6 ms·

Scientists discover the highest energy gamma-rays ever from a pulsar

45 points by wglb 3y ago

asicsp 3y ago
>These dead stars are almost entirely made up of neutrons and are incredibly dense: a teaspoon of their material has a mass of more than five billion tons, or about 900 times the mass of the Great Pyramid of Giza Five billion tons packed within a teaspoon volume!? Incredible.
- tomohelix 3y ago
  When it comes to cosmic scales, it is literally unimaginable by the puny human mind. I don't know about others but I frankly can't really comprehend what does the mass of an entire mountain condensed into a single pebble mean. And there are stars full of this stuff. And there are stars spinning so fast its magnetic waves would rip the iron out of my blood and destroy the physics that hold my atoms together just because I am standing a few billions miles away from it. It is absolutely humbling and make it ridiculous to think that there were men ages ago who thought the universe was created solely for human and somehow we, the sacks of meat so fragile it bursts at every miniscule amount of agitation, were "made" as some special, supreme beings in the universe and all of creations. Hilarious and sad.
  - JackFr 3y ago
    [flagged]
    - tomohelix 3y ago
      [flagged]
      - JackFr 3y ago
        Apologies. My response was too snarky and too clever by half. My point was that it’s easy to miss our own hubris when measuring our present ideas against the past, and that a bit of circumspection is well taken.
        swayvil 3y ago
        The ancients thought that space was filled with giant balls of glowing gas. What fools they were.
      - deleted 3y ago
        [deleted]
  - mikub 3y ago
    I find all this really incredible as well. But at the same time I also find it really 'mindblowing' that I am able to think about why and how all of this stuff was made, and while thinking about it, there will always come a point where you have to at least 'think' about an creator. Not that I think it was made especially for us, but it's still very strange. Somewhere I read when you think about the universe it is like "The Universe thinking about itself.".
    - tomohelix 3y ago
      I agree. I actually think that is a very common thought, at least from what I have seen with my colleagues who are mostly scientists in engineering and biotech. It could be because of our background but the kind of complexity and seemingly genius engineering solutions in some biological systems just boggle the mind and make us question how it happened. We often handwave them with evolution and sure we can come up with some ideas of how it actually evolved but at some point I personally felt some explanations we got became too contrived and overly convenient and nearly unfalsifiable... To be honest though, I still don't think a creator is absolutely necessary. But I also think there is nothing wrong with the idea that there is one. I just personally don't think this creator, if exist, would belong to any of the major religion out there.
      - FluffyClouds 3y ago
        We are a tad beyond handwaving, but with all the information overload it's hard to recognize scientific breakthroughs anymore. Anyway thermodynamics did it. https://arxiv.org/abs/1203.3271 https://arxiv.org/abs/1203.3271 Most people won't like this answer, because it's too impersonal. Thus the search for a more inspiring origin story continues. There is no drama in thermodynamics, no love, no revenge, although there are explosions.
        tomohelix 3y ago
        That is a great paper! Yes, from my engineering school I know if we dig deep enough, it would all be thermodynamics. But I was not sure if anyone dig that deep yet. This paper seems to be deeper than what I thought was done. Strange how I didn't see it, seems very relevant especially with all the LLM rage these days.
  - hollander 3y ago
    > I frankly can't really comprehend what does the mass of an entire mountain condensed into a single pebble mean. Maybe turn it around. On a cosmic level, that mountain is nothing but a fluff of cottonwool, the earth a hot air balloon.
    - ourmandave 3y ago
      Or turn around again. Zoom out far enough and maybe there's a view where the pulsar is comparably no more that a lit sparkler. Note: This isn't an argument for god or whatever. Just thinking on scales where our "laughing in the rain" is a nightmare for ants.
      - itishappy 3y ago
