The Cosmic Horseshoe gravitational lens. The newly discovered ultramassive blackhole lies at the centre of the orange galaxy. Far behind it is a blue galaxy that is being warped into the horseshoe shaped ring by distortions in spacetime created by the immense mass of the foreground orange galaxy.
Credit: NASA/ESA
Astronomers from the University of Portsmouth's Institute of Cosmology and Gravitation , working in partnership with those from the Universidade Federal do Rio Grande in Brazil, have discovered potentially the most massive black hole ever detected.
The giant cosmic phenomenon is 10,000 times heavier than the black hole at the centre of our own Milky Way galaxy and close to the theoretical upper limit of what is possible in the Universe.
Such is the enormousness of the ultramassive black hole's size, it equates to 36 billion solar masses, according to a new paper published in Monthly Notices of the Royal Astronomical Society .
It exists in one of the most massive galaxies ever observed - the Cosmic Horseshoe - which is so big it distorts spacetime and warps the passing light of a background galaxy into a giant horseshoe-shaped Einstein ring .
It is thought that every galaxy in the Universe has a supermassive black hole at its centre and that bigger galaxies host bigger ones, known as ultramassive black holes.
"This is amongst the top 10 most massive black holes ever discovered, and quite possibly the most massive," said researcher Thomas Collett , Professor of Astrophysics at the University of Portsmouth.
"Most of the other black hole mass measurements are indirect and have quite large uncertainties, so we really don't know for sure which is biggest. However, we've got much more certainty about the mass of this black hole thanks."
Researchers detected the Cosmic Horseshoe black hole using a combination of gravitational lensing and stellar kinematics (the study of the motion of stars within galaxies and the speed and way they move around black holes).
The latter is seen as the gold standard for measuring black hole masses, but doesn't really work outside of the very nearby universe because galaxies appear too small on the sky to resolve the region where a supermassive or ultramassive black hole lies.
Adding in gravitational lensing helped the team "push much further out into the universe", Professor Collett explained.
"We detected the effect of the black hole in two ways - it is altering the path that light takes as it travels past the black hole and it is causing the stars in the inner regions of its host galaxy to move extremely quickly - almost 400 kilometres per second.
"By combining these two measurements we can be completely confident that the black hole is real."
Lead researcher, PhD candidate Carlos Melo, of the Universidade Federal do Rio Grande do Sul (UFRGS) in Brazil, added: "What is particularly exciting is that this method allows us to detect and measure the mass of these hidden ultramassive black holes across the universe, even when they are completely silent."
The Cosmic Horseshoe black hole is located a long way away from Earth, at a distance of some 5 billion light-years. Our own galaxy, the Milky Way, hosts a 4 million solar mass black hole. Currently it's not growing fast enough to blast out energy as a quasar but we know it has done in the past, and it may well do again in the future.
The Andromeda Galaxy and our Milky Way are moving together and are expected to merge in about 4.5 billion years.
"It is likely that all of the supermassive black holes that were originally in the companion galaxies have also now merged to form the ultramassive black hole that we have detected," said Professor Collett.
The discovery of the Cosmic Horseshoe black hole came as the researchers were studying the galaxy's dark matter distribution in an attempt to learn more about the mysterious hypothetical substance.
Now that they've realised their new method works for black holes, they hope to use data from the European Space Agency's Euclid space telescope to detect more supermassive black holes and their hosts to help understand how black holes stop galaxies forming stars.
