A team of astronomers led by Dr. James Nightingale from the Centre for Extragalactic Astronomy at Durham University have discovered one of the biggest black holes ever found, exploiting a phenomenon called gravitational lensing, whereby the gravitational field of a foreground galaxy both bends and magnifies the light from a more distant luminous object, altering the far object’s appearance as viewed from Earth. They used the DiRAC facility to model how light is bent by the distribution of matter inside the galaxy Abell 1201, roughly 2 billion light years distant, and found at its heart an ultramassive black hole (BH), over 30 billion times the mass of our Sun and roughly 30% of the total mass of stars in the Milky Way – a scale rarely seen by astronomers.
Profiting from the computational power available at both the DiRAC Data Intensive Service (CSD3) at Cambridge and the Memory Intensive Service (COSMA8) at Durham, the team used numerical ray-tracing techniques to reconstruct the appearance of the distant object following lensing by the gravitational field of the foreground object, repeating the calculation hundreds of thousands of times in a nested sampling process, each time including a different mass BH to augment the visible and dark matter distribution, until the optimum match to actual images captured by the Hubble Space Telescope was achieved (see accompanying video). This is the first measurement of a BH mass using this technique, and the findings are published in the journal Monthly Notices of the Royal Astronomical Society.
According to Dr Nightingale, this BH is one of the biggest ever detected and close to the upper limit of how large they can grow in realistic cosmological scenarios. Most of the largest BHs that we know of are in an active state, where matter pulled in close to the black hole heats up and releases energy in the form of light, X-rays, and other radiation. The gravitational lensing technique makes it possible to study inactive BHs, something not currently possible in distant galaxies. The study opens up the tantalising possibility that astronomers can discover far more inactive and ultramassive BHs than previously thought, thereby offering a clue as to how they grew so large.
The research was supported by the UK Space Agency, the Royal Society, the Science and Technology Facilities Council (STFC) and the European Research Council.
Press releases pertaining to the research can be found below:
https://www.bbc.co.uk/news/uk-england-tyne-65109663
James Nightingale was also announced as one of this year’s Ernest Rutherford Fellowship winners, associated with Newcastle University. Information here.
