The Bullet Group (SL2S J08544-0121) is a newly merging

group of galaxies A galaxy group or group of galaxies (GrG) is an aggregation of galaxies comprising about 50 or fewer gravitationally bound members, each at least as luminous as the Milky Way (about 1010 times the luminosity of the Sun); collections of galaxies ...

, a merger between two galaxy groups to form a new larger one, that recently had a high speed collision between the two component groups. The group exhibits separation between its

dark matter In astronomy, dark matter is an invisible and hypothetical form of matter that does not interact with light or other electromagnetic radiation. Dark matter is implied by gravity, gravitational effects that cannot be explained by general relat ...

and

baryonic matter In particle physics, a baryon is a type of composite subatomic particle that contains an odd number of valence quarks, conventionally three. Protons and neutrons are examples of baryons; because baryons are composed of quarks, they belong to ...

components. The galaxies occur in two clumps, while the gas has expanded into a billowing cloud encompassing all three clumps. As of 2014, it is one of the few galaxy clusters known to show separation between the dark matter and baryonic matter components. The group is named after the

Bullet Cluster The Bullet Cluster (1E 0657-56) consists of two colliding clusters of galaxies. Strictly speaking, the name ''Bullet Cluster'' refers to the smaller subcluster, moving away from the larger one. It is at a comoving radial distance of . The obje ...

, a similar merging

galaxy cluster A galaxy cluster, or a cluster of galaxies, is a structure that consists of anywhere from hundreds to thousands of galaxies that are bound together by gravity, with typical masses ranging from 1014 to 1015 solar masses. Clusters consist of galax ...

, except on a smaller scale, being of groups instead of clusters. The bimodal distribution of galaxies was found at discovery in 2008. The galaxy group is a

gravitational lens A gravitational lens is matter, such as a galaxy cluster, cluster of galaxies or a point particle, that bends light from a distant source as it travels toward an observer. The amount of gravitational lensing is described by Albert Einstein's Ge ...

and strongly lenses a more distant

galaxy A galaxy is a Physical system, system of stars, stellar remnants, interstellar medium, interstellar gas, cosmic dust, dust, and dark matter bound together by gravity. The word is derived from the Ancient Greek, Greek ' (), literally 'milky', ...

behind it, at z=~1.2

Characteristics

As of 2014, the group is the smallest mass object to exhibit separation between its dark matter and baryonic matter components. The galaxy group is dominated by one elliptical galaxy, situated in one of the two concentrations, while the other node has two large bright galaxies, which do not dominate the group. The group has an apparent radius of 200

arcsecond A minute of arc, arcminute (abbreviated as arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of a degree. Since one degree is of a turn, or complete rotation, one arcminute is of a tu ...

s, and a virial radius of 1

megaparsec The parsec (symbol: pc) is a unit of length used to measure the large distances to astronomical objects outside the Solar System, approximately equal to or (AU), i.e. . The parsec unit is obtained by the use of parallax and trigonometry, and ...

References

{{galaxy Galaxy clusters Dark matter Hydra (constellation)

Characteristics

See also

References