        That's us! We're not bathed in pulsar brilliance, we're picking up the sparse but energetic photons it emits from far far away. We cannot see the "highest energy pulsar" with our naked eyes.
      - swayvil 3y ago
        >This isn't an argument for god or whatever... It better not be. This is a proper orthodox forum.
  - rad_gruchalski 3y ago
    Paraphrasing: There are 100 billion galaxies in the observable universe, each galaxy contains approximately 100 billion of stars. It takes 100s of thousands years travelling at the speed of light to get from one end of the galaxy to the other. It takes 100s of millions to billions of years to get from one galaxy to another. And all those galaxies are moving away from each other at mind boggling speeds 73 kilometres per second. It’s humbling. And we kill each other for silly reasons. We are so significant, yet so insignificant.
    - Aerroon 3y ago
      >It takes 100s of thousands years travelling at the speed of light to get from one end of the galaxy to the other. The crazy thing is that at a constant 1g acceleration you could get to the Andromeda galaxy in your lifetime. Andromeda might be 4 million light years away, but relativistic effects mean that only about 30 years would pass for you. Of course, constant 1g acceleration would require an unimaginable amount of energy (and something to thrust with). At 1.5g-s you could make it in 20.
  - swayvil 3y ago
    I dunno man. Every generation thinks they have the answers and that their ancestors were fools.
  - itishappy 3y ago
    > When it comes to cosmic scales, it is literally unimaginable by the puny human mind. One of my favorite mind-benders is that on some level, we embody cosmic scales of our own. The "biggest length" is our observable universe is 10^26 m. The "smallest length" is the Plank length at 10^-35 m. That puts the "middle length" at about a millimeter, or (very roughly) human scale.
  - stronglikedan 3y ago
    > what does the mass of an entire mountain condensed into a single pebble mean I find it easier to comprehend in the subatomic context, picturing the space between particles like the space between stars and planets on the cosmic scale. Mash all the stars and planets together in, say, our solar system, and the entire solar system would only be about the size of the sun. Then repeat that for all the solar systems in the Milky Way, and the entire Milky Way would only be about the size of the black hole at the center. Relatively, of course!
  - swayvil 3y ago
    Your ideas about the world are drawn from what you see. Maybe you see something they didn't see. Maybe they see something you didn't see.
- op00to 3y ago
  It is now that I recommend you read Dragons Egg, a hard sci-fi book about a species that evolved on the surface of a neutron star. I am contractually obligated to mention this any time I hear neutron stars mentioned.
  - automatic6131 3y ago
    That must have inspired Stephen Baxter's Flux, which is about artificial humans, living just inside the skin of a neutron star.
    - op00to 3y ago
      thank you for the recommendation! :)
- nine_k 3y ago
  Matter is mostly empty space. Atomic nuclei are small, the electron clouds around them are pretty far away. From this point if view, ordinary matter is more like foam, or aerogel, with very little matter spread over a large volume. Neutron stars are made if matter with very little empty space embedded into it. This is why they are so small.
comboy 3y ago
So I was wondering if it could be that at the point of measurement it was moving very fast towards us. Napkin math says for photons to have 200 times more energy than expected it would need to be moving at 0.99995c. Huh.
- sime2009 3y ago
  It's a photon. Photons always have speed = 1C.
  - tux3 3y ago
    (in a vacuum)
  - StevenHarlow 3y ago
    Technically no, photons don't always have a speed of 1C, as C is the speed of light _in a vacuum_. In more dense matter the speed of light will slow down.
    - uoaei 3y ago
      Technically true and also completely irrelevant for this thread.
      - deleted 3y ago
        [deleted]
  - rainbowzootsuit 3y ago
    "If the emitter is coming towards us that would blue-shift photons," is, I think, the point of the previous person's comment.
  - comboy 3y ago
    I'm talking about the pulsar speed. https://en.wikipedia.org/wiki/Relativistic_Doppler_effect https://en.wikipedia.org/wiki/Relativistic_Doppler_effect
