Great Attractor

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Panoramic view of the entire near-infrared sky. The location of the Great Attractor is shown following the long blue arrow at bottom right. 2MASS LSS chart-NEW Nasa.jpg
Panoramic view of the entire near-infrared sky. The location of the Great Attractor is shown following the long blue arrow at bottom right.
Hubble Space Telescope image showing part of the Norma cluster, including ESO 137-002 Gran Atractor.jpg
Hubble Space Telescope image showing part of the Norma cluster, including ESO 137-002

The Great Attractor is a region of gravitational attraction in intergalactic space and the apparent central gravitational point of the Laniakea Supercluster of galaxies that includes the Milky Way galaxy, as well as about 100,000 other galaxies.

Contents

The observed attraction suggests a localized concentration of mass having the order of 1016 solar masses. [1] However, it is obscured by the Milky Way's galactic plane, lying behind the Zone of Avoidance (ZOA), so that in visible light wavelengths, the Great Attractor is difficult to observe directly. [2]

The attraction is observable by its effect on the motion of galaxies and their associated clusters over a region of hundreds of millions of light-years across the universe. These galaxies are observable above and below the Zone of Avoidance; all are redshifted in accordance with the Hubble flow, indicating that they are receding relative to the Milky Way and to each other, but the variations in their redshifts are large enough and regular enough to reveal that they are slightly drawn towards the attraction. The variations in their redshifts are known as peculiar velocities, and cover a range from about +700 km/s to −700 km/s, depending on the angular deviation from the direction to the Great Attractor. The Great Attractor itself is moving towards the Shapley Supercluster. [2]

History

The Great Attractor was named by Alan Dressler in 1987, [3] [4] following decades of redshift surveys that built up a large dataset of redshift values. The redshift values and distance measurements independent of redshift measurements were then combined to create maps of peculiar velocity. [4] : 274 

Through a series of peculiar velocity tests, astrophysicists found that the Milky Way was moving in the direction of the constellation of Centaurus at about 600 km/s. [ citation needed ] Then, the discovery of cosmic microwave background (CMB) dipoles was used to reflect the motion of the Local Group of galaxies towards the Great Attractor. [5] The 1980s brought many discoveries about the Great Attractor, such as the fact that the Milky Way is not the only galaxy impacted. Approximately 400 elliptical galaxies are moving toward the Great Attractor beyond the Zone of Avoidance caused by the Milky Way galaxy light.

Intense efforts to work through the difficulties caused by the occlusion by the Milky Way during the late 1990s identified the Norma Cluster at the center of the Great Attractor region. [1]

Location

The first indications of a deviation from uniform expansion of the universe were reported in 1973 and again in 1978. The location of the Great Attractor was finally determined in 1986: It is situated at a distance of somewhere between 150 and 250 Mly (million light-years) (47–79  Mpc), the larger being the most recent estimate, away from the Milky Way, in the direction of the constellations Triangulum Australe (The Southern Triangle) and Norma (The Carpenter's Square). [6] While objects in that direction lie in the Zone of Avoidance (the part of the night sky obscured by the Milky Way galaxy) and are thus difficult to study with visible wavelengths, X-ray observations have revealed that region of space to be dominated by the Norma Cluster (ACO 3627), [7] [8] a massive cluster of galaxies containing a preponderance of large, old galaxies, many of which are colliding with their neighbours and radiating large amounts of radio waves.

Debate over apparent mass

In 1992, much of the apparent signal of the Great Attractor was attributed to a statistical effect called Malmquist bias . [9] In 2005, astronomers conducting an X-ray survey of part of the sky known as the Clusters in the Zone of Avoidance (CIZA) project reported that the Great Attractor was actually only one tenth the mass that scientists had originally estimated. The survey also confirmed earlier theories that the Milky Way galaxy is in fact being pulled toward a much more massive cluster of galaxies near the Shapley Supercluster, which lies beyond the Great Attractor, and which is called the Shapley Attractor. [10]

Norma Wall

View of the region of the Great Attractor, with Pavo II, Norma, Cen-Crux and the CIZA J1324.7-5736 clusters forming the Norma Wall. Great Attractor and Norma Wall.jpg
View of the region of the Great Attractor, with Pavo II, Norma, Cen-Crux and the CIZA J1324.7-5736 clusters forming the Norma Wall.

