A new astronomical study has revealed that the large variations in light observed in one of the Earth's closest black holes are caused by a deformation in its accretion disk - a structure made of plasma and hydrogen that rotates around a central body.
The explosion at MAXI object J1820+070, located 9,600 light-years from us, was discovered in 2018 by a Japanese telescope on the International Space Station and observed by amateur astronomers for nearly a year. Having remained brilliant for so many months, she was closely followed by members of the American Association of Variable Star Observers, as well as researchers from South Africa, France, the United States and the United Kingdom.
The luminous variations found are one of the three brightest transient X-ray phenomena ever seen, which occur in binary systems composed of a low-mass star and a much more compact object. In this case, the object is a black hole that is at least eight times as massive as our Sun.
The normal star material is pulled by the compact object into its surrounding gas accretion disk, moving in a spiral,” explains Phil Charles, research team member, in a note. When the material in the disk becomes hot and unstable and accumulates in the black hole, explosions can occur that release large amounts of energy, according to the researcher at the University of Southampton, UK. Published this Tuesday (26) in the Monthly Notices of the Royal Astronomical Society, the study details how an enormous emission of X-rays leaves an area close to the black hole and radiates surrounding matter. The accretion disk is then heated to a temperature of about 9,700 degrees Celsius and becomes visible light. As the X-ray burst decreases, therefore, the glare is also reduced.
But three months after the initial boom, the light curve varied for 17 hours, although the amount of X-rays remained stable. The only viable explanation found by the scientists was that the radiation would be causing the disk to bend and a consequent increase in its area, causing the brightness to grow as well. Such behavior has already been observed in binary systems with more massive stars, but never in a black hole with a low-mass pair. "This object has a lot to teach us about the endpoints of stellar evolution and the formation of compact objects," celebrates Charles.
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