Consequently, not very much is actually known about neutron stars. One of the most important open problems in modeling neutron stars is just coming up with the most basic relationship you can, namely the "equation of state." This is simply a relationship between the density and the pressure within the neutron star. The equation of state of normal stars was effectively developed in the 19th century with the development of statistical mechanics. The equation of state of white dwarfs was developed by Chandrasekhar in the 1930s, not long after the development of quantum mechanics (and while Chandrasekhar was on a boat traveling from India to England!). But the equation of state for neutron stars is still unknown.
A major consequence of the equation of state is that it predicts the maximum mass of the object. In the case of a white dwarf, Chandrasekhar showed that the equation of state implied that the maximum mass had to be about 1.44 times the mass of the Sun (this is now appropriately known as the Chandrasekhar limit). But because the equation of state of neutron stars is not known, it is not known what the maximum mass of a neutron star is. Therefore, discovering more massive neutron stars is very important because it can possibly rule out certain equations of state. This, in turn, tells us a little bit more about what physical processes are going on in the neutron star.
Since the problem is so theoretically intractable astrophysicists usually have to neglect or simplify certain aspects of the physics considerably. If the equation of state that comes out of these assumptions can be ruled out, this means that one of these assumptions must be faulty, and some of the underlying physics that was neglected turns out to be important after all.
I am the biggest astronomy nerd and watch loads of TV shows about it (the only thing apart from dinosaur stuff that I watch on TV actually!) and when scientists talk about the numbers involved in stellar objects it still blows my mind every time.
"Just a single sugar-cube worth of neutron-star material would weigh 100 million tons here on Earth, or about the same as the entire human population"
I struggle to visualize that...
On a side note, "'Neutron stars are as mysterious as they are fascinating', said Thankful Cromartie..." - Possibly the coolest name I've ever heard :)
Scales are simultaneously intuitive and yet mind bending. Never ceases to amaze me either.
The 2.17 M_sun figure is instead the hypothesised upper limit on the neutron star mass, derived from the equations of state that survive recent LIGO observations.
Would it just fall right through whatever it's sat on or would it instantly expand into something less dense?
If somehow you could keep it confined, it would drop through whatever it was put on, through the entire Earth, and pop up at the other side. I suppose it would keep oscillating and eventually settle in the core.
Ok, on that note... what would it expand as? I mean, would it be a physical substance, like particles of something like a gas or a plasma?
I assume it'd be quite hot (putting it mildly!)
If kmm's guesstimate of 5e26 joules is accurate, we're well beyond "extinguishing multicellular life" and in the realm of eliminating Earth entirely, which requires a minimum of 5.97e24 joules: https://en.wikipedia.org/wiki/Gravitational_binding_energy 1% efficiency of transfer to the Earth is probably attainable.
The energy density contained within a bit of neutron star matter makes a big explosion, and that will likely dominate over the more exotic processes.
Not sure what that ejecta would look like...but if I had to guess, it would be release a shitload of energy as it came out from under compression, and would eventually condense into normal matter, much of it comprised of the sort of heavy elements not easily created via stellar nucleosynthesis.
Imagine a cloud of incandescent radioactive gold dust weighing as much as multiple earths, and you've got the idea.
Obviously it's time for bed because reading this makes me want to toss a quarter in it to see what happens.
So what you would see is more of a slow fadeout as the object shrinks and gets redder and dimmer, until you can't see anything at all. In the limit as the object gets smaller and the photons get dimmer, you end up with something that emits no light and is the size of the black hole silouette.
In reality, the initial collapse probably won't include all the mass of the object, including any dust or gas orbiting nearby it. So your lovely "fading from sight" black hole will be there, but obscured by the raging maelstrom (always wanted to use that word) of material now circling the plug-hole around it and heated to $DEITY knows what temperature.
throw void into black hole (becomes neutron star)
throw little piece of black hole into neutron star (becomes black hole)
aah. little theory.
blackhole mass can be used to convert neutron star to a blackhole.
A balance between blackhole and neutron star.
2. What would be medieval would be a superstitious reaction to units of measurement as if they were purity religion cult signifiers rather than simple rational concepts to be converted between at will, depending on the task at hand.
English miles aren't.
Also, the conversion wasn't done correctly, there was no need to convert it al all, and SI units are the preferred unit of measurement in science.
And I think that the press release is in error here. There was no radius measurement proposed in the Nature Astronomy paper. However, the radius in the press release is far to large. See:
https://i.imgur.com/Y34OspJ.png (From https://arxiv.org/pdf/1603.02698.pdf)
Something on the order of 6-10 miles for a 2.14 M neutron star is much more appropriate.
Notice that this measurement may rule out some of our models (mostly the gray lines on the left of the chart) that don't predict neutron stars this massive.
In nautical miles it would be closer to 15 ;-)
I love HN comments, but this reminds me of the flame war threads that has very little relationship to the original subject :) Cheers!
I'd be more inclined to use leagues, which, when used at sea, in the English-speaking world, are usually three nautical miles or five point five five six kilometers.
So about 5.39 leagues across.
Since we use ships when we go to space and sea, I like the idea that space ships are naval.
The issue is rather that we don't know what all that star stuff becomes once it goes into the black hole, though there are theories. The problem is that the defining feature of a black hole, its even horizon, by necessity means there is no way of knowing what theory is correct since nothing happening inside is supposed to matter to us.
So before we can make any real progress on the interior of black holes we thus need to figure out exactly in what sense the event horizon leaks information, if it does.
