Scientists find a hidden black hole using new detection method

Katie Ramirez
November 4, 2019

It had been thought that a star would need to have a minimum of roughly five to seven times the mass of the Sun to form a black hole when it eventually reaches the end of its cycle and collapses in on itself.

Both black holes and neutron stars could hold exciting information about the elements on Earth and about how stars live and die. That changed in 2017, when the Laser Interferometer Gravitational-Wave Observatory (LIGO) caught a merger of two black holes, one of which was 25 times the mass of the sun, and the other 31 times the mass of the sun. 'Black holes that size are a big deal-we hadn't seen them before'.

Todd Thompson, a professor at Ohio State University and the lead author of the study, said that spotting it was "needle-in-the-haystack kind of search". As the black hole takes away matter from the nearby star, it emits X-rays which makes them easy to spot.

Scientists also had known that black holes were 5-15 times the mass of the sun, and the neutron stars that were 2.5 times the sun's mass collapsed into black holes.

Measured as 3.3 solar masses, it is slightly above the highest neutron star mass observed so far (2.1 solar masses) and lower than four solar masses - the theoretical lower limit for black holes.

Black holes are usually formed when an extremely massive star dies in a supernova.

What is a black hole?

Black holes can be phenomenally big. "The finding [s] sound very reasonable", but not unexpected, as astronomers know that lower mass black holes exist.

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If one star dies, the other still orbits the space where it existed, even if that space is now filled by a black hole or neutron star.

'Immediately, everyone was like "wow", because it was such a spectacular thing, ' Thompson says. On the other hand, there are supermassive black holes that have a mass equivalent to a few million suns. However, LIGO's discovery proved that black holes could be larger.

While narrowing down the list of stars to the most likely candidates, Thompson and his colleagues found a giant red star orbiting something smaller than the smallest known black hole but larger than any known neutron star.

Thus, Thompson chose to see if he could solve that mystery. Researchers sifted through Apache Point Observatory Galactic Evolution Experiment (APOGEE) data as part of their work, looking for evidence of stars orbiting around something.

Thompson said he looks forward to future discoveries, such as information about the incline of the star's orbit around the dark object that the European Space Agency's Gaia spacecraft might gather in an upcoming mission. Since the brightness kept changing, scientists were able to identify a low-mass black hole.

So this dark, mysterious object "could be the most massive neutron star ever seen", right at the boundary after which it can't exist, Thompson said. He gave the data to a graduate research associate at Ohio State, Tharindu Jayasinghe, who compiled thousands of images of each potential binary system from ASAS-SN, the All-Sky Automated Survey for Supernovae.

By combining data, Thompson started looking for stars that showed that change, indicating that they might be orbiting a black hole. 'The masses of things tell us about their formation and evolution, and they tell us about their nature'.

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