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'Black neutron star' discovery changes astronomy
- not2b 6y agoMaybe there's a zone between neutron stars and black holes where the object consists at least partly of quark-gluon plasma because the neutrons have been forced together until they break, but it's a hair too small to form a black hole.
- ajross 6y agoMy understanding is that that's been ruled out by fairly routine QCD work. Dark-energy stars are the exotic material du jour in this space.
- pdonis 6y agoThere is no such thing as "too small to form a black hole". There is no minimum mass for a black hole. There is a maximum mass for white dwarfs and neutron stars; for white dwarfs, it's about 1.4 solar masses, and for neutron stars, it's somewhere between about 1.5 and 3 solar masses. We can't pin it down for neutron stars any closer because we have a poor understanding of the equation of state of matter in the relevant density and pressure regime. I don't know if quark-gluon plasma is even stable in the relevant density and pressure regime, but if it is, I suppose there could be a maximum mass for a quark-gluon plasma "star" that was somewhat larger than the maximum mass for a neutron star, so there would be a range of masses where gravitational collapse could stop at a quark-gluon plasma star instead of a neutron star, and would not go on to form a black hole.
- perl4ever 6y ago>There is no such thing as "too small to form a black hole". >There is no minimum mass for a black hole. The first sentence could be true, but it's not implied by the second sentence being true.
- pdonis 6y agoHm, yes, I should probably clarify what I meant: what determines whether an object undergoing gravitational collapse forms a black hole is not whether or not it is too small to form a black hole, but whether or not it is too large to form anything else. There is no minimum mass for a black hole, but every stable state of matter we know of short of a black hole has a maximum mass. (And there are good theoretical reasons to suspect that every stable state of matter short of a black hole must have a maximum mass, even if we haven't yet discovered all of the possible ones.) So a collapsing object that is under the maximum mass limit for some stable state other than a black hole (white dwarf, neutron star, etc.) could be said to be "too small to form a black hole" in one sense (since it won't end up collapsing to a black hole), but I think it's more useful to view things in terms of it not being too large to form a stable state short of a black hole.
- deepspace 6y agoI am pretty sure that is what the parent commenter to your first reply meant, at least that is how I understood their question. Semantics aside, I would like to know if one of the possible states you mention might be "more dense than a neutron star but not dense enough to collapse into a black hole"? I.e. some kind of quark-gluon plasma or other exotic state?
- pdonis 6y ago> I would like to know if one of the possible states you mention might be "more dense than a neutron star but not dense enough to collapse into a black hole"? I.e. some kind of quark-gluon plasma or other exotic state? I'm not aware of any such state that is known, and ajross commented upthread (a sibling to my original comment) that he thinks a quark-gluon plasma state has been ruled out by QCD work. I have seen some papers about the "dark energy stars" he mentions in the same comment, but I don't know of any proposed observational test for such objects and they seem highly speculative to me. Note, btw, that there isn't an awful lot of room for objects more dense than a neutron star but which can remain stable against collapse to a black hole. There is a theorem called Buchdahl's Theorem that says that any stable object that doesn't collapse to a black hole must have a radius at least 9/8 of the Schwarzschild radius corresponding to its mass. The denser neutron stars are already fairly close to this limit.
- _joe 6y agoThe hard upper limit on a neutron star mass, the Rhoades-Ruffini limit, is at 3.2 solar masses. This discovery is significant, because we never found a collapsed object in the 2-3 solar masses range, but it definitely doesn't need new physics to be explained.
- philipov 6y agoThere is in fact a minimum mass for a black hole. That's called the Plank Mass, which is the amount of mass that forms a Black Hole with a size of 1 plank length. This is also the maximum mass of an elementary point particle.
- mhh__ 6y agoIf you can show that there's probably a nobel prize waiting for you
- pdonis 6y ago> There is in fact a minimum mass for a black hole. That's called the Plank Mass This is a speculative hypothesis at this point, since we do not have a good theory of quantum gravity. A lot of physicists think it will turn out to be true once we do have a good theory of quantum gravity, but it's still a speculative hypothesis at this point. > This is also the maximum mass of an elementary point particle. This is part of the same speculative hypothesis.