  - 3y ago
deleted 3y ago
[deleted]
nullandvoid 3y ago
I have a question - what would happen if you were to drop one of these spoons of matter that weigh 5 billion tonnes onto the floor right now, where would it stop?
- c4mpute 3y ago
  It would sink into the center of the earth and then oscillate around the center until friction stops it dead center. Materials in the earth's crust and mantle are not strong enough to stop that mass from sinking ever deeper. But that assumes that this spoon of matter were stable in that state, which it isn't. That kind of density can only be held up with some force like gravity keeping up the pressure. The gravity of that spoonful is insufficient, so the internal pressure will drive apart the neutrons. The effects would probably look like a very very large nuke or large asteroid impact.
  - ben_w 3y ago
    Very large asteroid, too big for a nuke: https://www.wolframalpha.com/input?i=%280.782343+MeV+%2F+neutron+mass%29+*+5e12+kg+in+megatons+of+TNT+equivalent+ https://www.wolframalpha.com/input?i=%280.782343+MeV+%2F+neu... ~89 billion megatons of TNT equivalent
    - raattgift 3y ago
      What motivates your first factor? 0.782343 MeV is the free neutron beta decay; where in the solar system are the free neutrons minutes after they are magically teleported to terrestrial ground zero as a something like a (degenerate, possibly ultra-relativistic) Fermi gas? I think most attempts to arrive at an answer will end up somewhere between half and virtually all of them being "not very close" (~ light-minutes) away, and that's assuming one corrects for the differences in escape velocities. (The equatorial escape velocity of a spinning neutron star is in tenths of the speed of light, thus the sobriquet "relativistic star"). Without this correction, it is likely the bulk of the expanding drop of Fermi gas just exits the atmosphere in milliseconds (timed by terrestrial stopwatches), with time dilation extending the mean lifetime of the free neutrons in the drop comparably to the extended lifetime of atmospheric muons from cosmic rays. The bulk of the beta decays happen at a distance from terrestrial ground zero best measured in astronomical units. If we play Star Trek transporter games such that the neutrons arrive at ground zero at rest in local East-North-Up coordinates, you'd want to know the internal kinetic energy (KE) density of the (pure-)neutron star, which will be in the range of 20-40 for x in 10^{x} J m^-3. The 10^25ish or even 10^30ish joules of KE will be released from our several cm^3 spoonful practically all at once and practically omnidirectionally from ground zero (so again, most free neutron decays happen at ~ AU distances from ground zero because they'll zip right through the atmosphere). The expansion of the suddenly unpressurized gas of neutrons will make a mess, particularly the fraction that slams into and through the ground. Part of the mess is neutron scattering physics, and I have no expertise there, but I would guess there wouldn't be any free neutrons near ground zero (and probably not within the solid Earth) in ~minutes. Additionally, one might compare the R-process <https://en.wikipedia.org/wiki/R-process https://en.wikipedia.org/wiki/R-process> for kilonovas in which a binary neutron star collision ejects high-neutron-density matter which decompresses pretty spectacularly, forming lots of heavy elements. To summarize, I think the free neutron decay timescale (mean lifetime ~ 15 minutes, multiply by ln 2 if you prefer half-life) is simply too long after the neutron star material is teleported to Earth: any free neutrons that haven't been absorbed into heavy nuclei likely will be millions of kilometres away from ground zero when they decay.
chasil 3y ago
The Vela pulsar is also quite famous for being one of six known optical pulsars (the most famous being the Crab). https://en.wikipedia.org/wiki/Optical_pulsar https://en.wikipedia.org/wiki/Optical_pulsar "It has the third-brightest optical component of all known pulsars (V = 23.6 mag) which pulses twice for every single radio pulse. The Vela pulsar is the brightest persistent object in the high-energy gamma-ray sky... "Glitches are sudden spin-ups in the rotation of pulsars. Vela is the best known of all the glitching pulsars, with glitches occurring on average every three years. https://en.wikipedia.org/wiki/Vela_Pulsar https://en.wikipedia.org/wiki/Vela_Pulsar
deleted 3y ago
[deleted]

