Dark galaxy

Last updated

A dark galaxy is a hypothesized galaxy with no (or very few) stars. They received their name because they have no visible stars [1] but may be detectable if they contain significant amounts of gas. Astronomers have long theorized the existence of dark galaxies, but there are no confirmed examples to date. [2] Dark galaxies are distinct from intergalactic gas clouds caused by galactic tidal interactions, since these gas clouds do not contain dark matter, so they do not technically qualify as galaxies. Distinguishing between intergalactic gas clouds and galaxies is difficult; most candidate dark galaxies turn out to be tidal gas clouds. [3] The best candidate dark galaxies to date include HI1225+01, [4] AGC229385, [5] and numerous gas clouds detected in studies of quasars.

Contents

On 25 August 2016, astronomers reported that Dragonfly 44, an ultra diffuse galaxy (UDG) with the mass of the Milky Way galaxy, but with nearly no discernable stars or galactic structure, is made almost entirely of dark matter. [6] [7] [8]

Observational evidence

Large surveys with sensitive but low-resolution radio telescopes like Arecibo or the Parkes Telescope look for 21-cm emission from atomic hydrogen in galaxies. These surveys are then matched to optical surveys to identify any objects with no optical counterpart; i.e., sources with no stars. [9]

Another way astronomers search for dark galaxies is to look for hydrogen absorption lines in the spectra of background quasars. This technique has revealed many intergalactic clouds of hydrogen, but following up on candidate dark galaxies is difficult, since these sources tend to be too far away and are often optically drowned out by the bright light from the quasars.

Nature of dark galaxies

Origin

In 2005, astronomers discovered gas cloud VIRGOHI21 and attempted to determine what it was and why it exerted such a massive gravitational pull on galaxy NGC 4254. After years of ruling out other possible explanations, some have concluded that VIRGOHI21 is a dark galaxy. [10]

Size

The actual size of dark galaxies is unknown because they cannot be observed with normal telescopes. There have been various estimations, ranging from double the size of the Milky Way [11] to the size of a small quasar.

Structure

Dark galaxies are theoretically composed of dark matter, hydrogen and dust. [10] Some scientists support the idea that dark galaxies may contain stars. [12] Yet the exact composition of dark galaxies remains unknown because there is no conclusive way to identify them. Nevertheless, astronomers estimate that the mass of the gas in these galaxies is approximately one billion times that of the Sun. [13]

Methodology to observe dark bodies

Dark galaxies contain no visible stars and are invisible to optical telescopes. The Arecibo Galaxy Environment Survey (AGES) harnessed the Arecibo radio telescope to search for dark galaxies, which are predicted to contain detectable amounts of neutral hydrogen. The Arecibo radio telescope was useful where others are not because of its ability to detect the emission from this neutral hydrogen, specifically the 21-cm line.

Alternative theories

Scientists say that the galaxies we see today only began to create stars after dark galaxies. Based on numerous scientific assertions, dark galaxies played a big role in many of the galaxies astronomers and scientists see today. Martin Haehnel, from Kavli Institute for Cosmology at the University of Cambridge, claims that the precursor to the Milky Way galaxy was actually a much smaller bright galaxy that had merged with dark galaxies nearby to form the Milky Way we currently see. Multiple scientists agree that dark galaxies are building blocks of modern galaxies. Sebastian Cantalupo of the University of California, Santa Cruz, agrees with this theory. He goes on to say, "In our current theory of galaxy formation, we believe that big galaxies form from the merger of smaller galaxies. Dark galaxies bring to big galaxies a lot of gas, which then accelerates star formation in the bigger galaxies." Scientists have specific techniques they use to locate these dark galaxies. These techniques have the capability of teaching us more about other special events that occur in the universe; for instance, the "cosmic web". This "web" is made of invisible filaments of gas and dark matter believed to permeate the universe, as well as "feeding and building galaxies and galaxy clusters where the filaments intersect." [13]

Potential dark galaxies

FAST J0139+4328

Located 94 million light years away from Earth, this galaxy is visible in radio waves with minimal visible light. [14]

HE0450-2958

HE0450-2958 is a quasar at redshift z=0.285. Hubble Space Telescope images showed that the quasar is located at the edge of a large cloud of gas, but no host galaxy was detected for the quasar. The authors of the Hubble study suggested that one possible scenario was that the quasar is located in a dark galaxy. [15] However, subsequent analysis by other groups found no evidence that the host galaxy is anomalously dark, and demonstrated that a normal host galaxy is probably present, [16] [17] so the observations do not support the dark galaxy interpretation.

