Hoag's Object

Last updated
Hoag's Object
Hoag's object.jpg
Hoag's Object, taken by the Hubble Space Telescope in July 2001
Observation data (J2000 epoch)
Constellation Serpens Caput
Right ascension 15h 17m 14.4s [1]
Declination +21° 35′ 08″ [1]
Redshift 12740±50 km/s [1] [2]
Distance 612.8±9.4  Mly (187.9±2.9  Mpc ) [2] [a]
Apparent magnitude  (B)16.2 [1]
Characteristics
Type (RP)E0 or (RP)SA0/a [3]
Size45.41 kiloparsecs (148,000 light-years) [1] [4]
(diameter; D25 isophote)
Apparent size  (V)0.28′ × 0.28′ [1]
Notable featuresRing galaxy
Other designations
PGC 54559, [1] PRC D-51 [1]

Hoag's Object is an unusual ring galaxy in the constellation of Serpens Caput. [5] It is named after Arthur Hoag, who discovered it in 1950 and identified it as either a planetary nebula or a peculiar galaxy. [6] The galaxy has a D25 isophotal diameter of 45.41 kiloparsecs (148,000 light-years ). [1]

Contents

Characteristics

A nearly perfect ring of young hot blue stars circles the older yellow nucleus of this ring galaxy c. 600 million light-years away in the constellation Serpens. The ring structure is so perfect and circular that it has been referred to as "The most perfect ring galaxy". [7] The diameter of the 6 arcsecond inner core of the galaxy is about 17±0.7 kly (5.3±0.2 kpc) while the surrounding ring has an inner 28″ diameter of 75±3 kly (24.8±1.1 kpc) and an outer 45″ diameter of 121±4 kly (39.9±1.7 kpc). [2] The galaxy is estimated to have a mass of 700 billion suns. [8] By comparison, the Milky Way galaxy has an estimated diameter of 150–200 kly and consists of between 100 and 500 billion stars and a mass between 800 billion and 1.54 trillion suns. [9] [10]

The gap separating the two stellar populations may contain some star clusters that are almost too faint to see. Though ring galaxies are rare, another more distant ring galaxy (SDSS J151713.93+213516.8) [11] can be seen through Hoag's Object, between the nucleus and the outer ring of the galaxy, at roughly the one o'clock position in the image shown here.

Noah Brosch and colleagues showed that the luminous ring lies at the inner edge of a much larger neutral hydrogen ring. [7]

History and formation

Even though Hoag's Object was clearly shown on the Palomar Star Survey, it was not included in either the Morphological Catalogue of Galaxies , the Catalogue of Galaxies and Clusters of Galaxies , or the catalogue of galactic planetary nebulae . [2]

In the initial announcement of his discovery, Hoag proposed the hypothesis that the visible ring was a product of gravitational lensing. This idea was later discarded because the nucleus and the ring have the same redshift, and because more advanced telescopes revealed the ring's knotty structure, which would not be visible if the galaxy were a product of gravitational lensing. [12]

Many of the galaxy's details remain mysterious, foremost of which is how it formed. So-called "classic" ring galaxies are generally formed by the collision of a small galaxy with a larger disk-shaped galaxy, producing a density wave in the disk that leads to a characteristic ring-like appearance. Such an event would have happened at least 2–3 billion years ago, [12] and may have resembled the processes that form polar-ring galaxies. However, there is no sign of any second galaxy that would have acted as the "bullet", and the likely older core of Hoag's Object has a very low velocity relative to the ring, making the typical formation hypothesis quite unlikely. [12] Observations with one of the most sensitive telescopes have also failed to uncover any faint galaxy fragments that should be observable in a collision scenario. However, a team of scientists that analyzes the galaxy admits that "if the carnage happened more than 3 billion years ago, there might not be any detritus left to see." [13]

Noah Brosch suggested that Hoag's Object might be a product of an extreme "bar instability" that occurred a few billion years ago in a barred spiral galaxy. [14] Schweizer et al [12] claim this is an unlikely hypothesis because the nucleus of the object is spheroidal, whereas the nucleus of a barred spiral galaxy is disc-shaped, among other reasons. However, they admit evidence is somewhat thin for this particular dispute to be settled satisfactorily.

A few other galaxies share the primary characteristics of Hoag's Object, including a bright detached ring of stars, but their centers are elongated or barred, and they may exhibit some spiral structure. While none matches Hoag's Object in symmetry, these galaxies are known to some as Hoag-type galaxies. [15] [16]

See also

Notes

^ 1974 O'Connell paper [2] assumes a Hubble constant of 75; this figure adjusts for 2013's 67.8±0.77 (km/s)/Mpc.

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">Quasar</span> Active galactic nucleus containing a supermassive black hole

A quasar is an extremely luminous active galactic nucleus (AGN). It is sometimes known as a quasi-stellar object, abbreviated QSO. The emission from an AGN is powered by a supermassive black hole with a mass ranging from millions to tens of billions of solar masses, surrounded by a gaseous accretion disc. Gas in the disc falling towards the black hole heats up and releases energy in the form of electromagnetic radiation. The radiant energy of quasars is enormous; the most powerful quasars have luminosities thousands of times greater than that of a galaxy such as the Milky Way. Quasars are usually categorized as a subclass of the more general category of AGN. The redshifts of quasars are of cosmological origin.