- wnoise 6y agoThere is no reason beyond numerology to believe that any of the Planck units actually mean anything.
- dogma1138 6y agoPlank Units represent physical constants, they are there to make equations and more importantly hypotheses/predictions continue to work in a world where measurements can be constantly refined. Hence they their actual SI values have quite a bit over the years. This is also why Plank units aren’t used much outside of theoretical physics and cosmology which are fields where using absolute value based on current measurements won’t mean that much.
- Dylan16807 6y agoYeah, okay, but we're talking about stellar objects. In that context, there is no minimum mass for a black hole. If you can figure out a way to cram the mass together. But that was the point of the first comment anyway, that if you didn't quite get enough mass+density that you might get something weird.
- BurningFrog 6y ago> for white dwarfs, it's about 1.4 solar masses, and for neutron stars, it's somewhere between about 1.5 and 3 solar masses. A simple thought is that a 2.6 solar mass object could form by two ~1.3 solar mass objects merging.
- joe_the_user 6y agoLike a Quark Star, say? The wikipedia article mentions a number of hypothetical exotic star types. https://en.wikipedia.org/wiki/Quark_star https://en.wikipedia.org/wiki/Quark_star
- empath75 6y agoCouldn’t it just be a normal, non-collapsed star? I’m sure they thought of that, just curious how they ruled it out.
- dandare 6y agoIt would be probably ripped apart into an accretion disc thus no gravitational waves. But i like your question and I hate it when articles omit the to mention and explain layman's explanations.
- dmurray 6y agoYeah, the article really seems to be missing an important point. It's written something like - we never observe any super dense thing between 2 solar masses and 5 solar masses - 2 solar masses is the maximum for a neutron star, because otherwise it would collapse and become a black hole - 5 solar masses is the minimum for a black hole, because...?
- ISL 6y agoIt is the minimum thought to be possible for a black hole produced by standard stellar evolution. GR has no limit, large or small, on the size of a black hole. Such black holes could be formed by another mechanism -- in the big bang ("primordial" black holes) or from the merger of neutron stars. What has everyone atwitter about this is that, given the standard plan for things, these objects should be very rare. To have seen even one example this early in the history of gravitational-wave observation is a surprise. Either there are more primordial black holes than people think, supernovae don't work like we expect (historically a pretty good bet), neutron stars find each other and merge more often than people think, or there's another process for making mass-gap objects that people don't know about.
- gliese1337 6y agoI would think neutron stars accumulating material from a binary companion ought to be reasonably common. Unlike white dwarfs, they won't be able to blow themselves apart in supernovae, so they should just keep accumulating mass until they collapse into very small black holes.
- lifeisstillgood 6y agoThere was a thread earlier today on how VC forms did or did not invent tech. Invention is the wrong word - this stuff here, science, does the invention. the rest of us do the "evenly distributed" part later on. And can I make a suggestion to us all as we barrel towards elections and post lockdown changes - write to your representatives, show them this and say "more funds, more" Let's double the science budget in every western democracy.
- garmaine 6y agoDiscovery is not invention. These are fundamentally different things. Scientists don’t think like engineers.
- yummypaint 6y agoAs a professional scientist, i think most of what i do day to day is engineering. There is no product or customer, but you are absolutely working within a set of design constraints to make a tool to perform a task. It makes a tremendous difference whether your engineering budget is being paid by basic research grants or venture capitalists. Funding science is a proven method of producing new tech which may subsequently be of interest to the for-profit people. The kinds of innovation that come out of big government funded science projects can never be produced exclusively by organizations whose purpose is to demonstrate growth to shareholders quarter over quarter.
