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If a star had a black hoke at the center wouldn't it eat the star?
by pattmayne 3y ago
If a star had a black hoke at the center wouldn't it eat the star?
- dcminter 3y agoThe paper answers this question amongst others.
- pdonis 3y agoNot necessarily. A black hole doesn't have any stronger gravity than an ordinary object of the same mass. And matter falling into the hole would radiate strongly (the paper calls this "accretion luminosity"), which would help to maintain an equilibrium with the rest of the star. That's the kind of model the paper is studying. How long such an equilibrium can last is a different question. The paper only briefly comments on this when it says that the time scale of the numerical simulations they did is of the same order as the hydrodynamic timescale of the Sun. That means, roughly, the time it would take the Sun to collapse to a white dwarf if fusion reactions in its core stopped, which is, I believe, tens of millions of years. So a star with a black hole at the center would not have the same lifetime as an ordinary main sequence star with similar mass, but it would have a long enough lifetime that would could not conclusively rule out that at least some stars we see have black holes at their centers.
- hinkley 3y agoA black hole at the center of a gaseous body would mess with the fusion cycle would it not? There’s no pressurized core at the center. Just a drain that all pressure exits into.
- jiggawatts 3y agoIt would be like a pinhole leak. A large enough container can maintain pressure even with a few small holes letting the contents slowly stream out.
- joot82 3y agoit would only be a pinhole at first, though start to grow quite rapidly(? no idea in what time scale?) and at some point consume the sun quite violently from within, no?
- pdonis 3y ago> no idea in what time scale? The numerical simulations in the paper go on for a time on the order of the Sun's hydrodynamic time scale, which is tens of millions of years. After that time has elapsed, yes, the star could be completely consumed by the hole.
- Sharlin 3y agoIt's very very difficult to "drain" anything through a molecule-sized hole.
- andrewflnr 3y agoFWIW, the sun's schwarzchild radius is more like inches than Angstroms. Still small compared to the sun, but not that small.
- pdonis 3y ago> the sun's schwarzchild radius is more like inches than Angstroms. No, it's not inches, it's about 3 kilometers. But the holes at the center of stars that the paper is talking about have tiny masses, much, much smaller than those of the stars they are inside. Their schwarzschild radius could indeed be of the order of Angstroms.
- andrewflnr 3y agoOops. I didn't remember it being that much bigger than Earth's.
- Sharlin 3y agoThe article is not talking about solar-mass BHs but ~asteroid-mass ones, with a Schwarzschild radius on the order of nanometers to micrometers.
- hinkley 3y agoHow do you catch a molecule sized black hole? Maybe in stellar nurseries? But then the black hole has been feeding for a very long time. Yes?
- pdonis 3y ago> A black hole at the center of a gaseous body would mess with the fusion cycle would it not? Not necessarily. That's the sort of question the paper investigates, and it finds models for which fusion can continue in the star's core for an extended period of time. > There’s no pressurized core at the center. Yes, there is, because, as I noted, the matter falling into the hole radiates strongly, and the radiation has pressure.
- pointlessone 3y agoI thought infalling matter radiates because of friction in accretion disc. Does a similar structure form in a much denser interior of a star?
- hinkley 3y agoWould there be a disk at the center of a star? Not a lot of angular momentum there.
- pdonis 3y agoMatter falling into a spinning black hole surrounded mostly by vacuum forms an accretion disc. But friction and heating and radiation will occur in infalling matter no matter how it is falling in. A black hole inside a star would probably not just have an accretion disc, it would have accretion happening in all directions. But the accretion would still involve friction and heating and radiation.
- hinkley 3y agoHow do you capture a PBH unless there’s substantial, fast mass (momentum) transfer from the star to the black hole? Otherwise the ballistic trajectory would carry it out and through. Wouldn’t you be more likely to find a PBH orbiting a main sequence star? Or gone altogether?
- hinkley 3y agoIt came to me while doing some housework that this feels like “what if the moon crashed into the earth?” The moon cannot crash into the earth. Any alien that could make that happen would be so terrifyingly powerful they wouldn’t have to crash the moon into the earth. It would be the twentieth most interesting way to doom us. Tidal waves would be easier.
- the8472 3y agohttps://en.wikipedia.org/wiki/Quasi-star https://en.wikipedia.org/wiki/Quasi-star also mentioned in the paper, powered by larger black holes
- LorenPechtel 3y agoIt's not stable, it's that the consumption rate is low enough the star can live quite a while.
- gjm11 3y ago"For many readers, intuition from astrophysics will suggest that a star that captures a PBH will be short lived and look nothing like a star dur- ing that life. However, we will show that stars with very low mass PBHs could be very long lived with many surviving their entire main sequence phase. Ultimately the evolution is highly sensitive to the accretion physics, which is the subject of the following sections."
- ars 3y agoAs usual with black holes there is zero mention of time dilation. In actuality time is frozen near one, and matter takes an infinite time to fall in, so I don't see how it could eat anything.
- SonicScrub 3y agoWhen referring to black holes, "falling in" means going past the event horizon. For all practical purposes for us on the outside of the singularity, this is "having fallen into the black hole" as any object is gone to us forever once having done so. We don't use falling in to mean touching the singularity, which as you noted, does indeed take infinite time. Using the definition this way isn't particularly useful.
- Calavar 3y agoI don't think that's right. This is my understanding: It takes an infinite time to cross the event horizon from the perspective of a distant, stationary observer, but a finite time from the perspective of the object that is actually falling towards the black hole. Once past the event horizon, reaching the singularity takes a finite amount of time from the perspective of the falling object. From the point of view of a distant external observer, time from event horizon to singularity is a meaningless question because the events inside the event horizon are causaully disconnected from the events outside of the event horizon.
- DiscourseFan 3y agoGuys uh, I don't think we have a lot of empirical evidence from people who've gone near black holes and returned.
- ko27 3y agoYour explanation is wrong. For an outside observer, time dilation approaches infinity at the event horizon. Singularities don't even exist for an outside observer, they have yet to happen in the infinite future.
- 3y ago
- WhiteNoiz3 3y agoI hadn't known this until recently, but it's theorized that in the early universe there were super huge stars that had black holes in them - https://en.wikipedia.org/wiki/Quasi-star https://en.wikipedia.org/wiki/Quasi-star