A massive galaxy filament, called the Norma Wall (also called Great Attractor Wall [11] ) is located at the center of the supposed position of the Great Attractor. The Norma Wall contains the clusters Pavo II, Norma, Centaurus-Crux and CIZA J1324.7−5736. The most massive cluster in this region is the Norma supercluster. [12] Later studies found that the wall continues over to the constellations of Centaurus and Vela. [11]

Laniakea Supercluster

The proposed Laniakea Supercluster is defined as the Great Attractor's basin. It covers approximately four main galaxy superclusters, including superclusters of Virgo and Hydra–Centaurus, and spans across 500 million light years. Because it is not dense enough to be gravitationally bound, it should be dispersing as the universe expands, but it is instead anchored by a gravitational focal point. Thus the Great Attractor would be the core of the new supercluster. The local flows of the Laniakea supercluster converge in the region of the Norma and Centaurus Clusters, approximately at the position of the Great Attractor. [13]

See also

Related Research Articles

<span class="mw-page-title-main">Supercluster</span> Large group of smaller galaxy clusters or galaxy groups

A supercluster is a large group of smaller galaxy clusters or galaxy groups; they are among the largest known structures in the universe. The Milky Way is part of the Local Group galaxy group, which in turn is part of the Virgo Supercluster, which is part of the Laniakea Supercluster, which is part of the Pisces–Cetus Supercluster Complex. The large size and low density of superclusters means that they, unlike clusters, expand with the Hubble expansion. The number of superclusters in the observable universe is estimated to be 10 million.

<span class="mw-page-title-main">Timeline of knowledge about galaxies, clusters of galaxies, and large-scale structure</span>

The following is a timeline of galaxies, clusters of galaxies, and large-scale structure of the universe.

<span class="mw-page-title-main">Virgo Supercluster</span> Former supercluster

The Local Supercluster is a formerly defined supercluster containing the Virgo Cluster and Local Group, which itself contains the Milky Way and Andromeda galaxies, as well as others. At least 100 galaxy groups and clusters are located within its diameter of 33 megaparsecs. The Virgo SC is one of about 10 million superclusters in the observable universe and is in the Pisces–Cetus Supercluster Complex, a galaxy filament.

<span class="mw-page-title-main">Supergalactic coordinate system</span>

The supergalactic coordinate system is a reference frame for the supercluster of galaxies that contains the Milky Way galaxy, referenced to a local relatively flat collection of galaxy clusters used to define the supergalactic plane.

The Great Wall, sometimes specifically referred to as the CfA2 Great Wall, is an immense galaxy filament. It is one of the largest known superstructures in the observable universe.

<span class="mw-page-title-main">Zone of Avoidance</span> Area of sky obscured by the Milky Way

The Zone of Avoidance, or Zone of Galactic Obscuration (ZGO), is the area of the sky that is obscured by the Milky Way.

<span class="mw-page-title-main">Hydra–Centaurus Supercluster</span> Former galaxy supercluster

The Hydra–Centaurus Supercluster, or the Hydra and Centaurus Superclusters, was a previously defined supercluster in two parts, which prior to the identification of Laniakea Supercluster in 2014 is the closest neighbour of the former Virgo Supercluster. Its center is located about 39 Mpc (127 Mly) away, with it extending to a maximum distance of around 69 Mpc (225 Mly).

<span class="mw-page-title-main">Norma Cluster</span> Galaxy cluster in the constellation Norma

The Norma Cluster (ACO 3627 or Abell 3627) is a rich cluster of galaxies located near the center of the Great Attractor; it is about 68 Mpc (222 Mly) distant. Although it is both nearby and bright, it is difficult to observe because it is located in the Zone of Avoidance, a region near the plane of the Milky Way. Consequently, the cluster is severely obscured by interstellar dust at optical wavelengths. Its mass is estimated to be on the order of 1015 solar masses.

<span class="mw-page-title-main">Shapley Supercluster</span> Largest concentration of galaxies in our local universe

The Shapley Supercluster or Shapley Concentration is the largest concentration of galaxies in our nearby universe that forms a gravitationally interacting unit, thereby pulling itself together instead of expanding with the universe. It appears as a striking overdensity in the distribution of galaxies in the constellation of Centaurus. It is 650 million light-years away (z=0.046).

<span class="mw-page-title-main">Pavo–Indus Supercluster</span> Neighboring supercluster in the constellations Pavo, Indus and Telescopium

The Pavo–Indus Supercluster is a neighboring supercluster located about 60–70 Mpc (196–228 Mly) away in the constellations of Pavo, Indus, and Telescopium. The supercluster contains three main clusters, Abell 3656, Abell 3698, and Abell 3742.

