Timeline of knowledge about galaxies, clusters of galaxies, and large-scale structure

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


Pre-20th century

Early 20th century

Mid-20th century

Late 20th century

Early 21st century

See also

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<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 hundred million 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">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. 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">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">Virgo Supercluster</span> Galactic supercluster containing the Virgo Cluster

The Virgo Supercluster or the Local Supercluster is a mass concentration of galaxies 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">Great Attractor</span> Apparent gravitational anomaly at the center of the local Laniakea Supercluster

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

<span class="mw-page-title-main">Astronomical object</span> Large natural physical entity in space

An astronomical object, celestial object, stellar object or heavenly body is a naturally occurring physical entity, association, or structure that exists within the observable universe. In astronomy, the terms object and body are often used interchangeably. However, an astronomical body or celestial body is a single, tightly bound, contiguous entity, while an astronomical or celestial object is a complex, less cohesively bound structure, which may consist of multiple bodies or even other objects with substructures.

<span class="mw-page-title-main">Spiral galaxy</span> Class of galaxy that has spiral structures extending from their cores.

Spiral galaxies form a class of galaxy originally described by Edwin Hubble in his 1936 work The Realm of the Nebulae and, as such, form part of the Hubble sequence. Most spiral galaxies consist of a flat, rotating disk containing stars, gas and dust, and a central concentration of stars known as the bulge. These are often surrounded by a much fainter halo of stars, many of which reside in globular clusters.

<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.

<span class="mw-page-title-main">Interacting galaxy</span> Galaxies with interacting gravitational fields

Interacting galaxies are galaxies whose gravitational fields result in a disturbance of one another. An example of a minor interaction is a satellite galaxy disturbing the primary galaxy's spiral arms. An example of a major interaction is a galactic collision, which may lead to a galaxy merger.

<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">NGC 4889</span> Galaxy in the constellation Coma Berenices

NGC 4889 is an E4 supergiant elliptical galaxy. It was discovered in 1785 by the British astronomer Frederick William Herschel I, who catalogued it as a bright, nebulous patch. The brightest galaxy within the northern Coma Cluster, it is located at a median distance of 94 million parsecs from Earth. At the core of the galaxy is a supermassive black hole that heats the intracluster medium through the action of friction from infalling gases and dust. The gamma ray bursts from the galaxy extend out to several million light years of the cluster.

<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 gravitationally bound galactic superclusters. These massive, thread-like formations can reach 80 megaparsecs h−1 and form the boundaries between voids. Galaxy filaments form the cosmic web and define the overall structure of the observable universe.

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">BX442</span> Distant grand design spiral galaxy in the constellation Pegasus

BX442 (Q2343-BX442) is a grand design spiral galaxy of type Sc. It has a companion dwarf galaxy. It is the most distant known grand design spiral galaxy in the universe, with a redshift of z=2.1765 ± 0.0001. Although commonly referred to as the oldest known grand design spiral galaxy in the universe, it is more accurately the earliest such galaxy known to exist in the universe, with a lookback time (the difference between the age of the universe now and the age of the universe at the time light left the galaxy) of 10.7 billion years in the concordance cosmology. This time estimate means that structure seen in BX442 developed roughly 3 billion years after the Big Bang. It is 15 kiloparsecs (50 kly) in diameter, and has a mass of 6 × 1010 solar masses.

<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 is the galaxy supercluster that is home to the Milky Way and approximately 100,000 other nearby galaxies.

The following outline is provided as an overview of and topical guide to galaxies:

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.

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".


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