If 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.
One 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.
This 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!
Oh 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!
I 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 :-)
Seconded.
As I mentioned when this last came up, I encourage to read also Stephen Baxter's "Flux". (Even crazier, here the lifeforms dwell inside the neutron star, in the neutron superfluid.)
I read this as a kid and forgotten the name of the book. Thank you - it is indeed very, very, hard sci-fi and even the story is somewhat boring still interesting to read
I 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.
It's not quite as simple as that because the dynamics of black hole formation in the transitional mass range seem likely to be somewhat complex. When big stars age and cool they can undergo massive dynamic changes, such as the red giant phase and triggering a supernova. Current models for these changes indicate that stars in this transitional mass range are expected to 'blow themselves to bits' to put it bluntly and not leave a remnant big enough to collapse into a black hole.
This is where the mass gap comes from. Stars smaller than the mass gap are modelled to become neutron stars, stars in the mass gap are too unstable to end up forming black holes. Only stars bigger than the mass gap range are believed to have gravity fields strong enough to overcome these instabilities and undergo complete collapse.
That's the model anyway. The discovery of an object in this mass range calls those models into question and that's why it's such as useful and interesting find. That's the short version. In fact there are several possible models, and this will hopefully help us exclude some and refine others.
I agree the question of how it formed is a bit more complex, but what it is seems pretty straightforward.
Some plausible formation mechanisms include primordial black hole and neutron star merger. It could also be some other alignment of statistically improbable events. We've only found one so far, after all.
I 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.
A star could form in that mass range, but we don't think it could remain stable enough to collapse at that mass range at the end of it's life as a star. Our current models indicate we would expect it to blast off enough mass that the remnant would be too small to undergo complete gravitational collapse. That's why finding one is so interesting and useful.
I 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.
On an unrelated note is there a service that translates news into this type of summary? I can't be the only person willing to fork over money for something like that.
They used to be called "science journalists". I think the reason they disappeared may have something to do with the fact that we (largely) stopped forking over money for what they did.
That summary should be the first sentence of the story (or a subtitle). Instead of a "service" that rewrites badly written stories maybe we need journalists who can write.
Maybe 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.
There 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.
Hm, 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.
I 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?
> 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.
There's something on Wikipedia about how maybe all black holes are basically a ball of subatomic stuff, termed a "fuzzball", with a diameter equal to where escape velocity reaches c. This appeals to me, because falling past an event horizon, let alone reaching a singularity, seems like it can't be physical.
As the article notes, this is a speculation in string theory. Since it has no testable consequences, it remains a speculation.
> falling past an event horizon, let alone reaching a singularity, seems like it can't be physical
"Seems like" is not a good indicator in relativity; lots of things in relativity are counterintuitive. This is one of them. The classical GR model of black holes is perfectly consistent. It's possible that there are quantum corrections that prevent that exact model from being realized in our actual universe, but until we have a good theory of quantum gravity that has actually passed some experimental tests, the classical GR model of black holes is the best we have.
>Since it has no testable consequences, it remains a speculation.
But why should it not be the default? I wonder if you're reacting to "string theory" which I am not promoting specifically, just the idea there is something that doesn't collapse any further, call it quarks or strings or whatever.
The page says there are testable consequences, I think, but assuming there are none, what are the testable consequences of the contrary - i.e. the existence of a singularity or the possibility of crossing the event horizon?
Reading popularized accounts of renormalization gave me the idea that when a physical theory spits out infinities, it's got to be inadequate. Whatever ideas don't give infinities are probably better. Regardless of whether you can test just yet.
If you disagree, why? Why say "this is the way relativity is" when relativity is guaranteed to be wrong?
Why should what not be the default? The speculations of string theory? Um, because they're speculations?
>* just the idea there is something that doesn't collapse any further*
Because our best current theories, the ones we have actually tested experimentally, say that once you are over the maximum mass limit of stable states of matter, there is no alternative to collapse to a black hole.
If someone comes up with a better theory that makes different predictions, and has that better theory confirmed by evidence, then our default will change. But until that happens, our default is what our best current theories that have been confirmed by evidence say.
> what are the testable consequences of the contrary - i.e. the existence of a singularity or the possibility of crossing the event horizon?
