News archive 2007

Black hole found in ‘dwarf' galaxy

17 Jan 2007, PR 05/07

Astronomers, including King's astrophysics and cosmology expert, Dr Ignacio Ferreras, have found evidence of a supermassive black hole at the heart of a tiny galaxy about 54 million light years away from the Milky Way galaxy – where Earth resides.

VCC128 is an elliptical dwarf galaxy, about one per cent the size of the Milky Way, located in the Virgo Cluster.

‘The detection has only been possible because of the superb spatial resolution of the Hubble Space Telescope', explains Ignacio Ferreras, King's lecturer in the Department of Physics. ‘VCC128 is effectively the smallest galaxy in which there is a supermassive black hole.'

Dr Ferreras, who joined King's Department of Physics from University College London in 2005, is undertaking research in the areas of galaxy formation and evolution; cosmology; and star formation.

Black holes lie at the centre of many galaxies, and have gravitational fields so powerful that nothing – not even light – can escape. Supermassive black holes are so large that their mass can equal anywhere between 100,000 to 10 billion times that of our own Sun.

Victor P Debattista of the University of Washington and lead author of a poster presented at the American Astronomical Society annual meeting in Seattle last week, detailing the discovery, continues: ‘It is only the second time a supermassive black hole has been discerned in a dwarf galaxy, and only the third time that astronomers have observed a double nucleus at the heart of a galaxy.'

Co-authors are Ignacio Ferreras, Anna Pasquali of the Max-Planck-Institut für Astronomie in Germany, Anil Seth at the Centre for Astrophysics at Harvard University, Sven De Rijcke of the Universiteit Gent in Belgium, and Lorenzo Morelli of Pontificia Universidad Catolica in Chile.

Hubble Space Telescope
The scientists were sifting through archived data from the Hubble Space Telescope when they found the supermassive black hole. They were studying the nuclei of dwarf galaxies, which are thought to form from globular clusters, tightly packed spherical collections of stars that orbit a galaxy. As they examined the properties of the nuclei, they discovered one galaxy – VCC 128 – that had a double nucleus.

Ultimately they determined the double nucleus is made up of two points of light from stars collected at opposite ends of a ring surrounding a black hole. Using the 3.5-metre telescope at the Apache Point Observatory in New Mexico, they measured properties of the light from the nucleus and found it is made up of a ring of stars at least 1 billion years old, meaning the system probably is very stable.

‘The fact we were able to find a very massive black hole here – conceivably more massive than the one at the centre of our own Milky Way – tells us that, in some cases at least, black holes can form and be retained by small galaxies. It is also impressive because it had been thought that a galaxy this small should not be able to host a black hole,' Dr Debattista said.

The researchers believe the black hole has at least about the same mass as the ring of stars surrounding it, ranging from 6 million to 50 million times the mass of our sun.

‘After this discovery, one could speculate whether other dwarf galaxies may harbour similar black holes but lie beyond the resolution limit of the Hubble Space Telescope,' noted Dr Ferreras. The findings will help in understanding the processes occurring in low-mass dwarf galaxies as they travel through space and merge with other dwarfs to form larger galaxies. As that happens, their black holes also become more massive.






Notes to editors

King's College London
King's College London is the fourth oldest university in England with more than 13,700 undergraduates and nearly 5,600 graduate students in nine schools of study based at five London campuses. It is a member of the Russell Group: a coalition of the UK's major research-based universities. The College has had 24 of its subject-areas awarded the highest rating of 5* and 5 for research quality, demonstrating excellence at an international level, and it has recently received an excellent result in its audit by the Quality Assurance Agency.

King's has a particularly distinguished reputation in the humanities, law, international relations, medicine, nursing and the sciences, and has played a major role in many of the advances that have shaped modern life, such as the discovery of the structure of DNA. It is the largest centre for the education of healthcare professionals in Europe and is home to four Medical Research Council Centres, more than any other university.

King's is in the top group of UK universities for research earnings, with income from grants and contracts of more than £100 million, and has an annual turnover of more than £363 million.



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