Astronomers discover nearest ‘black hole’ to Earth, located only 1,600 light years away

Astronomers using the NOIRLab of the NSF's International Gemini Observatory have discovered the black hole closest to Earth. For the first time, the existence of a stellar-mass black hole in a state of inactivity has been established inside the Milky Way. With barely 1600 light-years separating it from Earth, it presents an intriguing opportunity to learn more about how binary systems form.

Black holes are the most extreme objects in the cosmos. The supermassive counterparts of these incomprehensibly dense objects are likely located at the centres of all very large galaxies.

Black holes of stellar masses are far more common, and it is predicted that the Milky Way is home to 100 million of them. These black holes are five to one hundred times as massive as the Sun. A very limited number of "active" black holes have been verified so far, in contrast to the many more "dormant" black holes that have not been discovered yet because they do not flash intensely in X-rays when they devour stuff from a nearby star partner.

Gaia BH1 is the designation given to the nearest black hole to Earth by astronomers using the Gemini North telescope in Hawaii, one of the twin telescopes of the International Gemini Observatory managed by the National Science Foundation's NOIRLab.

The previous record holder was an X-ray pair in the constellation Monoceros, but this new object is three times closer to Earth. This sleeping black hole in the constellation Ophiuchus is around 1600 light-years distant and is roughly 10 times as massive as our Sun. To get to this conclusion, scientists had to conduct painstaking investigations of the black hole's companion, a Sun-like star that circles it at about the same distance that the Earth orbits the Sun.

"Take the Solar System, put a black hole where the Sun is, and the Sun where the Earth is, and you get this system," explained Kareem El-Badry, an astrophysicist at the Center for Astrophysics | Harvard & Smithsonian and the Max Planck Institute for Astronomy, and the lead author of the paper describing this discovery.

Despite the fact that there are likely millions of stellar-mass black holes wandering the Milky Way, the ones that have been detected were disclosed by their energising interactions with a partner star. X-rays and material jets are emitted when superheated material from a nearby star falls into a black hole. Dormant black holes (those that aren't actively consuming matter) just absorb the space around them.

The researchers began by looking at data from the European Space Agency's Gaia satellite to establish whether or not a black hole may exist in the system. Gaia observed the very small changes in the star's velocity caused by a massive, unseen object.

Gemini North's Gemini Multi-Object Spectrograph was utilised by El-Badry and his colleagues to conduct an in-depth analysis of the system. This instrument precisely measured the companion star's velocity as it orbited the black hole, thus establishing the orbital period. The Gemini follow-up observations were crucial in constraining the orbital velocity and, hence, the masses of the two components in the binary system, allowing the scientists to identify the central body as a black hole about 10 times as big as our Sun.

The team depended on Gemini North's superb observing capabilities and on Gemini's ability to send data on short notice since they had a brief window in which to perform their follow-up observations.

Astronomers' existing understanding of the development of binary systems struggles to account for the peculiar configuration of the Gaia BH1 system. The newly detected black hole would have had a progenitor star with a mass at least 20 times that of the Sun.

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Only a few million years would have passed in its brief existence. If both stars had formed at the same time, the larger one would have expanded rapidly into a supergiant, devouring the smaller one before the latter could mature into a main-sequence star that burns hydrogen like our Sun.

Despite what the findings of the black hole pair suggest, it is unclear how the solar-mass star could have survived that period and emerged as a seemingly normal star. The solar-mass star is expected to have a far closer orbit than what is actually seen, according to theoretical models that do allow for life.

This reveals the presence of an as-yet-unexplored population of latent black holes in binaries, and may also imply that we have significant knowledge gaps regarding the formation and evolution of black holes in binary systems.

(With inputs from ANI)