Science & Technology

Misaligned gas discs could be ‘overfeeding’ Black Holes

an artist's impression of a black hole and accretion disc system
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UK scientists have made the first observation of gas falling into a black hole at 30% of the speed of light offering support to the theory that misaligned gas discs around black holes can cause material to fall directly into the space-time event. In the process, liberating huge amounts of energy. 

The team, led by Professor Ken Pounds of the University of Leicester, used data provided by the  European Space Agency’s X-ray observatory XMM-Newton to observe the black hole at the centre of the galaxy PG211+143. The results appear in the latest edition of the scientific journal Monthly Notices of the Royal Astronomical Society. 

“The galaxy we were observing with XMM-Newton has a 40 million solar mass black hole which is very bright and evidently well fed,” Professor 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.”

“We were 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.” Pound continued.

artist's impression of the XMM Newton X-ray telescope (ESA)

artist’s impression of the XMM Newton X-ray telescope (ESA)


The findings are of particular interest as the swallowing of matter by black holes via accretion, is the most efficient method of extracting energy from matter. For example, comparing accretion onto a black hole to the most common form of nuclear-fusion reaction in the universe, hydrogen burning. We find that hydrogen burning liberates about 0.7% of the energy locked within the matter involved. This is compared to an accretion efficiency of approximately up to 50% for certain non-rotating (Kerr) black holes. This energy is released as heat and light.

It is commonly believed that the centre of all galaxies, including our own, contain a supermassive black hole at its centre. The energy efficiency of the accretion process means that these objects referred to as active galactic nuclei (AGN) or quasars are the most luminous objects in the universe if there is enough matter surrounding them to be consumed.

A misaligned disc around a supermassive black hole (Ponuds, Nixon, et al)

A misaligned disc around a supermassive black hole (Pounds, Nixon, et al

Because of the compactness of black holes and the law of conservation of angular momentum, this gas is usually moving too fast to fall directly into the black hole, instead, forming an accretion disc around the object. It is the massive frictional forces within the gas, a product of the black hole’s massive gravitational effect that creates a violent enough environment to achieve such effective energy liberation.

These findings show that there are cases in which gas and other matter can fall directly into a black hole.

It has been commonly assumed that these accretion discs are aligned with the plane of rotation of the black hole. This new finding shines a light on what the effect of a misaligned accretion disc may be, specifically on the speed at which the matter falls on the surface of the black hole.

Professor Pound and his team examined the x-ray spectra of galaxy PG211+143, a Seyfert galaxy located one billion light years away in the direction of the constellation Coma Berenices taken from the XMM-Newton observatory.

The researchers found that the spectra was strongly red-shifted showing it to be falling into the black hole a roughly 30% of the speed of light, about 100,000 kilometres per second. The gas was found to be feeding almost directly into the black hole, likely as a result of its close proximity to its event horizon – the point at which nothing, including light, can escape the black hole.

This observation lends credence to theoretical developments which also originate from the University of Leicester achieved by the use of the Dirac supercomputer facility to simulate the “tearing” of misaligned accreting systems. This research has shown that rings of gas can break off and collide with each other causing shocks thus cancelling their rotation, which is what allows them to fall directly into the black hole.

The research also implies that ‘chaotic accretion’ from misaligned discs may well be common for supermassive black holes. This may explain why black holes formed in the early Universe grew to such extraordinarily large sizes. Black holes accepting matter directly in this way would spin slower and be able to accept more gas and grow their masses more rapidly than previously believed.

Original research available here.


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