The Indian Space Research Organisation’s (ISRO) AstroSat’s full multi-wavelength capabilities have enabled an international team of scientists to unravel the mysteries surrounding the X-ray binary system MAXI J1820+070, hosting a black hole.

AstroSat is India’s first multi-wavelength space observatory which was launched in September 2015 and now a comprehensive study presents unique insights into the behaviour of this transient black hole X-ray binary during its 2018 outburst.

According to ISRO, MAXI J1820+070, positioned around 9800 light-years distant from Earth, is a transient black hole X-ray binary.

It was first detected during its outburst in 2018 using the MAXI instrument aboard the International Space Station (ISS). Because of its proximity to Earth and its remarkable brightness upon discovery, emerging as the second brightest object in the X-ray sky, MAXI J1820+070 garnered significant attention within the astronomy community.

AstroSat, equipped with three X-ray payloads and a UV telescope, captured soft and hard X-ray emissions and far ultraviolet radiation, painting a detailed portrait of the near and distant regions surrounding the black hole in MAXI J1820+070.

Prof. Dipankar Bhattacharya, chairperson of the AstroSat Science Working Group and a co-author of this study, said “This is the first time the full capability of all the co-pointed instruments in AstroSat have been used in unison, supplemented by ground-based observations, and the results are fascinating. I am happy to be a part of this unique investigation of one of the most interesting Black Hole sources discovered in recent times”.

The space agency further said that the significance of this study extends beyond MAXI J1820+070, highlighting the pivotal role of AstroSat in advancing the understanding of transient black hole X-ray binaries.

“With its unique multi-wavelength capabilities, AstroSat opens doors to further exploration of diverse astrophysical phenomena, laying the groundwork for future endeavours in the field,” the space agency said.

Scientists have no reported evidence of the true conditions in Hell, perhaps because no one has ever returned to tell the tale. Hell has been imagined as a supremely uncomfortable place, hot and hostile to bodily forms of human life.

Thanks to a huge astronomical survey of the entire sky, we have now found what may be the most hellish place in the universe.

In a new paper in Nature Astronomy, we describe a black hole surrounded by the largest and brightest disc of captive matter ever discovered. The object, called J0529-4351, is therefore also the brightest object found so far in the universe.

Supermassive black holes

Astronomers have already found around one million fast-growing supermassive black holes across the universe, the kind that sit at the centres of galaxies and are as massive as millions or billions of Suns.

To grow rapidly, they pull stars and gas clouds out of stable orbits and drag them into a ring of orbiting material called an accretion disc. Once there, very little material escapes; the disc is a mere holding pattern for material that will soon be devoured by the black hole.

The disc is heated by friction as the material in it rubs together. Pack in enough material and the glow of the heat gets so bright that it outshines thousands of galaxies and makes the black hole’s feeding frenzy visible to us on Earth, more than 12 billion light years away.

The fastest-growing black hole in the universe

The accretion disc of J0529-4351 emits light that is 500 trillion times more intense than that of our Sun. Such a staggering amount of energy can only be released if the black hole eats about a Sun worth of material every day.

It must also have a large mass already. Our data indicate J0529-4351 is 15 to 20 billion times the mass of our Sun.

There is no need to be afraid of such black holes. The light from this monster has taken more than 12 billion years to reach us, which means it would have stopped growing long ago.

In the nearby universe, we see that supermassive black holes these days are mostly sleeping giants.

Black holes losing their grip

The age of the black hole feeding frenzy is over because the gas floating around in galaxies has mostly been turned into stars. And after billions of years the stars have sorted themselves into orderly patterns: they are mostly on long, neat orbits around the black holes that sleep in the cores of their galaxies.

Even if a star dove suddenly down towards the black hole, it would most likely carry out a slingshot manoeuvre and escape again in a different direction.

Space probes use slingshot manoeuvres like this to get a boost from Jupiter to access hard-to-reach parts of the Solar System. But imagine if space were more crowded, and our probe ran into one coming the other way: the two would crash together and explode into a cloud of debris that would rapidly fall into Jupiter’s atmosphere.

Such collisions between stars were commonplace in the disorder of the young universe, and black holes were the early beneficiaries of the chaos.

