NICER Mission Maps a New Black Hole called J1820

NICER Mission Maps a New Black Hole called J1820

NICER Mission Maps a New Black Hole called J1820
Image Credits: Astronomy Lovers

The Neutron star Interior Composition Explorer (NICER) of NASA allowed the researchers to study a new stellar-mass black hole called J1820.

NICER found this massive black hole (10 times the mass of the Sun) by detecting the X-rays emitting from it as it consumed material from a companion star. The name given to this newly-discovered black hole is MAXI J1820+070 while it is commonly known as J1820. The light echoes formed by these X-rays reflected off the swirling gas around the black hole, which showed the changes in the size and shape of the environment. Erin Kara, an Astrophysicist from the University of Maryland who presented these findings at the 233rd meeting of the American Astronomical Society, referred to all that by saying,

“NICER has allowed us to measure light echoes closer to a stellar-mass black hole than ever before. Previously, these light echoes off the inner accretion disk were only seen in supermassive black holes, which are millions to billions of solar masses and undergo changes slowly. Stellar black holes like J1820 have much lower masses and evolve much faster, so we can see changes play out on human timescales.”

History of J1820

J1820 is around 10,000 light-years away from us and is located towards the constellation Leo. The Gaia Mission of the European Space Agency (ESA) identified the companion star in the system. Scientists had absolutely no idea about the existence of this black hole until March 2018. On the 11th of March, the Monitor of All-Sky X-ray Image (MAXI) of the Japan Aerospace Exploration Agency spotted a huge outburst of X-rays. Consequently, J1820 turned into one of the brightest sources of X-rays in the sky. NICER was quick to observe this extraordinary transition and continues to follow the fading tail of the eruption. Zaven Arzoumanian, the Co-author of the paper who serves as a Science Lead for the NICER mission, talked about that in the following words:

“NICER was designed to be sensitive enough to study faint, incredibly dense objects called neutron stars. We’re pleased at how useful it’s also proven in studying these very X-ray-bright stellar-mass black holes.”

NICER’s Observations of J1820

Astrophysicists want to improve their understanding about the changes in the shape and size of the corona and the accretion disk as a black hole attracts material from its companion star. They somehow manage to do that successfully, they will be able to shed light on the evolution of supermassive black holes over millions of years. Similarly, they can also study the effects of these black holes on the galaxies in which they reside. A popular method to record these changes is called the ‘X-ray Reverberation Mapping’, which uses X-rays reflections to determine this key information.

Previous observations of X-ray echoes from stellar black holes revealed that the inner edge of the accretion disk can lie at long distances from the event horizon. On the other hand, X-ray Reverberation Mapping of supermassive black holes showed that the inner edge of the accretion disk is incredibly close to the event horizon. The latest research revealed that the behavior of the stellar mass J1820 is similar to its supermassive cousins. NICER’s observations of J1820 showed a continuous decrease in lag time between the initial flare of X-rays and the echo off the disk. This clearly indicated that the X-rays traveled shorter and shorter distances before they were reflected. Jack Steiner, an Astrophysicist at the Massachusetts Institute of Technology, said,

“This is the first time that we’ve seen this kind of evidence that it’s the corona shrinking during this particular phase of outburst evolution. 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.”

Iron K Line of J1820

The researching team used a specific signal called the ‘Iron K Line’ to confirm the decreased lag time. Whenever X-rays from the corona collide with iron atoms in the disk, they start glowing. However, the slower speed of time, in a stronger gravitational field, stretches the X-ray wavelengths for the observer (NICER). The team discovered that the stretched Iron K Line remained constant for J1820 which meant that the inner edge of the disk remained close to the black hole. These observations gave scientists some new insights about how energy is released in this process.   

You can have a closer look at the black hole in the following video:

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