9 ms·

Neutron stars seem like what you would see in a black hole if the interesting parts weren't shrouded by an event horizon. Although I suppose the event horizon d

by ohazi 5y ago

Neutron stars seem like what you would see in a black hole if the interesting parts weren't shrouded by an event horizon. Although I suppose the event horizon does give you jets. But yeah, city-sized objects with the density of an atomic nucleus. Pretty mind-bending! (literally, I guess?)

ramraj07 5y ago
The “how to build a black hole” video from PBS space time says that’s how you do it - you start with a neutron star and keep adding more mass to it, which paradoxically makes it smaller until it becomes smaller than its swarzchild radius, becoming a black hole. Blew my mind and anyone else’s when I share the video with them! https://youtu.be/xx4562gesw0 https://youtu.be/xx4562gesw0
- cletus 5y ago
  That depends on what size of black hole you want to make. It works for large black holes (you need sufficient mass for the gravitational forces to be sufficient) but those black holes aren’t that useful. Smaller black holes are harder to construct but way more useful.
  - willis936 5y ago
    It's simple, just deflate spacetime!
  - elseweather 5y ago
    I'm curious what useful applications we have for black holes of any size
    - jakeogh 5y ago
      It's assumed that little ones are the most efficient mass to energy converters, via Hawking radiation.
    - cletus 5y ago
      There are actually a lot of theoretical applications. Black holes are likely the most efficient form of power generation that we currently know of. Black hole propulsion may well be the best form of interstellar starship propulsion. Black holes may also be the ultimate computer. If the universe continues based on it current understanding then eventually all the stars will be dead and the universe will be a dark place. The Black hole era will last trillions of time as long but may well be the golden age of civilization. Each of these topics is a rabbit hole.
    - ThrustVectoring 5y ago
      The theoretical limit of how efficiently you can turn energy into useful work depends on how cold your energy sink is. The coldest energy sink in an ever-expanding universe gets colder over time as everything spreads out and the fixed amount of energy occupies more and more space. So the hypothetical optimal end-state of an extremely old civilization is hibernating a bunch of very stable mass until the extreme far future, at which point they can drip-feed it into a black hole to do some extremely efficient computation.
- firebaze 5y ago
  Really don't want to be dismissive, but this guy appears to me as having one gesture (both hands towards the viewer, to underscore the graveness of his words), a good haircut and that's about it. If find it hard to take a presentation like this serious. Most of the mentioned facts are right as far as i can judge it without having a major in physics, but to me this is so very much worse than a link to backreaction (Sabine Hossenfelder), startswithabang (Ethan Siegel) or almost any other serious physics blog out there as anything else. I suppose this will get downvoted, and I'm fine with that, but please explain to me why a self-promoting video guy with probably 5% understanding of the matter compared to a serious pop-sci blog is so relevant to you. Heck, even wikipedia has more information than this clip. And it doesn't cost 13 minutes + ads, just 5 minutes to read. It's not a paradox a neutron star gets smaller the more mass you add to it. This is also true for Jupiter-sized objects; it is a function of density, matter and gravity, and not related (in this case) to special relativity.
  - nynx 5y ago
    Matt O'Dowd is a well-known physicist. I'm not sure why you feel that you can judge him so quickly.
  - ramraj07 5y ago
    I have no idea what you’re talking about? It’s a pbs YouTube channel, the host is a professor in astrophysics and has generally made sure he doesn’t oversimplify anything. I like Sabine’s videos sometimes when she’s not bonkers kookoo but this guys not trying to be controversial.
