A team of UK astronomers has detected gas being sucked into a supermassive black hole at the core of a galaxy one billion light years from Earth that is racing inward at an extraordinary 30 percent the speed of light, or roughly 100,000 kilometres (62,000 miles) per second.
Black holes with millions to billions of times the mass of the Sun are believed to lurk in the cores of most, if not all, major galaxies. By definition, the black holes cannot be seen, but they can be detected by the radiation emitted as gas and dust are pulled in and heated to enormous temperatures before crossing the point of no return – the event horizon – and vanishing from the knowable universe.
But even supermassive black holes are so compact gas tends to rotate around them instead of falling straight in, forming a spinning accretion disk in which material spirals inward as it is accelerated by the hole’s enormous gravity.
Astronomers assumed the disk would be aligned with the black hole’s rotation axis, but it was not required. As it turns out, misaligned rotation can result in multiple rings of debris, providing a mechanism for gas and even entire stars to be pulled into a super-massive black hole from any direction.
A team led by Ken Pounds of the University of Leicester used the European Space Agency’s XMM-Newton X-ray telescope to observe the surroundings of a 40-million-solar-mass black hole at the heart of a Seyfert galaxy known as PG1211+143 in the constellation Coma Berenices.
They observed strongly red-shifted spectra showing trapped gas, with almost no rotation around the hole, being pulled in at 30 percent the speed of light. The observation agreed with theoretical work that simulated the formation of misaligned accretion disks and subsequent collisions.
The UK’s Dirac supercomputer facility indicated such collision would cancel out the rings’ rotation, allowing gas to fall directly into the black hole.
“The galaxy we were observing with XMM-Newton has a 40 million solar mass black hole which is very bright and evidently well fed,” Pounds said. “Indeed, some 15 years ago we detected a powerful wind indicating the hole was being over-fed. While such winds are now found in many active galaxies, PG1211+143 has now yielded another ‘first’, with the detection of matter plunging directly into the hole itself.”
He said XMM-Newton was able to follow “an Earth-sized clump of matter for about a day, as it was pulled towards the black hole, accelerating to a third of the velocity of light before being swallowed up by the hole.”
Misaligned accretion disks may be common around supermassive black holes, which would spin more slowly and rapidly grow, providing an explanation for how holes that formed in the immediate aftermath of the Big Bang quickly gained so much mass.