A strange black hole with a massive distortion in its accretion disk has been discovered

An international team of astrophysicists from South Africa, the UK, France and the US have found a large variation in the brightness of light seen around one of the closest black holes in our galaxy, 9,600 light-years from Earth, and they conclude that it is caused by a huge distortion in its accretion disk

This object, MAXI J1820+070, erupted as a new transient X-ray source in March 2018 and was discovered by a Japanese X-ray telescope on the International Space Station. These transients, systems that exhibit strong outbursts, are binary stars that include a low-mass star similar to our Sun and a much more compact object that could be a white dwarf, neutron star, or black hole. In this case MAXI J1820+070 has a black hole whose mass is at least eight times greater than the mass of our Sun.

The first findings have now been published in the important international journal Monthly Notices of the Royal Astronomical Society, and the lead author is Dr. Jessimol Thomas, a postdoctoral research fellow at the South African Astronomical Observatory.

The discovery presented in the article was discovered from an extensive and detailed light curve received over almost a year from dedicated enthusiasts from around the world who are part of the AAVSO (American Association of Variable Star Observers). MAXI J1820+070 is one of the three brightest X-ray transients ever observed, a result of its proximity to Earth and being outside the obscuring plane of our Milky Way galaxy. It remained bright for many months, and this allowed so many enthusiasts to follow it.

Professor Phil Charles, a researcher at the University of Southampton and a member of the research team, explained: “Material from the normal star is drawn by the compact object into the accretion disk of swirling gas that surrounds it. Large bursts happen when the material in the disk becomes hot and unstable, adsorbs into the black hole and releases copious amounts of energy before it passes the event horizon. This process is chaotic and very variable, and the time periods vary from milliseconds to months."

The research team created the system's bra, which shows how a huge output of X-ray radiation emanates from very close to the black hole, then irradiates the surrounding material, specifically the accretion disk, heating it to a temperature of up to around 10,000K, which appears as visible light emitted. This is why when the X-ray burst is small, so is the optical light.

But something unexpected happened nearly three months after the eruption began when the optical light curve began to modulate enormously—a bit like flipping a dimmer switch up and down and nearly doubled its brightness at its peak—over a period of about 17 hours. But there was no change in the x-ray output, which remained constant. Small, quasi-periodic visible modulations have previously been seen in the outbursts of other X-ray transients, but nothing of this magnitude had ever been seen before.