Astronomers have discovered the closest black hole to Earth, which researchers refer to as Gaia BH1. The dormant black hole weighs about 10 times the mass of the Sun and is located about 1,600 light-years away in the constellation Ophiuchus, making it three times closer to Earth than its previous record holder, an X-ray binary system in the constellation. Unicorn. The discovery was made possible by excellent observations of the motion of the black hole’s satellite, a Sun-like star orbiting the black hole at about the same distance as the Earth from the Sun.

“Take the solar system, put a black hole where the sun is, and put the sun where the Earth is, and you have this system,” explains astrophysicist Karim El-Badri of the Center for Astrophysics | Harvard & Smithsonian and Max Planck Institute for Astronomy and lead author of the paper describing the discovery. “Although many claims have been made that such systems have been discovered, nearly all of these discoveries were later refuted. This is the first definitive detection of a Sun-like star orbiting widely around a stellar-mass black hole in our galaxy.”

Black holes are the most extreme objects in the universe. Supermassive versions of these incredibly dense objects are likely at the centers of all major galaxies. Stellar-mass black holes weighing about 5-100 times the mass of the Sun are much more common, there are about 100 million of them in the Milky Way alone. However, only a few have been confirmed to date, and nearly all of them are “active,” meaning they shine brightly in X-rays because, unlike stationary black holes, they consume material from a nearby stellar moon.

Although there are possibly millions of stellar-mass black holes circulating in the Milky Way galaxy, very few detected have been detected through their energetic interactions with a companion star. As material from a nearby star spirals into the black hole, it overheats and produces powerful X-rays and jets of material. If a black hole is not actively feeding (i.e. sleeping), it simply merges with its surroundings.

“For the past four years, I’ve been investigating dormant black holes using a wide variety of datasets and methods,” says El-Badri. “My previous efforts – and those of others – have found a range of binaries masquerading as black holes, but this search has borne fruit for the first time.”

The team first analyzed data from the European Space Agency’s Gaia spacecraft, identifying the system as a potential black hole. Gaia recorded small irregularities in the star’s motion caused by the gravitational force of an object of invisible mass. To study the system in more detail, the team made 39 observations around the world over four months with six different telescopes.

The first observation was made in July with the Center for Astrophysics telescope using the 6.5-metre Magellan Baade telescope at Las Campanas Observatory in Chile. After this observation suggested that the binary system might contain a black hole, the team submitted offers of time at the discretion of several executives – or requests for time-critical observations – to study the system with other telescopes; this will offer a number of advantages, including higher spectral resolution. ability and sensitivity to ultraviolet and near-infrared radiation.

One such telescope the team referenced was the Gemini Multi-Object Spectrograph instrument at Gemini North, a telescope operated by NSF’s NOIRLab in Hawaii. Subsequent Gemini observations helped limit the orbital motion, and therefore masses, of the two components in the binary system, allowing the team to identify the central body as a black hole about 10 times larger than our Sun.

“Our follow-up Gemini observations confirmed beyond reasonable doubt that the binary system contains a normal star and at least one dormant black hole,” explains El-Badri. “We couldn’t find a plausible astrophysical scenario that could explain the observed trajectory of a system that does not contain at least one black hole.”

Data from these observations caught the system’s attention and eliminated all models that did not contain black holes.

Current astronomers’ models of binary systems evolution struggle to explain how the particular configuration of the Gaia BH1 system might have arisen. In particular, the progenitor star, which later turned into the newly discovered black hole, would have had at least 20 times the mass of our Sun. This means that it will only live for a few million years. If both stars had formed at the same time, this massive star would quickly become a supergiant, swell and swallow the other star before transforming into a true hydrogen-burning main-sequence star like our Sun.

It is not entirely clear how a solar-mass star could survive this event and remain an apparently normal star, as observations of the binary black hole system show. Theoretical models that allow for survival predict that a solar-mass star should be in a much narrower orbit than actually observed. This could indicate significant gaps in scientists’ understanding of how black holes form and evolve in binary systems, and may indicate the existence of an as yet undiscovered black hole population in binary systems.

“Interestingly, this system does not fit easily into standard models of binary evolution,” concludes El-Badri. “It raises a lot of questions about how this binary system formed and how many of these dormant black holes there are.”