Scientists have discovered a relatively small black hole next to a star in the constellation Ophiuchus, about 1,600 light-years away. It is now the closest known black hole to Earth.
Black holes are the densest objects in the universe (sorry, neutron stars). Whether it’s a small stellar-mass black hole or a supermassive black hole at the center of a galaxy, the gravitational fields of these objects are so strong that not even photons can escape their event horizon.
The recently discovered black hole, named “Gaia BH1”, is so close to us that the previous record holder was three times as far away from Earth as it was. Details about its discovery, along with the Sun-like stars orbiting it, were published this week in Monthly Notices of the Royal Astronomical Society.
The object was discovered by the Gemini North Telescope in Hawaii (part of the International Gemini Observatory) along with data from the European Space Agency’s Gaia spacecraft. Gaia’s data suggest that the star’s motion is a bit odd for a single object, appearing as if the gravity of a massive object is affecting its motion.
Follow-up observations with the Gemini North telescope determined the precise orbital period of the companion star, helping the team to better estimate the mass of the unseen object.
“While there are many claims to have detected such a system, but almost all of these discoveries were subsequently refuted. This is the first unambiguous detection of a Sun-like star in the large orbit of a stellar-mass black hole in the Milky Way.”
Remember, a light-year is about 6 trillion miles, so at a distance of 1,600 light-years, nearby black holes are only relatively close. Voyager, the furthest space mission ever traveled by humans, has been away from Earth for nearly 50 years, coming within 15 billion miles of Earth. Alpha Centauri is the closest star system to Earth, about 4.24 light-years away.
Because light cannot escape black holes, they are most easily observed when they are surrounded by the superheated matter they accreted. This is the case with the black hole at the center of the Messier 87 galaxy and Sagittarius A* at the center of the Milky Way. Both black holes were photographed by the Event Horizon Telescope Collaboration, allowing you to see where the black holes are lurking thanks to the warm glow of matter.
But when black holes aren’t actively “feeding,” they’re hard to spot. That is, when they are not accreting matter, heating it, and releasing X-rays in the process. “Gaia BH1” is one such example, which is invisible except for its gravitational effect on the star.
Karim Badri said: “Our follow-up observations of Gemini confirmed beyond reasonable doubt that the binary contains a normal star and at least one dormant black hole. We could not find any plausible astrophysical scenarios, to explain the orbits of observed systems that do not contain at least one black hole.”
But current models of binary systems, which include a black hole and a star, cannot explain the “Gaia BH1” system. According to NOIRLab, the star in the system that was engulfed by the black hole was so massive that it should have devoured another (ie, still-existing) star in the system before the black hole formed.
Observing more black hole binary systems will help astrophysicists refine their models of how these systems form and evolve. Space observatories like IXPE and NASA’s NICER and NuSTAR will help in this effort by scrutinizing the high-energy X-rays feeding black holes.、
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