Hot answers tagged

4

There are very high energetic cosmic rays. The most energetic cosmic rays measured by the Auger observatorium for example have energies in excess of $10^{19}$ eV. They measure a few of those per year. At these energies they are no longer able to identify what type of particle it is, but it is believed to be predominantly protons and iron. These particles are ...


3

One can use the Doppler effect, which will shift spectral lines to the red at the side the rotates away from us and towards the blue on the side that rotates towards us. This is being used by astronomers who measure "rotational broadening" on stars which can not be resolved in telescopes. In that case it's all about measuring the rate of rotation, of course, ...


3

Your question What is the potential energy of a black hole? doesn't make sense because energy is a somewhat tricky concept to deal with in GR. If we treat the black hole as fixed we can study the motion of a test particle falling into it, and we find that there is a quantity analogous to total energy that is constant as the particle falls in. So in ...


2

You could try measuring the effects of the Lense-Thirring effect. It is an example of frame dragging. Essentially, an object that is orbiting near a massive object that is also rotating will have its axis undergo a change in its orientation. There are two problems here: The rotating object must be large. The rotating object must not be rotating slowly. ...


2

Coadding is not an especially precise term, I don't think, but in general it just means stacking or combining images --- very literally, just 'adding-together'. I usually hear this in terms of stacking images of the same field (e.g. of an optical image), but I think it can also be used to mean mosaic images, even in arbitrary parameter spaces. See for ...


2

Your case is not quite watertight - it hinges in your assertion that the optical light that is seen comes from some way out from the black hole (SMBH). The thing is that gravitational redshift can be larger than 0.2 and it is also aided by the relativistic transverse Doppler effect in the orbiting material. Some details: Gravitational redshift around a ...


2

Without knowing much about Jean's instability I can probably help you with the derivation of the expression. You start with the expression in 1) and expand it to first order in $\delta P$ and $\delta R$. Then you use that $R_0$ and $P_0$ are stationary solutions i.e $\ddot{R_0}=0$ thus $GmM/R_0^2= 4 \pi R_0^2 P_0$. You can use this to simplify the ...


1

From Wikipedia, from New Scientist According to Krzysztof Stanek of Ohio State University, one of the principal investigators at ASAS-SN, "If it was in our own galaxy, it would shine brighter than the full moon; there would be no night, and it would be easily seen during the day."[6] [6] ...


1

The invisible mass in the universe as you mentioned refers to mass which is not visible using electromagnetic radiation. It is called dark matter and was detected by the virtue of its gravitational effects. The diameter of the universe doesn't play much role in your question. Secondly, there can be many massive things which can't be seen by EM radiation but ...


1

You have$\frac E{m_0}$, the energy divided by the rest mass is $\gamma=\sqrt{1-\frac{v^2}{c^2}}$. The proper time is lab time divided by $\gamma$. Since you have a fixed $E$, as $m_0 \to 0, \gamma \to \infty$ and the proper time goes to $0$. For the last part, you are supposed to assume that an $11$ MeV neutrino arrived $7$ seconds before a $7$ MeV ...


1

Black holes are in the realm of General Relativity. In GR even the law of conservation of energy is under question when approaching singularities of the GR solution. Potential energy is a concept that comes with conservation of energy. Where the singularity in the black hole solutions is dominating, one cannot talk in terms of energy conservation and ...


1

The negative sign for the partial decay widths denote the sign of the corresponding reduced width amplitude in the R-Matrix formalism, which is what the author of this paper (and everybody else analyzing cross sections of low-energy nuclear reactions) is using to do his analyses. He's using the R-Matrix code SAMMY, which sadly has very little documentation. ...



Only top voted, non community-wiki answers of a minimum length are eligible