<span class="mw-page-title-main">Galaxy filament</span> Largest structures in the universe, made of galaxies

In cosmology, galaxy filaments are the largest known structures in the universe, consisting of walls of galactic superclusters. These massive, thread-like formations can commonly reach 50/h to 80/h megaparsecs —with the largest found to date being the Hercules-Corona Borealis Great Wall at around 3 gigaparsecs (9.8 Gly) in length—and form the boundaries between voids. Due to the accelerating expansion of the universe, the individual clusters of gravitationally bound galaxies that make up galaxy filaments are moving away from each other at an accelerated rate; in the far future they will dissolve.

The Pisces–Cetus Supercluster Complex is a galaxy filament. It includes the Laniakea Supercluster which contains the Virgo Supercluster lobe which in turn contains the Local Group, the galaxy cluster that includes the Milky Way. This filament is adjacent to the Perseus–Pegasus Filament.

<span class="mw-page-title-main">Laniakea Supercluster</span> Galaxy supercluster that is home to the Milky Way Galaxy and many more galaxies

The Laniakea Supercluster or the Local Supercluster is the galaxy supercluster that is home to the Milky Way and approximately 100,000 other nearby galaxies.

The Taurus Void is a vast, near-empty region of space situated between the Perseus–Pisces Supercluster and the Virgo Supercluster. The Taurus void is unique because of its relatively close proximity to Earth, and because it helps to define the edge of latter's home supercluster, the Virgo Supercluster. Despite its close proximity to Earth, the Taurus Void is not well-studied because it is partially obscured by the Milky Way when viewed from Earth. In contrast to its ambiguous boundary in the section of sky obscured by the Milky Way, the Taurus Void has a very well-defined boundary with the Perseus–Pisces supercluster.

The Vela Supercluster (Vela SCl, VSCL) is a massive galactic supercluster about 265.5 megaparsecs (870 million light-years) away within the vicinity of the Zone of Avoidance, centered on the constellation Vela. It is one of the largest structures found in the universe, covering about 25 × 20 degrees of the sky. It consists of two walls: a broad main wall and a secondary merging wall. The combined dimensions of the walls are 115 km/s Mpc on the major dimensions and 90 km/s Mpc on the minor ones, which corresponds to about 385 million and 300 million light years, respectively. It is about 1,000 times the mass of the Milky Way galaxy, which corresponds to a mass of 1 × 1015 M☉. About 20 initial galaxy clusters have been identified spectroscopically.

<span class="mw-page-title-main">Southern Supercluster</span> Closest neighboring galaxy supercluster

The Southern Supercluster is a nearby supercluster located around 19.5 Mpc (63.6 Mly) in the constellations of Cetus, Fornax, Eridanus, Horologium, and Dorado. It was first identified in 1953 by Gérard de Vaucouleurs.

Daniel Pomarède is a staff scientist at the Institute of Research into the Fundamental Laws of the Universe, CEA Paris-Saclay University. He co-discovered Laniakea, our home supercluster of galaxies, and Ho'oleilana, a spherical shell-like structure 1 billion light-years in diameter found in the distribution of galaxies, possibly the remnant of a Baryon Acoustic Oscillation. Specialized in data visualization and cosmography, a branch of cosmology dedicated to mapping the Universe, he also co-authored the discoveries of the Dipole Repeller and of the Cold Spot Repeller, two large influential cosmic voids, and the discovery of the South Pole Wall, a large-scale structure located in the direction of the south celestial pole beyond the southern frontiers of Laniakea.

<span class="mw-page-title-main">South Pole Wall</span> Massive cosmic structure

The South Pole Wall is a massive cosmic structure formed by a giant wall of galaxies that extends across at least 1.37 billion light-years of space, the nearest light of which is aged about half a billion light-years. The structure, in its astronomical angle, is dense in five known places including one very near to the celestial South Pole and is, according to the international team of astronomers that discovered the South Pole Wall, "...the largest contiguous feature in the local volume and comparable to the Sloan Great Wall at half the distance ...". Its discovery was announced by Daniel Pomarède of Paris-Saclay University and R. Brent Tully and colleagues of the University of Hawaiʻi in July 2020. Pomarède explained, "One might wonder how such a large and not-so distant structure remained unnoticed. This is due to its location in a region of the sky that has not been completely surveyed, and where direct observations are hindered by foreground patches of galactic dust and clouds. We have found it thanks to its gravitational influence, imprinted in the velocities of a sample of galaxies".

