Astronomers Discover Black Hole Hiding In Plain Sight In Earth's "Backyard"

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An artist's illustration of the HR 6819 system. The system comprises two stars (both in blue) orbiting around a black hole (in red) (Credit: ESO/L. Calçada)

Given that each light-year — defined as the distance light travels in one Earth year — is about 6 trillion miles (9 trillion km), a black hole that lies 1,000 light-years away may not seem very close. However, to astronomers who are accustomed to cosmic distance scales, the recently-discovered HR 6819's black hole, which lies in the constellation Telescopium, is an extremely close neighbor.

"On the scale of the Milky Way, it's in our backyard," said Thomas Rivinius, an astronomer at the European Southern Observatory (ESO) in Chile who led the research. "Almost on our doorstep." The scientist says it is so close that the black hole's two orbiting stars can be observed with the naked eye in the Southern Hemisphere's skies on a clear night.

A wide-field image of the region of the sky, in the constellation Telescopium ,where HR 6819 is located (Credit: ESO/Digitized Sky Survey / Davide De Martin / CC BY by/4.0/Creative Commons)

A black hole forms when a massive dying star collapses under its own gravity and shrinks until all of its mass is contained in an infinitely dense point called a singularity. Since black holes do not allow light to escape, they remain invisible until their strong gravitational pull starts to draw in nearby stars. The process is so luminous that it can be observed from Earth. "Sometimes they [black holes] become the brightest objects in the sky," says Erin Kara, an astrophysicist at MIT who studies black holes. However, since HR 6819's two stars are too far away to be pulled in by its gravity, the black hole managed to remain undetected despite being so close to Earth.

“It seems like it’s been hiding in plain sight,” says astronomer Kareem El-Badry, a Ph.D. student at the University of California, Berkeley, who specializes in binary star systems but wasn’t involved with the study. “It’s a bright enough star [system] that people have been studying it since the 80s, but it seems like it’s had some surprises.”

The ESO astronomers stumbled upon the discovery when they began analyzing the data collected on the HR 6819 system as part of their research on stars that orbit in pairs. They found that unlike other binary star systems, which move in synch, HR 6819's inner star was orbiting at a much faster pace than its outer star. This led the astronomers to suspect there was a third object located at the center of the star system. After further investigating the inner star's motion and orbit pattern, the team came to the conclusion that the unseen​​​​​​ body is a black hole – the remnant of a third star which had once been a part of the HR 6819 star system. Their calculations suggest that the black hole has a mass roughly four times that of our Sun.

The discovery, published in the journal Astronomy & Astrophysics on May 6, 2020, is giving scientists hope that there are many more black holes near Earth that are just waiting to be discovered. "It's important to emphasize that it's the closest we've found yet," says Sera Markoff, an astrophysicist at the University of Amsterdam who was not involved with the latest research. "There might be closer ones."

Resources: TheAtlantic.com, Vox.com, Gizmondo.com

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141 Comments
  • zaks
    zaksSunday, July 5, 2020 at 8:19 am
    Wow kinda cool.
    • lovereading310
      lovereading310Friday, June 26, 2020 at 7:19 pm
      This is very interesting!
      • robloxuser
        robloxuserWednesday, June 10, 2020 at 12:58 pm
        wow that's cool but it will be a little scary if it sucked up Earth right?
        • schooler
          schoolerThursday, June 4, 2020 at 11:25 am
          irk, its so cool how it acts like!
          • daniella_reader
            daniella_readerThursday, June 4, 2020 at 10:54 am
            Ya they are very cool lol but there kinda scary a little lol leave a like pls and a reply pls. Do it especially if you agree
            • soccerpum3
              soccerpum3Monday, June 8, 2020 at 8:56 pm
              I love science it's so cool that we can be learning this
            • e_r_k_s
              e_r_k_sMonday, June 1, 2020 at 9:28 am
              Black Holes are a very cool lol
            • chrismas
              chrismasThursday, May 28, 2020 at 1:46 pm
              so cool
              • elizabethan
                elizabethanThursday, May 28, 2020 at 6:01 am
                That is so cool.Like me if you agree.
                • schooler
                  schoolerThursday, June 4, 2020 at 11:26 am
                  Yeah, cool enough to knock my socks off!
                • lizzzy_winkle
                  lizzzy_winkleWednesday, May 27, 2020 at 7:19 pm
                  It's so pretty.
                  • legendofzelda
                    legendofzeldaWednesday, May 27, 2020 at 12:13 pm
                    Ark survival evolved!