The application of physical theory to celestial systems such as stars, planets, galaxies, supernovae, and black holes. Astrophysics proper is concerned with explaining phenomena more so than making observations, the latter falling under the purview of astronomy.

learn more… | top users | synonyms

3
votes
1answer
426 views

Standard gravitational parameter - different formulas

Why we have two formulas for Standard Gravitational Parameter: $$\mu=GM \ \,{\rm and}\, \mu = rv^2 \ .$$ I don't see any direct connection between the two formulas. How can we derive the second from ...
1
vote
1answer
53 views

How can fusion within the sun be possible if there is no such thing as helium-2 (2 protons, no neutrons)

As stated in the question where does the sun(or other star) get the necessary neutron in order to produce the Helium atom? and how does this process occur (explain how the neutron incorporates).
2
votes
0answers
72 views

What does kinetic energy at infinity mean in terms of supernovae?

I have noticed that in some paper that the term "kinetic energy at infinity" is used. I understand what potential energy with reference to infinity mean, but what does the term kinetic energy of ...
23
votes
5answers
2k views

Why do we deal only with large scale magnetic fields in astrophysics, and not electric fields?

In astrophysics there is a lot going on about strong, large scale magnetic fields: in stars (prominences), magnetic dynamos, compact accretors collimating jets, etc. There's even a special ...
2
votes
1answer
342 views

How did all of the heavy elements on earth get here?

I have often read that a first generation star went supernova and seeded our solar system. It is well known that stars that go supernova are the source of elements heavier than iron. I guess I am ...
1
vote
1answer
59 views

How does velocity relate to energy difference in Compton scattering?

I'm having trouble understanding what my professor is getting at asking in this question. I just visited her office and her explanation minutely helped. I'm hoping to get a bit more clarity on what is ...
4
votes
2answers
97 views

Is the coldest place in the universe likely to be artificial or natural?

The Boomerang Nebula is often cited as one of the coldest natural places in the universe at 1 K, but that's about 10 orders of magnitude off from what's been created in a lab. Are there theoretical ...
8
votes
4answers
7k views

How long does a supernova last?

Just what the title indicates. Is a supernova over instantaneously? Or, does the (for want of a better word) explosion continue for a while? What is/are the order of timescales involved? EDIT: ...
3
votes
1answer
91 views

Mass loss in Red Giants via dusty-winds and chromosphere activity

I'm reading some literature on mass loss in the RGB/AGB branches and so far I'm getting a lot of information regarding mass loss via dusty-winds/pulsations but almost no explanation of mass loss by ...
11
votes
4answers
5k views

Why does Venus rotate the opposite direction as other planets?

Given: Law of Conservation of Angular Momentum. Reverse spinning with dense atmosphere (92 times > Earth & CO2 dominant sulphur based). Surface same degree of aging all over. Hypothetical large ...
33
votes
9answers
11k views

Can Jupiter be ignited?

Our solar system itself contains two candidate "Earths" One is Jupiter's moon Europa and another is Saturn's moon Titan. Both of them have the problem of having at low temperature as Sun's heat ...
1
vote
0answers
43 views

Do the different observed Type Ia supernovae have similar explosion energy?

I have been trying to read about the energetics of observed supernovae for some time. And while the observed core-collapse supernovae have many scientific papers about them trying to estimate the ...
5
votes
1answer
177 views

How to calculate the kinetic energy of supernova ejecta?

I believed I could use $0.5\times M_{ej} V_{ej}^2$, with $M_{ej}$ being the ejected mass and $V_{ej}$ being the velocity of the ejected mass. But I noticed in this and this that the the mean velocity ...
0
votes
0answers
30 views

Resources on Solar Neutrino Physics

For a project I'm doing for an introductory Astrophysics course, I'm trying to understand the nuances of solar neutrino physics. However, most of what is said while explaining neutrino oscillations ...
0
votes
4answers
2k views

What cosmic event would cause Sun rising from the west?

I'm wondering what kind of astronomical or geological events would cause the reversal of Earth's rotation. For instance, Is a meteorite passing very close to Earth able to reverse its rotation? Can ...
7
votes
4answers
320 views

Can a planet form before the parent star ignites?

I'm unable to find an answer to my questions via my searches. This questions pertains to the timeline of a star system creation. My question: During the creation of a star system, can satellite ...
3
votes
3answers
338 views

Dark age of universe when all fusion process ceases?

