Research: The halo of highly energized electrons around the black hole dramatically shrinks during the frenzy of feeding –

Now astronomers from MIT and elsewhere have discovered "echoes" in this outbreak of X-ray radiation, which they think may be the hint that black holes develop during an outbreak. In a study published today in the magazine NatureThe group reports that the black hole consumes huge amounts of star material, the corona – halo of highly energized electrons surrounding the black hole – shrinks sharply from an initial width of about 100 kilometers (approximately the width of Massachusetts). ) to only 10 kilometers in a good month.

Findings are the first evidence that the corona shrinks like a black hole or accumulates. The results also show that the corona is the one that drives the evolution of the black hole in the most extreme phase of its outbreak.

"This is the first time that we have seen this kind of evidence that the corona in this period erupts the evolution of cramps," says Jack Steiner, researcher at the MIT Cavalli Institute of Astrophysics and Space Research. "The Korona is still quite mysterious, and we still have a poor understanding of what this is. But now we have evidence that the thing that is developing in the system is the structure of the very core. "

Steiner's co-authors MIT are Ronald Remillard and first author Erin Kara.

X-ray echoes

The black hole, which was detected on March 11, was named MAXI J1820 + 070 for the instrument that it detected. The Maxi X-ray Observatory (MAXI) mission is a set of X-ray detectors installed in the Japanese International Space Station (ISS) experimental module that monitors the entire sky due to X-ray bursts and outbreaks.

Soon after the instrument got a black hole outbreak, Steiner and his co-workers began to observe the event with NASA's Neutron Star of the Interior Composition Explorer or NICER, another instrument on the ISS, partially designed by MIT, to measure the amount and time of the upcoming X-ray photons.

"This blossoming black hole came to the scene and was almost totally undamaged, so we got a very intuitive look at what's happening," says Steiner.

A typical outbreak can occur when a black hole sucks huge quantities of material from a nearby star. This material accumulates around a black hole in a vortex well known as the acrecision disc that can traverse millions of miles. The material in the disc that is closer to the center of the black hole rotates faster, causing the friction that warms up the disk.

"Gas in the center is a million degrees of temperature," says Steiner. "When you heat something hot, it shines like X-rays. This disc can crawl and float its gas down to a central black hole to approximately the value of Everest gas per second. And that's when it goes into an outbreak, which usually takes about one year. "

Scientists have previously noticed that X-ray photons emitted by the acrylic disc can ping-pong from high-energy electrons into a black hole corona. Steiner says that some of these photons can be dispersed "to infinity," while others are dispersed back to the acrecipine disk as X-rays with higher energy.

Using NICER, the team succeeded in gathering extremely accurate measurements of the energy and time of photonic X-ray photons throughout the outbreak of the black hole. It is important that they pick up "echoes" or lagging between low-energy photons (those initially released by the acrecipical disc) and high-energy photons (X-rays that are probably interacting with coronal electrons). In one month, the researchers noticed that the length of these backlogs was significantly reduced, indicating that the distance between the coronal and acrecice discs also shrunk. But was there a disc or a corona that was changing?

In order to answer this, researchers measured the signature that astronomers have known as the "iron line" – a feature that is excreted by iron atoms in the acrecice disc only when they are under voltage, for example by reflection of x-ray photons. corona electrons. The iron can measure the internal limit of the acrecision disc.

When researchers measured the iron line throughout the outbreak, no measurable change was found, indicating that the disc itself does not move in shape but remains relatively stable. Together with evidence of X-rays, they have decided that the corona must be changed and reduced due to an outbreak of a black hole.

"We see that the corona starts like this inflated, 100-kilometer foot inside the internal acrylic disk, then shrinks to about 10 kilometers in about a month," says Steiner. "This is the first unambiguous example of coronal shrinkage when the disc is stable."

"NICER has allowed us to measure light reflections closer to the black hole of the star mass than ever before," adds Kara. "Previously, these light reflections from the internal acrylic disc were only visible in supermassive black holes, which are millions to billions of solar masses and have been evolving for millions of years. Stellar black holes, such as the J1820, have much lower mass and evolve much faster so that we can see changes in human time scales. "

Although it is not clear exactly what causes the coron, Steiner speculates that the cloud of high-energy electrons is compressed due to the strong pressure caused by the gas plaza that descends through the acrecice disc.

The findings provide a new insight into the important phase of the outbreak of the black hole, known as the transition from hard to soft state. Scientists knew that a black hole at some point early in the outbreak shifted from the "hard" stage in which the coronal energy is dominated, into the "soft" phase, which is better regulated by the emissions of the acrecice disc.

"This transition indicates a fundamental change in the black hole mode," says Steiner. "But we do not know exactly what is happening. How does the passage of the black hole from the predominant corona to your disk? Does the disc move and assume, is the corona changed and diffused in some way? This is something that people have tried to decipher for decades, and now this is a final work on what is happening at this transitional stage and that the corona is changing. «

This research is partially supported by NASA through the NICER mission and the Astrophysical Research Program.