Journal Article

An actively accreting massive black hole in the dwarf starburst galaxy Henize 2-10

Johnson, Kelsey E., Brogan, Crystal L., Reines, Amy E., Sivakoff, Gregory R.

2011

Overview

Bursting onto the scene The starburst in Henize 2-10, a relatively nearby blue compact dwarf galaxy, has attracted the attention of astronomers for decades, in part because of its prodigious rate of star formation — ten times that of the Large Magellanic Cloud. Now a study of Henize 2-10 at centimetre radio wavelengths and in the near-infrared reveals a compact radio source at its centre that is spatially coincident with a hard X-ray source. This points to the presence of an actively accreting massive black hole, but one not associated with a bulge, a nuclear star cluster or any other well-defined nucleus. This means that Henize 2-10 may reflect an early phase of black hole and galaxy evolution that has not been observed previously. Henize 2-10 is a nearby dwarf starburst galaxy that may be similar to galaxies in the infant Universe. It is reported that Henize 2-10 contains a compact radio source at the dynamical centre of the galaxy that is spatially coincident with a hard X-ray source, from which it is concluded that Henize 2-10 harbours an actively accreting central black hole with a mass of approximately one million solar masses. The results confirm that nearby star-forming dwarf galaxies can indeed form massive black holes, and by implication so can their primordial counterparts. Supermassive black holes are now thought to lie at the heart of every giant galaxy with a spheroidal component, including our own Milky Way 1 , 2 . The birth and growth of the first ‘seed’ black holes in the earlier Universe, however, is observationally unconstrained 3 and we are only beginning to piece together a scenario for their subsequent evolution 4 . Here we report that the nearby dwarf starburst galaxy Henize 2-10 (refs 5 and 6 ) contains a compact radio source at the dynamical centre of the galaxy that is spatially coincident with a hard X-ray source. From these observations, we conclude that Henize 2-10 harbours an actively accreting central black hole with a mass of approximately one million solar masses. This nearby dwarf galaxy, simultaneously hosting a massive black hole and an extreme burst of star formation, is analogous in many ways to galaxies in the infant Universe during the early stages of black-hole growth and galaxy mass assembly. Our results confirm that nearby star-forming dwarf galaxies can indeed form massive black holes, and that by implication so can their primordial counterparts. Moreover, the lack of a substantial spheroidal component in Henize 2-10 indicates that supermassive black-hole growth may precede the build-up of galaxy spheroids.

• Publisher: Nature Publishing Group UK,Nature Publishing Group
• Subject: Astronomy / Astrophysics / Black holes / Black holes (Astronomy) / Characteristics and properties of external galaxies and extragalactic objects / Discovery and exploration / Dwarf galaxies (elliptical, irregular, and spheroidal) / Earth, ocean, space / Exact sciences and technology / Galactic nuclei (including black holes), circumnuclear matter, and bulges / Humanities and Social Sciences / letter / multidisciplinary / Normal galaxies. Extragalactic objects and systems (by type) / Observations / Quasars. Active or peculiar galaxies, objects, and systems / Science / Science (multidisciplinary) / Star & galaxy formation / Starburst galaxies and infrared excess galaxies / Stars & galaxies / Stellar systems. Galactic and extragalactic objects and systems. The universe