28
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 ...
- 18k
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 ...
- 36k
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 ...
- 4,260
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
...
- 10.2k
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 ...
- 450
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 ...
- 146k
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 ...
- 146k
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 ...
- 826
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 ...
- 14k
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. ...
- 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 ...
- 16.4k
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 ...
- 5,526
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 ...
- 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 ...
- 146k
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 ...
- 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 ...
- 1,208
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 ...
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-...
- 5,526
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 ...
- 225
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 ...
- 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 ...
- 5,300
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