A starburst galaxy is a galaxy undergoing an exceptionally high rate of star formation, as compared to the long-term average rate of star formation in the galaxy or the star formation rate observed in most other galaxies. For example, the star formation rate of the Milky Way galaxy is approximately 3 M☉/yr, however, starburst galaxies can experience star formation rates that are more than a factor of 100 times greater. In a starburst galaxy, the rate of star formation is so large that the galaxy will consume all of its gas reservoir, from which the stars are forming, on a timescale much shorter than the age of the galaxy. As such, the starburst nature of a galaxy is a phase, and one that typically occupies a brief period of a galaxy's evolution. The majority of starburst galaxies are in the midst of a merger or close encounter with another galaxy. Starburst galaxies include M82, NGC 4038/NGC 4039 (the Antennae Galaxies), and IC 10.
Starburst galaxies are defined by these three interrelated factors:
Commonly used definitions include:
Mergers and tidal interactions between gas-rich galaxies play a large role in driving starbursts. Galaxies in the midst of a starburst frequently show tidal tails, an indication of a close encounter with another galaxy, or are in the midst of a merger. Interactions between galaxies that do not merge can trigger unstable rotation modes, such as the bar instability, which causes gas to be funneled towards the nucleus and ignites bursts of star formation near the galactic nucleus. It has been shown that there is a strong correlation between the lopsidedness of a galaxy and the youth of its stellar population, with more lopsided galaxies having younger central stellar populations. As lopsidedness can be caused by tidal interactions and mergers between galaxies, this result gives further evidence that mergers and tidal interactions can induce central star formation in a galaxy and drive a starburst.
Classifying types of starburst galaxies is difficult since starburst galaxies do not represent a specific type in and of themselves. Starbursts can occur in disk galaxies, and irregular galaxies often exhibit knots of starburst spread throughout the irregular galaxy. Nevertheless, astronomers typically classify starburst galaxies based on their most distinct observational characteristics. Some of the categorizations include:
Firstly, a starburst galaxy must have a large supply of gas available to form stars. The burst itself may be triggered by a close encounter with another galaxy (such as M81/M82), a collision with another galaxy (such as the Antennae), or by another process which forces material into the centre of the galaxy (such as a stellar bar).
The inside of the starburst is quite an extreme environment. The large amounts of gas mean that very massive stars are formed. Young, hot stars ionize the gas (mainly hydrogen) around them, creating H II regions. Groups of very hot stars are known as OB associations. These stars burn very bright and very fast, and are quite likely to explode at the end of their lives as supernovae.
After the supernova explosion, the ejected material expands and becomes a supernova remnant. These remnants interact with the surrounding environment within the starburst (the interstellar medium) and can be the site of naturally occurring masers.
Studying nearby starburst galaxies can help us determine the history of galaxy formation and evolution. Large numbers of the very distant galaxies seen, for example, in the Hubble Deep Field are known to be starbursts, but they are too far away to be studied in any detail. Observing nearby examples and exploring their characteristics can give us an idea of what was happening in the early universe as the light we see from these distant galaxies left them when the universe was much younger (see redshift). However, starburst galaxies seem to be quite rare in our local universe, and are more common further away - indicating that there were more of them billions of years ago. All galaxies were closer together then, and therefore more likely to be influenced by each other's gravity. More frequent encounters produced more starbursts as galactic forms evolved with the expanding universe.
M82 is the archetypal starburst galaxy. Its high level of star formation is due to a close encounter with the nearby spiral M81. Maps of the regions made with radio telescopes show large streams of neutral hydrogen connecting the two galaxies, also as a result of the encounter. Radio images of the central regions of M82 also show a large number of young supernova remnants, left behind when the more massive stars created in the starburst came to the end of their lives. The Antennae is another starburst system, detailed by a Hubble picture, released in 1997.