<span class="mw-page-title-main">Andromeda Galaxy</span> Barred spiral galaxy in the Local Group

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) 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.

<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">Galactic Center</span> Rotational center of the Milky Way galaxy

The Galactic Center is the barycenter of the Milky Way and a corresponding point on the rotational axis of the galaxy. Its central massive object is a supermassive black hole of about 4 million solar masses, which is called Sagittarius A*, a compact radio source which is almost exactly at the galactic rotational center. The Galactic Center is approximately 8 kiloparsecs (26,000 ly) away from Earth in the direction of the constellations Sagittarius, Ophiuchus, and Scorpius, where the Milky Way appears brightest, visually close to the Butterfly Cluster (M6) or the star Shaula, south to the Pipe Nebula.

<span class="mw-page-title-main">Einstein ring</span> Feature seen when light is gravitationally lensed by an object

An Einstein ring, also known as an Einstein–Chwolson ring or Chwolson ring, is created when light from a galaxy or star passes by a massive object en route to the Earth. Due to gravitational lensing, the light is diverted, making it seem to come from different places. If source, lens, and observer are all in perfect alignment (syzygy), the light appears as a ring.

<span class="mw-page-title-main">Whirlpool Galaxy</span> Galaxy in the constellation Canes Venatici

The Whirlpool Galaxy, also known as Messier 51a (M51a) or NGC 5194, is an interacting grand-design spiral galaxy with a Seyfert 2 active galactic nucleus. It lies in the constellation Canes Venatici, and was the first galaxy to be classified as a spiral galaxy. It is 7.22 megaparsecs away and 23.58 kiloparsecs (76,900 ly) in diameter.

<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">Omega Centauri</span> Globular cluster in the constellation Centaurus

Omega Centauri is a globular cluster in the constellation of Centaurus that was first identified as a non-stellar object by Edmond Halley in 1677. Located at a distance of 17,090 light-years, it is the largest known globular cluster in the Milky Way at a diameter of roughly 150 light-years. It is estimated to contain approximately 10 million stars, with a total mass of 4 million solar masses, making it the most massive known globular cluster in the Milky Way.

<span class="mw-page-title-main">Messier 18</span> Open cluster in the constellation Sagittarius

Messier 18 or M18, also designated NGC 6613 and sometimes known as the Black Swan Cluster, is an open cluster of stars in the constellation Sagittarius. It was discovered by Charles Messier in 1764 and included in his list of comet-like objects. From the perspective of Earth, M18 is situated between the Omega Nebula (M17) and the Small Sagittarius Star Cloud (M24).

<span class="mw-page-title-main">NGC 891</span> Galaxy in the constellation Andromeda

NGC 891 is an edge-on unbarred spiral galaxy about 30 million light-years away in the constellation Andromeda. It was discovered by William Herschel on October 6, 1784. The galaxy is a member of the NGC 1023 group of galaxies in the Local Supercluster. It has an H II nucleus.

<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.

<span class="mw-page-title-main">IC 1101</span> Galaxy in the constellation Virgo

IC 1101 is a class S0 supergiant (cD) lenticular galaxy at the center of the Abell 2029 galaxy cluster. It has an isophotal diameter at about 123.65 to 169.61 kiloparsecs. It possesses a diffuse core which is the largest known core of any galaxy to date, and contains a supermassive black hole, one of the largest discovered. IC 1101 is located at 354.0 megaparsecs from Earth. It was discovered on 19 June 1790, by the British astronomer William Herschel.

<span class="mw-page-title-main">NGC 1073</span> Barred spiral galaxy in the constellation Cetus

NGC 1073 is a barred spiral galaxy in the constellation Cetus. The galaxy is estimated to be about 55 million light years from Earth, possess a disk spanning an estimated 80,000 light years in diameter, and likely contains a type of active core, called an HII nucleus.

<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">Malin 1</span> Spiral galaxy in the constellation Coma Berenices

Malin 1 is a giant low surface brightness (LSB) spiral galaxy. It is located 1.19 billion light-years (366 Mpc) away in the constellation Coma Berenices, near the North Galactic Pole. It is one of the largest known spiral galaxies, with an approximate diameter of 650,000 light-years (200,000 pc), thus over six times the diameter of our Milky Way. It was discovered by astronomer David Malin in 1986 and is the first LSB galaxy verified to exist. Its high surface brightness central spiral is 30,000 light-years (9,200 pc) across, with a bulge of 10,000 light-years (3,100 pc). The central spiral is a SB0a type barred-spiral.