<span class="mw-page-title-main">ESO 383-76</span> Galaxy in the constellation Centaurus

ESO 383-76 is an elongated, X-ray luminous supergiant elliptical galaxy, residing as the dominant, brightest cluster galaxy (BCG) of the Abell 3571 galaxy cluster, the sixth-brightest in the sky at X-ray wavelengths. It is located at the distance of 200.6 megaparsecs from Earth, and is possibly a member of the large Shapley Supercluster. With a diameter of about 540.89 kiloparsecs, it is one of the largest galaxies known. It also contains a supermassive black hole, one of the most massive known with mass estimates varying from 2 billion M☉ to 28 billion M☉.

References

  1. 1 2 Kraan-Korteweg, Renée C. (2005-07-22). Röser, Siegfried (ed.). Cosmological Structures behind the Milky Way. Wiley. pp. 48–75. arXiv: astro-ph/0502217 . doi:10.1002/3527608966.ch3. ISBN   978-3-527-40608-1.
  2. 1 2 "What is the Great Attractor?". Universe Today. 14 July 2014. Retrieved 24 June 2018.
  3. ↑ Dressler, Alan (1987). "The Large-Scale Streaming of Galaxies". Scientific American. 257 (3): 46–55. ISSN   0036-8733. JSTOR   24979477.
  4. 1 2 Strauss, Michael A.; Willick, Jeffrey A. (1995-10-01). "The density and peculiar velocity fields of nearby galaxies". Physics Reports. 261 (5): 271–431. arXiv: astro-ph/9502079 . Bibcode:1995PhR...261..271S. doi:10.1016/0370-1573(95)00013-7. ISSN   0370-1573.
  5. ↑ "Cosmic Microwave Background Dipole | COSMOS". astronomy.swin.edu.au. Retrieved 2022-03-14.
  6. ↑ "Hubble focuses on "the Great Attractor"". NASA. 18 January 2013. Retrieved 24 October 2020.
  7. ↑ Kraan-Korteweg, Renée C. (2000). "Galaxies behind the Milky Way and the Great Attractor". From the Sun to the Great Attractor. Lecture Notes in Physics. Vol. 556. Berlin, Heidelberg: Springer. pp. 301–344. CiteSeerX   10.1.1.338.3806 . doi:10.1007/3-540-45371-7_8. ISBN   978-3-540-41064-5. S2CID   14507443.
  8. ↑ Mukai, Koji; Mushotzky, Rich; Masetti, Maggie. "The Great Attractor". NASA's Ask an Astrophysicist. Archived from the original on 18 February 2003. It is now thought that the Great Attractor is probably a supercluster, with Abell 3627 near its center.
  9. ↑ Stephen D. Landy; Alexander S. Szalay (June 1992). "A general analytical solution to the problem of Malmquist bias due to lognormal distance errors". The Astrophysical Journal . 391: 494–501. Bibcode:1992ApJ...391..494L. doi:10.1086/171365. ISSN   0004-637X. Wikidata   Q55968841.
  10. ↑ "X-rays reveal what makes the Milky Way move" (Press release). Ifa.hawaii.edu. 11 January 2006. Retrieved 24 October 2020.
  11. 1 2 Jarrett, T. H.; Koribalski, B. S.; Kraan-Korteweg, R. C.; Woudt, P. A.; Whitney, B. A.; Meade, M. R.; Babler, B.; Churchwell, E.; Benjamin, R. A.; Indebetouw, R. (March 2007). "Discovery of Two Galaxies Deeply Embedded in the Great Attractor Wall". The Astronomical Journal. 133 (3): 979–986. arXiv: astro-ph/0611397 . Bibcode:2007AJ....133..979J. doi:10.1086/510668. ISSN   0004-6256. S2CID   5930404.
  12. ↑ Woudt, P. A.; Kraan-Korteweg, R. C.; Lucey, J.; Fairall, A. P.; Moore, S. A. W. (2008-01-01). "The Norma cluster (ACO 3627) - I. A dynamical analysis of the most massive cluster in the Great Attractor". Monthly Notices of the Royal Astronomical Society. 383 (2): 445–457. arXiv: 0706.2227 . Bibcode:2008MNRAS.383..445W. doi: 10.1111/j.1365-2966.2007.12571.x . ISSN   0035-8711.
  13. ↑ R. Brent Tully; Hélène Courtois; Yehuda Hoffman; Daniel Pomarède (3 September 2014). "The Laniakea supercluster of galaxies". Nature . 513 (7516): 71–73. arXiv: 1409.0880 . Bibcode:2014Natur.513...71T. doi:10.1038/NATURE13674. ISSN   1476-4687. PMID   25186900. S2CID   205240232. Wikidata   Q28314882.

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