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

phys.org

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

#41

Post by swayvil »

tomohelix wrote: post #4
asicsp wrote: post #2

> 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.

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 becau…

I dunno man. Every generation thinks they have the answers and that their ancestors were fools.

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

#42

Post by lazide »

sime2009 wrote: post #7
comboy wrote: post #3

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.

It's a photon. Photons always have speed = 1C.

Blueshift == relative speed difference, which manifests for a photon in the form of more energy in the form of a shorter wavelength no? Gamma rays being an extreme example.

That much blueshift means that much more relative speed towards us.

Redshift being the corresponding speed difference ‘away’.

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

#44

Post by [deleted] »

uoaei wrote: post #13
StevenHarlow wrote: post #10

Earlier quoted context omitted.

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.

Technically true and also completely irrelevant for this thread.

[deleted]

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

#45

Post by swayvil »

JackFr wrote: post #25
tomohelix wrote: post #12

Earlier quoted context omitted.

[flagged]

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.

The ancients thought that space was filled with giant balls of glowing gas. What fools they were.

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

#46

Post by chasil »

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

"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

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

#47

Post by Aerroon »

rad_gruchalski wrote: post #23
tomohelix wrote: post #4

Earlier quoted context omitted.

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 becau…

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 p…

>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.

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

#49

Post by ben_w »

raattgift wrote: post #40
ben_w wrote: post #20

Earlier quoted context omitted.

Very large asteroid, too big for a nuke: https://www.wolframalpha.com/input?i=%280.782343+MeV+%2F+neu... ~89 billion megatons of TNT equivalent

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)…

> 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

Mean free path of free neutrons moving past normal matter is only in the order of centimetres, exactly how many centimetres depends on the neutron energy and the specific nuclei it's interacting with, but still order of centimetres.

Given the relative masses, I can assume the air above will be exploded out of the way; but the half going down will have all of the earth as a moderator… and also serve as a neutron-absorbing backstop that will probably increase the actual yield.

I'm also ignoring any binding energy between the neutrons. I'm basically treating them as disconnected from the first moment, which may be a terrible idea, but AFAIK nobody actually knows how long a macroscopic combination of this scale would remain stable for.

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

#50

Post by ben_w »

AnimalMuppet wrote: post #32
johndunne wrote: post #27

Earlier quoted context omitted.

Black hole's aren't matter, they're pure gravitational binding energy. A neutron star becomes a black hole when the neutrons pushing against each other can't push back at the gravitational forces (neutron degeneracy pressure) and the neutrons do something we're not sure of... but whatever happens, they're crushed down into something smaller than a neutron star; into a singuality and we see the result.. a black hole.…

> Black hole's aren't matter, they're pure gravitational binding energy. Could you expand on this a bit? What exactly do you mean, and what is your basis for saying that it's true?

In GR, black holes have only three distinguishable properties: mass, charge, and angular momentum. If you have one made from matter, one from antimatter, and one from sufficiently concentrated light, all three are indistinguishable.

As I'm not a physicist, I wouldn't risk phrasing this as "pure gravitational binding energy" just in case this has a specific and different meaning.

I read the interior of an event horizon immediately causes problems with quantum mechanics' no-cloning rule, so I suspect the actual problem here is "QM and GR are fighting again" and we can't get any answer until we've resolved that.

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