". Monthly Notices of the Royal Astronomical Society. 49 (2): 65–66. Bibcode:1888MNRAS..49...65R. doi: 10.1093/mnras/49.2.65 .
  30. ↑ LIBRARY, ROYAL ASTRONOMICAL SOCIETY/SCIENCE PHOTO. "Andromeda Galaxy, 19th century – Stock Image – C014/5148". Science Photo Library.
  31. ↑ Slipher, Vesto M. (1913). "The Radial Velocity of the Andromeda Nebula". Lowell Observatory Bulletin . 1 (8): 56–57. Bibcode:1913LowOB...2...56S.
  32. ↑ "Seite:Allgemeine Naturgeschichte und Theorie des Himmels.djvu/41 – Wikisource". de.wikisource.org (in German).
  33. 1 2 Karachentsev, Igor D.; Karachentseva, Valentina E.; Huchtmeier, Walter K.; Makarov, Dmitry I. (2004). "A Catalog of Neighboring Galaxies". Astronomical Journal . 127 (4): 2031–2068. Bibcode:2004AJ....127.2031K. doi: 10.1086/382905 .
  34. 1 2 McConnachie, Alan W.; Irwin, Michael J.; Ferguson, Annette M. N.; et al. (2005). "Distances and metallicities for 17 Local Group galaxies". Monthly Notices of the Royal Astronomical Society . 356 (4): 979–997. arXiv: astro-ph/0410489 . Bibcode:2005MNRAS.356..979M. doi:10.1111/j.1365-2966.2004.08514.x.
  35. ↑ Curtis, Heber Doust (1988). "Novae in Spiral Nebulae and the Island Universe Theory". Publications of the Astronomical Society of the Pacific . 100: 6. Bibcode:1988PASP..100....6C. doi: 10.1086/132128 .
  36. 1 2 Hubble, Edwin P. (1929). "A spiral nebula as a stellar system, Messier 31". Astrophysical Journal . 69: 103–158. Bibcode:1929ApJ....69..103H. doi: 10.1086/143167 .
  37. 1 2 Baade, Walter (1944). "The Resolution of Messier 32, NGC 205, and the Central Region of the Andromeda Nebula". Astrophysical Journal . 100: 137. Bibcode:1944ApJ...100..137B. doi: 10.1086/144650 .
  38. ↑ Gribbin, John R. (2001). The Birth of Time: How Astronomers Measure the Age of the Universe. Yale University Press. p. 151. ISBN   978-0-300-08914-1.
  39. ↑ Brown, Robert Hanbury; Hazard, Cyril (1950). "Radio-frequency Radiation from the Great Nebula in Andromeda (M.31)". Nature . 166 (4230): 901–902. Bibcode:1950Natur.166..901B. doi:10.1038/166901a0. S2CID   4170236.
  40. ↑ Brown, Robert Hanbury; Hazard, Cyril (1951). "Radio emission from the Andromeda nebula". MNRAS . 111 (4): 357–367. Bibcode:1951MNRAS.111..357B. doi: 10.1093/mnras/111.4.357 .
  41. ↑ van der Kruit, Piet C.; Allen, Ronald J. (1976). "The Radio Continuum Morphology of Spiral Galaxies". Annual Review of Astronomy and Astrophysics . 14 (1): 417–445. Bibcode:1976ARA&A..14..417V. doi:10.1146/annurev.aa.14.090176.002221.
  42. ↑ Ingrosso, Gabriele; Calchi Novati, Sebastiano; De Paolis, Francesco; et al. (2009). "Pixel-lensing as a way to detect extrasolar planets in M31". Monthly Notices of the Royal Astronomical Society . 399 (1): 219–228. arXiv: 0906.1050 . Bibcode:2009MNRAS.399..219I. doi:10.1111/j.1365-2966.2009.15184.x. S2CID   6606414.
  43. ↑ Beck, Rainer; Berkhuijsen, Elly M.; Giessuebel, Rene; et al. (2020). "Magnetic fields and cosmic rays in M 31". Astronomy & Astrophysics . 633: A5. arXiv: 1910.09634 . Bibcode:2020A&A...633A...5B. doi:10.1051/0004-6361/201936481. S2CID   204824172.
