WASHINGTON, July 18 (Reuters) – Astronomers have spotted what they are calling a cosmic “needle in a haystack” in a galaxy adjacent to our own galaxy – a black hole that is not only classified as dormant but appears to be unborn. The explosion of a dead star.
Researchers said Monday that it differs from all other known black holes because it is “x-ray quiet” — not emitting the powerful X-ray radiation that is gobbling up nearby material with its strong gravitational pull — and it was not born. A stellar explosion called a supernova.
Black holes are incredibly dense objects with gravity that even light cannot escape.
It, with a mass at least nine times that of our Sun, was found in the Tarantula Nebula region of the Large Magellanic Cloud galaxy and is located about 160,000 light-years from Earth. A light year is the distance light travels 5.9 trillion miles (9.5 trillion km) in one year.
An extremely bright and hot blue star with 25 times the mass of the Sun orbits in a stellar marriage with the black hole. This so-called binary system has been named VFTS 243. Researchers believe that the companion star may also become a black hole and merge with another.
Dormant black holes, which are considered relatively common, are difficult to detect because they interact so little with their surroundings. Several previously proposed candidates have been debunked with further studies, including by members of the team that made the discovery.
“The challenge is finding those objects,” said Tomer Schenar, a research associate in astronomy at the University of Amsterdam and lead author of the study, published in the journal Nature Astronomy. “We identified a needle in a haystack.”
“This is the first object discovered after astronomers have searched for decades,” said Karim El-Badri, an astronomer at the Harvard and Smithsonian Center for Astrophysics and study co-author.
The researchers used six years of observations from the European Southern Observatory’s Very Large Telescope in Chile.
There are different categories of black holes. The smallest, like the newly discovered ones, are so-called stellar-mass black holes that are formed by the destruction of massive individual stars at the end of their life cycles. There are also intermediate-mass black holes as well as massive supermassive black holes that reside at the center of most galaxies.
“Black holes are intrinsically dark objects. They do not emit any light. So, to find black holes, we usually look at binary systems in which we see a bright star orbiting a second, undetected object,” said. Study co-author Julia Bodensteiner, a postdoctoral research fellow at the European Southern Observatory in Munich.
The collapse of massive stars into black holes is generally assumed to be associated with a powerful supernova explosion. In this case, a star with 20 times the mass of our Sun ejected some of its material into space during its death and then collapsed in on itself without exploding.
The shape of its companion’s orbit gives evidence that there is no explosion.
“The system’s orbit is almost perfectly circular,” Shennar said.
If a supernova had occurred, the force of the explosion would have kicked the newly formed black hole in a random direction and acquired an elliptical rather than circular orbit, Shennar added.
Black holes can be ruthlessly ravenous, with whatever material — gas, dust, and stars — wanders within their gravity.
“Black holes can only be ruthlessly ravenous if there’s something nearby that they can eat. Usually, we can detect them if they’re receiving material from a companion star, a process we call accretion,” Bodensteiner said.
Shennar added, “In so-called dormant black hole systems, the companion is far enough away that material does not accumulate around the black hole to heat up and emit X-rays. Instead, the black hole is swallowed immediately.”