Skip to main content

Astronomers discover black hole in Earth’s galactic backyard

Astronomers have discovered the closest black hole to Earth ever found, located just 1,000 light-years away.

It is part of an unusual triple system called HR 6819, consisting of two stars and a black hole all orbiting the same point, according to research published in the journal Astronomy & Astrophysics.

Recommended Videos

Black holes absorb everything that comes close to them, even light, so it is essentially impossible to observe one directly. In this case, the astronomers with the European Southern Observatory (ESO) were able to locate the black hole using the MPG/ESO 2.2-meter telescope at the La Silla Observatory in Chile to look at the movements of one of the other stars in the system.

Milky Way shines over snowy La Silla
La Silla Observatory sitting beneath a spray of stars from our Milky Way. On the far left is the MPG/ESO 2.2-metre telescope, which has snow on its dome. ESO/José Francisco Salgado

“The main effect this black hole has is the gravitational pull on the companion star,” Dietrich Baade, ESO’s Emeritus Astronomer, told Digital Trends. “The companion star is visible to the naked eye, so it’s quite easy to take high-resolution and high-quality spectra, and to measure from the Doppler shift the rate of velocity of the star.”

The Doppler shift is the phenomenon where the frequency of waves appears to change due to motion between the source and the observer — like how a siren sounds different when an ambulance approaches and then drives away.

Using this shift, the researchers saw how the star was moving and inferred the presence of a black hole.

“If the star is moving around, there must be a reason for that,” Baade explained. “And since stars interact only gravitationally, at least at that level, there must be a big mass nearby. And if one cannot see that mass, and the mass is above a certain level, then it must be a black hole.”

Using the observations, the researchers were able to calculate that the object in the HR 6819 system has a mass about five times that of our sun, or about 1.5 million times that of the Earth, indicating that it must be a black hole.

The system is also notable for an unusual feature, being a triple system in which two stars and one black hole orbit around the same center of mass.

This artist’s impression shows the orbits of the objects in the HR 6819 triple system
This artist’s impression shows the orbits of the objects in the HR 6819 triple system. This system is made up of an inner binary with one star (orbit in blue) and a newly discovered black hole (orbit in red), as well as a third star in a wider orbit (also in blue). ESO/L. Calçada

“This triple system is a type called a hierarchical system, which means that two of the objects are very close to each other and the third object is rather far away,” Baade said.

“In the inner binary, there is a luminous star which is bright enough to be seen with the naked eye, which is orbited by the black hole. And then these two stars, in turn, are orbited by a second luminous star which is further away.”

The black hole’s triple system could help astronomers study elusive gravitational waves in the future. The system itself is not likely to be a source of these waves, but what it does provide is a model of what a system with two black holes orbiting each other might look like.

Two Black Holes Merging
An illustration of two black holes merging CalTech

When two binary black holes merge, the tremendous amount of energy this event gives off creates a dramatic distortion of space. This distortion would be one of the strongest sources of gravitational waves in the universe, and would be detectable through projects like LIGO (Laser Interferometer Gravitational-Wave Observatory).

But astronomers aren’t sure what would cause a binary pair of black holes to merge. One suggestion is that the mergers could be caused by a third star orbiting the pair.

By studying the movement of the two stars and one black hole in the HR 6819 system, astronomers can build up a blueprint of triple systems that could teach them about how these binary black hole mergers could occur.

Baade said he’s been studying this particular system on and off for 20 years.

While Baade said the researchers were thrilled to finally nail down the system’s unique composition, it was a bittersweet victory: The team’s leader, Stan Štefl died in a car accident in 2014 before their findings could be published.

“It was very rewarding to bring it to this positive and conclusive end,” Baade said. “But it’s of course very sad that our friend Stan Štefl could not celebrate the success with us.”

Georgina Torbet
Georgina has been the space writer at Digital Trends space writer for six years, covering human space exploration, planetary…
Astronomers discover rare ‘exo-Venus’ just 40 light-years away
Gliese 12 b, which orbits a cool, red dwarf star located just 40 light-years away, promises to tell astronomers more about how planets close to their stars retain or lose their atmospheres. In this artist’s concept, Gliese 12 b is shown retaining a thin atmosphere.

Gliese 12 b, which orbits a cool, red dwarf star located just 40 light-years away, promises to tell astronomers more about how planets close to their stars retain or lose their atmospheres. In this artist’s concept, Gliese 12 b is shown retaining a thin atmosphere. NASA/JPL-Caltech/R. Hurt (Caltech-IPAC)

Astronomers have discovered a rare type of planet called an "exo-Venus," which is between the size of Earth and Venus and is located just 40 light-years away -- practically in our back yard. Although scientists think that planets of this size could be very common in our galaxy, they are hard to identify because they are so much smaller than the big gas giants that are more commonly discovered. This new planet also seems to have similar temperatures to Earth, and studying it could help to explain how atmospheres develop and how Earth became habitable.

Read more
NASA 360-degree video shows what it’s like to plunge into a black hole
A black hole according to NASA's 360-degree video.

360 Video: NASA Simulation Shows a Flight Around a Black Hole

If you were having a bad day, plunging into a black hole would be enough to really top it off. Apparently, you’d experience a process known as “spaghettification” in which the black hole’s enormous gravitational force would compress your entire body while stretching it out at the same time, leaving you a bit noodle-like. Falling into a supermassive black hole would be a slightly less horrendous experience, apparently.

Read more
Biggest stellar black hole to date discovered in our galaxy
Astronomers have found the most massive stellar black hole in our galaxy, thanks to the wobbling motion it induces on a companion star. This artist’s impression shows the orbits of both the star and the black hole, dubbed Gaia BH3, around their common centre of mass. This wobbling was measured over several years with the European Space Agency’s Gaia mission. Additional data from other telescopes, including ESO’s Very Large Telescope in Chile, confirmed that the mass of this black hole is 33 times that of our Sun. The chemical composition of the companion star suggests that the black hole was formed after the collapse of a massive star with very few heavy elements, or metals, as predicted by theory.

Black holes generally come in two sizes: big and really big. As they are so dense, they are measured in terms of mass rather than size, and astronomers call these two groups of stellar mass black holes (as in, equivalent to the mass of the sun) and supermassive black holes. Why there are hardly any intermediate-mass black holes is an ongoing question in astronomy research, and the most massive stellar mass black holes known in our galaxy tend to be up to 20 times the mass of the sun. Recently, though, astronomers have discovered a much larger stellar mass black hole that weighs 33 times the mass of the sun.

Not only is this new discovery the most massive stellar black hole discovered in our galaxy to date but it is also surprisingly close to us. Located just 2,000 light-years away, it is one of the closest known black holes to Earth.

Read more