  44. ↑ Holland, Stephen (1998). "The Distance to the M31 Globular Cluster System". Astronomical Journal . 115 (5): 1916–1920. arXiv: astro-ph/9802088 . Bibcode:1998AJ....115.1916H. doi:10.1086/300348. S2CID   16333316.
  45. ↑ Stanek, Krzysztof Z.; Garnavich, Peter M. (1998). "Distance to M31 With the HST and Hipparcos Red Clump Stars". Astrophysical Journal Letters . 503 (2): 131–141. arXiv: astro-ph/9802121 . Bibcode:1998ApJ...503L.131S. doi:10.1086/311539. S2CID   6383832.
  46. 1 2 Hammer, F; Yang, Y B; Wang, J L; Ibata, R; Flores, H; Puech, M (1 April 2018). "A 2–3 billion year old major merger paradigm for the Andromeda galaxy and its outskirts". Monthly Notices of the Royal Astronomical Society. 475 (2): 2754–2767. arXiv: 1801.04279 . doi:10.1093/mnras/stx3343.
  47. ↑ D’Souza, Richard; Bell, Eric F. (September 2018). "The Andromeda galaxy's most important merger about 2 billion years ago as M32's likely progenitor". Nature Astronomy. 2 (9): 737–743. arXiv: 1807.08819 . Bibcode:2018NatAs...2..737D. doi:10.1038/s41550-018-0533-x. ISSN   2397-3366. S2CID   256713163.
  48. ↑ Dorman, Claire E.; Guhathakurta, Puragra; Seth, Anil C.; Weisz, Daniel R.; Bell, Eric F.; Dalcanton, Julianne J.; Gilbert, Karoline M.; Hamren, Katherine M.; Lewis, Alexia R.; Skillman, Evan D.; Toloba, Elisa; Williams, Benjamin F. (9 April 2015). "A CLEAR AGE–VELOCITY DISPERSION CORRELATION IN ANDROMEDA'S STELLAR DISK". The Astrophysical Journal. 803 (1): 24. arXiv: 1502.03820 . Bibcode:2015ApJ...803...24D. doi:10.1088/0004-637X/803/1/24. S2CID   119223754.
  49. ↑ Williams, Benjamin F.; Dalcanton, Julianne J.; Dolphin, Andrew E.; Weisz, Daniel R.; Lewis, Alexia R.; Lang, Dustin; Bell, Eric F.; Boyer, Martha; Fouesneau, Morgan; Gilbert, Karoline M.; Monachesi, Antonela; Skillman, Evan (5 June 2015). "A GLOBAL STAR-FORMING EPISODE IN M31 2–4 GYR AGO". The Astrophysical Journal. 806 (1): 48. arXiv: 1504.02120 . Bibcode:2015ApJ...806...48W. doi:10.1088/0004-637X/806/1/48. S2CID   118435748.
  50. ↑ Ibata, Rodrigo; Irwin, Michael; Lewis, Geraint; Ferguson, Annette M. N.; Tanvir, Nial (July 2001). "A giant stream of metal-rich stars in the halo of the galaxy M31". Nature. 412 (6842): 49–52. arXiv: astro-ph/0107090 . Bibcode:2001Natur.412...49I. doi:10.1038/35083506. PMID   11452300. S2CID   4413139.
  51. ↑ Patel, Ekta; Besla, Gurtina; Sohn, Sangmo Tony (1 February 2017). "Orbits of massive satellite galaxies – I. A close look at the Large Magellanic Cloud and a new orbital history for M33". Monthly Notices of the Royal Astronomical Society. 464 (4): 3825–3849. doi:10.1093/mnras/stw2616. hdl: 10150/623269 .
  52. ↑ "Hubble Finds Giant Halo Around the Andromeda Galaxy" . Retrieved 14 June 2015.
  53. ↑ Peñarrubia, Jorge; Ma, Yin-Zhe; Walker, Matthew G.; McConnachie, Alan W. (29 July 2014). "A dynamical model of the local cosmic expansion". Monthly Notices of the Royal Astronomical Society. 433 (3): 2204–2222. arXiv: 1405.0306 . Bibcode:2014MNRAS.443.2204P. doi:10.1093/mnras/stu879. S2CID   119295582.
  54. 1 2 Kafle, Prajwal R.; Sharma, Sanjib; Lewis, Geraint F.; et al. (2018). "The need for speed: escape velocity and dynamical mass measurements of the Andromeda galaxy". Monthly Notices of the Royal Astronomical Society. 475 (3): 4043–4054. arXiv: 1801.03949 . Bibcode:2018MNRAS.475.4043K. doi:10.1093/mnras/sty082. S2CID   54039546.
