A black hole is formed when massive stars reach the end of their existence: they collapse under the influence of their own gravity. When such a star is part of a binary star – a system of two orbiting stars – the process results in a black hole orbiting a bright companion star. This black hole is called “sleeping” if it does not emit large amounts of X-rays. Black holes usually betray their existence based on X-rays.
A needle in a haystack
Astronomers believe that thousands of these dormant black holes exist. However, this is only the first time that one has been found outside our galaxy. Since dormant black holes have almost no interaction with their environment, they are very difficult to find. “We’ve been searching for such black-hole binary stars for more than two years,” co-author Julia Bodensteiner said. “We’ve discovered a needle in a haystack,” says lead researcher Tomer Schnarer (Institute of Astronomy at KU Leuven). KU Leuven was responsible for the research.
The research team examined nearly a thousand massive stars in a particular nebula in the Large Magellanic Cloud, looking for samples that could have accompanying black holes. This is how they got to the sleeping black hole.
The discovery also gives the team more information about the formation of black holes. Astronomers know that a black hole forms when the core of a massive, dying star collapses, but it remains uncertain whether this is accompanied by a powerful explosion called a supernova.
“The star that formed the black hole appears to have collapsed completely, with no sign of a previous explosion,” Tomer Schnaar said. “More evidence for this direct collapse scenario has been discovered recently, but our research is arguably some of the strongest. This has huge implications for the origin of black hole merger in the universe.”
