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Paul Colby
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Aren’t you assuming a 2.2 solar mass star will retain 2.2 solar masses in its later stages? Not a bad assumption, I admit, but an assumption nonetheless.
You are exactly correct. As you saw from information above, a black hole is created when the core is above somewhere between 2.2 and 3 solar masses (no one knows the maximum neutron star mass). So one might expect any star above 3 solar masses to make a black hole. But that's not true, they don't even supernova at all, and everything below maybe 8 solar masses (Betelgeuse) creates a white dwarf instead of going supernova. Why is that?Paul Colby said:Well, I only need a factor of 11,780. Seriously, stars can gain and lose mass. One of the first things I looked at with the telescope I bought a while back, was the ring nebula. A star that burped out a small fraction of its mass not that long ago. There are stars that do this periodically. Can one rule out from observation such slowish mass ejections as a means of avoiding BH at end of life? Along this line, do we see as many neutron stars as we’d expect?
No, I am assuming a 10 solar mass star will leave behind a 2.2 solar mass core. I believe I wrote that,Paul Colby said:Aren’t you assuming a 2.2 solar mass star will retain 2.2 solar masses in its later stages?
But maybe it is easier to not bother deriving "progenitors"? Start straight from SN?Vanadium 50 said:Note that about half a percent of the visible stars are SN progenitors. If you want to start playing with that, you need to keep to the constraint of how many progenitors we see. You could even turn the question around - given how few BHs we see, why do we see so many progenitors?
Yes that's a good way to get insight. We can even venture out of the Milky Way and look at SN 1987a, where JWST was able to find the neutron star. I'm not sure how the neutron star shows up in infrared light, but in any event, it has been seen. So we're getting pretty good at linking SNe to NSs if they make them, but you want to consider the ones expected to make BHs and ask if we have any way to detect those. I think we already know the answer will be no, but the exact reasons for this is what we are discussing.snorkack said:Ask it this way: out of the 6 visible supernovae of last millennium, SN1054 formed a neutron star. What did the other 5 do? Can we name any black hole we observe as formed by a historic supernova?
So, what is the observed branching ratio of supernovae for results - neutron star, nothing, black hole?Vanadium 50 said:There are two possibilities:
That's it.
- We make fewer than we think.
- We detect fewer than we think.
Now, the thread was restarted by someone who didn't like my estimation of #1. He has not shared a calculation, but there is a big difference between one supernova every 30 years and one every 600,000 years.
But not for very long. A few million years and off they go. Seven of the nearby ones don't pulse at all - they are just weak x-rays sources. Once their surface cools, on a similar timescale, they can only be detected gravitationally or by accretion x-rays, and in both cases, it should be easier to detect BH's.Ken G said:because NSs have their own beams that you only have to be in the path of to see.
Many.Ken G said:pretend we have no radio antennas to see pulsars, so NSs are just as hard to find as BHs. What fraction of the NSs we now know about would we still know about?
OK that's a good point, gravitational detectability can last billions of years, so one can ask how many NSs are known by their pulsing, and how many are known gravitationally. Since the Wiki says only 1/20 of known pulsars are in binaries, we see that many more of them are known by their pulses than by their gravitational effects. The question is then, of those 1/20 that are in binaries, how many of them do we know only from their gravitational effects? We might end up deciding that without pulsars, we'd only know some 1/100 or less of the NSs we currently know about. That's not so far from the shortfall of BHs you are pointing out. So it still sounds like the combination of how few are in binaries, and how hard they are to detect in binaries, accounts for how few BHs we know about.Vanadium 50 said:But not for very long. A few million years and off they go. Seven of the nearby ones don't pulse at all - they are just weak x-rays sources. Once their surface cools, on a similar timescale, they can only be detected gravitationally or by accretion x-rays, and in both cases, it should be easier to detect BH's.
Perhaps there is a problem with the Wiki claim that only 1/20 of NSs are in binaries, they might not be including this very large number of Xray sources that are not specifically identified as NSs but which probably are. However, if we include those, why can't many of them be BHs?Vanadium 50 said:Many.
Of the nearby ones I mentioned, seven are radio quiet x-ray sources. If you look at Chandra data, globular clusters have many x-ray sources, not all of which are neutron stars, to be sure, but a lot of them are. These are all in the outer part of the cluster; there are too many in the core to separate one from its neighbors.
There are some nice pictures from Chandra on this, and nicer ones with composites with optical pictures of the globular. Since globulars are gas-poor, these are probably oversampling neutron stars in binary systems.
Yes, binaries do allow conditions to keep the pulsars shining, making them more visible as with black holes. But I do think it's true that most pulsars are not in binaries (consider for example those two most famous pulsars, Vela and Crab). So there is an advantage for seeing pulsars that black holes don't share.Vanadium 50 said:I am not confident of the Wikipedia claim. Apart from the general issue of a wide range of validity, I don't think we know that number well. Consider this - if we only detected millisecond pulsars, we would conclude that all neutron stars are in binaries.
There can be some mass selection effects. Massive stars tend to orbit other massive stars, since angular momentum storage is more or less the purpose of forming in binaries, so it's most efficient to split the mass up more or less equally. Still, you point out that NSs often have red dwarf companions, which surprises me for a different reason. A low mass companion should be lost when the supernova occurs, since the NS progenitor is losing most of its mass. So how do those NSs end up with red dwarfs bound to them?Vanadium 50 said:Looking at some globular cluster data, it looks like the 1/20 number is more like 1/10 or higher. Is this sample less biased? I don't know - it is certainly differently biased. And, as has been said, most companions are red dwarfs (for obvious reasons) and most of the searches thus far for unseen companions have (again, for obvious reasons) concentrated on brighter stars.
The nearest black hole orbits (or rather, is orbited by) a G main-sequence star. So a few thousand times brighter than a red dwarf.
I do not know.Ken G said:So how do those NSs end up with red dwarfs bound to them?
I agree that whether it has 2 solar masses or 3 shouldn't matter much, but that's why I'm wondering why those Xray sources in the globulars couldn't be a whole lot of BHs along with even more NSs. If so, the question is not so much where are the BHs, it is where are the BHs and NSs that we see in globulars that we don't see nearer to us in the galactic disk. So maybe it does have to do with gravitational capture in high density star clusters, which lights up the accretion. But I don't know how often one expects a wandering BH to grab a low mass companion.Vanadium 50 said:I do not know.
These are from globular cluster data, and that may be relevant. Since gravitational capture requires at least three bodies, the greater star density in globulars may play a part. Or maybe it has nothing to do with that. It sounds unlikely, but other features of globulars - low metals, low gas, and such sound even less likely.
One thing I do strongly suspect is that whatever the reason is, it does not depend on the remnant being a black hole or neutron star.
Neither do I. It surely happens more in globulars than it the local galactic neighborhood, but that doesn't say anything about how often it happens. After all, one in a million is larger than one in a billion, but that doesn't make it large.Ken G said:But I don't know how often one expects a wandering BH to grab a low mass companion.
The next release of Gaia data promises to be a goldmine for the study of binary systems and the discovery of more dormant black holes in our galaxy. “We have been working extremely hard to improve the way we process specific datasets compared to the previous data release (DR3), so we expect to uncover many more black holes in DR4,” concludes Berry Holl of the University of Geneva, in Switzerland, member of the Gaia collaboration.