Object 112: Norma Cluster

Podcast release date: 27 November 2023

Right ascension: 16:14:22.5


Epoch: ICRS

Constellation: Norma

Corresponding Earth location: About 1400 km from Antarctica in the Pacific Ocean

This episode's coordinates point to a cluster of galaxies called the Norma Cluster. It would have been cool if this constellation was named after someone called Norma, such as, for example, Norma Jeane Baker, but instead the Norma Cluster is named after the constellation in which it is found (although technically it straddles the borders between the constellation Norma and another one named Triangulum Australe). It would be cool if the constellation Norma was named after someone called Norma, but instead the constellation's name is derived from the extended Latin phrase "Norma et Regula" or "the set square and the ruler" [1]. In other words, this constellation was supposed to represent the type of square used by draftspeople for making technical diagrams. This is another idiotic constellation invented by the eighteenth century French astronomer and general weirdo Nicolas Louis de la Caille [1], and like many of his other idiotic constellations, it's located in the southern hemisphere and composed of a bunch of faint stars that are nearly impossible to see and could represent virtually anything you could imagine.

Anyway, the Norma Cluster was originally found by George Abell working with Harold Corwin. George Abell was a twentieth century expert at finding clusters of galaxies by spending enormous amounts of time staring at photographic plates, so a lot of clusters are named after him (and indeed the Norma Cluster is also known as Abell 3627). The discovery of the Norma Cluster was published in 1989, six years after Abell's death, by Harold Corwin working with Ronald Olowin, although they both still credit George Abell as the lead author on the publication [2].

The Norma Cluster is rather large. The estimated mass is about 1 quadrillion times the mass of the Sun [3]; for reference, one quadrillion is 1015, or a 1 followed by 15 zeroes. (I had to look that up.) This is roughly 1000 times the mass of the Milky Way. Around 300 galaxies have been identified as members of the cluster [4], but that number is probably much smaller than the actual number of galaxies in the Norma Cluster for two reasons. First, the cluster is located at a distance of about 230 million light years (70 Mpc) [5], which means that it's going to be difficult to see any of the fainter or smaller galaxies in the cluster. Second, astronomers on Earth need to look through the plane of the Milky Way to see the cluster, and interstellar dust within the plane of our galaxy tends to obscure the galaxies within the Norma Cluster. This is why the cluster was not discovered until the 1980s. The cluster also contains a huge amount of really hot X-ray emitting gas located in between the galaxies in the cluster. Many other clusters of galaxies contain this type of hot gas, but the Norma Cluster is so massive that it is actually one of the brightest clusters in the sky in terms of X-ray emission [6]. However, despite the fact that astronomers really like studying the Norma Cluster because it is such an unusually large cluster of galaxies, this is not the most interesting thing about this cluster.

The Norma Cluster is potentially most notably known as part of a much much larger object called the Great Attractor [7]. At this point, if you've seen the movie Men in Black, you might be thinking of that one scene with the bouncing ball, although they seem to imply that the Great Attractor is a single individual that identifies as male [8], which never made sense to me. Anyway, in astronomy, the Great Attractor was something that was initially hypothesized in the mid-1980s by people doing surveys of galaxies in the nearby universe who noticed that, on extremely large scales, galaxies were not moving as expected based on the expansion of the universe but instead seems to be gravitationally drawn towards some sort of much larger object that, as of that time, had not been identified [9, 10]. In the mid-1990s, people figured out that things were moving towards a large concentration of galaxies 50 quadrillion times the mass of the Sun in a location heavily obscured by the plane of the Milky Way that they named the Great Attractor, and the newly-discovered Norma Cluster was identified as being located at the center of this much larger object [7].

These and subsequent discoveries have had major implications for understanding how large-scale structures in the universe form. Galaxies are thought to have formed within a billion years after the Big Bang, but it seemed to take a couple more billions of years for many of these galaxies to form gravitationally bound clusters. This is mainly because it takes time for gravity to affect things on really large scales, so it's not possible to form very large gravitationally bound objects like clusters of galaxies right away. In the present, those clusters of galaxies are now forming into gravitationally bound superclusters. Our Milky Way is located within a gravitationally bound group of galaxies called the Local Group, and that group lies within a much larger structure called the Local Supercluster which is centered within the Virgo Cluster. The Local Supercluster as well as a few other nearby superclusters are part of an even larger object called the Laniakea Supercluster [11], which was named this because Brent Tully, who was the person who lead the team that discovered the cluster, lives in Hawaii, and he probably thought that it would be really cool to give this cluster a Hawaiian name. (By the way, Laniakea means "immense heaven" [12].)

All of the galaxies and groups and clusters of galaxies within the Laniakea Supercluster are being gravitationally pulled into the supercluster's center, and that is either the Norma Cluster itself or very near to where the Norma Cluster is located. You could therefore conclude that, in the grand scheme of things, the Great Attractor, including the Norma Cluster, is going to have an incredibly huge influence on our galaxy and our Solar System, although the timescales are so long that the Sun will have probably expanded to form a red giant and consumed the Earth before transforming into a white dwarf, so we won't be around to see what happens.


[1] Ridpath, Ian, Star tales, 1988

[2] Abell, George O. et al., A Catalog of Rich Clusters of Galaxies, 1989, Astrophysical Journal Supplement Series, 70, 1

[3] Woudt, P. A. et al., The Norma cluster (ACO 3627) - I. A dynamical analysis of the most massive cluster in the Great Attractor, 2008, Monthly Notices of the Royal Astronomical Society, 383, 445

[4] Skelton, R. E. et al., The Norma cluster (ACO3627) - II. The near-infrared Ks-band luminosity function, 2009, Monthly Notices of the Royal Astronomical Society, 396, 2367

[5] Mutabazi, T., The Distance and Peculiar Velocity of the Norma Cluster (ACO3627) Using the Near-infrared J- and Ks-band Fundamental Plane Relations, 2021, Astrophysical Journal, 911, 16

[6] Boehringer, H. et al., Abell 3627: A Nearby, X-Ray Bright, and Massive Galaxy Cluster, 1996, Astrophysical Journal, 467, 168

[7] Kraan-Korteweg, R. C. et al., A nearby massive galaxy cluster behind the Milky Way, 1996, Nature, 379, 519

[8] Quotes.net, Men in Black Quotes, 2023, STANDS4 LLC

[9] Dressler, Alan, The Supergalactic Plane Redshift Survey: A Candidate for the Great Attractor, 1988, Astrophysical Journal, 329, 519

[10] Lynden-Bell, D. et al., Photometry and Spectroscopy of Elliptical Galaxies. V. Galaxy Streaming toward the New Supergalactic Center, 1988, Astrophysical Journal, 326, 19

[11] Tully, R. Brent et al., The Laniakea supercluster of galaxies, 2014, Nature, 513, 71

[12] Sample, Ian, Milky Way is on the outskirts of 'immeasurable heaven' supercluster, 2014, The Guardian


Podcast and Website: George J. Bendo

Music: Immersion by Sascha Ende

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