We cannot directly observe events at or below the event horizon from the outside, but we can test for the possibility indirectly by looking for the evidence that we would expect to see if something else happened, i.e., evidence that collapse stops somewhere short of the horizon. So far, in cases of objects which are above the known maximum mass limits, we have seen no evidence that anything stops the collapse short of the horizon. If we ever do see such evidence, it will be evidence that our best current theories need to be modified. But so far, as I have said, we have not seen any such evidence.
Speculating about other possible theories, in the absence of any evidence such as I have described, is fine as long as they are understood to be speculations. But in the absence of such evidence, the "default" remains as I have stated it above.
> Reading popularized accounts of renormalization gave me the idea that when a physical theory spits out infinities, it's got to be inadequate.
Not inadequate; incomplete. Yes, physicists pretty much agree that GR must be incomplete because it predicts infinities in certain particular regimes. But that only means the theory is incomplete in those regimes: at the singularities predicted at the centers of black holes. The black hole event horizon is not such a regime; GR predicts no infinities there whatsoever. So there is no reason to consider GR incomplete at the black hole event horizon, or even well below it, all the way down to the singularity, on these grounds.
> Whatever ideas don't give infinities are probably better.
Not at all. The fact that a current theory is believed to be incomplete because it has infinities in a particular regime, does not at all imply that any theory that does not have infinities in that particular regime must be better. That is simply faulty logic. The fact that many string theorists proclaim it does not make the logic any less faulty.
> relativity is guaranteed to be wrong
No, relativity is believed to be incomplete in one particular regime. That is very, very different from "wrong".
>But so far, as I have said, we have not seen any such evidence.
So, if there is evidence that the fuzzball theory is not accurate, then why did you say it's not testable?
Please be clear - I don't know if it's testable, nor if it's been (explicitly or implicitly) tested.
My point is that I think the correct application of Occam's razor in the absence of evidence would be to prefer theories that don't involve unlimited collapse providing they are consistent with known physics outside the extreme conditions in a black hole.
I have no expertise in physics, but this is a philosophical issue/opinion.
Even without any theory that prevents total collapse, due to relativistic time dilation, we can't see that total collapse in any amount of time, so it's always going to be premature to declare the matter settled.
> if there is evidence that the fuzzball theory is not accurate
That's not what I said. I said we have no evidence that gravitational collapse of an object over the maximum mass limit for any stable state other than a black hole, stops short of the event horizon of a black hole. In other words, we have no evidence that would require us to modify our best current theory of gravity, GR.
That is not at all the same as saying that we have evidence that the fuzzball theory is not accurate. To have such evidence, we would first have to have some actual predictions made by the fuzzball theory as to what we should expect to see in gravitational collapse of objects over the maximum mass limit for all other known stable states (neutron stars, etc.). I am not aware of any such predictions from the fuzzball theory. All I am aware of are hand-waving speculations that have not led to any testable predictions. That's why I said the fuzzball theory is not testable.
> I think the correct application of Occam's razor in the absence of evidence would be to prefer theories that don't involve unlimited collapse providing they are consistent with known physics outside the extreme conditions in a black hole.
Even if I were to accept this claim for the sake of argument, it would still require that we know fuzzball theory is consistent with known physics outside of a black hole event horizon. We don't even know that much; string theorists have yet to prove that string theory actually matches the predictions of our best current theories in all regimes outside of the extreme cases under discussion. They believe that string theory does match those predictions, but believing is not the same as proving.
The 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.
There 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.
> 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.
Plank 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.
The 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.
It was detected by gravitational waves via LIGO & friends as a merger of two very dense objects, much denser than your average star. Normal star densities would tear themselves to pieces/devolve into a novae instead of merging like this.
It 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.
It 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.
I 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.
As 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.
So 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.
No - 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.
« This result means that it is possible to have _something_ in this range »
What would it even mean for it not to be possible? Two neutron stars of appropriate size collide -- you end up with something. I'm sure the physics are interesting in this range, but I have a hard time understanding how it could just not be possible. (Rare, yes.)
Question? 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.
"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.
My 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
That'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.
There 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.
All science is not coming up with new theories. Lots of science is developing tests that can prove/disprove a theory repeatedly and consistently. That sounds a lot like engineering to me.
As 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.
The 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."
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!!