Scientists have discovered an astronomical “needle in a haystack” in a nearby Milky Way galaxy: a special type of “silent” black hole that may be the first of its kind detected outside our galaxy.
About 160,000 light-years from the Milky Way in the Tarantula Nebula region of the Large Magellanic Cloud, this newly discovered black hole formed like others: with the collapse of a star.
But it’s different because it’s “X-ray silent,” in that it was found without the tell-tale signs of X-rays, researchers led by University astrophysicist Tomer Shenar reported this week. from Amsterdam in the Netherlands in the journal Nature. Astronomy. Astronomers typically find black holes by identifying radiation emitted by matter sucked into the mysterious region of space.
“We identified a ‘needle in a haystack,'” Shenar said in a discussion of the results on the Harvard-Smithsonian Center for Astrophysics website.
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“No sign of a previous explosion”
Also different about this black hole, which weighs nine times the mass of our sun and orbits a hot blue star with 25 times the mass of the sun: the star that collapsed to create the black hole is gone without the typical explosion or “kick” on her collapse, according to the researchers.
“The star that formed the black hole…appears to have collapsed entirely, with no signs of a previous explosion,” Shenar said. “Evidence for this ‘direct collapse’ scenario has emerged recently, but our study provides arguably one of the most direct indications. This has huge implications for the origin of black hole mergers in the cosmos. “
Other possible candidates have been identified before, but the researchers say this is the first “dormant” stellar-mass black hole to be unambiguously detected outside the Milky Way.
Astronomers examined nearly 1,000 stars by analyzing six years of observations with the European Southern Observatory’s Very Large Telescope in Chile.
Kareem El-Badry, an astrophysicist at the Center for Astrophysics who earned the nickname “black hole destroyer” because of his propensity for debunking black hole discoveries, said he was skeptical when asked to confirm the findings.
“I had my doubts. But I couldn’t find a plausible explanation for the data that didn’t implicate a black hole,” El-Badry said. “Of course, I expect other people in the field to look carefully at our analysis and try to cobble together alternative models. … It’s a very exciting project to be involved in.”
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