Actually, according to current theory, there shouldn’t be such a thing: a black hole with 70 times the mass of our sun. But researchers have now found one in our Milky Way galaxy.
Hat has surprised many researchers: an international team of researchers has tracked down an unexpectedly heavy black hole around 15,000 light years deep in the Milky Way. The object with catalog number LB-1 has about 70 times as much mass as our sun. That is more than double the upper limit that astronomers have so far assumed for so-called stellar black holes that arise from a dying star. Jifeng Liu’s team from the Chinese Academy of Sciences presents its surprising discovery in the journal “ Nature ”.
In the center of our home galaxy – as in most galaxies – there is a supermassive black hole with a million times the mass of our sun. In addition, it is estimated that the Milky Way contains around 100 million stellar black holes. They arise when a very massive star collapses under its own weight at the end of its existence because the counterpressure caused by the nuclear fusion in the interior dries up.
Stars with the chemical composition typical of our galaxy should, however, blow most of their mass into space in the form of powerful stellar winds before they finally collapse. Such massive residues as the one now observed should not be left behind.
“According to most current models of stellar evolution, black holes of this mass should not even exist in our galaxy,” emphasized Liu in a press release from the academy. “LB-1 is twice as massive as we thought possible. Now theorists have to face the challenge of explaining how it came about. “
In fact, the Ligo gravitational wave observatory in the USA had previously picked up signals from merging stellar black holes with up to 50 solar masses, albeit from galaxies billions of light years away with different chemical requirements. The observation of LB-1 now shows that such apparently over-heavy black holes also exist in our own galaxy, the researchers emphasize. “This discovery forces us to put our models of the formation of stellar black holes to the test,” quotes the Akademie Ligo director David Reitze from the University of Florida, who was not involved in the current work.
Since black holes normally do not emit light, Liu’s researchers used a trick to track down LB-1: The black hole has a companion star that is eight times as massive as our sun and orbits the black hole once in 79 days. Around half of the time it moves towards us and the other half slightly away from us. This can be seen in the light of the star. Much like a police siren sounds brighter as long as the car is driving towards us and darker as it is moving away, the star’s light is a little bluer as it is moving towards us and a little redder as it is moving away.
Most of the other known black holes have been discovered by ingesting matter that becomes extremely hot and therefore lights up brightly before disappearing into the gullet of the gravity monster.