HVC 127-41-330

HVC 127-41-330 is a cloud rotating at high speed between Andromeda and the Triangulum Galaxy. Astronomer Josh Simon considers this cloud to be a dark galaxy because of the speed of its rotation and its predicted mass. [18] [19]

J0613+52

On 26 January 2023, astronomers reported the observation of J0613+52, a possible dark galaxy. [20] It was discovered with the Green Bank Telescope when it was accidentally pointed to the wrong coordinates. Stars could possibly exist in it but none have been actually observed as of yet. [21]

Nube

Nube was discovered in 18 October 2023 by analyzing deep optical imagery of an area in Stripe 82. Due to its low surface brightness, Nube is classified as an "almost dark galaxy." [22]

Smith's Cloud

Smith's Cloud is a candidate to be a dark galaxy, due to its projected mass and survival of encounters with the Milky Way. [23]

VIRGOHI21

Initially discovered in 2000, VIRGOHI21 was announced in February 2005 as a good candidate to be a true dark galaxy. [12] [24] [25] [26] It was detected in 21-cm surveys, and was suspected to be a possible cosmic partner to the galaxy NGC 4254. This unusual-looking galaxy appears to be one partner in a cosmic collision, and appeared to show dynamics consistent with a dark galaxy (and apparently inconsistent with the predictions of the Modified Newtonian Dynamics (MOND) theory). [27] However, further observations revealed that VIRGOHI21 was an intergalactic gas cloud, stripped from NGC4254 by a high speed collision. [28] [29] [30] The high speed interaction was caused by infall into the Virgo cluster.

See also

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">Molecular cloud</span> Type of interstellar cloud

A molecular cloud, sometimes called a stellar nursery (if star formation is occurring within), is a type of interstellar cloud, the density and size of which permit absorption nebulae, the formation of molecules (most commonly molecular hydrogen, H2), and the formation of H II regions. This is in contrast to other areas of the interstellar medium that contain predominantly ionized gas.

<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 diameter of about 46.56 kiloparsecs and is approximately 765 kpc 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">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">Supermassive black hole</span> Largest type of black hole

A supermassive black hole is the largest type of black hole, with its mass being on the order of hundreds of thousands, or millions to billions, of times the mass of the Sun (M☉). Black holes are a class of astronomical objects that have undergone gravitational collapse, leaving behind spheroidal regions of space from which nothing can escape, not even light. Observational evidence indicates that almost every large galaxy has a supermassive black hole at its center. For example, the Milky Way galaxy has a supermassive black hole at its center, corresponding to the radio source Sagittarius A*. Accretion of interstellar gas onto supermassive black holes is the process responsible for powering active galactic nuclei (AGNs) and quasars.

<span class="mw-page-title-main">Stellar population</span> Grouping of stars by similar metallicity

In 1944, Walter Baade categorized groups of stars within the Milky Way into stellar populations. In the abstract of the article by Baade, he recognizes that Jan Oort originally conceived this type of classification in 1926.

In physical cosmology, a protogalaxy, which could also be called a "primeval galaxy", is a cloud of gas which is forming into a galaxy. It is believed that the rate of star formation during this period of galactic evolution will determine whether a galaxy is a spiral or elliptical galaxy; a slower star formation tends to produce a spiral galaxy. The smaller clumps of gas in a protogalaxy form into stars.

<span class="mw-page-title-main">Reionization</span> Process that caused matter to reionize early in the history of the Universe

In the fields of Big Bang theory and cosmology, reionization is the process that caused electrically neutral atoms in the universe to reionize after the lapse of the "dark ages".

The Sloan Digital Sky Survey or SDSS is a major multi-spectral imaging and spectroscopic redshift survey using a dedicated 2.5-m wide-angle optical telescope at Apache Point Observatory in New Mexico, United States. The project began in 2000 and was named after the Alfred P. Sloan Foundation, which contributed significant funding.

<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">Messier 94</span> Galaxy in the constellation Canes Venatici

Messier 94 is a spiral galaxy in the mid-northern constellation Canes Venatici. It was discovered by Pierre Méchain in 1781, and catalogued by Charles Messier two days later. Although some references describe M94 as a barred spiral galaxy, the "bar" structure appears to be more oval-shaped. The galaxy has two ring structures.

VIRGOHI21 is an extended region of neutral hydrogen (HI) in the Virgo cluster discovered in 2005. Analysis of its internal motion indicates that it may contain a large amount of dark matter, as much as a small galaxy. Since VIRGOHI21 apparently contains no stars, this would make it one of the first detected dark galaxies. Skeptics of this interpretation argue that VIRGOHI21 is simply a tidal tail of the nearby galaxy NGC 4254.

<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.

The Milky Way has several smaller galaxies gravitationally bound to it, as part of the Milky Way subgroup, which is part of the local galaxy cluster, the Local Group.