Accretion discs – a no-go zone for space travellers

Accretion discs are gateways to a place whence nothing returns, but they are also profoundly unfriendly to life in themselves. They are like giant storm cells, whose clouds glow at temperatures reaching several tens of thousands of degrees Celsius.

The clouds are moving faster and faster as we get closer to the hole, and speeds can reach 100,000 kilometres per second. They move as far in a second as the Earth moves in an hour.

The disc around J0529-4351 is seven light years across. That is one and a half times the distance from the Sun to its nearest neighbour, Alpha Centauri.

Why only now?

If this is the brightest thing in the universe, why has it only been spotted now? In short, it’s because the universe is full of glowing black holes.

The world’s telescopes produce so much data that astronomers use sophisticated machine learning tools to sift through it all. Machine learning, by its nature, tends to find things that are similar to what has been found before.

This makes machine learning excellent at finding run-of-the-mill accretion discs around black holes – roughly a million have been detected so far – but not so good at spotting rare outliers like J0529-4351. In 2015, a Chinese team almost missed a remarkably fast-growing black hole picked out by an algorithm because it seemed too extreme to be real.

In our recent work, we were aiming to find all the most extreme objects, the most luminous and most rapidly growing black holes, so we avoided using machine learning tools that were guided by too much prior knowledge. Instead we used more old-fashioned methods to search through new data covering the entire sky, with excellent results.

Our work also depended on Australia’s current 10-year partnership with the European Southern Observatory, an organisation funded by several European countries with a huge array of astronomical facilities.

The interaction between a supermassive black hole in a galaxy named 2MASX J02301709+2836050 and a star orbiting it is seen in this image captured by the Pan-STARRS telescope, in Hawaii, U.S., in an undated handout image provided by NASA.
| Photo Credit: Reuters

Black holes, celestial objects known for their gluttony, usually eat stars unlucky enough to stray too close to them in one big gulp, annihilating them with their enormous gravitational pull. But some, it turns out, tend to snack rather than gorge.

Researchers said they have observed a supermassive black hole at the center of a relatively nearby galaxy as it takes bites out of a star similar in size and composition to our sun, consuming material equal to about three times Earth’s mass each time the star makes a close pass on its elongated oval-shaped obit.

Black holes are extraordinarily dense objects with gravity so strong that not even light can escape.

The star is located about 520 million light years from our solar system. A light year is the distance light travels in a year, 5.9 trillion miles (9.5 trillion km). It was observed being plundered by a supermassive black hole at the heart of a spiral-shaped galaxy.

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As such black holes go, this one is relatively small, estimated to have a mass a few hundred thousand times larger than the sun. The supermassive black hole at the center of our galaxy, called Sagittarius A*, possesses about 4 million times the mass of our sun. Some other galaxies harbor supermassive black holes hundreds of millions times the mass of the sun.

Most galaxies have such black holes at their center, and the environment around them can be among the most violent places in the universe.

Most of the data used by the scientists in the new study came from NASA’s orbiting Neil Gehrels Swift Observatory.

The star was observed orbiting the black hole every 20 to 30 days. At one end of its orbit, it ventures near enough to the black hole to have some material from its stellar atmosphere sucked away, or accreted, each time it passes – but not so close as to have the whole star shredded. Such an event is called a “repeating partial tidal disruption.”

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The stellar material that falls into the black hole heats up to around 3.6 million degrees Fahrenheit (2 million degrees Celsius), unleashing an immense amount of X-rays. Those were detected by the space observatory.

“What’s most likely to happen is the star’s orbit will gradually decay and it will get closer and closer to the supermassive black hole until it gets close enough to be completely disrupted,” said astrophysicist Rob Eyles-Ferris of the University of Leicester in England, one of the authors of the study published this week in the journal Nature Astronomy.

“That process is likely to take years at least – more likely decades or centuries,” Eyles-Ferris added.

This marked the first time that scientists had observed a sun-like star being repeatedly snacked upon by a supermassive black hole.

“There are lots of unanswered questions about tidal disruption events and exactly how the orbit of the star affects them,” Eyles-Ferris said. “It’s a very fast-moving field at the moment. This one has shown us that new discoveries could come at any time.”