A small black hole outside the Milky Way galaxy that is quietly hanging around minding its own business.
The team says this marks the first time we have been able to definitively detect and identify a dormant black hole that is not within the confines of our own galaxy.
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An ‘Invisible’ Black Hole Has Been Discovered Outside Of The Milky Way
While a similar discovery was announced last year, evidence of its true identity left some room for doubt. According to the authors, this new finding is a solid bet.
Of course, this object isn’t that far from the Milky Way, which is located within a satellite galaxy called the Large Magellanic Cloud.
But the discovery is one that could help us find more such black holes in the future, and has implications for beginning our understanding of black hole formation.
The team behind the report is clearly excited, not least because their dubious reputation casts doubt on previous dormant black hole findings.
“For the first time, our team came together to report, rather than dismiss, the discovery of a black hole,” said astronomer Tomer Schenar of the University of Amsterdam in the Netherlands.
“We identified a ‘needle in a haystack’.” Black holes are tricky little beasts. Their extreme density creates a super-gravitational field which means that even light waves through space – the fastest anything in the universe can travel – are able to achieve escape velocity. Is.
This implies they are covered in murkiness, emanating no light that we can recognize.
The exception is when they are actively “feeding”, or growing content. This is a messy process that produces a telltale signature of X-ray radiation from the immediate vicinity around the black hole. Passive, or silent, black holes are more or less invisible.
In any case, that annoying gravity can part with it… assuming you know what to look like.
If a stellar mass black hole is in a binary system with another star, the orbital motion of the companion that appears to be empty can indicate the presence of the black hole.
Not all dark masses are black holes, though. Other astronomers have been fooled before, the most famous example being the black hole that is the closest to Earth yet discovered.
A small, dim companion whose light cannot be discerned could be the culprit, meaning no option can be ruled out. Shinar and his team members,
including astronomers Karim al-Badri of the Harvard-Smithsonian Center for Astrophysics and Julia Bodensteiner of the European Southern Observatory, are among those who have painstakingly debunked such discoveries.
But that doesn’t mean they think such black holes aren’t out there. Only that the evidence needs to be watertight. “For more than two years now, we have been looking for such black hole-binary systems,” Bodensteiner explained.
The focus of their search was the Tarantula Nebula in the Large Magellanic Cloud, a brilliant nursery where young, supermassive stars can be found.
The researchers studied, in detail, about 1,000 of these young massive stars, looking for gradual wobbles of binary orbits. When any two objects orbit each other, they do so around a mutual center of gravity called their barycenter.
For an Earth-Sun system, the barycenter would be so close to the center of the Sun that it would be difficult to see the star orbiting it from any great distance.
If the Earth were wider, it would be much easier to track the orbit of the barycenter. We can detect this oscillating motion, or radial motion,
in the spectrum of light from the object as it expands at longer (red) wavelengths moving away from us, and contracts at shorter (blue) wavelengths moving toward us.
The team looked for a pattern for these spectral shifts and found success – with a massive blue-white O-type star, 25 times the mass of the Sun, about 160,000 light-years away.
When they calculated the mass of the object that could cause the observed dip, they found that the companion was 9 times the mass of the Sun.
At this mass, a black hole’s event horizon would only be around 27 km (17 mi). And yet, it was invisible. The upper mass limit for neutron stars is about 2.3 times that of the Sun, so these stars are ruled out.
Their sample excluded other stars that were sinking, using the team’s techniques to detect light from faint companion stars, and to model light expected from a faint companion of the observed mass.
None of the alternative explanations fits the observational data. “I had my doubts when Toomer asked me to double-check my results,” Al-Badri said.
“But I couldn’t find a plausible explanation for the data that didn’t involve a black hole.” The binary, named VFTS 243, could provide important clues about how black holes form.
Scientists believe there are several scenarios. The first is a massive supernova in which an unstable star explodes, blasting its outer material into space while the core collapses into a black hole, created by fire and fury.
The other is a direct collapse in which a dying star, no longer supported by the outward pressure provided by nuclear fusion…collapses in on itself, not with an explosion but with a silent Kerr Flume.
“The star that produced the black hole in VFTS 243 has completely collapsed, with no trace of a previous explosion,” Shennar said. “Evidence for this ‘direct collapse’ scenario is only recently emerging, but our study provides arguably the most direct indication yet. There are more implications.”
However, after investigating many other black hole discoveries, the team now invites other astronomers to check them out. A fair of fairs.
