Hyper-Luminous X-ray source 1, commonly known as HLX-1, is an

intermediate-mass black hole An intermediate-mass black hole (IMBH) is a class of black hole with mass in the range of one hundred to one hundred thousand (102–105) solar masses: significantly higher than stellar black holes but lower than the hundred thousand to more than ...

candidate located in the lenticular galaxy ESO 243-49 about 290 million light-years from Earth. The mass of its central black hole is estimated to be approximately 20,000 solar masses. The source was discovered at the Institut de Recherche en Astrophysique et Planétologie (IRAP, formerly the CESR), Toulouse, France and gained interest from the scientific community because of strong evidence supporting it as an intermediate-mass black hole. HLX-1 is possibly the remnant of a dwarf galaxy that may have been in a

galactic collision Interacting galaxies (''colliding galaxies'') are galaxies whose gravitational fields result in a disturbance of one another. Major mergers occur between galaxies with similar amounts of mass, whereas minor mergers involve galaxies with masses ...

with ESO 243-49.

Discovery

The object was first observed in November 2004, in which it was seen as a source emitting X-rays in the outskirts of the

spiral galaxy Spiral galaxies form a galaxy morphological classification, class of galaxy originally described by Edwin Hubble in his 1936 work ''The Realm of the Nebulae''

ESO 243-49 and was catalogued as 2XMM J011028.1-460421, but nicknamed "HLX-1". In 2008, a team of astronomers led by Natalie Webb at the Institut de Recherche en Astrophysique et Planétologie in

Toulouse Toulouse (, ; ; ) is a city in southern France, the Prefectures in France, prefecture of the Haute-Garonne department and of the Occitania (administrative region), Occitania region. The city is on the banks of the Garonne, River Garonne, from ...

France France, officially the French Republic, is a country located primarily in Western Europe. Overseas France, Its overseas regions and territories include French Guiana in South America, Saint Pierre and Miquelon in the Atlantic Ocean#North Atlan ...

, discovered HLX-1 and from the very high X-ray luminosity (~, 0.2–10.0 keV), as well as its X-ray characteristics, proposed that it was an intermediate mass black hole candidate. Follow up analysis using further X-ray, optical and radio observations support the intermediate-mass black hole nature. In 2012, further work showed that there was a small cluster of stars amassed around HLX-1, leading Sean Farrell and collaborators to conclude that the black hole was once the galactic center of a dwarf galaxy, which was consumed by ESO 243-49. Farrell remarked, "The fact that there's a very young cluster of stars indicates that the intermediate-mass black hole may have originated as the central black hole in a very low-mass dwarf galaxy. The dwarf galaxy was then swallowed by the more massive galaxy.".

ESO 243-49

ESO 243-49 is a

lenticular galaxy A lenticular galaxy (denoted S0) is a Galaxy morphological classification, type of galaxy intermediate between an elliptical galaxy, elliptical (denoted E) and a spiral galaxy in galaxy morphological classification schemes. It contains a large-s ...

in the southern

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The first constellati ...

of Phoenix. It is located at a distance of approximately from the

Milky Way The Milky Way or Milky Way Galaxy is the galaxy that includes the Solar System, with the name describing the #Appearance, galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars in other arms of the galax ...

galaxy. ESO 243-49 is a member of the Abell 2877

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 ...

, which has 89 known members. It lies at a projected separation of about from the dominant central cluster galaxy, IC 1633. The morphological classification of ESO 243-49 is S0a, indicating this is a lenticular galaxy. It is being viewed edge-on from the perspective of the Earth. An attempt in 2015 to detect radio continuum emission of neutral hydrogen from this galaxy was unsuccessful, suggesting it is a gas poor galaxy compared to similar field galaxies. This may be the result of its gas reservoir being depleted due to its location near the center of a galaxy cluster. The galaxy has prominent dust lanes around the nucleus, while UV emission from the bulge region suggests

star formation Star formation is the process by which dense regions within molecular clouds in interstellar space—sometimes referred to as "stellar nurseries" or "star-forming regions"—Jeans instability, collapse and form stars. As a branch of astronomy, sta ...

is in progress. These may be indications that the galaxy has recently undergone a minor merger event. In contrast, the disk of the galaxy consists of old stars that suggest general star formation was quenched a few billion years after the galaxy formed.

References

{{DEFAULTSORT:HLX-1 Phoenix (constellation) Intermediate-mass black holes Lenticular galaxies