  - gizmo686 5y ago
    That self-promoting video guy is an astrophysicist, with a significant amount of papers published about black holes. You are free to not like his mass-market material, but from a technical level, he is quite qualified to talk about the subject. https://en.wikipedia.org/wiki/Matt_O%27Dowd_(astrophysicist) https://en.wikipedia.org/wiki/Matt_O%27Dowd_(astrophysicist) https://www.mattodowd.space/ https://www.mattodowd.space/ https://ui.adsabs.harvard.edu/search/p_=0&q=author%3A%22O'Dowd%2C%20M.%20J.%22&sort=date%20desc%2C%20bibcode%20desc https://ui.adsabs.harvard.edu/search/p_=0&q=author%3A%22O'Do...
- hinkley 5y ago
  I've seen a couple astrophysics videos over the last few years that put forward the theory that many black holes are the result of a neutron star forming in a binary or trinary star system. The initial explosion and the ejecta creating a situation where the neutron star begins to siphon material off of its partner.
ravi-delia 5y ago
I was under the possibly incorrect impression that black holes result when the gravitational force is so great that it even overcomes Pauli's exclusion principle, collapsing the neutrons into an overlapping mass of staggering density. Now that I write that out, I'm a little more doubtful.
- btilly 5y ago
  Close. Giant blue stars burn all of the way up to the most stable element of all, which is iron. And then collects an iron core. As the core grows, the star shrinks and the pressure in the middle grows. Once the pressure in the middle is high enough, it overcomes the Pauli exclusion principle and electrons merge with protons to become neutrons with a release of energy, which mostly comes out as neutrinos. Once a bit of that core disappears, the stuff around falls into the new gap, hits it, goes under way more pressure and the same thing happens. This starts a chain reaction that causes a supernova. The core collapses into a neutron star while the release of energy blows the outer shell out to eventually become a nebulae. If the initial star was big enough, the newly created neutron star is big enough to transform into a black hole. Otherwise it is left as a neutron star. If it forms a neutron star, the spin speeds up thanks to the collapse. Typical time to rotate can be anywhere from milliseconds to seconds. We can tell that because its magnetic field also gets trapped and forms a strong beam along the north and south magnetic poles. Since magnetic poles do not generally line up with the rotational poles, that beam becomes like a searchlight. If we're in the path of that beam, we see a pulsar, and the frequency of the pulsar is the rotational speed of the neutron star. This is probably way more than you wanted to know. :-) I probably also am going to get corrected on some details in 3, 2, 1...
  - hinkley 5y ago
    I was shocked to learn how long it takes a photon produced at the center of the sun by a fusion event to reach earth. The layers upon layers of subatomic particles that are all interacting in these tight quarters is simply astounding. I've heard this same theory on supernovas from a number of people in or around physics, but I always wonder how handwavy it is, whether we actually understand how that works yet, and how different (confusing) the real process is from the given one.
CuriouslyC 5y ago
Imagine if black holes were just neutron stars made of second or third generation quark "neutrons."
hinkley 5y ago
I remember the infinities of black holes being a challenge to explain to my artsy friends after reading A Brief History of Time. Correct me if I'm wrong, but isn't the curvature of space around - and within - a neutron star substantial enough that euclidean geometry doesn't really hold anymore? The volume of a basketball is the surface area x R/3, but is that true of a neutron star? I was under the impression that the difference between Euclid and actual was statistically significant, to the point that you get the wrong behavior if you don't account for it.