|M82||I0||Archetype starburst galaxy|
|The Antennae||SB(s)m pec /
|This is actually two colliding galaxies|
|IC 10||dIrr||Mild starburst galaxy|
|HXMM01||Extreme starburst merging galaxies|
|HFLS3||Unusually large intense starburst galaxy|
|NGC 1569||IBm||Dwarf galaxy undergoing a galaxy-wide starburst|
|NGC 2146||SB(s)ab pec|
|NGC 1705||SA0− pec|
|NGC 1614||SB(s)c pec||Merging with another galaxy|
|NGC 6946||SAB(rs)cd||Also known as fireworks galaxy for frequent supernovae|
|Baby Boom Galaxy||Brightest starburst galaxy in distant universe|
|Centaurus A||E(p)||Only known case of an "Elliptical Starburst" Galaxy|
|Haro 11||Emits Lyman continuum photons|
|Sculptor Galaxy||SAB(s)c||Nearest starburst galaxy.||,|
The Baby Boom Galaxy is a starburst galaxy located 12.2 billion light years away. Discovered by NASA's Spitzer Science Center at the California Institute of Technology, the galaxy is the record holder for the brightest starburst galaxy in the very distant universe, with brightness being a measure of its extreme star-formation rate. The Baby Boom Galaxy has been nicknamed "the extreme stellar machine" because it is seen producing stars at a rate of up to 4,000 per year (one star every 2.2 hours). The Milky Way galaxy in which Earth resides turns out an average of just 10 stars per year.Hen 2-10
Hen 2-10, also known as He 2-10 and Henize 2-10, is a dwarf starburst galaxy located 34 million light years away in the constellation of Pyxis. The galaxy is believed to be an early stage starburst galaxy. A black hole was later discovered near the center of the dwarf galaxy, suggesting that the black holes found at the center of most large galaxies may have formed before the galaxies themselves. Recent estimates have placed the mass of this black hole around 3×106 M☉, and the mass of the entire dwarf galaxy at about 1×1010 M☉.MS 1512-cB58
MS 1512-cB58 is a galaxy in the Boötes constellation. It is a starburst galaxy that is being strongly gravitationally lensed, magnifying its apparent size by 30−50 times.Messier 82
Messier 82 (also known as NGC 3034, Cigar Galaxy or M82) is a starburst galaxy approximately 12 million light-years away in the constellation Ursa Major. A member of the M81 Group, it is about five times more luminous than the whole Milky Way and has a center one hundred times more luminous than our galaxy's center. The starburst activity is thought to have been triggered by interaction with neighboring galaxy M81. As the closest starburst galaxy to Earth, M82 is the prototypical example of this galaxy type. SN 2014J, a type Ia supernova, was discovered in the galaxy on 21 January 2014. In 2014, in studying M82, scientists discovered the brightest pulsar yet known, designated M82 X-2.NGC 1140
NGC 1140 is an irregular galaxy in the southern constellation of Eridanus. Estimates made using the Tully–Fisher method put the galaxy at about 59 million light years (18 megaparsecs). It was discovered on 22 November 1786 by William Herschel, and was described as "pretty bright, small, round, stellar" by John Louis Emil Dreyer, the compiler of the New General Catalogue.NGC 1140 is a starburst galaxy, meaning it is forming stars at a very fast rate. In fact, while it is only a tenth as wide as the Milky Way, it is producing stars at a rate of 0.65 M☉/yr, about the same as the Milky Way. The image taken by the Hubble Space Telescope shows bright blue and red regions of star formation, similar to NGC 1569. The starburst is estimated to have began about 5 million years ago. Its low metallicity (the ratio of hydrogen and helium to other elements) makes NGC 1140 similar to primordial galaxies.Wolf–Rayet stars, a class of blue, massive, and luminous stars, are present in this galaxy; in fact, NGC 1140 has so many of them that their spectra also appear in the galaxy's spectrum. These types of galaxies are known Wolf–Rayet galaxies, and are fairly rare because Wolf–Rayet stars have short lives.NGC 1222
NGC 1222 is an early-type lenticular galaxy located in the constellation of Eridanus. The galaxy was discovered on 5 December 1883 by the French astronomer Édouard Stephan. John Louis Emil Dreyer, the compiler of the New General Catalogue, described it as a "pretty faint, small, round nebula" and noted the presence of a "very faint star" superposed on the galaxy.NGC 1222's morphological type of S0− would suggest that it should have a mostly smooth profile and a very dull appearance. However, the galaxy was imaged by the Hubble Space Telescope in 2016, and the image showed that there were several bright blue star forming regions, as well as dark reddish areas of interstellar dust. NGC 1222 is currently interacting with and swallowing two dwarf galaxies that are supplying the gas and dust needed to become a starburst galaxy.NGC 1334
