First detection of matter falling into a black hole at 30 percent of the speed of light

A UK team of astronomers report the first detection of matter falling into a black hole at 30 percent of the speed of light, located in the centre of the billion-light year distant galaxy PG1211+143. The team, led by Professor Ken Pounds of the University of Leicester, used data from the European Space Agency's X-ray observatory XMM-Newton to observe the black hole. Their results appear in a new paper in Monthly Notices of the Royal Astronomical Society.

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Credit: K. Pounds et al. / University of Leicester

Characteristic disc structure from the simulation of a misaligned disc around a spinning black hole.

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This artist’s rendering illustrates new findings about a star shredded by a black hole. When a star wanders too close to a black hole, intense tidal forces rip the star apart.

In these events, called “tidal disruptions,” some of the stellar debris is flung outward at high speed while the rest falls toward the black hole. This causes a distinct X-ray flare that can last for a few years.

During the tidal disruption event, filaments containing much of the star's mass fall toward the black hole. Eventually these gaseous filaments merge into a smooth, hot disk glowing brightly in X-rays.

As the disk forms, its central region heats up tremendously, which drives a flow of material, called a wind, away from the disk.

Matter falling toward a black hole collects into a rotating disk, where it becomes compressed and heated before eventually spilling over the black hole's event horizon, the point beyond which nothing can escape and astronomers cannot observe.

A mysterious and intense X-ray source near the black hole shines onto the surface layers of the accretion disk, causing iron atoms to radiate characteristic emission -- what astronomers call the iron K line -- at about 6,000 to 7,000 electron volts. The inner part of the disk is orbiting the black hole so fast that the effects of Einstein's relativity come into play -- most notably, how time slows down close to the black hole.

These relativistic effects broaden and distort the X-ray signal in a unique way. When the X-ray source near NGC 4151's black hole flares up, the accretion disk reflects the emission about half an hour later.

Moving at the speed of light, the X-rays associated with the echo must have traveled an additional 400 million miles -- equivalent to about four times Earth's average distance from the sun -- than those that came to us directly from the flare.

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