  55. ↑ Kafle, Prajwal R.; Sharma, Sanjib; Lewis, Geraint F.; Robotham, Aaron S G.; Driver, Simon P. (2018). "The need for speed: Escape velocity and dynamical mass measurements of the Andromeda galaxy". Monthly Notices of the Royal Astronomical Society. 475 (3): 4043–4054. arXiv: 1801.03949 . Bibcode:2018MNRAS.475.4043K. doi:10.1093/mnras/sty082. S2CID   54039546.
  56. ↑ "Milky Way ties with neighbour in galactic arms race". 15 February 2018.
  57. ↑ Science, Samantha Mathewson 2018-02-20T19:05:26Z; Astronomy (20 February 2018). "The Andromeda Galaxy Is Not Bigger Than the Milky Way After All". Space.com.{{cite web}}: CS1 maint: numeric names: authors list (link)
  58. 1 2 Kalirai, Jasonjot Singh; Gilbert, Karoline M.; Guhathakurta, Puragra; et al. (2006). "The Metal-Poor Halo of the Andromeda Spiral Galaxy (M31)". Astrophysical Journal . 648 (1): 389–404. arXiv: astro-ph/0605170 . Bibcode:2006ApJ...648..389K. doi:10.1086/505697. S2CID   15396448.
  59. ↑ Barmby, Pauline; Ashby, Matthew L. N.; Bianchi, Luciana; et al. (2006). "Dusty Waves on a Starry Sea: The Mid-Infrared View of M31". The Astrophysical Journal. 650 (1): L45–L49. arXiv: astro-ph/0608593 . Bibcode:2006ApJ...650L..45B. doi:10.1086/508626. S2CID   16780719.
  60. ↑ Barmby, Pauline; Ashby, Matthew L. N.; Bianchi, Luciana; et al. (2007). "Erratum: Dusty Waves on a Starry Sea: The Mid-Infrared View of M31". The Astrophysical Journal. 655 (1): L61. Bibcode:2007ApJ...655L..61B. doi: 10.1086/511682 .
  61. 1 2 Tamm, Antti; Tempel, Elmo; Tenjes, Peeter; et al. (2012). "Stellar mass map and dark matter distribution in M 31". Astronomy & Astrophysics. 546: A4. arXiv: 1208.5712 . Bibcode:2012A&A...546A...4T. doi:10.1051/0004-6361/201220065. S2CID   54728023.
  62. ↑ Kafle, Prajwal R.; Sharma, Sanjib; Lewis, Geraint F.; Robotham, Aaron S G.; Driver, Simon P. (2018). "The Need for Speed: Escape velocity and dynamical mass measurements of the Andromeda galaxy". Monthly Notices of the Royal Astronomical Society. 475 (3): 4043–4054. arXiv: 1801.03949 . Bibcode:2018MNRAS.475.4043K. doi:10.1093/mnras/sty082. S2CID   54039546.
  63. ↑ Downer, Bethany; Telescope, ESA/Hubble (10 March 2019). "Hubble & Gaia Reveal Weight of the Milky Way: 1.5 Trillion Solar Masses".
  64. ↑ Starr, Michelle (8 March 2019). "The Latest Calculation of Milky Way's Mass Just Changed What We Know About Our Galaxy". ScienceAlert.com. Archived from the original on 8 March 2019. Retrieved 8 March 2019.
  65. ↑ Watkins, Laura L.; et al. (2 February 2019). "Evidence for an Intermediate-Mass Milky Way from Gaia DR2 Halo Globular Cluster Motions". The Astrophysical Journal. 873 (2): 118. arXiv: 1804.11348 . Bibcode:2019ApJ...873..118W. doi: 10.3847/1538-4357/ab089f . S2CID   85463973.
  66. ↑ Braun, Robert; Thilker, David A.; Walterbos, René A. M.; Corbelli, Edvige (2009). "A Wide-Field High-Resolution H I Mosaic of Messier 31. I. Opaque Atomic Gas and Star Formation Rate Density". The Astrophysical Journal. 695 (2): 937–953. arXiv: 0901.4154 . Bibcode:2009ApJ...695..937B. doi:10.1088/0004-637X/695/2/937. S2CID   17996197.