In contrast, while we don't really know what happens to matter inside a neutron star, its surface remains visible to us and so we have been able to discard many different theories about what goes inside it. There is still debate about the precise equation of state, which correspond to different internal structure the various models represent and so different ideas of how a neutron star is made up.
Honestly, I don't know how much difference there are between the various models, but pretty crazy sounding ideas are still popping up, so there must be at least some space left.
Right. As far as "an observer at infinity" is concerned, all that in-falling matter gets asymptotically closer to the event horizon and never crosses it.
One way to reframe the situation which I quite like: Black holes have no insides.
Also, the process that compresses matter to the point it collapses to a black hole is very destructive; there is no reasonable way to form a black hole in the middle of the star.
So we need to find the Meltdown/Specter-like vulnerabilities of black holes? I wonder how many problems that would cause the universe.
(There are nit-picky theoretical ways in which a black hole can evaporate, keyword "Hawking Radiation", but as far as I know that hasn't been observed, because it's too weak and too far away. But even then we learn about its surface/event horizon, not its inside).
This is a "numerical observation", so a simulation. And not of a black hole, but of a model of a black hole in one dimension in a Bose-Einstein-Condensate.
Nobody has created a black hole in a lab and measured its radiation.
But sure, if you want, we can discount that specific study and focus on others that use different methods to detect it that aren't "just simulations"
That way the space expansion in the origin of the universe could just be the black hole forming and quickly eating more mass of its surrounding and thus expanding. Also would explain a lot of things related to lack of anti-matter and such since the part of the outer universe our blackhole ate wouldn't necessarily have an even distribution.
Well, regardless of whether or not our universe is contained within a black hole, basically no one thinks there is literally a singularity of infinite density inside of black holes. It's just what relativity states (and we already know relativity isn't a complete explanation, especially in regards to some of these incredibly extreme situations) and treating black holes like they contain incredibly massive quantities of mass while basically being a point-particle works for all of our day to day purposes.
String theory and loop quantum gravity both explain black holes without needing a singularity, and every astrophysicist that I've spoken to a read comments from discussing this topic has basically said "Yeah, it's not a singularity, we just don't know what it is, and that whole singularity thing is close enough"
What actually happens is that the object shrinks
- according the to the currently accepted models into a single dimensional point. The mass now being confined to a singularity, the gradient of the gravity as you get near becomes extreme, reaching infinity at the singularity. The gradient never could get so extreme before because the mass was diffused over a much bigger volume.
Imagine replacing the Sun with a black hole of equal mass. Apart from the lack of visible light, the gravity we here on Earth would experience would be exactly the same as before, as would every single planet that is currently orbiting. What would change is the distribution of mass inside the sun. The event horizon would be at about 6kms from the Singularity. You could now hypothetically approach the Sun to within ~10km from the center and still stay outside of the event horizon, but the gravity gradient at that point would be unimaginable. The difference in force applied to a the feet and the head of a hypothetical astronaut in orbit would disintegrate them into atoms, which themselves would possibly be squished into spindles.
With the sun as it is currently, even if you could somehow get to within 10kms of the center, the majority of the mass of the sun would be actually outside of this sphere so the net gravity you'd experience would be negligible (compared to the black hole scenario).
The way I picture it, is once you reach the black-hole state, there is a regime change which make it more easy to gulp matter in. I guess how big and how fast it grows depends how much mass there is nearby to concentrate.
Once formed they tend to an equilibrium with their surrounding dictated by the balance mass-in/evaporation-out.
It's true that they don't have a stellar wind that pushes gas away, but they are born in the void left by their progenitor star, and once they start accreting there will be radiation pushing things again.
So, either way the black hole is is sucking up mass faster than a star.
Black holes are not constantly growing.
Hawking radiation for a 1 solar mass black hole represents less than 1 atom of material lost per billion years (~10^67 years vs ~10^57 atoms) They gain more than that even without a noticeable accretion disk inside our current galaxy.
It’s only very very long time frames after black holes collect this material that they start losing mass on average.
From what I've gathered, evaporation seems to be a really slow process. So I figured that it only gets bigger. The remaining question is how fast.
We know there are very big black holes, though they were formed when conditions were different. I was wondering if there were possibility of a small one slowly by accretion growing into one, and was thinking maybe that if you are already very close to the black hole limit, maybe the neighborhood is also crowded and you could start a snow-ball effect.
There is also the dark-matter/dark-energy issue if it exists, when you are a neutron star, you can pass freely but once a black hole you should collect it as you go.
On a scale of atom, this star and black hole what would be the mass density ?
Another fun fact is that the magnetic field energy density alone near the surface of a pulsar (1e12 gauss and up) is about that of lead. (~40 g/cm^3).
A black hole seems to be just the next "step" in terms of something super-massive, but then why are neutron star's more of a mystery?
By contrast, although neutron stars are less "extreme", they end up in a regime where the physics becomes much more difficult. The gravity is strong enough that you still need general relativity, but because the object is extended rather than a singularity, there's also a bunch of "stuff" which needs to be described as well. This means that you need to add in quantum electrodynamics and quantum chromodynamics. Furthermore, it's thought that at these densities you end up with some sort of a superfluid which means you need fluid dynamics and statistical physics to model its behavior, all of which is extremely difficult.
That said, there is another sense in which we could say that black holes are actually more mysterious than neutron stars. Although the physics of neutron stars is very complicated, we at least know what all the fundamental equations are. In the case of black holes if we want to understand physics near the singularity we would need a theory of quantum gravity which we currently don't have.