For the first time, the Hubble Space Telescope has discovered a single object in our galaxy – the invisible, spectral remnants of a once-bright star.
When stars are large enough to make our sun look like dwarf stars, they explode to form supernovae. The rest of the nucleus is crushed by its own gravity to form a black hole.
Sometimes an explosion can speed up a black hole, moving through the galaxy like a pinball. Theoretically, scientists should know many roaming black holes, but they are very difficult to identify because they are literally invisible in space.
Astronomers believe that 100 million black holes are moving freely in our galaxy. Now, researchers believe they have found one of these objects. The discovery came six years after it was dedicated to observations – astronomers managed to accurately measure the mass of this extremely cosmic object.
The black hole is 5000 light-years away, located in the spiral arm of the Milky Way, known as Sagittarius. This observation led the research team to estimate that the nearest isolated black hole from Earth could be only 80 light-years away.
But if black holes can’t be separated from the void of space, then how did Hubble recognize this?
The extremely strong gravitational field of black holes distorts the space around them, creating the conditions for distortion or amplification of stellar radiation with lines behind them. This phenomenon is called gravitational lensing. Ground-based telescopes peek into the millions of stars in the center of the Milky Way galaxy and detect this fleeting glow that indicates that a large object has passed between you and the star.
Hubble is well positioned to pursue these observations. Two different teams of researchers studied the observations to determine the mass of the object. Both studies have been accepted for publication in The Astrophysical Journal.
One of the teams led by Hubble instrument scientist and astronomer Kailash Sahu at the Space Telescope Science Institute in Baltimore determined that the black hole weighs seven times the mass of our Sun.
Another team, led by Casey Lam and Jessica Lou, PhD students, associate professors of astronomy at the University of California-Berkeley, established a small range for the mass of objects between 1.6 and 4.4 times that of the Sun. According to this estimate, the object could be a black hole or a neutron star. Neutron stars are incredibly dense remnants of exploded stars.
“Whatever it is, this object is the first dark stellar fossil found to orbit the galaxy, which has no other stars,” Lam said in a statement.
The black hole went into the center of the Milky Way galaxy in front of a background star 19,000 light-years from Earth and extended its starlight for 270 days. Astronomers have had a hard time determining their measurements because they have seen a bright star just behind the black hole.
“It’s like trying to measure the small movements of a firefly next to a glowing lightbulb,” Sahu said in a statement. “In order to accurately measure the deflection of a dim light source, we had to dilute the light of a nearby glowing star.”
Sahu’s team estimates that the object may be traveling at 160,000 kilometers per hour, faster than most of the stars in that part of the galaxy, while Lu and Lam’s team estimates it to be 108,000 kilometers per hour.
Further data and observations by Hubble and further analysis can resolve doubts about the identity of the object. Astronomers are still searching for these invisible single objects, like needles in a haystack, which could help them understand how stars evolve and die.
“With the microlensing process, we are able to examine and weigh these compact, isolated objects. I think we have opened a new window for these black objects, which cannot be seen in any other way, “said Lou.