‘Light Echoes’ From A Distant Black Hole Show It ‘Shrank Dramatically’ After Gorging On A Star

NASA’s Neutron star Interior Composition Explorer (NICER) telescope has helped astronomers gain unprecedented insight into what happens to a black hole after it gobbles up a star.

In a new study published this week in the journal Nature, a team of scientists from NASA, the Massachusetts Institute of Technology (MIT), and the University of Maryland details the interesting case of a recently discovered black hole that went through a dramatic slim-down after gorging on a nearby star.

The black hole in question is MAXI J1820+070 (henceforth named J1820) — a stellar-mass black hole about 10 times more massive than the sun, located some 10,000 light-years from Earth in the direction of the Leo constellation. The object was first spotted on March 11, 2018, after Japan’s Monitor of All-sky X-ray Image (MAXI) instrument mounted on the International Space Station (ISS) picked up a very powerful X-ray signal coming from its direction.

According to MIT News, the X-ray flare produced by the black hole was estimated to be six times brighter than the Crab Nebula.

“This black hole went from being completely unobservable to being one of the brightest sources in the X-ray sky over timescales of just a few days,” said lead study author Erin Kara, an astrophysicist at the University of Maryland at College Park.

Intrigued by this discovery, the team began observing the black hole with NICER, also stationed on the ISS. Their efforts led to an even more spectacular find, which unveiled new details on black hole evolution.

The X-ray signals traced back to J1820 were generated by the black hole during a process known a tidal disruption event. As the Inquisitr previously reported, this is produced when a black hole devours a passing star, shredding it into a stream of hot gas that gathers around the black hole into an accretion disk. The gaseous material that makes up the disk is then absorbed by the black hole, which emits vast amounts of radiation in the process.

After pointing NICER at J1820 to study its X-ray emissions, the scientists uncovered that the black hole had begun to shrink following its stellar feast. By keeping track of what astronomers refer to as “light echoes” — or the waves of X-ray light bouncing off the accretion disk — NICER revealed that the black hole had considerably reduced in size, losing a significant portion of its corona.

As Sky & Telescope points out, the corona of a black hole is a haze of high-energy electrons that hovers over the black hole and its accretion disk. These highly energetic particles float above the poles of the black hole and can heat up to about 1.8 billion degrees Fahrenheit, notes Space.

This artist's illustration shows how a black hole's corona can create a flare of X-rays that shoots away from the system.
This artist's illustration shows how a black hole's corona can create a flare of X-rays that shoots away from the system.Featured image credit: NASA/JPL-Caltech

“NICER has allowed us to measure light echoes closer to a stellar-mass black hole than ever before,” said Kara.

“Similar to how bats use echolocation to map out a dark cave, we measured light echoes to measure the region close to the black hole.”

By comparing the original MAXI detection with the NICE data gathered after the tidal disruption event, the team was able to calculate how the black hole’s size and shape changed over time. Their calculations showed that J1820’s corona “shrank dramatically” after the initial outburst, shaving off about 90 percent of its size in a little more than a month.

“We see that the corona starts off as this bloated, 100-kilometer [60 miles] blob inside the inner accretion disk, then shrinks down to something like 10 kilometers [six miles], over about a month,” said study co-author Jack Steiner, an MIT astrophysicist.

“This is the first unambiguous case of a corona shrinking while the disk is stable.”

While the team is still unsure why the corona underwent such a dramatic change, the finding shed new light into the evolution of black holes.

“The corona is still pretty mysterious, and we still have a loose understanding of what it is. But we now have evidence that the thing that’s evolving in the system is the structure of the corona itself,” said Steiner.

The new discovery could help astronomers better understand what goes on inside supermassive black holes as well, states CNET. By learning more about the behavior of matter within these mammoth structures, scientists could uncover how they influence the galaxies that host them.

Although supermassive black holes “are 1,000 times less massive than the galaxies in which they reside, they actually are a main driver in the evolution of the galaxies,” explained Kara.