  67. ↑ Draine, Bruce T.; Aniano, Gonzalo; Krause, Oliver; et al. (2014). "Andromeda's Dust". The Astrophysical Journal. 780 (2): 172. arXiv: 1306.2304 . Bibcode:2014ApJ...780..172D. doi:10.1088/0004-637X/780/2/172. S2CID   118999676.
  68. ↑ "HubbleSite – NewsCenter – Hubble Finds Giant Halo Around the Andromeda Galaxy (05/07/2015) – The Full Story". hubblesite.org. Retrieved 7 May 2015.
  69. ↑ Gebhard, Marissa (7 May 2015). "Hubble finds massive halo around the Andromeda Galaxy". University of Notre Dame News.
  70. ↑ Lehner, Nicolas; Howk, Chris; Wakker, Bart (25 April 2014). "Evidence for a Massive, Extended Circumgalactic Medium Around the Andromeda Galaxy". The Astrophysical Journal. 804 (2): 79. arXiv: 1404.6540 . Bibcode:2015ApJ...804...79L. doi:10.1088/0004-637x/804/2/79. S2CID   31505650.
  71. ↑ "NASA's Hubble Finds Giant Halo Around the Andromeda Galaxy". 7 May 2015. Retrieved 7 May 2015.
  72. 1 2 van den Bergh, Sidney (1999). "The local group of galaxies". Astronomy and Astrophysics Review . 9 (3–4): 273–318. Bibcode:1999A&ARv...9..273V. doi:10.1007/s001590050019. S2CID   119392899.
  73. ↑ Moskvitch, Katia (25 November 2010). "Andromeda 'born in a collision'". BBC News . Archived from the original on 26 November 2010. Retrieved 25 November 2010.
  74. ↑ Karachentsev, Igor D.; Karachentseva, Valentina E.; Huchtmeier, Walter K.; Makarov, Dmitry I. (2003). "A Catalog of Neighboring Galaxies". The Astronomical Journal. 127 (4): 2031–2068. Bibcode:2004AJ....127.2031K. doi: 10.1086/382905 .
  75. ↑ McCall, Marshall L. (2014). "A Council of Giants". Monthly Notices of the Royal Astronomical Society. 440 (1): 405–426. arXiv: 1403.3667 . Bibcode:2014MNRAS.440..405M. doi:10.1093/mnras/stu199. S2CID   119087190.
  76. ↑ Tempel, Elmo; Tamm, Antti; Tenjes, Peeter (2010). "Dust-corrected surface photometry of M 31 from Spitzer far-infrared observations". Astronomy and Astrophysics. 509: A91. arXiv: 0912.0124 . Bibcode:2010A&A...509A..91T. doi:10.1051/0004-6361/200912186. S2CID   118705514. wA91.
  77. ↑ Liller, William; Mayer, Ben (1987). "The Rate of Nova Production in the Galaxy". Publications of the Astronomical Society of the Pacific . 99: 606–609. Bibcode:1987PASP...99..606L. doi: 10.1086/132021 . S2CID   122526653.
  78. ↑ Mutch, Simon J.; Croton, Darren J.; Poole, Gregory B. (2011). "The Mid-life Crisis of the Milky Way and M31". The Astrophysical Journal. 736 (2): 84. arXiv: 1105.2564 . Bibcode:2011ApJ...736...84M. doi:10.1088/0004-637X/736/2/84. S2CID   119280671.
  79. ↑ Beaton, Rachael L.; Majewski, Steven R.; Guhathakurta, Puragra; et al. (2006). "Unveiling the Boxy Bulge and Bar of the Andromeda Spiral Galaxy". Astrophysical Journal Letters . 658 (2): L91. arXiv: astro-ph/0605239 . Bibcode:2007ApJ...658L..91B. doi:10.1086/514333. S2CID   889325.
  80. ↑ "Dimensions of Galaxies". ned.ipac.caltech.edu.
  81. ↑ "Atlas of the Andromeda Galaxy". ned.ipac.caltech.edu.
  82. ↑ "Astronomers Find Evidence of an Extreme Warp in the Stellar Disk of the Andromeda Galaxy" (Press release). UC Santa Cruz. 9 January 2001. Archived from the original on 19 May 2006. Retrieved 24 May 2006.
