What lies behind a black hole's event horizon, or the point of no return where nothing escapes, remains a mystery. Astronomers, however, can still observe areas around this region.
In a new study, which was published in the Monthly Notices of the Royal Astronomical Society on Sept. 3, a team of researchers reported for the first time seeing the signature of a clump of matter falling directly into a distant black hole at nearly 30 percent the speed of light.
Study researcher Ken Pounds, of the University of Leicester, and colleagues were able to make the observation using the European Space Agency's orbiting XMM-Newton X-ray observatory, the biggest scientific satellite ever built in Europe.
The observed black hole lies at the center of the galaxy PG211+143, which is located about one billion light-years away.
PG211+143 is a Seyfert galaxy, which means it has a very bright compact core with strong infrared emission. Astronomers think that the compact source of radiation at the galactic center is a black hole beaming out high-energy matter. The researchers said that the supermassive black hole is 40 million times more massive than the sun.
"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," Pounds said in a statement published by the Royal Astronomical Society.
The researchers observed X-ray signatures of iron, calcium, argon, sulfur, and silicon that form an Earth-sized gas clump. They also found that the light was redshifted, which means that matter is falling directly into the black hole at a third the speed of light, or 100,000 kilometers per second. The gas then disappeared without evidence of rotation.
"We report here the first detection of a physically realistic redshifted absorption line spectrum, consistent with highly ionized matter falling inwards at v∼0.3c," the researchers wrote in their study.
The infalling gas showing no rotation is an interesting observation because this is not always observed. Black holes are so compact that gas almost always rotates too much to fall directly in.
The observation nonetheless aligns with a recent theoretical work. The work, which used the DIRAC supercomputer in the UK, has shown that rings of gas can break off and collide with each other. This cancels out their rotation and allows gas to fall directly toward the black hole.