Huge-LQG

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Huge-LQG CCLQG.png
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Above: Map of the Huge-LQG noted by black circles, adjacent to the Clowes–Campusano LQG in red crosses. Map is by Roger Clowes of University of Central Lancashire. Each black circle and red cross on the map is a quasar similar to this one. Bottom: Image of the bright quasar 3C 273.

The Huge Large Quasar Group, (Huge-LQG, also called U1.27) is a possible structure or pseudo-structure of 73 quasars, referred to as a large quasar group, that measures about 4 billion light-years across. At its discovery, it was identified as the largest and the most massive known structure in the observable universe, [1] [2] [3] though it has been superseded by the Hercules–Corona Borealis Great Wall at 10 billion light-years. [4] There are also issues about its structure (see Dispute section below).

Contents

Discovery

Roger G. Clowes, together with colleagues from the University of Central Lancashire in Preston, United Kingdom, had reported on January 11, 2013 a grouping of quasars within the vicinity of the constellation Leo. They used data from the DR7QSO catalogue of the comprehensive Sloan Digital Sky Survey, a major multi-imaging and spectroscopic redshift survey of the sky. They reported that the grouping was, as they announced, the largest known structure in the observable universe. The structure was initially discovered in November 2012 and took two months of verification before its announcement. News about the structure's announcement spread worldwide, and has received great attention from the scientific community.

Characteristics

The Huge-LQG was estimated to be about 1.24  Gpc in length, by 640 Mpc and 370 Mpc on the other dimensions, and contains 73 quasars, respectively. [5] Quasars are very luminous active galactic nuclei, thought to be supermassive black holes feeding on matter. Since they are only found in dense regions of the universe, quasars can be used to find overdensities of matter within the universe. It has the approximate binding mass of 6.1×1018 (6.1 trillion (long scale) or 6.1 quintillion (short scale)) M☉. The Huge-LQG was initially named U1.27 due to its average redshift of 1.27 (where the "U" refers to a connected unit of quasars), [3] placing its distance at about 9 billion light-years from Earth. [6]

The Huge-LQG is 615 Mpc from the Clowes–Campusano LQG (U1.28), a group of 34 quasars also discovered by Clowes in 1991.

Cosmological principle

In Clowes' initial announcement of the structure, he has reported that the structure has contradicted the cosmological principle. The cosmological principle implies that at sufficiently large scales, the universe is approximately homogeneous, meaning that the statistical fluctuations in quantities such as the matter density between different regions of the universe are small. However, different definitions exist for the homogeneity scale above which these fluctuations may be considered sufficiently small, and the appropriate definition depends on the context in which it is used. Jaswant Yadav et al. have suggested a definition of the homogeneity scale based on the fractal dimension of the universe; they conclude that, according to this definition, an upper limit for the homogeneity scale in the universe is 260/h Mpc. [7] Some studies that have attempted to measure the homogeneity scale according to this definition have found values in the range 70–130/h Mpc. [8] [9] [10]

The Sloan Great Wall, discovered in 2003, has a length of 423 Mpc, [11] which is marginally larger than the homogeneity scale as defined above.

The Huge-LQG is three times longer than, and twice as wide as the Yadav et al. upper limit to the homogeneity scale, and has therefore been claimed to challenge our understanding of the universe on large scales. [3]

However, due to the existence of long-range correlations, it is known that structures can be found in the distribution of galaxies in the universe that extend over scales larger than the homogeneity scale. [12]

Dispute

One of the questions that arose after the discovery of the Huge-LQG was regarding the method used in its identification. In the initial paper by Clowes et al., the standard used was statistical friend-of-friends method, which has also been used to identify other similar LQGs.

This method has been put into question in a paper by Seshadri Nadathur from the University of Bielefeld. By utilizing a new map that includes all the quasars in the region (including those not included from the 73 quasars of the group), the presence of a structure became less noticeable.