- mturmon 6y agoThe GP comment did over-reach...I agree that many scientists do indeed do engineering. I work at a lab that builds expensive, highly-specialized scientific instruments, and the scientists who lead that kind of work are right at the edge of what's possible in engineering an instrument that can make a scientific measurement. They get super-excited about stuff like new CCDs, exotic semiconductor doping, high-precision clocks, and detector cooling technologies. But there are also other scientists who aren't engineering-focused in that same way. They mostly want someone else to make the measurement, and to scoop up the data later and analyze it. Although come to think of it, many of those scientists do have a focus on the technologies for analysis - say, machine learning or large-scale cloud computations. One way I used to conceptualize whatever science/engineering divide there is, is in terms of the Myers-Briggs [* ] J/P distinction. Namely, J = judging = engineering, P = perceiving = science. I.e., "build a gizmo to figure this out" vs. "think abstractly about the consequences of theory." [* ] Subject to the usual caveats.
- cogman10 6y agoQuestion? Could something like this explain "dark matter"? Like, is it possible that space is more full of matter than we think? Or is my understanding of dark matter just way off.
- variaga 6y ago"Something like this" is one of the competing theories for what dark matter is, although I think the current consensus is that it cannot explain _all_ the dark matter effects, so there must be something else too. see: https://en.wikipedia.org/wiki/Massive_compact_halo_object https://en.wikipedia.org/wiki/Massive_compact_halo_object
- ddrt 6y agoNow I’ve got Macho man stuck in my head. Thanks.
- pavel_lishin 6y agoMy understanding is that at this point we're pretty sure that dark matter does not interact with the rest of the universe via anything but gravity: https://en.wikipedia.org/wiki/Bullet_Cluster https://en.wikipedia.org/wiki/Bullet_Cluster
- credit_guy 6y agoThat's very unlikely to be the case (although I'm not a physicist). I think it's more likely that under "normal" conditions dark matter does not interact with the luminous matter except via gravity. However, under extraordinarily energetic conditions, it might have some interactions. I guess that's the hope behind people proposing larger and larger accelerators (like the successor to the LHC). The medium of a neutron star is probably more energetic than anything we can hope to create here on Earth in the next few hundred years. So, over there dark matter may interact with normal matter, and if we know what to look for we may be able to detect that. For example, maybe we see some unusual spectrum that cannot be explained with regular atoms from the regular periodic table. Who knows. From what I heard, what's going on inside a neutron star involves both quantum mechanics and generalized relativity, and we can't model that quite well, so it's very difficult to say if something weird being observed there is a result of dark matter interactions or simply a not yet understood effect of normal matter being subjected to very extreme conditions. Bottom line: being able to observe neutron stars could lead to a better understanding of matter.
- the8472 6y agoIs the title something the BBC came up with? The paper itself certainly doesn't mention anything about neutron stars that are cool. https://iopscience.iop.org/article/10.3847/2041-8213/ab960f https://iopscience.iop.org/article/10.3847/2041-8213/ab960f
- viscanti 6y agoThe title comes from interviewing one of the authors of the paper. It's a term one of the authors of the paper used to explain this. Presumably the way they communicate with journalists (and the broader public) is different than how they communicate with other experts in their field through their paper. There are lots of things to criticize the media for, but this doesn't seem like one of them.
- phyzome 6y agoSo... merger of two neutron stars, resulting in a black hole? If we see black hole mergers all the time, why not neutron star mergers?
- mirimir 6y agoLIGO has detected at least one neutron star merger.
- netcraft 6y agoAs the other person responded, they have seen a neutron star merger, and I believe that is the one they were able to observe with EM radiation as well. Also this event they suspect the larger mass was a black hole, they aren't sure of the smaller one.
- phyzome 6y agoSo that means this object could well have been the result of such a merger, right? I guess I'm not sure what all the fuss is about. "Oh neat, we found something in this mass gap" seems reasonable, but the "changes astronomy" headline seems completely unsupported.
