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The University of Southampton

Researchers reveal close-up look at whirlpool around gigantic black hole

Published: 30 November 2018
“Broad Line Region” in a quasar
Artist’s impression of the “Broad Line Region” in a quasar. Copyright: L. Calcada/ESO.

An international team of scientists have been able to measure gas spinning about a supermassive black hole in a distance galaxy for the first time. The team, which includes the University of Southampton, were also able to gauge its mass with unprecedented precision – a crucial step to understanding galaxy evolution.

The group of astronomers, including Dr Sebastian Hoenig of the University of Southampton, used a new instrument called GRAVITY, which combines the light of four of the largest infrared telescopes on earth, hosted by the European Southern Observatory (ESO) in Chile, to look deep into the heart of the quasar 3C273 to observe the structure of rapidly moving gas around the central black hole, known as the ‘broad line region’.

Quasars play a fundamental role in the history of the Universe, as their evolution is intricately tied to galaxy growth and they are known to contain supermassive black holes. More than 50 years ago, the astronomer Maarten Schmidt identified the first ‘quasi-stellar object’ or quasar, named 3C 273, as an extremely bright but distant object.

The energy emitted by such a quasar is much greater than in a normal galaxy such as our Milky Way and cannot be produced by regular fusion processes in stars. Instead, astronomers assume that gravitational energy is converted into heat as material is being swallowed by an extremely massive black hole.

While scientists assume that basically all large galaxies harbour a massive black hole at their centre, so far they have only been able to study in detail one in our Milky Way.

“This result marks a milestone in our endeavour to understand supermassive black holes. We achieved resolving the gas circling around a black hole on a scale comparable to our solar system in a galaxy 2.5 billion light years away,” said Dr Hoenig, whose work helped to interpret the new findings unearthed by GRAVITY. 


Artist’s impression of the accretion disk and jet of a supermassive black hole similar as in the centre of 3C273.
Copyright: L. Calcada/ESO

Reinhard Genzel, head of the infrared research group at MPE, added: “This is the first time that we can study the immediate environs of a massive black hole outside our home galaxy, the Milky Way.”

GRAVITY’s innovative interferometry technique boosts the magnification of the individual 8.2-m telescopes to a resolution power equivalent to a 130m-sized telescope. Thus the astronomers can distinguish structures at the level of 10 micro-arcseconds, which corresponds to an object the size of a £1-coin on the Moon.  The astronomy group at the University of Southampton is one of the UK’s centres for infrared interferometry and specialises in modelling and interpreting interferometry data from supermassive black holes.

Dr Hoenig commented: “We were able to use these observations to determine the mass of the supermassive black hole in this quasar. It is clear that GRAVITY has the potential to bring a sea change to our understanding of these unique objects, how they grow, and how they influence their host galaxies.

“GRAVITY allowed us to resolve the so-called ‘broad line region’ for the first time ever, and to observe the motion of individual gas clouds around the central black hole”, explained Eckhard Sturm, lead author from the Max Planck Institute for Extraterrestrial Physics (MPE). “Our observations reveal that the gas clouds do whirl around the central black hole.”


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