A lonely black hole may be the first known rugged black hole

A solitary object in the sky — massive but much smaller than the sun — is wandering the galaxy thousands of light-years from Earth. It may be the first isolated black hole in the star mass detected in the Milky Way. Or it could be one of the heaviest known neutron stars.

The stargazer first appeared in 2011 when its gravity increased the light of a more distant star. But at the time, his true nature escaped the investigators. Now, two teams of astronomers have studied images from the Hubble Space Telescope to explain the identity of the traveler, and come to different conclusions.

The mysterious rogue is a black hole roughly seven times larger than the sun, a group reported in a press release. Journal of Astrophysics. Or it’s a little lighter – only two to four times the weight of our nearest star – and so it’s an unusually light black hole or a strange neutron star, another group reported in a press release. Astrophysical Journal Letters.

Neutron stars and black holes in the mass of stars are formed at the end of life when massive stars — at least several times the size of the sun — fall under their gravity. Astronomers estimate that about one billion neutron stars and about 100 million black holes in the star mass are hidden in our galaxy (SN: 18/8/17). But these objects are not easily recognizable. Neutron stars are so small — the size of a city — that they do not produce much light. And black holes do not emit light.

To detect objects of this type, scientists usually observe how they affect the environment. “The only way we can find these is if they affect something else,” said Kailash Sahu, an astronomer at the Space Telescope Science Institute in Baltimore.

So far, scientists have detected nearly two dozen black holes in the star mass. (Slight black holes are small in the middle of most galaxies, including ours, compared to existing supermassive rebels (SN: 18/01/21).) To do this, researchers have seen how these objects interact with those close to the sky. When a black hole is blocked in a gravitational dance with another star, it removes matter from its partner. As this material falls into a black hole, it emits X-rays, which can be detected by telescopes orbiting the Earth.

But finding black holes in binary systems does not paint the whole picture of the kingdom of black holes. Since these objects are constantly forming matter, it is difficult to determine the mass they formed. And since birth weight is a key feature of a black hole, Sahu says it is a major impediment to studying binary systems. “If we want to understand the properties of black holes, it’s best to find isolated ones.”

Researchers have been searching for solitary black holes in the sky for more than a decade. The research is based on Einstein’s theory of general relativity, which states that any massive object, even an invisible one, bends space around it (SN: 2/3/21). This curvature increases and distorts the light of the background stars, a phenomenon known as the gravitational microlens. By measuring changes in the brightness and apparent position of stars, scientists can calculate the mass of an intermediate object acting as a lens, a technique that also rounds up some planets outside the sun (SN: 24/7/17).

In 2011, researchers announced that they had seen a star that suddenly became 200 times brighter. But these initial observations, made through telescopes in Chile and New Zealand, could not clarify whether the apparent position of the stars was also changing. And this information is essential for determining the mass of the intermediate object. If it were a heavy weight, its gravity would distort the space so much that the star seems to move. But the “big” change in the position of the stars would also be very small and difficult to detect. And unfortunately, the fine details of astronomical images taken by Earth telescopes are often blurred due to the turbulent atmosphere on our planet (SN: 20/7/29).

To avoid this boundary on Earth, two independent groups of astronomers turned to the Hubble Space Telescope. This observatory can take very accurate pictures, as it orbits most of the Earth’s atmosphere.

Both groups found that the location of the stars had changed over the years. One of the groups led by Sahu concluded that the star-shaped dance was caused by an object seven times the size of the sun. A star of that mass would have shone in Hubble images, but the researchers saw nothing. Something heavy and dark must have been a black hole, the group said.

But another team of researchers, led by astronomer Casey Lam of the University of California, Berkeley, found different results. Lam and his colleagues calculated that the mass of the lensing object was less than two or four times the mass of the sun. So it could be a neutron star or a black hole, the team concluded.

However, it is an intriguing object, says astronomer Jessica Lu, a member of UC Berkeley’s Lam team. That’s because it’s a bit weird in terms of mass. It is one of the most massive neutron stars ever found, or one of the most massive black holes known, according to Lu. “It’s located in this strange region that we call the mass gap.”

Despite the disagreements, the results are thrilling, says Will M. Farr, an astrophysicist at Stony Brook University in New York who did not participate in the study. “It’s very exciting to work on the instrumental frontier in the true avant-garde of what’s remarkable.”

Leave a Comment