<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">Galaxy merger</span> Merger whereby at least two galaxies collide

Galaxy mergers can occur when two galaxies collide. They are the most violent type of galaxy interaction. The gravitational interactions between galaxies and the friction between the gas and dust have major effects on the galaxies involved. The exact effects of such mergers depend on a wide variety of parameters such as collision angles, speeds, and relative size/composition, and are currently an extremely active area of research. Galaxy mergers are important because the merger rate is a fundamental measurement of galaxy evolution. The merger rate also provides astronomers with clues about how galaxies bulked up over time.

<span class="mw-page-title-main">Smith's Cloud</span> High velocity cloud in the constellation Aquila

Smith's Cloud is a high-velocity cloud of hydrogen gas located in the constellation Aquila at Galactic coordinates l = 39°, b = −13°. The cloud was discovered in 1963 by Gail Bieger, née Smith, who was an astronomy student at Leiden University in the Netherlands.

<span class="mw-page-title-main">Hanny's Voorwerp</span> Astronomical object appearing as a bright blob, discovered by Hanny van Arkel

Hanny's Voorwerp, is a type of astronomical object called a quasar ionization echo. It was discovered in 2007 by Dutch schoolteacher Hanny van Arkel while she was participating as a volunteer in the Galaxy Zoo project, part of the Zooniverse group of citizen science websites. Photographically, it appears as a bright blob close to spiral galaxy IC 2497 in the constellation Leo Minor.