  83. ↑ Rubin, Vera C.; Ford, W. Kent Jr. (1970). "Rotation of the Andromeda Nebula from a Spectroscopic Survey of Emission". Astrophysical Journal . 159: 379. Bibcode:1970ApJ...159..379R. doi:10.1086/150317. S2CID   122756867.
  84. ↑ Arp, Halton (1964). "Spiral Structure in M31". Astrophysical Journal . 139: 1045. Bibcode:1964ApJ...139.1045A. doi: 10.1086/147844 .
  85. ↑ van den Bergh, Sidney (1991). "The Stellar Populations of M31". Publications of the Astronomical Society of the Pacific. 103: 1053–1068. Bibcode:1991PASP..103.1053V. doi: 10.1086/132925 . S2CID   249711674.
  86. ↑ Hodge, Paul W. (1966). Galaxies and Cosmology. McGraw Hill.
  87. ↑ Simien, François; Pellet, André; Monnet, Guy; et al. (1978). "The spiral structure of M31 – A morphological approach". Astronomy and Astrophysics. 67 (1): 73–79. Bibcode:1978A&A....67...73S.
  88. ↑ Haas, Martin (2000). "Cold dust in M31 as mapped by ISO". The Interstellar Medium in M31 and M33. Proceedings 232. WE-Heraeus Seminar: 69–72. Bibcode:2000immm.proc...69H.
  89. ↑ Walterbos, René A. M.; Kennicutt, Robert C. Jr. (1988). "An optical study of stars and dust in the Andromeda galaxy". Astronomy and Astrophysics. 198: 61–86. Bibcode:1988A&A...198...61W.
  90. 1 2 Gordon, Karl D.; Bailin, J.; Engelbracht, Charles W.; et al. (2006). "Spitzer MIPS Infrared Imaging of M31: Further Evidence for a Spiral-Ring Composite Structure". The Astrophysical Journal. 638 (2): L87–L92. arXiv: astro-ph/0601314 . Bibcode:2006ApJ...638L..87G. doi:10.1086/501046. S2CID   15495044.
  91. ↑ Braun, Robert (1991). "The distribution and kinematics of neutral gas, HI region in M31". Astrophysical Journal . 372: 54–66. Bibcode:1991ApJ...372...54B. doi:10.1086/169954.
  92. ↑ "ISO unveils the hidden rings of Andromeda" (Press release). European Space Agency. 14 October 1998. Retrieved 24 May 2006.
  93. ↑ Morrison, Heather; Caldwell, Nelson; Harding, Paul; et al. (2008). "Young Star Clusters in M 31". Galaxies in the Local Volume. Astrophysics and Space Science Proceedings. Vol. 5. pp. 227–230. arXiv: 0708.3856 . Bibcode:2008ASSP....5..227M. doi:10.1007/978-1-4020-6933-8_50. ISBN   978-1-4020-6932-1. S2CID   17519849.
  94. ↑ Pagani, Laurent; Lequeux, James; Cesarsky, Diego; et al. (1999). "Mid-infrared and far-ultraviolet observations of the star-forming ring of M 31". Astronomy & Astrophysics. 351: 447–458. arXiv: astro-ph/9909347 . Bibcode:1999A&A...351..447P.
  95. ↑ Aguilar, David A.; Pulliam, Christine (18 October 2006). "Busted! Astronomers Nab Culprit in Galactic Hit-and-Run". Harvard-Smithsonian Center for Astrophysics. Archived from the original on 8 October 2014. Retrieved 6 October 2014.
  96. ↑ Block, David L.; Bournaud, Frédéric; Combes, Françoise; et al. (2006). "An almost head-on collision as the origin of the two off-centre rings in the Andromeda galaxy". Nature. 443 (1): 832–834. arXiv: astro-ph/0610543 . Bibcode:2006Natur.443..832B. doi:10.1038/nature05184. PMID   17051212. S2CID   4426420.
  97. ↑ Bullock, James S.; Johnston, Kathryn V. (2005). "Tracing Galaxy Formation with Stellar Halos I: Methods". Astrophysical Journal . 635 (2): 931–949. arXiv: astro-ph/0506467 . Bibcode:2005ApJ...635..931B. doi:10.1086/497422. S2CID   14500541.