45 points by wglb 3y ago

>These dead stars are almost entirely made up of neutrons and are incredibly dense: a teaspoon of their material has a mass of more than five billion tons, or about 900 times the mass of the Great Pyramid of Giza Five billion tons packed within a teaspoon volume!? Incredible.

tomohelix 3y ago
When it comes to cosmic scales, it is literally unimaginable by the puny human mind. I don't know about others but I frankly can't really comprehend what does the mass of an entire mountain condensed into a single pebble mean. And there are stars full of this stuff. And there are stars spinning so fast its magnetic waves would rip the iron out of my blood and destroy the physics that hold my atoms together just because I am standing a few billions miles away from it. It is absolutely humbling and make it ridiculous to think that there were men ages ago who thought the universe was created solely for human and somehow we, the sacks of meat so fragile it bursts at every miniscule amount of agitation, were "made" as some special, supreme beings in the universe and all of creations. Hilarious and sad.
- JackFr 3y ago
  [flagged]
  - tomohelix 3y ago
    [flagged]
    - JackFr 3y ago
      Apologies. My response was too snarky and too clever by half. My point was that it’s easy to miss our own hubris when measuring our present ideas against the past, and that a bit of circumspection is well taken.
      - swayvil 3y ago
        The ancients thought that space was filled with giant balls of glowing gas. What fools they were.
    - deleted 3y ago
      [deleted]
- mikub 3y ago
  I find all this really incredible as well. But at the same time I also find it really 'mindblowing' that I am able to think about why and how all of this stuff was made, and while thinking about it, there will always come a point where you have to at least 'think' about an creator. Not that I think it was made especially for us, but it's still very strange. Somewhere I read when you think about the universe it is like "The Universe thinking about itself.".
  - tomohelix 3y ago
    I agree. I actually think that is a very common thought, at least from what I have seen with my colleagues who are mostly scientists in engineering and biotech. It could be because of our background but the kind of complexity and seemingly genius engineering solutions in some biological systems just boggle the mind and make us question how it happened. We often handwave them with evolution and sure we can come up with some ideas of how it actually evolved but at some point I personally felt some explanations we got became too contrived and overly convenient and nearly unfalsifiable... To be honest though, I still don't think a creator is absolutely necessary. But I also think there is nothing wrong with the idea that there is one. I just personally don't think this creator, if exist, would belong to any of the major religion out there.
    - FluffyClouds 3y ago
      We are a tad beyond handwaving, but with all the information overload it's hard to recognize scientific breakthroughs anymore. Anyway thermodynamics did it. https://arxiv.org/abs/1203.3271 https://arxiv.org/abs/1203.3271 Most people won't like this answer, because it's too impersonal. Thus the search for a more inspiring origin story continues. There is no drama in thermodynamics, no love, no revenge, although there are explosions.
      - tomohelix 3y ago
        That is a great paper! Yes, from my engineering school I know if we dig deep enough, it would all be thermodynamics. But I was not sure if anyone dig that deep yet. This paper seems to be deeper than what I thought was done. Strange how I didn't see it, seems very relevant especially with all the LLM rage these days.
- hollander 3y ago