References

  1. ↑ "First evidence of dark galaxies from the early Universe spotted". Zmescience.com. 2012-07-11. Retrieved 2012-08-13.
  2. ↑ Cannon, John M.; Martinkus, Charlotte P.; Leisman, Lukas; Haynes, Martha P.; Adams, Elizabeth A. K.; Giovanelli, Riccardo; Hallenbeck, Gregory; Janowiecki, Steven; Jones, Michael (2015-02-01). "The Alfalfa "Almost Darks" Campaign: Pilot VLA HI Observations of Five High Mass-To-Light Ratio Systems". The Astronomical Journal. 149 (2): 72. arXiv: 1412.3018 . Bibcode:2015AJ....149...72C. doi:10.1088/0004-6256/149/2/72. ISSN   0004-6256. S2CID   118592858.
  3. ↑ Oosterloo, T. A.; Heald, G. H.; De Blok, W. J. G. (2013). "Is GBT 1355+5439 a dark galaxy?". Astronomy & Astrophysics. 555: L7. arXiv: 1306.6148 . Bibcode:2013A&A...555L...7O. doi:10.1051/0004-6361/201321965. S2CID   118402005.
  4. ↑ "The Arecibo Legacy Fast ALFA Survey". egg.astro.cornell.edu. Retrieved 2015-09-29.
  5. ↑ Janowiecki, Steven; Leisman, Lukas; Józsa, Gyula; Salzer, John J.; Haynes, Martha P.; Giovanelli, Riccardo; Rhode, Katherine L.; Cannon, John M.; Adams, Elizabeth A. K. (2015-03-01). "(Almost) Dark HI Sources in the ALFALFA Survey: The Intriguing Case of HI1232+20". The Astrophysical Journal. 801 (2): 96. arXiv: 1502.01296 . Bibcode:2015ApJ...801...96J. doi:10.1088/0004-637X/801/2/96. ISSN   0004-637X. S2CID   119271121.
  6. ↑ Van Dokkum, Pieter; et al. (25 August 2016). "A High Stellar Velocity Dispersion and ~100 Globular Clusters For The Ultra-Diffuse Galaxy Dragonfly 44". The Astrophysical Journal Letters . 828 (1): L6. arXiv: 1606.06291 . Bibcode:2016ApJ...828L...6V. doi: 10.3847/2041-8205/828/1/L6 . S2CID   1275440.
  7. ↑ Hall, Shannon (25 August 2016). "Ghost galaxy is 99.99 per cent dark matter with almost no stars". New Scientist . Retrieved 27 August 2016.
  8. ↑ Feltman, Rachael (26 August 2016). "A new class of galaxy has been discovered, one made almost entirely of dark matter". The Washington Post . Retrieved 26 August 2016.
  9. ↑ "The existence and detection of optically dark galaxies by 21-cm surveys". academic.oup.com. doi:10.1111/j.1365-2966.2006.10247.x . Retrieved 2024-03-12.
  10. 1 2 Fraser Cain (2007-06-14). "No Stars Shine in This Dark Galaxy". Universetoday.com. Retrieved 2012-08-13.
  11. ↑ "Arecibo Survey Produces Dark Galaxy Candidate". Spacedaily.com. 2006-04-07. Retrieved 2012-08-13.
  12. 1 2 Stuart Clark. "Dark galaxy' continues to puzzle astronomers". New Scientist . Retrieved 2008-02-26.
  13. 1 2 "First Direct Detection Sheds Light On Dark Galaxies". Zmescience.com. Retrieved 22 December 2012.
  14. ↑ "Mysterious Dark Galaxy Emits No Visible Light, Scientists Say". 10 February 2023.
  15. ↑ Magain P.; et al. (2005). "Discovery of a bright quasar without a massive host galaxy". Nature. 437 (7057): 381–4. arXiv: astro-ph/0509433 . Bibcode:2005Natur.437..381M. doi:10.1038/nature04013. PMID   16163349. S2CID   4303895.
  16. ↑ Merritt, David; et al. (2006). "The nature of the HE0450-2958 system". Monthly Notices of the Royal Astronomical Society . 367 (4): 1746–1750. arXiv: astro-ph/0511315 . Bibcode:2006MNRAS.367.1746M. doi:10.1111/j.1365-2966.2006.10093.x. S2CID   55834970.
  17. ↑ Kim, Minjin; Ho, Luis; Peng, Chien; Im, Myungshin (2007). "The Host Galaxy of the Quasar HE 0450-2958". The Astrophysical Journal. 658 (1): 107–113. arXiv: astro-ph/0611411 . Bibcode:2007ApJ...658..107K. doi:10.1086/510846. S2CID   14375599.
  18. ↑ Josh Simon (2005). "Dark Matter in Dwarf Galaxies: Observational Tests of the Cold Dark Matter Paradigm on Small Scales" (PDF): 4273. Bibcode:2005PhDT.........2S. Archived from the original (PDF) on 2006-09-13.{{cite journal}}: Cite journal requires |journal= (help)
  19. ↑ Battersby, Stephen (2003-10-20). "Astronomers find first 'dark galaxy'". New Scientist. Retrieved December 22, 2012.
  20. ↑ Overbye, Dennis (26 January 2024). "What Do You Call a Galaxy Without Stars? - To dark matter and dark energy, add dark galaxies — collections of stars so sparse and faint that they are all but invisible". The New York Times . Archived from the original on 26 January 2024.
  21. ↑ Malusky, Jill (2024-01-08). "Astronomers Accidentally Discover Dark Primordial Galaxy". Green Bank Observatory. Archived from the original on 2024-03-09. Retrieved 2024-03-10.
  22. ↑ "Astronomers discover new almost dark galaxy". Phys.org. Retrieved 2024-02-06.
  23. ↑ "Dark galaxy crashing into the Milky Way". New Scientist. No. 2735. 22 November 2009. Retrieved 2009-12-12.
  24. ↑ Clark, Stuart (2005-02-23). "Astronomers claim first 'dark galaxy' find". NewScientist.com news service. Retrieved 2006-10-26.
  25. ↑ Shiga, David (2005-02-26). "Ghostly Galaxy: Massive, dark cloud intrigues scientists". Science News Online. 167 (9): 131. doi:10.2307/4015891. JSTOR   4015891. Archived from the original on 2011-05-24. Retrieved 2008-09-14.
  26. ↑ Britt, Roy (2005-02-23). "First Invisible Galaxy Discovered in Cosmology Breakthrough". Space.com.
  27. ↑ Funkhouser, Scott (2005). "Testing MOND with VirgoHI21". Monthly Notices of the Royal Astronomical Society. 364 (1): 237. arXiv: astro-ph/0503104 . Bibcode:2005MNRAS.364..237F. doi:10.1111/j.1365-2966.2005.09565.x. S2CID   119368923.
  28. ↑ Kent, Brian R.; Giovanelli, Riccardo; Haynes, Martha P.; Saintonge, Amélie; Stierwalt, Sabrina; Balonek, Thomas; Brosch, Noah; Catinella, Barbara; Koopmann, Rebecca A. (2007-08-01). "Optically Unseen H I Detections toward the Virgo Cluster Detected in the Arecibo Legacy Fast ALFA Survey". The Astrophysical Journal Letters. 665 (1): L15–L18. Bibcode:2007ApJ...665L..15K. doi: 10.1086/521100 . ISSN   0004-637X.
  29. ↑ Duc, Pierre-Alain; Bournaud, Frederic (2008-02-01). "Tidal Debris from High-Velocity Collisions as Fake Dark Galaxies: A Numerical Model of VIRGOHI 21". The Astrophysical Journal. 673 (2): 787–797. arXiv: 0710.3867 . Bibcode:2008ApJ...673..787D. doi:10.1086/524868. ISSN   0004-637X. S2CID   15348867.
  30. ↑ Haynes, Martha P.; Giovanelli, Riccardo; Kent, Brian R. (2007). "NGC 4254: An Act of Harassment Uncovered by the Arecibo Legacy Fast ALFA Survey". Astrophysical Journal . 665 (1): L19–22. arXiv: 0707.0113 . Bibcode:2007ApJ...665L..19H. doi:10.1086/521188. S2CID   12930657.
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.