  98. ↑ Lauer, Tod R.; Faber, Sandra M.; Groth, Edward J.; et al. (1993). "Planetary camera observations of the double nucleus of M31" (PDF). Astronomical Journal . 106 (4): 1436–1447, 1710–1712. Bibcode:1993AJ....106.1436L. doi:10.1086/116737.
  99. ↑ Bender, Ralf; Kormendy, John; Bower, Gary; et al. (2005). "HST STIS Spectroscopy of the Triple Nucleus of M31: Two Nested Disks in Keplerian Rotation around a Supermassive Black Hole". Astrophysical Journal . 631 (1): 280–300. arXiv: astro-ph/0509839 . Bibcode:2005ApJ...631..280B. doi:10.1086/432434. S2CID   53415285.
  100. ↑ Gebhardt, Karl; Bender, Ralf; Bower, Gary; et al. (June 2000). "A Relationship between Nuclear Black Hole Mass and Galaxy Velocity Dispersion". The Astrophysical Journal. 539 (1): L13–L16. arXiv: astro-ph/0006289 . Bibcode:2000ApJ...539L..13G. doi:10.1086/312840. S2CID   11737403.
  101. 1 2 Tremaine, Scott (1995). "An Eccentric-Disk Model for the Nucleus of M31". Astronomical Journal . 110: 628–633. arXiv: astro-ph/9502065 . Bibcode:1995AJ....110..628T. doi:10.1086/117548. S2CID   8408528.
  102. ↑ Akiba, Tatsuya; Madigan, Ann-Marie (1 November 2021). "On the Formation of an Eccentric Nuclear Disk following the Gravitational Recoil Kick of a Supermassive Black Hole". The Astrophysical Journal Letters. 921 (1): L12. arXiv: 2110.10163 . Bibcode:2021ApJ...921L..12A. doi: 10.3847/2041-8213/ac30d9 . ISSN   2041-8205. S2CID   239049969.
  103. ↑ "Hubble Space Telescope Finds a Double Nucleus in the Andromeda Galaxy" (Press release). Hubble News Desk. 20 July 1993. Retrieved 26 May 2006.
  104. ↑ Schewe, Phillip F.; Stein, Ben (26 July 1993). "The Andromeda Galaxy has a Double Nucleus". Physics News Update. American Institute of Physics. Archived from the original on 15 August 2009. Retrieved 10 July 2009.
  105. ↑ Fujimoto, Mitsuaki; Hayakawa, Satio; Kato, Takako (1969). "Correlation between the Densities of X-Ray Sources and Interstellar Gas". Astrophysics and Space Science . 4 (1): 64–83. Bibcode:1969Ap&SS...4...64F. doi:10.1007/BF00651263. S2CID   120251156.
  106. ↑ Peterson, Laurence E. (1973). "Hard Cosmic X-Ray Sources". In Bradt, Hale; Giacconi, Riccardo (eds.). X- and Gamma-Ray Astronomy, Proceedings of IAU Symposium no. 55 held in Madrid, Spain, 11–13 May 1972. Vol. 55. International Astronomical Union. pp. 51–73. Bibcode:1973IAUS...55...51P. doi:10.1007/978-94-010-2585-0_5. ISBN   978-90-277-0337-8.{{cite book}}: |journal= ignored (help)
  107. ↑ Marelli, Martino; Tiengo, Andrea; De Luca, Andrea; et al. (2017). "Discovery of periodic dips in the brightest hard X-ray source of M31 with EXTraS". The Astrophysical Journal Letters. 851 (2): L27. arXiv: 1711.05540 . Bibcode:2017ApJ...851L..27M. doi: 10.3847/2041-8213/aa9b2e . S2CID   119266242.
  108. ↑ Barnard, Robin; Kolb, Ulrich C.; Osborne, Julian P. (2005). "Timing the bright X-ray population of the core of M31 with XMM-Newton". arXiv: astro-ph/0508284 .
  109. ↑ "Andromeda Galaxy Scanned with High-Energy X-ray Vision". Jet Propulsion Laboratory . 5 January 2016. Retrieved 22 September 2018.
  110. ↑ Prostak, Sergio (14 December 2012). "Microquasar in Andromeda Galaxy Amazes Astronomers". Sci-News.com.
  111. ↑ "Star cluster in the Andromeda galaxy". ESA. 4 September 2015. Retrieved 7 September 2015.