- netcraft 6y agoNo - neutron stars can merge to form a black hole or a larger neutron star, but it was thought that this mass-gap is beyond a threshold that was too small to form a black hole, but too large to still be a neutron star. The fuss is that this mass-gap has been something that was theorized but also backed up by a (lack of) astronomical observations. This result means that it is possible to have _something_ in this range, and the fact that it was detected so "early" in gravitational wave observations suggests that they are more common than we otherwise would have thought, again from theory and previous observations. Hence, there's something we don't understand about these objects.
- phyzome 6y ago
- guender 6y agoNo, neutron stars are not supported by neutron degeneracy pressure. It’s the repulsive short distance interaction of the strong force.
- xvilka 6y agoDo they speak about strange stars[1] (quark stars with strange quarks)? [1] https://en.m.wikipedia.org/wiki/Strange_star https://en.m.wikipedia.org/wiki/Strange_star
- gorgoiler 6y agoIf you haven’t read RL Forward’s Dragon’s Egg then take the weekend off and treat yourself. A 1980s hard sci-fi novel depicting the saga of a species called cheela: creatures who have evolved to live on the surface of a neutron star, where the forces of nature are so powerful that daily life is 1,000,000x faster than that of human beings. ...with hilarious consequences!!
- leejoramo 6y agoOne of the best hard SF books I have ever read. I agree with your description, but for those unfamiliar this is not a Terry Pratchett comedic story. Forward was a physicist who specialized in gravity.
- sophacles 6y agoOh cool - I read this as a kid and think of revisiting it from time to time, but couldn't remember what it was called, nor enough google-able details to find it. Thanks for mentioning it!
- at_a_remove 6y agoI have not read the sequel. His son wrote a book called The Owl that was not sci-fi at all, but I came across the news of the Dragon's Egg sequel when I went looking for The Owl.
- mkl 6y agoThis is a great novel, and very interesting and entertaining. I have also heard it described as a physics textbook masquerading as fiction, because it teaches you a lot!
- W0lf 6y agoI bought it this morning based on your suggestion and so far I really like it. Thanks! Edit: Coincidently, the first chapters of this book play in June 2020. Computers are very expensive devices where there's always hardly any money left to do long operations on it and everybody always prints out screens on large paper rolls :-)
- miohtama 6y ago
- hindsightbias 6y agoWhat happens when the neutron star is a pulsar?
- matco11 6y agoI believe this is the original source paper: https://iopscience.iop.org/article/10.3847/2041-8213/ab960f https://iopscience.iop.org/article/10.3847/2041-8213/ab960f
- goodcanadian 6y agoI was slightly frustrated when reading the article a couple of days ago, and now, when reading these comments. Most likely, there is nothing exotic here. Most likely, it is a black hole as everything heavier than a neutron star is most likely a black hole. Lower mass black holes should exist, and perhaps, we have finally found one. The next most likely possibility is that it is a neutron star which would suggest that our understanding of the mass limit of neutron stars is out. This is entirely possible as the physics of neutron stars is pretty extreme, but it seems a lot less likely to me. Now, I'm happy to keep an open mind as we don't know for sure and we haven't previously found anything in this mass range, but calling it a "black neutron star" implies something new and exotic when it probably isn't.
- incompatible 6y agoI think the article can be summarized as "A gravitational wave detector has found an object of 2.6 solar masses. Astronomers don't know whether it's an exotic type of neutron star or a light black hole". It doesn't seem especially surprising that objects of 2.6 solar masses could exist. It would be more surprising to me if they could not.
- PopeDotNinja 6y agoI like the idea that a neutron star can be right at the limit of becoming a black hole, but still be a star. Then a space pigeon flies down to the surface for a quick rest, and shhhhhllurrrrrp... black hole.
- Retric 6y agoThe mass limit depends on how fast it’s rotating, so they can simply slow down slightly and slurp, black hole.
- PopeDotNinja 6y agoIt blows my mind to think that shining a light on a black hole makes it grow.