<span class="mw-page-title-main">NGC 2775</span> Galaxy in the constellation Cancer

NGC 2775, also known as Caldwell 48, is a spiral galaxy in the constellation Cancer. It is 67 million light-years away from the Milky Way. It was discovered by William Herschel in 1783. NGC 2775 belongs to the Antlia-Hydra Cluster of galaxies and is the most prominent member of the NGC 2775 Group, a small galaxy group in the Virgo Super-cluster, along with the Local Group. Other members of the NGC 2775 Group include NGC 2777 and UGC 4781.

<span class="mw-page-title-main">LEDA 1000714</span> Hoag-type ring galaxy in the constellation Crater

LEDA 1000714 is a ring galaxy in the constellation Crater. LEDA 1000714 is one of a very rare group of galaxies called Hoag-type galaxies, named after the prototype, Hoag's Object – it is estimated that roughly 0.1% of all galaxies are this type.

<span class="mw-page-title-main">NGC 4800</span> Galaxy in constellation Canes Venatici

NGC 4800 is an isolated spiral galaxy in the constellation Canes Venatici, located at a distance of 95 megalight-years from the Milky Way. It was discovered by William Herschel on April 1, 1788. The morphological classification of this galaxy is SA(rs)b, indicating a spiral galaxy with no visual bar at the nucleus (SA), an incomplete ring structure (rs), and moderately-tightly wound spiral arms (b). The galactic plane is inclined to the line of sight by an angle of 43°, and the long axis is oriented along a position angle of 25°. There is a weak bar structure at the nucleus that is visible in the infrared.

References

  1. 1 2 3 4 5 6 7 8 9 "NED results for Hoag's Object". NASA/IPAC Extragalactic Database. Retrieved 2016-06-28.
  2. 1 2 3 4 5 R.W. O'Connell; J.D. Scargle; W.L.W. Sargent (1974). "The Nature of Hoag's Object". Astrophysical Journal . 191: 61–62. Bibcode:1974ApJ...191...61O. doi: 10.1086/152940 .
  3. ↑ Buta, Ronald J. (2017). "Galactic rings revisited – I. CVRHS classifications of 3962 ringed galaxies from the Galaxy Zoo 2 Database". Monthly Notices of the Royal Astronomical Society. 471 (4): 4027–4046. arXiv: 1707.06589 . Bibcode:2017MNRAS.471.4027B. doi: 10.1093/mnras/stx1829 .
  4. ↑ Adelman-Mccarthy, Jennifer K.; et al. (2008). "The Sixth Data Release of the Sloan Digital Sky Survey". The Astrophysical Journal Supplement Series. 175 (2): 297–313. arXiv: 0707.3413 . Bibcode:2008ApJS..175..297A. doi:10.1086/524984.
  5. ↑ Specktor, Brandon (3 December 2019). "Hoag's Object Is a Galaxy Within a Galaxy Within a Galaxy (and Nobody Knows Why)". Live Science . Retrieved 3 December 2019.
  6. ↑ A.A. Hoag (1950). "A peculiar object in Serpens". Astronomical Journal . 55: 170. Bibcode:1950AJ.....55Q.170H. doi: 10.1086/106427 .
  7. 1 2 N. Brosch; I. Finkelman; T. Oosterloo; G. Jozsa; A. Moiseev (2013). "HI in HO: Hoag's Object revisited". Monthly Notices of the Royal Astronomical Society . 435 (1): 199–206. arXiv: 1307.6368 . Bibcode:2013MNRAS.435..475B. doi: 10.1093/mnras/stt1348 .
  8. ↑ Schweizer, Francois; Ford, W. Kent; Jedrzejewski, Robert; Giovanelli, Riccardo (1987). "The Structure and Evolution of Hoag's Object". The Astrophysical Journal. 320: 454. Bibcode:1987ApJ...320..454S. doi: 10.1086/165562 .
  9. ↑ "Scientists discover what the Milky Way weighs". TheGuardian.com . 7 March 2019.
  10. ↑ "What Does the Milky Way Weigh? Hubble and Gaia Investigate". 6 March 2019.
  11. ↑ "SkyServer Object Explorer – SDSS J151713.93+213516.8".
  12. 1 2 3 4 F. Schweizer; W.K. Ford Jr.; R. Jederzejewski; R. Giovanelli (1987). "The structure and evolution of Hoag's object". Astrophysical Journal . 320: 454–463. Bibcode:1987ApJ...320..454S. doi: 10.1086/165562 .
  13. ↑ "Astrophile: Saturn-lookalike galaxy has a murky past". www.newscientist.com. Retrieved 2019-10-31.
  14. ↑ N. Brosch (1985). "The nature of Hoag's object – The perfect ringed galaxy". Astronomy and Astrophysics . 153 (1): 199–206. Bibcode:1985A&A...153..199B.
  15. ↑ at 10:26, Gavin Clarke (2017-01-04). "Astroboffins glimpse sighting of ultra-rare circular galaxy". www.theregister.co.uk. Retrieved 2019-10-31.{{cite web}}: CS1 maint: numeric names: authors list (link)
  16. ↑ Bob Berman (2015-11-13). "Weird Object: Hoags Object". Astronomy.com. Archived from the original on 2022-07-24. Retrieved 2019-10-31.
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.