  112. ↑ Barmby, Pauline; Huchra, John P. (2001). "M31 Globular Clusters in the Hubble Space Telescope Archive. I. Cluster Detection and Completeness". Astronomical Journal . 122 (5): 2458–2468. arXiv: astro-ph/0107401 . Bibcode:2001AJ....122.2458B. doi:10.1086/323457. S2CID   117895577.
  113. ↑ "Hubble Spies Globular Cluster in Neighboring Galaxy" (Press release). Hubble news desk STSci-1996-11. 24 April 1996. Archived from the original on 1 July 2006. Retrieved 26 May 2006.
  114. ↑ Meylan, Georges; Sarajedini, Ata; Jablonka, Pascale; et al. (2001). "G1 in M31 – Giant Globular Cluster or Core of a Dwarf Elliptical Galaxy?". Astronomical Journal . 122 (2): 830–841. arXiv: astro-ph/0105013 . Bibcode:2001AJ....122..830M. doi:10.1086/321166. S2CID   17778865.
  115. ↑ Ma, Jun; de Grijs, Richard; Yang, Yanbin; et al. (2006). "A 'super' star cluster grown old: the most massive star cluster in the Local Group". Monthly Notices of the Royal Astronomical Society. 368 (3): 1443–1450. arXiv: astro-ph/0602608 . Bibcode:2006MNRAS.368.1443M. doi:10.1111/j.1365-2966.2006.10231.x. S2CID   15947017.
  116. ↑ Cohen, Judith G. (2006). "The Not So Extraordinary Globular Cluster 037-B327 in M31" (PDF). The Astrophysical Journal. 653 (1): L21–L23. arXiv: astro-ph/0610863 . Bibcode:2006ApJ...653L..21C. doi:10.1086/510384. S2CID   1733902.
  117. ↑ Burstein, David; Li, Yong; Freeman, Kenneth C.; et al. (2004). "Globular Cluster and Galaxy Formation: M31, the Milky Way, and Implications for Globular Cluster Systems of Spiral Galaxies". Astrophysical Journal. 614 (1): 158–166. arXiv: astro-ph/0406564 . Bibcode:2004ApJ...614..158B. doi:10.1086/423334. S2CID   56003193.
  118. ↑ Huxor, Avon P.; Tanvir, Nial R.; Irwin, Michael J.; et al. (2005). "A new population of extended, luminous, star clusters in the halo of M31". Monthly Notices of the Royal Astronomical Society . 360 (3): 993–1006. arXiv: astro-ph/0412223 . Bibcode:2005MNRAS.360.1007H. doi:10.1111/j.1365-2966.2005.09086.x. S2CID   6215035.
  119. ↑ Pechetti, Renuka; Seth, Anil; Kamann, Sebastian; Caldwell, Nelson; Strader, Jay (January 2022). "Detection of a 100,000 M ⊙ black hole in M31's Most Massive Globular Cluster: A Tidally Stripped Nucleus". The Astrophysical Journal. 924 (2): 13. arXiv: 2111.08720 . Bibcode:2022ApJ...924...48P. doi: 10.3847/1538-4357/ac339f . S2CID   245876938.
  120. ↑ An, Jin H.; Evans, N. W.; Kerins, E.; Baillon, P.; Calchi Novati, S.; Carr, B. J.; Creze, M.; Giraud-Heraud, Y.; Gould, A.; Hewett, P.; Jetzer, Ph.; Kaplan, J.; Paulin-Henriksson, S.; Smartt, S. J.; Tsapras, Y.; Valls-Gabaud, D. (2004). "The Anomaly in the Candidate Microlensing Event PA-99-N2". The Astrophysical Journal. 601 (2): 845–857. arXiv: astro-ph/0310457 . Bibcode:2004ApJ...601..845A. doi:10.1086/380820. ISSN   0004-637X. S2CID   8312033.
  121. ↑ Higgs, C. R.; McConnachie, A. W. (2021). "Solo dwarfs IV: Comparing and contrasting satellite and isolated dwarf galaxies in the Local Group". Monthly Notices of the Royal Astronomical Society. 506 (2): 2766–2779. arXiv: 2106.12649 . doi:10.1093/mnras/stab1754.