by ohazi 5y ago

ramraj07 5y ago

The “how to build a black hole” video from PBS space time says that’s how you do it - you start with a neutron star and keep adding more mass to it, which paradoxically makes it smaller until it becomes smaller than its swarzchild radius, becoming a black hole. Blew my mind and anyone else’s when I share the video with them! https://youtu.be/xx4562gesw0 https://youtu.be/xx4562gesw0

cletus 5y ago
That depends on what size of black hole you want to make. It works for large black holes (you need sufficient mass for the gravitational forces to be sufficient) but those black holes aren’t that useful. Smaller black holes are harder to construct but way more useful.
- willis936 5y ago
  It's simple, just deflate spacetime!
- elseweather 5y ago
  I'm curious what useful applications we have for black holes of any size
  - jakeogh 5y ago
    It's assumed that little ones are the most efficient mass to energy converters, via Hawking radiation.
  - cletus 5y ago
    There are actually a lot of theoretical applications. Black holes are likely the most efficient form of power generation that we currently know of. Black hole propulsion may well be the best form of interstellar starship propulsion. Black holes may also be the ultimate computer. If the universe continues based on it current understanding then eventually all the stars will be dead and the universe will be a dark place. The Black hole era will last trillions of time as long but may well be the golden age of civilization. Each of these topics is a rabbit hole.
  - ThrustVectoring 5y ago
    The theoretical limit of how efficiently you can turn energy into useful work depends on how cold your energy sink is. The coldest energy sink in an ever-expanding universe gets colder over time as everything spreads out and the fixed amount of energy occupies more and more space. So the hypothetical optimal end-state of an extremely old civilization is hibernating a bunch of very stable mass until the extreme far future, at which point they can drip-feed it into a black hole to do some extremely efficient computation.
firebaze 5y ago
Really don't want to be dismissive, but this guy appears to me as having one gesture (both hands towards the viewer, to underscore the graveness of his words), a good haircut and that's about it. If find it hard to take a presentation like this serious. Most of the mentioned facts are right as far as i can judge it without having a major in physics, but to me this is so very much worse than a link to backreaction (Sabine Hossenfelder), startswithabang (Ethan Siegel) or almost any other serious physics blog out there as anything else. I suppose this will get downvoted, and I'm fine with that, but please explain to me why a self-promoting video guy with probably 5% understanding of the matter compared to a serious pop-sci blog is so relevant to you. Heck, even wikipedia has more information than this clip. And it doesn't cost 13 minutes + ads, just 5 minutes to read. It's not a paradox a neutron star gets smaller the more mass you add to it. This is also true for Jupiter-sized objects; it is a function of density, matter and gravity, and not related (in this case) to special relativity.
- nynx 5y ago
  Matt O'Dowd is a well-known physicist. I'm not sure why you feel that you can judge him so quickly.
- ramraj07 5y ago
  I have no idea what you’re talking about? It’s a pbs YouTube channel, the host is a professor in astrophysics and has generally made sure he doesn’t oversimplify anything. I like Sabine’s videos sometimes when she’s not bonkers kookoo but this guys not trying to be controversial.
- gizmo686 5y ago
  That self-promoting video guy is an astrophysicist, with a significant amount of papers published about black holes. You are free to not like his mass-market material, but from a technical level, he is quite qualified to talk about the subject. https://en.wikipedia.org/wiki/Matt_O%27Dowd_(astrophysicist) https://en.wikipedia.org/wiki/Matt_O%27Dowd_(astrophysicist) https://www.mattodowd.space/ https://www.mattodowd.space/ https://ui.adsabs.harvard.edu/search/p_=0&q=author%3A%22O'Dowd%2C%20M.%20J.%22&sort=date%20desc%2C%20bibcode%20desc https://ui.adsabs.harvard.edu/search/p_=0&q=author%3A%22O'Do...
hinkley 5y ago
I've seen a couple astrophysics videos over the last few years that put forward the theory that many black holes are the result of a neutron star forming in a binary or trinary star system. The initial explosion and the ejecta creating a situation where the neutron star begins to siphon material off of its partner.

ravi-delia 5y ago

I was under the possibly incorrect impression that black holes result when the gravitational force is so great that it even overcomes Pauli's exclusion principle, collapsing the neutrons into an overlapping mass of staggering density. Now that I write that out, I'm a little more doubtful.

btilly 5y ago
Close. Giant blue stars burn all of the way up to the most stable element of all, which is iron. And then collects an iron core. As the core grows, the star shrinks and the pressure in the middle grows. Once the pressure in the middle is high enough, it overcomes the Pauli exclusion principle and electrons merge with protons to become neutrons with a release of energy, which mostly comes out as neutrinos. Once a bit of that core disappears, the stuff around falls into the new gap, hits it, goes under way more pressure and the same thing happens. This starts a chain reaction that causes a supernova. The core collapses into a neutron star while the release of energy blows the outer shell out to eventually become a nebulae. If the initial star was big enough, the newly created neutron star is big enough to transform into a black hole. Otherwise it is left as a neutron star. If it forms a neutron star, the spin speeds up thanks to the collapse. Typical time to rotate can be anywhere from milliseconds to seconds. We can tell that because its magnetic field also gets trapped and forms a strong beam along the north and south magnetic poles. Since magnetic poles do not generally line up with the rotational poles, that beam becomes like a searchlight. If we're in the path of that beam, we see a pulsar, and the frequency of the pulsar is the rotational speed of the neutron star. This is probably way more than you wanted to know. :-) I probably also am going to get corrected on some details in 3, 2, 1...
- hinkley 5y ago
  I was shocked to learn how long it takes a photon produced at the center of the sun by a fusion event to reach earth. The layers upon layers of subatomic particles that are all interacting in these tight quarters is simply astounding. I've heard this same theory on supernovas from a number of people in or around physics, but I always wonder how handwavy it is, whether we actually understand how that works yet, and how different (confusing) the real process is from the given one.

CuriouslyC 5y ago

Imagine if black holes were just neutron stars made of second or third generation quark "neutrons."

hinkley 5y ago

I remember the infinities of black holes being a challenge to explain to my artsy friends after reading A Brief History of Time. Correct me if I'm wrong, but isn't the curvature of space around - and within - a neutron star substantial enough that euclidean geometry doesn't really hold anymore? The volume of a basketball is the surface area x R/3, but is that true of a neutron star? I was under the impression that the difference between Euclid and actual was statistically significant, to the point that you get the wrong behavior if you don't account for it.