NGC 1334 is a spiral galaxy located about 185 million light-years away in the constellation Perseus. It was discovered by astronomer Heinrich d'Arrest on February 14, 1863. NGC 1334 is a member of the Perseus Cluster and is a starburst galaxy. It also appears to have a complex disorted structure.NGC 2146
NGC 2146 is a barred spiral galaxy type SB(s)ab pec in the constellation Camelopardalis. The galaxy was discovered in 1876 by Friedrich August Theodor Winnecke.It has a diameter of 80,000 lyr. The galaxy's most conspicuous feature is the dusty lanes of a spiral arm lying across the core of the galaxy as seen from Earth, the arm having been bent 45 degrees by a close encounter with a smaller galaxy possibly NGC 2146a about 0.8 billion years ago. This close encounter is credited with the relatively high rates of star formation that qualify NGC 2146 as a starburst galaxy.NGC 3310
NGC 3310 is a grand design spiral galaxy in the constellation Ursa Major. It is a starburst galaxy and it is likely that NGC 3310 collided with one of its satellite galaxies about 100 million years ago, triggering widespread star formation. It is thought to be located approximately 46 million light-years away from the Earth, and is thought to be about 22,000 light-years wide.
The ring clusters of NGC 3310 have been undergoing starburst activity for at least the last 40 million years.NGC 3921
NGC 3921 is a interacting galaxy in the northern constellation of Ursa Major. Estimates using redshift put the galaxy at about 59 million light years (18 megaparsecs) away. It was discovered on 14 April 1789 by William Herschel, and it was described as "pretty faint, small, round" by John Louis Emil Dreyer, the compiler of the New General Catalogue.NGC 3921 is the remnant of a galaxy merger. The two progenitor galaxies are thought to have been disk galaxies that collided about 700 million years ago. The image shows noticeable star formation and structures like loops, indicative of galaxies interacting. Because of this, NGC 3921 was included in Halton Arp's Atlas of Peculiar Galaxies under the designation Arp 224.Being a starburst galaxy, NGC 3921 has important features. One of them is an ultraluminous X-ray source, designated X-2, with an X-ray luminosity of 8×1039 erg/s. Additionally, two candidates globular clusters have been detected within NGC 3921. They are both fairly young, and are about half as massive as Omega Centauri: this demonstrates that mergers of gas-rich galaxies can also create more metal-rich globular clusters.NGC 4236
NGC 4236 (also known as Caldwell 3) is a barred spiral galaxy located in the constellation Draco.
The galaxy is a member of the M81 Group, a group of galaxies located at a distance of approximately 11.7 Mly (3.6 Mpc) from Earth. The group also contains the spiral galaxy Messier 81 and the starburst galaxy Messier 82. NGC 4236 is located away from the central part of the M81 group at a distance of is 14.5 Mly (4.45 Mpc) from Earth.NGC 4414
NGC 4414 is an unbarred spiral galaxy about 62 million light-years away in the constellation Coma Berenices. It is a flocculent spiral galaxy, with short segments of spiral structure but without the dramatic well-defined spiral arms of a grand design spiral. In 1974 a supernova, SN 1974G, was observed and was the only supernova in this galaxy to be recorded until June 7, 2013 when SN 2013df was discovered at Magnitude 14.
It was imaged by the Hubble Space Telescope in 1995, as part of the HST's main mission to determine the distance to galaxies, and again in 1999 as part of the Hubble Heritage project. It has been part of an ongoing effort to study its Cepheid variable stars. The outer arms appear blue due to the continuing formation of young stars and include a possible luminous blue variable with an absolute magnitude of −10.NGC 4414 is also a very isolated galaxy without signs of past interactions with other galaxies and despite not being a starburst galaxy shows a high density and richness of gas - both atomic and molecular, with the former extending far beyond its optical disk.NGC 4414 is a member of the Coma I Group, a group of galaxies lying physically close to the Virgo Cluster.NGC 4490
NGC 4490, also known as the Cocoon Galaxy, is a barred spiral galaxy in the constellation Canes Venatici. It lies at a distance of 25 million light years from Earth. It interacts with its smaller companion NGC 4485 and as a result is a starburst galaxy. NGC 4490 and NGC 4485 are collectively known in the Atlas of Peculiar Galaxies as Arp 269. NGC 4490 is located 3/4° northwest of beta Canum Venaticorum and with apparent visual magnitude 9.8, can be observed with 15x100 binoculars. It is a member of Herschel 400 Catalogue. It belongs in Canes Venatici galaxy cloud II.
