But when they located a candidate in the system VFTS 243, they were initially skeptical. Co-author Kareem El-Badry, whom Shenar refers to as the "black hole destroyer," said “I had my doubts. But I could not find a plausible explanation for the data that did not involve a black hole.”
This black hole is around 9 times the mass of the Sun and circles a 25-solar-mass blue giant star. And strangely, the researchers could find no evidence of a supernova remnant.
When massive stars reach the end of their lives, it’s believed that their core collapses — into either a neutron star or a black hole — and their outer layers are expelled in a supernova explosion. At least that’s how physicists have typically understood it. But known black holes have been rarely paired with supernova remnants.
This black hole seems to be following that trend. "The star that formed the black hole in VFTS 243 appears to have collapsed entirely, with no sign of a previous explosion," said Shenar. This scenario is known as a direct collapse. Essentially, the progenitor star is so massive that its core collapses immediately into a black hole, preventing a supernova blast.
“Evidence for this ‘direct-collapse’ scenario has been emerging recently,” explained Shenar. “But our study arguably provides one of the most direct indications.”
According to the team, this finding not only “substantially impacts” the direct collapse scenario, but also has important implications for gravitational-wave researchers. Hundreds of X-ray quiet binaries are suspected to be hiding in the Milky Way and the Magellanic Clouds, and VFTS 243 is the first “unambiguous discovery” of such a system. Finding even more of these systems would have strong implications for the rate of black hole mergers scientists can expect to see.
“Of course I expect others in the field to pore over our analysis carefully, and to try to cook up alternative models,” said El-Badry. “It's a very exciting project to be involved in.”