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38 votes
5 answers
7k views

How exactly does Hawking radiation decrease the mass of black holes?

From what I understand so far, when one of virtual particles crosses the event horizon and the other does not, they can not annihilate each other. The latter wanders off into the universe (btw, is it ...
marko-36's user avatar
  • 621
21 votes
1 answer
492 views

Dark Matter Particle Candidates

Dark matter appears to dominate the matter component of the universe as compared to luminous, or baryonic, matter. Though it does not interact electromagnetically (it doesn't absorb, scatter, or emit ...
astromax's user avatar
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9 votes
1 answer
383 views

How are neutrinos produced in blazar jets?

I was watching the press release about measuring neutrinos and gamma rays from a distant blazar. One of the presenters mentioned that the neutrinos are associated with very high energy protons caught ...
PSR-1937-21's user avatar
9 votes
1 answer
177 views

What is happening with these solar particles detected near the Sun that is so newsworthy?

Phys.org's Team identifies low-energy solar particles from beyond Earth near the Sun links to the open access ApJ article Properties of Suprathermal-through-energetic He Ions Associated with Stream ...
uhoh's user avatar
  • 30.6k
5 votes
2 answers
839 views

Hubble expansion rate and reaction rates

I've come across sentences like ...the reaction rates (the number of reactions per particle per unit time) must be larger than the cosmic expansion rate $H(t)$ in order for the particles to maintain ...
Arnab Chowdhury's user avatar
5 votes
2 answers
189 views

Directionality of solar flares

I have read a number of articles about Coronal Mass Ejections (CME) and solar flares and I’m trying to establish how directional the radiation from them is. I am aware that radiation from these solar ...
Slarty's user avatar
  • 359
4 votes
1 answer
467 views

Have there been studies of "old photons" to see just how constant things like Planck constant has been?

The question Are photons aged? and answers therein have got me thinking: I vaguely remember hearing something about experiments where "old photons" were collected by large telescopes from very ...
uhoh's user avatar
  • 30.6k
4 votes
1 answer
245 views

Could Sgr A* be a core of dark matter instead of a supermassive black hole?

A recent paper (related news) shows that Sgr A* at the center of the Milky Way galaxy could be a dark matter core, instead of a supermassive black hole, according to their calculation using the ...
NeutronCat's user avatar
4 votes
1 answer
102 views

What are the sources of antimatter particles in the magnetosphere?

The PAMELA instrument detected antimatter particles in the Earth's magnetosphere. What are the sources of these particles? The answer to Source of high energy cosmic particles outlines the sources ...
Dave Gremlin's user avatar
  • 1,071
4 votes
0 answers
39 views

Total scattered flux and polarization for a ring of dust particles close to a star

I have an important problem and maybe some of you can help me with the following question: I have a mathematical expression for the total scattered flux in Jansky and the total linear polarized flux (...
Lyapunov's user avatar
3 votes
1 answer
136 views

When two galaxies with dark matter halos merge do they provide evidence for fermionic or bosonic dark matter?

If dark matter is made from fermions these should collide and cause dark matter to become denser in some places than others Bosons wont collide in this way so there should a different effect .So is ...
user avatar
3 votes
1 answer
101 views

What consequences does a positive muon anomalous magnetic moment have for astronomy?

On April 7th, 2021, the muon $(g-2)$ collaboration published Measurement of the Positive Muon Anomalous Magnetic Moment to 0.46 ppm, a result which made it to standard news, partly under headlines ...
B--rian's user avatar
  • 5,616
2 votes
1 answer
321 views

If w bosons can create dark matter neutrinos by decay, can they also create dark energy?

Dark energy is often associated with vacuum energy fluctuations. But the experimentally measured Casimir effect suggests that there is almost no vacuum energy.Because most of the vacuum energy is ...
user avatar
2 votes
0 answers
77 views

How do we know or predict which particles were present before Big Bang Nucleosynthesis occurred?

I'm reading Carroll and Ostlie's "An Introduction to Modern Astrophysics". In the BBN section, they describe that the universe contains a mixture of photons, electron-positron pairs, and ...
Astroturf's user avatar
  • 1,111
1 vote
4 answers
434 views

Absorption of light by matter

What determines whether or not photons can be absorbed by matter? Intuitively, the answer is that a charged particle can absorb photons (whether it's positively or negatively charged), and neutral ...
User3141's user avatar
  • 319
1 vote
1 answer
305 views

How can we know the density of particles in interstellar or intergalactic space and could that density form dark matter?

It is assumed that the density of particles in the empty space between stars or galaxies is extremely low. But how do we know this density? The space surrounding the Sun is contaminated by cosmic ...
Deschele Schilder's user avatar
1 vote
1 answer
95 views

Why are WIMP dark matter particles, if Majorana-like, expected to annihilate upon contact? But not neutrinos?

I have heard a lot recently about so-called 'dark stars'; stars that are formed with the help of the gravitational pull of dark matter, or perhaps entirely from self-annihilating Majorana-type dark ...
Kurt Hikes's user avatar
  • 5,097
1 vote
1 answer
277 views

Possible to use tachyons to explore black hole?

I read on a Wikipedia article lately that tachyons are theoretical particles which always travel at or above the speed of light. That means that when one passes us, we see two images, a blue shifted ...
Max0815's user avatar
  • 1,862
1 vote
1 answer
335 views

What could be past the particle horizon?

Forgive any kind of "dumb" question I may ask as this is a new interest of mine and I know it's purely hypothetical. If one were able to surpass light speed and the expansion of space to go beyond ...
CS2016's user avatar
  • 113
1 vote
0 answers
49 views

Is an alpha particle cosmic ray more easily deflected on its journey than a proton? Or vice versa?

Has everyone heard about the cosmic ray that hit Utah recently with an energy of about 240 EeV? Making it the third-highest-energy of all time? Scientists say it seems to have come from a void, and ...
Kurt Hikes's user avatar
  • 5,097
1 vote
0 answers
61 views

What happens when two galaxies each with relativistic jets collide?

Would the relativistic jets create new particles where they meet and would all the gas from the two accretion discs be blown away leaving just two black holes?
user avatar
1 vote
0 answers
60 views

How much does the Higgs field contribute to the energy of empty space?

The Higgs field was not spontaneously broken when the universe was young and hot (like I am not...:)). At the very high temperature that existed back then, the Higgs' energy of the Higgs field was non-...
Deschele Schilder's user avatar
1 vote
0 answers
41 views

Astrophysical particle spectroscopy; narrow-line particle sources (charged or uncharged) for things other than photons? Have any been detected?

Is Cosmic Ray Astronomy a thing? Is there an equivalent of the red shift effect for cosmic rays? have got me thinking and under this answer I've commented: That's a good point; there aren't as many ...
uhoh's user avatar
  • 30.6k