  > I frankly can't really comprehend what does the mass of an entire mountain condensed into a single pebble mean. Maybe turn it around. On a cosmic level, that mountain is nothing but a fluff of cottonwool, the earth a hot air balloon.
  - ourmandave 3y ago
    Or turn around again. Zoom out far enough and maybe there's a view where the pulsar is comparably no more that a lit sparkler. Note: This isn't an argument for god or whatever. Just thinking on scales where our "laughing in the rain" is a nightmare for ants.
    - itishappy 3y ago
      That's us! We're not bathed in pulsar brilliance, we're picking up the sparse but energetic photons it emits from far far away. We cannot see the "highest energy pulsar" with our naked eyes.
    - swayvil 3y ago
      >This isn't an argument for god or whatever... It better not be. This is a proper orthodox forum.
- rad_gruchalski 3y ago
  Paraphrasing: There are 100 billion galaxies in the observable universe, each galaxy contains approximately 100 billion of stars. It takes 100s of thousands years travelling at the speed of light to get from one end of the galaxy to the other. It takes 100s of millions to billions of years to get from one galaxy to another. And all those galaxies are moving away from each other at mind boggling speeds 73 kilometres per second. It’s humbling. And we kill each other for silly reasons. We are so significant, yet so insignificant.
  - Aerroon 3y ago
    >It takes 100s of thousands years travelling at the speed of light to get from one end of the galaxy to the other. The crazy thing is that at a constant 1g acceleration you could get to the Andromeda galaxy in your lifetime. Andromeda might be 4 million light years away, but relativistic effects mean that only about 30 years would pass for you. Of course, constant 1g acceleration would require an unimaginable amount of energy (and something to thrust with). At 1.5g-s you could make it in 20.
- swayvil 3y ago
  I dunno man. Every generation thinks they have the answers and that their ancestors were fools.
- itishappy 3y ago
  > When it comes to cosmic scales, it is literally unimaginable by the puny human mind. One of my favorite mind-benders is that on some level, we embody cosmic scales of our own. The "biggest length" is our observable universe is 10^26 m. The "smallest length" is the Plank length at 10^-35 m. That puts the "middle length" at about a millimeter, or (very roughly) human scale.
- stronglikedan 3y ago
  > what does the mass of an entire mountain condensed into a single pebble mean I find it easier to comprehend in the subatomic context, picturing the space between particles like the space between stars and planets on the cosmic scale. Mash all the stars and planets together in, say, our solar system, and the entire solar system would only be about the size of the sun. Then repeat that for all the solar systems in the Milky Way, and the entire Milky Way would only be about the size of the black hole at the center. Relatively, of course!
- swayvil 3y ago
  Your ideas about the world are drawn from what you see. Maybe you see something they didn't see. Maybe they see something you didn't see.
op00to 3y ago
It is now that I recommend you read Dragons Egg, a hard sci-fi book about a species that evolved on the surface of a neutron star. I am contractually obligated to mention this any time I hear neutron stars mentioned.
- automatic6131 3y ago
  That must have inspired Stephen Baxter's Flux, which is about artificial humans, living just inside the skin of a neutron star.
  - op00to 3y ago
    thank you for the recommendation! :)
nine_k 3y ago
Matter is mostly empty space. Atomic nuclei are small, the electron clouds around them are pretty far away. From this point if view, ordinary matter is more like foam, or aerogel, with very little matter spread over a large volume. Neutron stars are made if matter with very little empty space embedded into it. This is why they are so small.