After performing a number of statistical analyses on the quasar data, and finding extreme changes in the Huge-LQG membership and shape with small changes in the cluster finding parameters, he determined the probability that apparent clusters the size of the Huge-LQG would appear in a random assortment of quasars, by utilizing the similar friends-of-friends method originally used. Using a Monte Carlo method of at least a thousand runs, he generated a set of random points in three-dimensional space and identified 10,000 regions identical in size to that studied by Clowes, and filled them with randomly distributed quasars with the same position statistics as did the actual quasars in the sky. [10] The original method by Clowes produces at least a thousand clusterings identical to the Huge-LQG, even on regions where one should expect the distribution to be truly random. The data is supporting the study of the homogeneity scale by Yadav et al., [7] and that there is, therefore, no challenge to the cosmological principle. The identification of the Huge-LQG, together with the clusterings identified by Nadathur, is therefore referred to be false positive identifications or errors due to a miscalculation of the statistical measurement used, finally arriving at the conclusion that the Huge-LQG is not a real structure at all.

Nevertheless, Clowes et al. found independent support for the reality of the structure from its coincidence with Mg II absorbers (once-ionised magnesium gas, commonly used to probe distant galaxies). The Mg II gas suggests that the Huge-LQG is associated with an enhancement of the mass, rather than being a false positive identification. This point is not discussed by the critical paper. [10]

Further support for the reality of the Huge-LQG comes from the work of Hutsemékers et al. [13] in September 2014. They measured the polarization of quasars in the Huge-LQG and found "a remarkable correlation" of the polarization vectors on scales larger than 500 Mpc.

See also

Related Research Articles

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<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">Hubble's law</span> Observation in physical cosmology

Hubble's law, also known as the Hubble–Lemaître law, is the observation in physical cosmology that galaxies are moving away from Earth at speeds proportional to their distance. In other words, the farther they are, the faster they are moving away from Earth. The velocity of the galaxies has been determined by their redshift, a shift of the light they emit toward the red end of the visible spectrum. The discovery of Hubble's law is attributed to Edwin Hubble's work published in 1929.

In modern physical cosmology, the cosmological principle is the notion that the spatial distribution of matter in the universe is uniformly isotropic and homogeneous when viewed on a large enough scale, since the forces are expected to act equally throughout the universe on a large scale, and should, therefore, produce no observable inequalities in the large-scale structuring over the course of evolution of the matter field that was initially laid down by the Big Bang.

<span class="mw-page-title-main">Observable universe</span> All of space observable from the Earth at the present

The observable universe is a ball-shaped region of the universe comprising all matter that can be observed from Earth or its space-based telescopes and exploratory probes at the present time; the electromagnetic radiation from these objects has had time to reach the Solar System and Earth since the beginning of the cosmological expansion. Initially, it was estimated that there may be 2 trillion galaxies in the observable universe. That number was reduced in 2021 to only several hundred billion based on data from New Horizons. Assuming the universe is isotropic, the distance to the edge of the observable universe is roughly the same in every direction. That is, the observable universe is a spherical region centered on the observer. Every location in the universe has its own observable universe, which may or may not overlap with the one centered on Earth.

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<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.

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A large quasar group (LQG) is a collection of quasars that form what are thought to constitute the largest astronomical structures in the observable universe. LQGs are thought to be precursors to the sheets, walls and filaments of galaxies found in the relatively nearby universe.

The Clowes–Campusano LQG is a large quasar group, consisting of 34 quasars and measuring about 2 billion light-years across. It is one of the largest known superstructures in the observable universe. It is located near the larger Huge-LQG. It was discovered by the astronomers Roger Clowes and Luis Campusano in 1991.

U1.11 is a large quasar group located in the constellations of Leo and Virgo. It is one of the largest LQG's known, with the estimated maximum diameter of 780 Mpc and contains 38 quasars. It was discovered in 2011 during the course of the Sloan Digital Sky Survey. Until the discovery of the Huge-LQG in November 2012, it was the largest known structure in the universe, beating Clowes–Campusano LQG's 20-year record as largest known structure at the time of its discovery.

