X-ray pulse detected near event horizon as black hole devours star

Mindy Sparks
January 12, 2019

Astronomers from Massachusetts Institute of Technology (MIT) have detected X-ray pulses originating from an area very close to a black hole's event horizon, and they believe the source of this pulse could be a white dwarf.

The researchers published a paper on January 10 to provide some exciting new proof images about the way the black hole has been behaving over the manner of its preying over the gasses of the star and how it gobbles up the whole star.

Now researchers at MIT and elsewhere have pored through data from multiple telescopes' observations of the event, and discovered a curiously intense, stable, and periodic pulse, or signal, of X-rays, across all datasets.

Researchers from the USA and the Netherlands were looking at a "tidal disruption event" or TDE (the name for a star being destroyed by a black hole) that was detected in 2014.

An artist's impression showing hot gas orbiting in a disk around a rapidly-spinning black hole.

This new technique could also be particularly useful for spotting inactive black holes classed as dormant, which are hard to spot in space.

As the star was devoured, an event known as a tidal disruption flare occurred. Researchers claimed that this is the first time that tidal disruption flare to estimate the speed in which a black hole spins. Even at half that speed, the black hole is rotating at a truly unimaginable rate compared to anything humans are used to seeing.


"There have already been measurements of spins from black holes that are actively accreting", or acquiring more matter under the influence of gravity, the study's first author Dheeraj Pasham, Einstein Postdoctoral Fellow at the MIT Kavli Institute, told Gizmodo.

Scientists have charted the environment surrounding a stellar-mass black hole that is 10 times the mass of the Sun using NASA's Neutron star Interior Composition Explorer (NICER) payload aboard the International Space Station. It likely sits just outside the event horizon, but near the Innermost Stable Circular Orbit (ISCO) - the smallest orbit in which a particle can safely travel around a black hole. It was the first Time the researchers the Tear of a star for their spinning-were able to use calculations, Pasham. "But we saw it in all three telescopes". Figuring out a black hole's mass is a little easier, by the way, because the pull it has on the galaxy around it can be measured to calculate an estimate.

This white dwarf would not have been able to emit any detectable radiation on its own. A relatively low rotation rate would implicate mergers as the primary factor, because these random smashups likely wouldn't keep spinning the growing black hole up in the same direction.

"The fact that we can track this region of bright X-ray emission as it circles the black hole lets us track just how quickly material in the disk is spinning", Pasham said in the same statement.

As the black hole strips away the star, this volatile matter heats up to 1 million degrees Celsius as it gets pulled into a disk around the black hole, explained Pasham. "But now we have evidence that what is evolving in the system is the structure of the corona itself", he added.

However, "if you have a high-spin black hole, supermassive black hole, that's telling us that maybe steady accretion was dominant", Pasham said during a news conference at AAS Wednesday. "But at least in terms of the properties of the system, this scenario seems to work". "Their result suggests that tidal disruption events should be regularly followed up by x-ray telescopes to maximise our knowledge of their properties". Going forward, he hopes to identify similar stable patterns in other star-shredding events, from black holes that reside further back in space and time.

Pasham plans to look for, and hopefully spot, more of these dramatic events in the cosmos.

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