Do we have any observational direct verification and historic record of a star after going supernova was turned into a Black hole?
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8$\begingroup$ Please clarify what you mean by the loaded phrase "observational direct verification". Some would argue that we have no "direct observational verification" of GR black holes at all. $\endgroup$– ProfRobCommented Sep 4 at 11:21
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4$\begingroup$ @ProfRob The question is easy to understand: Have astronomers ever observed a black hole star before it became a black hole? $\endgroup$– Miss UnderstandsCommented Sep 4 at 12:54
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1$\begingroup$ @ProfRob For example, you observe the location of a supernova with your optical telescope then you go after a year and observe the same relative location in the sky and find an unusual gravitational pull at that same spot of apparent empty space where the star was located previously therefore inferring to a BH? This is a direct observation of such an event and historic record. On the other hand detecting extreme γ-radiation from the same location I consider not being direct observation proof. $\endgroup$– Markoul11Commented Sep 4 at 19:20
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3$\begingroup$ @Markoul11 - why would there be an 'unusual' gravitation pull? The mass of the supernova, minus energy released, went into the black hole. So, the gravitational force from that spot will be a bit less (because of the energy released) than from the original star. $\endgroup$– Jon CusterCommented Sep 4 at 20:18
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4$\begingroup$ @KyleKanos - well, yes, but observing that on a stellar scale is quite difficult in general. I suspect more that many folks would assume that the black hole has a larger gravitation effect than the precursor star which would be incorrect. $\endgroup$– Jon CusterCommented Sep 4 at 21:04
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2 Answers
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I believe the best observational evidence for the creation of black holes at the end of a massive star's life are not found in those that explode as supernovae but in those thought to collapse directly to black holes. The problem with a supernova event is that it might leave a neutron star or it might leave nothing at all. If you simply see no evidence for a remnant after a supernova explosion then that could mean it has left a black hole or it could mean it has left nothing at all. It is possible for the exploding star to have been part of a binary, in which case one could deploy the techniques used to study massive compact binary systems (e.g. study the accretion disc or the reflex motion of the companion) to try and establish that a black hole exists, but that is very difficult when the supernovae are extragalactic and hence very distant.
Instead, we have the cases where a previously identified massive star "suddenly" disappears with no explosion. There is no alternative model (afaik) to explain the disappearance of a massive star other than it reaching the end of its life and collapsing directly into a black hole. Example candidates are reported by Reynolds et al. (2015), Adams et al. (2017) and Neustadt et al. (2021).
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6$\begingroup$ @KDP No black hole has ever been discovered or confirmed by gravitational lensing and certainly not a stellar-mass black hole in another galaxy. An accretion disk IS evidence for a remnant but would only be present in a binary system; as I said $\endgroup$– ProfRobCommented Sep 4 at 18:20
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6$\begingroup$ The only alternative model that comes to mind would be whoever lives there finishing their Dyson Sphere... $\endgroup$– PerkinsCommented Sep 4 at 18:23
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2$\begingroup$ @Perkins maybe, if they could construct the whole thing on timescales of years, and mask any infrared signature. $\endgroup$– ProfRobCommented Sep 4 at 18:26
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3$\begingroup$ @KDP Those are supermassive black holes. Neither was a new discovery. $\endgroup$– ProfRobCommented Sep 4 at 18:40
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1$\begingroup$ @KDP why would there be a surrounding gas cloud? Black holes with an accretion disc that we know of are either supermassive or fed by a companion. $\endgroup$– ProfRobCommented Sep 4 at 18:46
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SN 1979C is a potential example, though it definitely depends on what counts as direct verification. See here for a paper which considers its bright and steady X-ray luminosity (tracked over 12 years) to be possible evidence for a stellar-mass black hole accreting material. However, they also consider an alternative explanation where the emissions come from a pulsar wind nebula.
SN 2022jli is another potential candidate. Oscillations in the light curve of the event are taken to imply the existence of a binary system consisting of a compact remnant and a companion star. See the paper here. In my skimming of the work it seems they do not really speculate on the exact nature of the remnant (whether it be a black hole or neutron star) other than a brief comment on p. 23 that if the remnant is a black hole, the event's Eddington luminosity ratio would be lower (and thus in my understanding more physically reasonable in a certain sense) than were the object a neutron star.