  122. ↑ Bekki, Kenji; Couch, Warrick J.; Drinkwater, Michael J.; et al. (2001). "A New Formation Model for M32: A Threshed Early-type Spiral?". Astrophysical Journal Letters . 557 (1): L39–L42. arXiv: astro-ph/0107117 . Bibcode:2001ApJ...557L..39B. doi:10.1086/323075. S2CID   18707442.
  123. ↑ Ibata, Rodrigo A.; Irwin, Michael J.; Lewis, Geraint F.; et al. (2001). "A giant stream of metal-rich stars in the halo of the galaxy M31". Nature . 412 (6842): 49–52. arXiv: astro-ph/0107090 . Bibcode:2001Natur.412...49I. doi:10.1038/35083506. PMID   11452300. S2CID   4413139.
  124. ↑ Young, Lisa M. (2000). "Properties of the Molecular Clouds in NGC 205". Astronomical Journal . 120 (5): 2460–2470. arXiv: astro-ph/0007169 . Bibcode:2000AJ....120.2460Y. doi:10.1086/316806. S2CID   18728927.
  125. ↑ Rudenko, Pavlo; Worthey, Guy; Mateo, Mario (2009). "Intermediate age clusters in the field containing M31 and M32 stars". The Astronomical Journal . 138 (6): 1985–1989. Bibcode:2009AJ....138.1985R. doi: 10.1088/0004-6256/138/6/1985 .
  126. ↑ "Messier Object 33". www.messier.seds.org. Archived from the original on 29 June 2023. Retrieved 21 May 2021.
  127. ↑ Koch, Andreas; Grebel, Eva K. (March 2006). "The Anisotropic Distribution of M31 Satellite Galaxies: A Polar Great Plane of Early-type Companions". Astronomical Journal . 131 (3): 1405–1415. arXiv: astro-ph/0509258 . Bibcode:2006AJ....131.1405K. doi:10.1086/499534. S2CID   3075266.
  128. ↑ Cowen, Ron (2012). "Andromeda on collision course with the Milky Way". Nature . doi:10.1038/nature.2012.10765. S2CID   124815138.
  129. ↑ O'Callaghan, Jonathan (14 May 2018). "Apart from Andromeda, are any other galaxies moving towards us?". Space Facts. Retrieved 3 April 2016.
  130. ↑ Cox, Thomas J.; Loeb, Abraham (2008). "The collision between the Milky Way and Andromeda". Monthly Notices of the Royal Astronomical Society . 386 (1): 461–474. arXiv: 0705.1170 . Bibcode:2008MNRAS.386..461C. doi:10.1111/j.1365-2966.2008.13048.x. S2CID   14964036.
  131. ↑ Cain, Fraser (2007). "When Our Galaxy Smashes Into Andromeda, What Happens to the Sun?". Universe Today . Archived from the original on 17 May 2007. Retrieved 16 May 2007.
  132. ↑ Plait, Phil (1 January 2014). "Yes, That Picture of the Moon and the Andromeda Galaxy Is About Right". Slate Magazine. Retrieved 29 July 2022.
  133. ↑ "Andromeda and the Moon collage". www.noirlab.edu. Retrieved 29 July 2022.
  134. ↑ "Can you see other galaxies without a telescope?". starchild.gsfc.nasa.gov.
  135. ↑ King, Bob (9 September 2015). "How to See the Farthest Thing You Can See". Sky & Telescope.
  136. ↑ Garner, Rob (20 February 2019). "Messier 33 (The Triangulum Galaxy)". NASA. Retrieved 6 August 2021.
  137. ↑ Harrington, Philip S. (2010). Cosmic Challenge: The Ultimate Observing List for Amateurs. Cambridge University Press. pp. 28–29. ISBN   9781139493680. But can [M81's] diffuse 7.9-magnitude glow actually be glimpsed without any optical aid? The answer is yes, but with a few important qualifications. Not only must the observing site be extraordinarily dark and completely absent of any atmospheric interferences, either natural or artificial, but the observer must have exceptionally keen vision.
  138. ↑ "M31.html". www.physics.ucla.edu.
  139. ↑ King, Bob (16 September 2015). "Watch Andromeda Blossom in Binoculars". Sky & Telescope.
  140. ↑ "Observing M31, the Andromeda Galaxy". Archived from the original on 5 August 2020. Retrieved 5 October 2016.
  141. ↑ "Globular Clusters in the Andromeda Galaxy". www.astronomy-mall.com.

This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.