Gaia Discovers Mysterious New Kind of Black Gap, and Two Are Hiding in Earth’s Cosmic Yard

Gaia Black Holes

The situation of the primary two black holes found by ESA’s Gaia mission within the Milky Approach. This map of our galaxy was additionally produced by the Gaia mission. Gaia’s Black Gap 1 is simply 1560 light-years away within the path of the constellation Ophiuchus, and Gaia’s Black Gap 2 is 3800 light-years away within the constellation Centaurus. In galactic phrases, these black holes are in our cosmic yard. Credit score: ESA/Gaia/DPAC; CC BY-SA 3.0 IGO

ESA’s Gaia mission helped uncover a brand new species

black gap
A black gap is a spot in area the place the gravitational area is so sturdy that not even mild can escape it. Astronomers classify black holes into three classes by measurement: tiny, stellar, and supermassive black holes. Tiny black holes may have a mass lower than our Solar, and supermassive black holes may have a mass equal to billions of our Solar.

“data-gt-translate-attributes=”[{” attribute=””>black hole. The new family already has two members, and both are closer to Earth than any other black hole that we know of.

A team of astronomers studied the orbits of stars tracked by Gaia and noticed that some of them wobbled on the sky, as if they were gravitationally influenced by massive objects. Several telescopes looked for the objects, but no light could be found, leaving only one possibility: black holes.

Gaia Spacecraft Artist's Impression

Gaia is an ambitious mission to chart a three-dimensional map of our Galaxy, the Milky Way, in the process revealing the composition, formation, and evolution of the Galaxy. Credit: ESAD. Ducros, 2013

New population of black holes

Using data from ESAs Gaia mission, astronomers have discovered not only the closest but also the second closest black hole to Earth. The black holes, Gaia BH1 and Gaia BH2, are respectively located just 1560 light-years away from us in the direction of the constellation Ophiuchus and 3800 light-years away in the constellation Centaurus. In galactic terms, these black holes reside in our cosmic backyard.

The two black holes were discovered by studying the movement of their companion stars. A strange wobble in the movement of the stars on the sky indicated that they are orbiting a very massive object. In both cases, the objects are approximately ten times more massive than our Sun. Other explanations for these massive companions, like double-star systems, were ruled out since they do not seem to emit any light.

Detecting Exoplanets With Astrometry

The wobble of stars on the sky is caused by the gravitational attraction from other stars, exoplanets or black holes. In this image the attracting object is an exoplanet. Credit: ESA

Until recently, all the black holes astronomers knew of were discovered by emission of light usually at X-ray and radio wavelengths produced by material falling in. The new black holes are truly black and can only be detected by their gravitational effects. The distance of the stars to the black hole, and the orbits of the stars around them, are much longer than for other known binary systems of black holes and stars. Those closer star-black hole pairs, called X-ray binaries, tend to be very bright in X-ray and radio light, and thus easier to find. But the new discoveries suggest that black holes in wider binaries are more common.

What sets this new group of black holes apart from the ones we already knew about is their wide separation from their companion stars. These black holes likely have a completely different formation history than X-ray binaries, explains Kareem El-Badry, discoverer of the new black holes and researcher at the Harvard-Smithsonian Center for Astrophysics in the US and the Max-Planck Institute for Astronomy in Heidelberg, Germany.

ESA’s Gaia mission helped uncover a brand new sort of black gap. The brand new household already has two members, each of that are nearer to Earth than some other black gap we all know. The 2 black holes have been found by learning extremely exact measurements of stellar positions and motions within the third launch of Gaias knowledge. An odd wobble within the movement of two stars within the sky has proven that they’re orbiting a really large object. In each instances, the objects are about ten instances extra large than our Solar. Different explanations for these large companions, comparable to binary star programs, have been dominated out as they don’t seem to emit mild. Gaia’s second black gap, BH2, is 3800 light-years away from Earth. It’s a binary system consisting of a crimson large star and presumably a black gap. On this animation of Gaia BH2, created in Gaia Sky, the orbits are precisely sized, however the backhole diameter is to not scale. Credit score: ESA/Gaia/DPAC, CC BY-SA 3.0 IGO

Movement of billions of stars

Black holes have been found utilizing Gaia knowledge. Gaia exactly measures the positions and actions of billions of stars. The movement of stars towards the sky can present substantial clues about objects that gravitationally affect these stars. These objects can embrace different stars, exoplanets, and even black holes.


