The closest black hole to our solar system has been discovered a mere 1,000 light-years from Earth. The black hole – which has a mass the equivalent to at least four suns – is completely invisible even to the most powerful of observatories, but orbits with two companion stars that are visible to the naked eye without the aid of a telescope or binoculars.
Black holes by themselves emit no light, and so are impossible to actually observe by telescope. However, astronomers can capture the light fingerprint from these gargantuan singularities when they are feeding. When planets and stars are torn apart by a black hole’s devastating gravitational influence, the resulting debris is drawn inexorably inwards towards the event horizon, and settles into what is known as an accretion disk.
As the cosmic debris moves closer to the point of no return, it accelerates and becomes super-heated, causing it to glow brightly and throw off massive amounts of radiation which can be spotted by Earthbound and orbital telescopes. Along with the creation of a glowing accretion disk, these monumental interactions can cause black holes to let off fantastic bursts of X-ray light, which are visible to certain observatories.
The singularity located in the HR 6819 system is rare even among stellar-mass black holes, in that it is interacting peacefully with its environment. In other words, it’s not in the process of violently ripping stars and planets apart, and so exhibits none of the light-based phenomena synonymous with black holes.
It is essentially invisible, yet the scientists behind the new study were able to infer its existence by tracking the orbital motions of the two stellar bodies that make up the remainder of the triple system.
The team stumbled across the black hole while carrying out a study of double star systems using the FEROS spectrograph mounted on the MPG/ESO 2.2-metre telescope in Chile. Upon analyzing their results, the astronomers realized that the two visible stars of HR 6819 seemed to be orbiting with an enormous invisible object.
They concluded that the hidden object, that emits no light yet had a mass over four times that of the Sun, had to be a black hole. The team was able to estimate the black hole’s mass by observing the orbits of the stars. The innermost star orbits with the singularity once every 40 days, while the outer star tracks a more distant path around the central pair.
The system in which the silent singularity resides is located just 1,000 light-years from Earth in the constellation of Telescopium, making it the closest known black hole to the Sun. The two stars of HR 6819 are so bright that they can be seen with the naked eye on a clear night by sky gazers in the Southern Hemisphere.
According to the authors of the study, the new discovery could be the tip of the iceberg. It is possible that many other planetary-mass black holes are also lurking in what appear to be dual star systems, and now the scientific community may know where to look in the hunt for more singularities.
By observing these hidden leviathans, astronomers can glean insights into the creation and evolution of the stars that collapsed to create the black holes that we, well, don’t see today.
Scroll down to watch an animation of the possible orbital paths of the black hole and its stellar companions.
The paper has been published in the journal Astronomy and Astrophysics.
Artist’s animation of the triple system with the closest black hole
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