This system HR 6819,
located about 1,000 light-years from Earth,
contains two stars that orbit a hidden black hole
several times larger than our sun.
Astronomers expect that hundreds of millions
of these "quiet" black holes
sit undiscovered in our galaxy.
sits just 1,000 light-years from Earth.
But the two stars that dance around it
can be seen with
the naked eye...
Located about 1,000
light-years away in the southern
constellation Telescopium, the
black hole weighs in at some four times the mass of our Sun, which
means it's only about 7.5 miles (12 kilometers) wide.
When they looked at the double star system HR 6819, they noticed that the inner star orbits quickly, while the outer star slowly chugs along. This meant the stars are not just circling each other. Some unseen third object has to be located near the center of the system.
The hidden object and the inner star dance around each other every 40 days.
Meanwhile, the outer star
slowly circles the pair much farther out. And because the invisible
object is at least four times the mass of the Sun, it can only be
black hole, the astronomers say.
For instance, on a dark, clear night in the Southern Hemisphere, you can actually see the two stars that orbit the black hole in HR 6819 with your naked eye.
But these extreme objects are actually not representative of what astronomers expect to be out there.
Though HR 6819 is one of just a few covert black holes ever found, there should be countless more just like it.
And as astronomers seek out more and more hiding black holes, they expect to find them closer and closer to Earth.
estimates there should be black holes within a few dozen light-years
of Earth, which would put them closer than some of the brightest
stars in our night sky.
is in the Cygnus X-1 system.
In this artist's concept, the black hole reveals itself to astronomers
steals material from blue supergiant star HDE 226868.
Researchers need to find them to test their theories of how stars both live and die.
Scientists are also still uncertain how living in a system with multiple large members affects the evolution of the stars within.
Another surprising unknown is that astronomers don't understand exactly how supernova explosions work.
But because some supernovae can produce black holes, one way to test competing theories is to compare the number and sizes of known black holes to what various supernova theories predict.
So, the more examples they add to the currently small list, the more accurately they can test whether they're right.
using observations made with the European
Southern Observatory MPG-ESO 2.2-meter telescope
Silla Observatory in Chile.
And though no planets are known in the system, if you were to visit a world circling the inner star, you'd be treated to a mysterious sight.
The same pattern would appear if the black hole passed in front of a bright background star.
The rest of the time, the black hole would only be seen when it consumed some stray bit of gas or a space rock.
Systems with multiple
stars account for most of the stars in our galaxy. So by looking for
more peculiar orbits within these systems, astronomers should be
able to uncover more hidden black holes.
Astronomers think that the violent events that give birth to black holes - supernova - also gives their stellar partners a gravitational kick that flings them into space.
And without being able to see how things orbit around it, it's currently impossible to detect a lone black hole.
So, for the foreseeable future, astronomers must continue searching multiple star systems to find these muted monsters.
She expects more evidence for quiet black holes is probably waiting to be found in archived observations.
And projects like the European Space Agency's Gaia spacecraft, which is currently working to map a billion stars, should uncover even more.
Vera C. Rubin
Observatory under construction in Chile - previously known as
Large Synoptic Survey Telescope - will photograph the entire
visible sky every few nights, unlocking a windfall of data on nearby