A team of researchers in the UK have observed matter falling into a black hole at 30% the speed of light. This is much faster than anything previously observed. The high velocity is a result of misaligned discs of material rotating around the black hole.

The galaxy in the study is named PG211+143 and it’s about a billion light years away from our Solar System. It’s a Seyfert galaxy, which means it is very bright and has a supermassive black hole (SMBH) in its center.  Matter falling into the hole from accretion discs causes its high energy output. But no matter has ever been observed falling this quickly into a black hole.

“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.” – Professor Ken Pounds, University of Leicester, Dept. of Physics and Astronomy.

The team behind the study is led by Professor Ken Pounds of the University of Leicester. Pounds and the other authors used data from the European Space Agency’s XMM-Newton observatory, which was launched in 1999 to observe interstellar x-ray sources. The study supports theoretical work already done.

Black holes are called ‘black’ because they have such strong gravitational force that not even light escape them. They are the subject of intense scrutiny because of their over-all importance in astronomy and astrophysics. They are intensely energetic, and are the most efficient objects at extracting energy from matter. And they get that energy from gas falling into the black hole.

Galaxies like PG211+143, and like our own Milky Way, have super massive black holes in their center. These monsters have millions or billions times as much matter as our Sun. They can become intensely energetic when enough matter flows into them, and then they’re called active galactic nuclei (AGN).

Black holes dwarf the Sun in terms of mass, but they are tiny, compact objects. They are surrounded by swirling discs of gas, but the black hole’s small size means that gas only falls in slowly. Most of the gas orbits the black hole, slowly and gradually spiralling into the hole through an accretion disc. An accretion disc is a sequence of circular orbits of decreasing size. As the gas gets closer and closer to the black hole, it speeds up and becomes hot and luminous. This is how black holes turn matter into energy. The intense gravity of the hole causes the gas in the disc to move faster and faster, until it starts radiating energy.

“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 Ken Pounds, University of Leicester, Dept. of Physics and Astronomy.

Astronomers assumed that these discs of in-flowing gas are in alignment with each other, like the planets on the ecliptic in our Solar System. But that’s not always the case. Clouds of gas and dust can fall into the black hole from any direction, so there’s really no reason that these accretion discs can’t be misaligned. The question has been, how do misaligned discs affect the in-fall of gas into a black hole?

This is where Professor Pounds and his team of collaborators come in. They used XMM-Newton to examine x-ray spectra from PG211+143.  They found that spectra was red-shifted and the matter they were observing was falling into the black hole at about 100,000 km/s, or about 30% of the speed of light. In astronomical terms the matter was very close to the hole. Its distance from the hole is only 20 times the size of the hole itself, and the matter had barely any rotational energy.

Theoretical work done using the Dirac supercomputer facility in the UK agrees with these observations. That work shows how accretion rings of gas can break off and collide with each other. That cancels out the rotational velocity of the gas, allowing the gas to fall into the black hole much more quickly. But until now, it has never been observed.

Prof. Pounds, from the University of Leicester’s Department of Physics and Astronomy, said: “The galaxy we were observing with XMM-Newton has a 40 million solar mass black hole which is very bright and evidently well fed. 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,” said Professor Pounds.

The study not only spotted this high-velocity in-flow of matter into a black hole, but in doing so it shed light on another mystery in astronomy. In the early universe, black holes quickly gained very large masses, but it was never clear why. Misaligned discs and the chaotic accretion of matter could be responsible for the fast-growing black holes in the early days of the universe.

Sources

• Royal Astronomical Society Press Release: “Matter Falling into a Black Hole at 30 Percent of the Speed of Light“
• Research Paper: “An ultrafast inflow in the luminous Seyfert PG1211+143“
• Universe Today’s Guide To Space