It was discovered by William Herschel in 1788. Two supernovae have been observed in NGC 4490, SN 1982F, and type II-P SN 2008ax, with peak magnitude 16.1.NGC 4527
NGC 4527 is a Spiral galaxy in the constellation Virgo.NGC 4861
NGC 4861, also known as Arp 266, is a galaxy in the constellation Canes Venatici. It was discovered by William Herschel on May 1, 1785.Morphological classification of NGC 4861 has proved relatively difficult. Its mass, size, and rotational velocity are consistent with it being a spiral galaxy. However, due to its highly irregular shape, it may also be classified as a dwarf irregular galaxy. In fact, since dwarf galaxies are less massive and have lower gravitational potentials, gases and other material for star formation can move within them much faster, causing the galaxy to become a specific type of starburst galaxy, called a blue compact dwarf galaxy.NGC 5930
NGC 5930 is a starburst galaxy in the constellation Boötes that is interacting with the nearby Seyfert galaxy NGC 5929. 5930 has a morphological classification of SAB(rs)b pec, indicating that it is a weakly-barred spiral galaxy with a poorly defined nuclear ring structure. It is inclined at an angle of 46° to the line of sight from the Earth.NGC 7673
NGC 7673 is a disturbed spiral galaxy located in the constellation Pegasus. The galaxy has recently experienced intense star formation activity and may therefore be referred to as a starburst galaxy.NGC 908
NGC 908 is an unbarred spiral galaxy in the constellation Cetus. It is at a distance of 60 million light years away from Earth. NGC 908 has vigorous star formation and is a starburst galaxy. The galaxy has three-arm spiral pattern, with two arms with peculiar morphology. The central bulge of the galaxy is bright. Cluster of young stars and star forming knots can be seen in the arms. Starburst activity and the peculiar morphology of the galaxy indicated it has a close encounter with another galaxy, although none is visible now. NGC 908 was discovered in 1786 by William Herschel. Two supernovae have been observed in NGC 908, SN 1994ai (Ic type, mag. 17) and SN 2006ce (Ia type, mag. 12.4). It is the main galaxy in the NGC 908 group, which also includes NGC 899, NGC 907 and IC 223.Starburst region
A starburst is an astrophysical process that involves star formation occurring at a rate that is large compared to the rate that is typically observed. This starburst activity will consume the available interstellar gas supply over a timespan that is much shorter than the lifetime of the galaxy. For example, the nebula NGC 6334 has a star formation rate estimated to be 3600 Solar Masses per million years compared the star formation rate of the entire Milky Way of about seven million solar masses per million years. Due to the high amount of star formation a starburst is usually accompanied by much higher gas pressure and a larger ratio of Hydrogen cyanide to Carbon monoxide Emission-lines than are usually observed.
Starburst can occur in entire galaxies or just regions of space. A starburst region is a region of space that is undergoing a large amount of star formation. For example, the Tarantula Nebula is a Nebula in the Large Magellanic Cloud which has one of the highest star formation rates in the Local Group. By contrast a starburst galaxy is an entire galaxy that is experiencing a very high star formation rate. One notable example being Messier 82 in which the gas pressure is 100 times greater than in the local neighborhood and it is forming stars at about the same rate as the Milky Way in a region about 600 parsecs across. At this rate M82 will consume its 200 million Solar Masses of atomic and molecular hydrogen in 100 Mega years (its Free-fall time).Starburst regions can occur in different shapes, for example in Messier 94 the inner ring is a star burst region. Messier 82 has a starburst core of about 600 parsec in diameter. Starbursts are common during galaxy mergers such as the Antennae Galaxies. In the case of mergers the starburst can either be local or galaxy wide depending on the galaxies and how they are merging.