References

  1. ↑ Aron, Jacob. "Largest structure challenges Einstein's smooth cosmos". New Scientist . Retrieved 14 January 2013.
  2. ↑ "Astronomers discover the largest structure in the universe". Royal astronomical society. Archived from the original on 2013-01-14. Retrieved 2013-01-13.
  3. 1 2 3 Clowes, Roger G.; Harris, Kathryn A.; Raghunathan, Srinivasan; Campusano, Luis E.; Söchting, Ilona K.; Graham, Matthew J. (2013-01-11). "A structure in the early Universe at z ~ 1.3 that exceeds the homogeneity scale of the R-W concordance cosmology". Monthly Notices of the Royal Astronomical Society. 1211 (4): 6256. arXiv: 1211.6256 . Bibcode:2013MNRAS.429.2910C. doi:10.1093/mnras/sts497. S2CID   486490.
  4. ↑ SciShow Space (21 July 2016). "The Impossibly Huge Quasar Group". YouTube .
  5. ↑ "The Largest Structure in Universe Discovered – Quasar Group 4 Billion Light-Years Wide Challenges Current Cosmology". Archived from the original on 15 January 2013. Retrieved 14 January 2013.
  6. ↑ Prostak, Sergio (11 January 2013). "Universe's Largest Structure Discovered". scinews.com. Retrieved 15 January 2013.
  7. 1 2 Yadav, Jaswant; Bagla, J. S.; Khandai, Nishikanta (25 February 2010). "Fractal dimension as a measure of the scale of homogeneity". Monthly Notices of the Royal Astronomical Society. 405 (3): 2009–2015. arXiv: 1001.0617 . Bibcode:2010MNRAS.405.2009Y. doi:10.1111/j.1365-2966.2010.16612.x. S2CID   118603499.
  8. ↑ Hogg, D.W.; et al. (2005). "Cosmic Homogeneity Demonstrated with Luminous Red Galaxies". The Astrophysical Journal. 624 (1): 54–58. arXiv: astro-ph/0411197 . Bibcode:2005ApJ...624...54H. doi:10.1086/429084. S2CID   15957886.
  9. ↑ Scrimgeour, Morag I.; et al. (2012). "The WiggleZ Dark Energy Survey: the transition to large-scale cosmic homogeneity". Monthly Notices of the Royal Astronomical Society. 425 (1): 116–134. arXiv: 1205.6812 . Bibcode:2012MNRAS.425..116S. doi:10.1111/j.1365-2966.2012.21402.x. S2CID   19959072.
  10. 1 2 3 Nadathur, Seshadri, (July 2013) "Seeing patterns in noise: gigaparsec-scale 'structures' that do not violate homogeneity". Monthly Notices of the Royal Astronomical Society in press. arXiv:1306.1700. Bibcode: 2013MNRAS.tmp.1690N doi : 10.1093/mnras/stt1028
  11. ↑ Gott, J. Richard III; et al. (May 2005). "A Map of the Universe". The Astrophysical Journal. 624 (2): 463–484. arXiv: astro-ph/0310571 . Bibcode:2005ApJ...624..463G. doi:10.1086/428890. S2CID   9654355.
  12. ↑ Gaite, Jose; Dominguez, Alvaro; Perez-Mercader, Juan (1999). "The fractal distribution of galaxies and the transition to homogeneity". The Astrophysical Journal. 522 (1): 5–8. arXiv: astro-ph/9812132 . Bibcode:1999ApJ...522L...5G. doi:10.1086/312204. S2CID   966351.
  13. ↑ Hutsemekers, D.; Braibant, L.; Pelgrims, V.; Sluse, D. (2014). "Alignment of quasar polarizations with large-scale structures". Astronomy & Astrophysics. 572: A18. arXiv: 1409.6098 . Bibcode:2014A&A...572A..18H. doi:10.1051/0004-6361/201424631. S2CID   56092977.

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