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Ghost black hole discovered through microlensing

Puppycow

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Puppycow
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Mysterious, ghost-like black hole may have been discovered by UC Berkeley researchers

"This is the first free-floating black hole or neutron star discovered with gravitational microlensing," Lu told the outlet. Lu has been hunting for free-floating black holes since 2008, and has been observing OB110462 since 2020. "With microlensing, we're able to probe these lonely, compact objects and weigh them. I think we have opened a new window onto these dark objects, which can't be seen any other way." Though black holes are typically invisible, researchers can use gravitational microlensing to see how they warp and distort light from distant stars with their powerful gravitational field.
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Isn't that crazy, if true? Something you can't even see except for how it lenses the light behind it. Sometimes you see black holes because they give off X-rays (from the accretion disk of course, not the black hole itself) or due to its effects on a nearby companion star. The first black hole ever discovered was called Cygnus X-1, which was found due to the X-rays that it gives off.

The article also mentions that our galaxy is estimated to contain about 200 million black holes. About 1 for every 1,000 stars.
 
theprestige said:
What part is the "if true" part?
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If what they are seeing is actually a black hole. They said it might be a neutron star. There's a range of possible masses and distances, and on the lower end it could possibly be a neutron star, but it seems more likely to be a black hole. Another team looking at the same data put the mass at about 7 solar masses and they think it's definitely a black hole. So it's probably right.
 
Whether a black hole or neutron star, is it wandering in this direction is the first question that springs to mind.

2,280 to 6,260 light years away isn't of immediate concern though.
 
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I did a bit on microlensing as part of a degree. That was concerning exoplanet detection, however. The telescopes really aren't all that big. At the time, the main groups looking at this phenomenon were MOA, in New Zealand, and OGLE, in Poland. Basically. you wait for a star to pass in front of a more distant star, just as this probable BH did. You see the spike in the brightness from the more distant star. Occasionally, you see a second smaller spike, a little while later (or earlier), indicating that a planet around the foreground star has also passed in front of the distant star.
This technique is nowhere near as prolific in making detections as other methods, such as transits and radial velocity. However, it is totally unbiased, and therefore gives us a good idea of the mass distribution of planets around stars in our galaxy.
 
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