comboy 3y ago

So I was wondering if it could be that at the point of measurement it was moving very fast towards us. Napkin math says for photons to have 200 times more energy than expected it would need to be moving at 0.99995c. Huh.

sime2009 3y ago
It's a photon. Photons always have speed = 1C.
- tux3 3y ago
  (in a vacuum)
- StevenHarlow 3y ago
  Technically no, photons don't always have a speed of 1C, as C is the speed of light _in a vacuum_. In more dense matter the speed of light will slow down.
  - uoaei 3y ago
    Technically true and also completely irrelevant for this thread.
    - deleted 3y ago
      [deleted]
- rainbowzootsuit 3y ago
  "If the emitter is coming towards us that would blue-shift photons," is, I think, the point of the previous person's comment.
- comboy 3y ago
  I'm talking about the pulsar speed. https://en.wikipedia.org/wiki/Relativistic_Doppler_effect https://en.wikipedia.org/wiki/Relativistic_Doppler_effect
- 3y ago

deleted 3y ago

[deleted]

nullandvoid 3y ago

I have a question - what would happen if you were to drop one of these spoons of matter that weigh 5 billion tonnes onto the floor right now, where would it stop?

c4mpute 3y ago
It would sink into the center of the earth and then oscillate around the center until friction stops it dead center. Materials in the earth's crust and mantle are not strong enough to stop that mass from sinking ever deeper. But that assumes that this spoon of matter were stable in that state, which it isn't. That kind of density can only be held up with some force like gravity keeping up the pressure. The gravity of that spoonful is insufficient, so the internal pressure will drive apart the neutrons. The effects would probably look like a very very large nuke or large asteroid impact.
- ben_w 3y ago
  Very large asteroid, too big for a nuke: https://www.wolframalpha.com/input?i=%280.782343+MeV+%2F+neutron+mass%29+*+5e12+kg+in+megatons+of+TNT+equivalent+ https://www.wolframalpha.com/input?i=%280.782343+MeV+%2F+neu... ~89 billion megatons of TNT equivalent
  - raattgift 3y ago
    What motivates your first factor? 0.782343 MeV is the free neutron beta decay; where in the solar system are the free neutrons minutes after they are magically teleported to terrestrial ground zero as a something like a (degenerate, possibly ultra-relativistic) Fermi gas? I think most attempts to arrive at an answer will end up somewhere between half and virtually all of them being "not very close" (~ light-minutes) away, and that's assuming one corrects for the differences in escape velocities. (The equatorial escape velocity of a spinning neutron star is in tenths of the speed of light, thus the sobriquet "relativistic star"). Without this correction, it is likely the bulk of the expanding drop of Fermi gas just exits the atmosphere in milliseconds (timed by terrestrial stopwatches), with time dilation extending the mean lifetime of the free neutrons in the drop comparably to the extended lifetime of atmospheric muons from cosmic rays. The bulk of the beta decays happen at a distance from terrestrial ground zero best measured in astronomical units. If we play Star Trek transporter games such that the neutrons arrive at ground zero at rest in local East-North-Up coordinates, you'd want to know the internal kinetic energy (KE) density of the (pure-)neutron star, which will be in the range of 20-40 for x in 10^{x} J m^-3. The 10^25ish or even 10^30ish joules of KE will be released from our several cm^3 spoonful practically all at once and practically omnidirectionally from ground zero (so again, most free neutron decays happen at ~ AU distances from ground zero because they'll zip right through the atmosphere). The expansion of the suddenly unpressurized gas of neutrons will make a mess, particularly the fraction that slams into and through the ground. Part of the mess is neutron scattering physics, and I have no expertise there, but I would guess there wouldn't be any free neutrons near ground zero (and probably not within the solid Earth) in ~minutes. Additionally, one might compare the R-process <https://en.wikipedia.org/wiki/R-process https://en.wikipedia.org/wiki/R-process> for kilonovas in which a binary neutron star collision ejects high-neutron-density matter which decompresses pretty spectacularly, forming lots of heavy elements. To summarize, I think the free neutron decay timescale (mean lifetime ~ 15 minutes, multiply by ln 2 if you prefer half-life) is simply too long after the neutron star material is teleported to Earth: any free neutrons that haven't been absorbed into heavy nuclei likely will be millions of kilometres away from ground zero when they decay.

chasil 3y ago

The Vela pulsar is also quite famous for being one of six known optical pulsars (the most famous being the Crab). https://en.wikipedia.org/wiki/Optical_pulsar https://en.wikipedia.org/wiki/Optical_pulsar "It has the third-brightest optical component of all known pulsars (V = 23.6 mag) which pulses twice for every single radio pulse. The Vela pulsar is the brightest persistent object in the high-energy gamma-ray sky... "Glitches are sudden spin-ups in the rotation of pulsars. Vela is the best known of all the glitching pulsars, with glitches occurring on average every three years. https://en.wikipedia.org/wiki/Vela_Pulsar https://en.wikipedia.org/wiki/Vela_Pulsar

deleted 3y ago

[deleted]