Hen 2-10, also known as He 2-10 and Henize 2-10, is a

dwarf Dwarf or dwarves may refer to: Common uses *Dwarf (folklore), a being from Germanic mythology and folklore * Dwarf, a person or animal with dwarfism Arts, entertainment, and media Fictional entities * Dwarf (''Dungeons & Dragons''), a humanoid ...

starburst galaxy A starburst galaxy is one 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 formatio ...

located 34 million

light years A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...

away in the constellation of

Pyxis Pyxis is a small and faint constellation in the southern sky. Abbreviated from Pyxis Nautica, its name is Latin for a mariner's compass (contrasting with Circinus, which represents a draftsman's compasses). Pyxis was introduced by Nicolas-Lo ...

. The galaxy is believed to be an early stage

. 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 , and the mass of the entire dwarf galaxy at about .

History

Henize 2-10 draws its name from a catalog of planetary nebulae assembled by astronomer

Karl Henize Karl Gordon Henize (;JPL-80 "NASA Creates Portrait of Life and ...

. Henize additionally noted that the object was identified in an unpublished paper by

Rudolph Minkowski Rudolph Minkowski (born Rudolf Leo Bernhard Minkowski ; ; May 28, 1895 – January 4, 1976) was a German-American astronomer. Biography Minkowski was the son of Marie Johanna Siegel and physiologist Oskar Minkowski. His uncle was Hermann Min ...

. The object was likely misidentified as a planetary nebula due to the galaxy's strong emission lines, a feature common of planetary nebulas. It was not until the 1970s when observations of Hen 2-10 indicated that the center of the object was a strong source of

radio waves Radio waves are a type of electromagnetic radiation with the longest wavelengths in the electromagnetic spectrum, typically with frequencies of 300 gigahertz (GHz) and below. At 300 GHz, the corresponding wavelength is 1 mm (short ...

that it was shown that Hen 2-10 was a dwarf galaxy rather than a planetary nebula. Supporting evidence for the reclassification came in the form of excess infrared emission and a higher than usual density of neutral hydrogen.

Structure

Hen 2-10 is a

featuring at least two star-forming regions near the center of the galaxy. These regions feature a variety of different substances, and multiple

super star clusters A super star cluster (SSC) is a very massive young open cluster that is thought to be the precursor of a globular cluster. These clusters called "super" because they are relatively more luminous and contain more mass than other young star clusters. ...

. A study of some of these SSCs estimates their age to be between 4 and 5 megayears. The galaxy also features emission typical of that in a

Wolf–Rayet star Wolf–Rayet stars, often abbreviated as WR stars, are a rare heterogeneous set of stars with unusual spectra showing prominent broad emission lines of ionised helium and highly ionised nitrogen or carbon. The spectra indicate very high surface ...

, further providing evidence for the starburst region of the galaxy. It was one of the first galaxies found to feature this emission. The strong prevalence of this emission has led to its classification as a Wolf–Rayet galaxy, a special subclass of starburst galaxy that features a higher than normal number of Wolf–Rayet stars. Furthermore, observations have shown irregularities in the southeast portion of the galaxy which could be interpreted as a

tidal tail A tidal tail is a thin, elongated region of stars and interstellar gas that extends into space from a galaxy. Tidal tails occur as a result of galactic tide forces between interacting galaxies. Examples of galaxies with tidal tails include the ...

. This tidal tail suggests that Hen 2-10 may have had past interactions with other galaxies, possibly even a merger event.

Central black hole

In 2011, a team of researchers studied the non-thermal emission of the galaxy center and indicated that the source strengths of radio waves are too strong to come from

x-ray binaries X-ray binaries are a class of binary stars that are luminous in X-rays. The X-rays are produced by matter falling from one component, called the ''donor'' (usually a relatively normal star), to the other component, called the ''accretor'', which ...

while the source strengths of x-rays are too strong to be supernova remnants. However, these sources do align with known data for black holes. This original paper postulated the mass of the black hole to be ~, but a newer study has refined the estimate to . The presence of SSCs near the center of the galaxy, and not a singular

nuclear star cluster A nuclear star cluster (NSC) or compact stellar nucleus (sometimes called young stellar nucleus) is a star cluster with high density and high luminosity near the center of mass of most galaxies. NSCs are the central massive objects of fainter ...

(NSC) has led some to believe that Hen 2-10 is a galaxy in its early years. The presence of the black hole is seen to be evidence of the dissipationless model of NSC formation. In this model, the SSCs will move to the center and form a singular NSC. Due to the black hole's relatively small mass, it is not believed to have a major effect on the timescale of this motion, although it is not yet understood how the black hole will affect the NSC formation. Ignoring the black hole indicates that the NSC should be fully formed in a few hundred million years.

References

{{DEFAULTSORT:Hen 2-10 24171 Dwarf galaxies Pyxis (constellation)