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31 votes

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

I'm going to give you an intuitive answer. Keep in mind, this is not the "actual" answer, as the Hawking radiation is quite a bit more complex than the typical pop-sci explanation with virtual ...
Florin Andrei's user avatar
10 votes

How are neutrinos produced in blazar jets?

Neutrinos are typically produced in AGN jets through what we refer to as hadronic processes. Protons are accelerated to relativistic speeds and interact with nearby photons. Depending on the ...
HDE 226868's user avatar
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9 votes

Hubble expansion rate and reaction rates

A more intuitive way to understand the comparison between the reaction rate $\Gamma$ and the Hubble rate $H$ is to take the reciprocal. $\Gamma^{-1}$ is the time between reactions. $H^{-1}$ is ...
Sten's user avatar
  • 4,753
9 votes

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

These lecture notes address the issues to some degree, especially on slides 33-35. Because in the strongly warped spacetime near the horizon, virtual particles made from vacuum fluctuations ...
Steve Linton's user avatar
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8 votes
Accepted

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

You can not check if a dimensional constant has changed because you can always reverse that change by a smart change of coordinates (system of units). Despite that, since the current Physics assumes ...
Catarina Alves's user avatar
7 votes

Absorption of light by matter

It is the other way around. An isolated, point-like charged particle like an electron cannot absorb a photon. It is forbidden, because energy and momentum cannot be simultaneously conserved. Only ...
ProfRob's user avatar
  • 153k
5 votes

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

The density of material in the interstellar medium is inferred from (i) the electromagnetic radiation it emits; (ii) its effect on electromagnetic radiation passing through it. Often these approaches ...
ProfRob's user avatar
  • 153k
5 votes

Directionality of solar flares

First, I have provided some background on these phenomena at: https://astronomy.stackexchange.com/a/16786/13663 Solar flares and coronal mass ejections (CMEs) are not the same phenomena. I am aware ...
honeste_vivere's user avatar
5 votes

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

The W boson has a lifetime of $3\times 10^{−25}$ seconds. So any big bang W bosons will have long decayed. So they are not a dark energy source. Also, they produce "hot" relativistic decay ...
Anders Sandberg's user avatar
4 votes

Hubble expansion rate and reaction rates

For a spatially flat Universe (described by FLRW metric), which is consistent with current observation, the scale factor itself is not so relevant. One can always redefine/scale it so that it is e.g. ...
Chen's user avatar
  • 41
4 votes

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

I'm going to say, "probably not", because (as tfb points out) we have very good evidence for SMBHs in other galaxies -- in particular galaxies with active nuclei where the phenomenon ...
Peter Erwin's user avatar
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3 votes

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

If I understand your question correctly, it is about EPI-Lo which a part of the Integrated Science Investigation of the Sun (ISʘIS) . The picture is also taken from there: EPI-Lo stands for Energetic ...
B--rian's user avatar
  • 5,616
2 votes

Absorption of light by matter

It's the electrons of an atom that absorb the energy of the photon, not the nucleus. The frequency of the incoming light wave is at or near the energy levels of the electrons in the matter. The ...
Codosaur's user avatar
  • 147
2 votes

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

There is no law of physics that prevents fermions getting arbitrarily close to each other. The Pauli Exclusion Principle says that no two fermions can occupy the same quantum state. Basically, this ...
ProfRob's user avatar
  • 153k
2 votes

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

I don't know if the experts will agree with this description, but here is how I understand it: Both space and the event horizon are in constant quantum fluctuation. Essentially, the event horizon has ...
Alsee's user avatar
  • 121
1 vote

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

Gluons actually annihilate, so do neutrinos, just more rarely than Neutralinos. Neutrinos, Gluons, WIMPS, Majorana particles are always neutral being a Truly Neutral Particle. These Majorana particles ...
Arjun's user avatar
  • 1,464
1 vote

Directionality of solar flares

I have just found this paper which seems very relevant: https://www.sciencedirect.com/science/article/abs/pii/S1350448799000633?via%3Dihub "Particles arising at some remote location from the sun ...
Slarty's user avatar
  • 359
1 vote

Absorption of light by matter

As @Codosaur mentioned earlier, it is the electrons that absorb the the energy of the photon and not the Nucleus. Let's take a theoretical example to see how this works. Imagine an atom without any ...
Infinity Milestone's user avatar
1 vote

What are the sources of antimatter particles in the magnetosphere?

Matter and antimatter particles are always produced as a pair. This particle physics' process is called pair production. If antimatter is detectable, it means that the antiparticle of a matter-...
B--rian's user avatar
  • 5,616
1 vote

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

Here's an analogy to Quantum Mechanics. A particle in QM can tunnel through an impossible barrier, which is how elements heavier than lead can have some of their neutrons "tunnel" out of the nucleus ...
SurpriseDog's user avatar
1 vote
Accepted

Possible to use tachyons to explore black hole?

Let's look at the validity of tachyons first. Travelling faster than light, as said by userLTK, would create time travel, which would create the famous paradox, the tachyonic antitelephone. The ...
Max0815's user avatar
  • 1,862
1 vote
Accepted

What could be past the particle horizon?

It sounds like your question is about the single most important principle of cosmology, called the cosmological principle. This asserts that as long as all our observations are consistent with the ...
Ken G's user avatar
  • 5,336

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