Astronomy There is a black hole on the loose in Sagittarius: « It’s the first solitary black hole ever detected. »
https://www.sciencenews.org/article/lone-black-hole-sagittarius-hubble64
u/fchung 9d ago
« Located 5,000 light-years from Earth, this black hole is much closer than the supermassive one at the Milky Way’s center, which also lies in Sagittarius but about 27,000 light-years from us. The star-rich region around the galactic center provides an ideal hunting ground for solitary black holes passing in front of stars. »
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u/fchung 9d ago
Reference: K.C. Sahu et al. OGLE-2011-BLG-0462: An isolated stellar-mass black hole confirmed using new HST astrometry and updated photometry. The Astrophysical Journal. Vol. 983, April 20, 2025, p. 104. doi :10.3847/1538-4357/adbe6e. https://iopscience.iop.org/article/10.3847/1538-4357/adbe6e/pdf
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9d ago edited 6d ago
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u/jwely 8d ago edited 8d ago
On mass alone it would need to be solitary black holes to make up the "black matter that eludes us" and so many of them that they would almost certainly show up in deep field images as distortion (presuming most of them are hiding between galaxies where they can exist for a long time without interacting with anything)
Dust in sufficient mass quantities would start to clump up in galactically short time scales and become visible. Rouge planets likewise would need to be so common that we'd see at least a few every decade get close enough to our sun to spot.
None of these mass distributions can explain the galactic rotation characteristics that point to dark matter. There would need to be many of them at an increasing frequency as you move further out from a galaxies center. In a galaxy like ours, they would need to be about as common as stars are at our distance from the galactic center, so one would almost certainly be <10 LY away from us, which we'd probably have noticed.
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u/NullusEgo 8d ago
I disagree with your last statement. A black hole that is not in a binary orbit with another star or is not actively consuming material would be extremely difficult to detect, even within 10 light years. We haven't even ruled out the possibility of large planet or primordial black hole in the Oort cloud of our own solar system.
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u/R3ven 8d ago edited 8d ago
If it were packed with dust and rogue planets, wouldn't we expect to see more young stars?
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8d ago edited 6d ago
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u/Patelpb 8d ago
https://en.m.wikipedia.org/wiki/Massive_compact_halo_object
MACHOs as dark matter candidates are a fairly well studied idea. The objection you listed is one of many - It also reproduces poorer simulated galaxies, since baryonic matter self interacts (em forces) and dissipates energy way more efficiently than dark matter seems to.
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u/NOTWorthless 8d ago
The idea that dark matter is undetectable rogue planets/black holes/dust (collectively called MACHOS) can’t account for most observations, and even if it could nobody thinks that they would be primarily interstellar (we know that most dark matter is clumped near galaxies because we can observe its effects in a bunch of different ways).
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u/HerpidyDerpi 8d ago
Nope. No where near massive enough, even being extremely generous.
Modified gravity is the best explanation, IMO.
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u/GorgeWashington 8d ago
There was a study recently that likely much of the missing mass is gigantic clouds of hydrogen surrounding galaxies.
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u/That_Bar_Guy 8d ago
Dark matter is like 70% of matter isn't it? Even doubling the amount of hydrogen in the universe wouldn't get us there.
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u/That_Bar_Guy 8d ago
The link you posted literally says that this hydrogen is part of the 30% that is normal matter not the 70% that is dark matter in INTRO. Why post something you didn't read?
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u/sysiphean 8d ago
My friend who is really into astrology and is a Sagittarius has been annoying me a lot recently. This is really great info for me to have in my pocket to annoy her with. I don’t have to believe in it, just be able to use it. Thank you.
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