How carefully the measured worth conforms to the right worth.

“data-gt-translate-attributes=”[{” attribute=””>accuracy of Gaias data was essential for this discovery. The black holes were found by spotting the tiny wobble of its companion star while orbiting around it. No other instrument is capable of such measurements, says Timo Prusti, ESAs Gaia project scientist.

Gaia provided accurate measurements of the movement in three directions, but to understand more precisely how the stars moved away and towards us, additional radial velocity measurements were needed. Ground-based observatories provided these for the newly found black holes, and this gave the final clue to conclude that the astronomers had detected black holes.

Invisible black holes

Black holes are often not completely invisible. When material falls onto them, they may emit light in radio and X-ray. For Gaias second black hole,

Even though we detected nothing, this information is incredibly valuable because it tells us a lot about the environment around a black hole.There are a lot of particles coming off the companion star in the form of stellar wind. But because we didnt see any radio light, that tells us the black hole isnt a great eater and not many particles are crossing its event horizon. We dont know why that is, but we want to find out! says Yvette Cendes who helped discover the second black hole and is an astronomer at the Harvard-Smithsonian Center for Astrophysics in the US.

The new type of black hole does not emit any light, making them practically invisible, probably because they are much further away from their companion stars. Gaia BH1 and Gaia BH2 have the most widely separated orbits of all known black holes. The fact that they are also the closest known black holes to Earth suggests that many more similar black holes in wide binaries are still waiting to be discovered.

This is very exciting because it now implies that these black holes in wide orbits are actually common in space more common than binaries where the black hole and star are closer. But the trouble is detecting them. The good news is that Gaia is still taking data, and its next data release (in 2025) will contain many more of these stars with mystery black hole companions in it, Yvette explains.

Gaias next data release will be based on 66 months of observations and will contain improved information on the orbits of stars. In the meantime, astronomers will be busy figuring out where these black holes in wide orbits come from.

Kareem El-Badry points out: We suspected that there could exist black holes in wider systems, but we were not sure how they would have formed. Their discovery means that we must adapt our theories about the evolution of binary star systems as it is not clear yet how these systems form.

Gaias Data Processing and Analysis Consortium is developing methods to identify astrometric binaries with compact companions. We expect to provide a good sample of candidates in the next Gaia data release, says team member Tsevi Mazeh from Tel Aviv University. The scientific community looks forward to further expand this new population of dormant black holes.

On June 13, 2022 Gaia released, for the first time, results from its non-single star processing. The Gaia binary star survey surpasses all the work on binary stars from the past two centuries. These two black holes were found by investigating two of the solutions from this catalog of more than 813,000 binary star systems. Gaia Data Release 4 is expected to further increase the accuracy of binary star solutions, possibly revealing many more exciting candidates for follow-up.

Reference: A red giant orbiting a black hole by Kareem El-Badry, Hans-Walter Rix, Yvette Cendes, Antonio C Rodriguez, Charlie Conroy, Eliot Quataert, Keith Hawkins, Eleonora Zari, Melissa Hobson, Katelyn Breivik, Arne Rau, Edo Berger, Sahar Shahaf, Rhys Seeburger, Kevin B Burdge, David W Latham, Lars A Buchhave, Allyson Bieryla, Dolev Bashi, Tsevi Mazeh and Simchon Faigler, 30 March 2023, Monthly Notices of the Royal Astronomical Society.
DOI: 10.1093/mnras/stad799

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