Some say we live in the golden age of the universe because there exits countless number of stars that shines in the dark universe. As the supply of gas for star formation is steadily being exhausted, ...
0
votes
0answers
46 views

Does the zero energy universe hold true on some mathematical grounds besides observations?

I was reading Stephen Hawking's 'The theory of everything' when I came across a very interesting type of universe, the 'zero energy universe' since then, I've read some websites but all they used to ...
17
votes
2answers
602 views

How can a spiral galaxy exist?

A spiral arm orbiting a central mass should be dispersed quite quickly as the outer elements would move more slowly than the inner ones. The Milky Way, is about 59 Galactic Years old, which, one would ...
6
votes
2answers
803 views

How to explain the existence of heavier elements in Population I stars and in Population II stars contain lighter one

Recently I read Astrophysics Notes where I found a statement that young stars are classified as Population I stars and relatively older one as Population II stars. Population I stars contain ...
23
votes
2answers
518 views

Experimental observation of matter/antimatter in the universe

Ordinary matter and antimatter have the same physical properties when it comes to, for example, spectroscopy. Hydrogen and antihydrogen atoms produce the same spectroscopy when excited, and adsorb the ...
2
votes
1answer
158 views

Why are cgs units the norm in astrophysics?

Other physics communities, e.g. the particle physics one, have their own set of units, custom-tailored to their own needs. Now, the astrophysics community is somewhat similar, in that a lot of ...
15
votes
4answers
518 views

Are Neutron stars transparent?

Neutrons have no charge so they would not, I think, interact with photons. Would a neutron star be transparent?
2
votes
1answer
53 views

Geophysical Effects of Supernova Neutrino Pulse

While neutrinos are generally totally harmless, a supernova produces enough of them at once that the neutrino flux would kill you if you could stand close enough (and not be killed by other means ...
9
votes
4answers
7k views

Size of universe after inflation?

Wikipedia states the period of inflation was from $10^{-36}$sec to around $10^{-33}$sec or $10^{-32}$sec after Big Bang, but it doesn't say what the size of the universe was when inflation ended. ...
1
vote
0answers
80 views

How to prove the Hubble law is the unique expansion law compatible with homogeneity and isotropy?

In the book physical foundations of cosmology, it saids that Hubble law is unique and a problem seems to be a hint of proving that. In order for a general expansion law,v=f(r,t), to be the same ...
0
votes
1answer
44 views

What is the power of the most powerful quasar found?

Trying to find an answer to this question, I came across many sources that are in complete in contradiction. For example Wikipedia states that a typical quasar has a power of $10^{40}$ watts while ...
2
votes
1answer
186 views

Maintaining local thermodynamic equilibrium (LTE) in radiating gas with a broad atomic transition line

Definitions / Background In LTE, Kirchoff's law for radiation holds: $$ \frac{j_{\nu}}{\alpha_{\nu}} = B_{\nu} (T) $$ where $j_{\nu}$ is the specific radiative emissivity, $\alpha_{\nu}$ is the ...
3
votes
1answer
46 views

Are the cylindrical and spherical form of Jeans' equations equivalent?

The question kind of says it all, what I really want to know is are the differences in their forms only due to the co-ordinate transform? And as such should a suitable spherical system satisfy ...
1
vote
1answer
107 views

Infinite number of universes? Black holes are guilty? [closed]

I was thinking, if the space is infinite, what if there are infinite number of spaces, inside our universe? I mean, everyone knows that black holes exist, but nobody knows what happens when you get ...
1
vote
2answers
93 views

Power radiated by a star, black body model

let's say I want to model a star of radius $R$ at a distance $r$ from the Earth. I need to show that the apparent luminosity for frequency $\nu$ is equal to $$\ell(\nu)=\frac{2\pi h}{c^2}\left( ...
12
votes
2answers
1k views

Temperature of a neutron star

In our everyday experience termperature is due to the motion of atoms, molecules, etc. A neutron star, where protons and electrons are fused together to form neutrons, is nothing but a huge nucleus ...
3
votes
3answers
469 views

Shouldn't stars disappear from our view due to expansion?

The currently accepted theory of the expansion of the universe would suggest that for any point in the universe, there is a 'boundary' (somewhat like the Schwarzschild radius) beyond which it cannot ...
18
votes
3answers
1k views

What stabilizes neutrons against beta decay in a neutron star?

Free neutrons are known to undergo beta decay with a half-life of slightly above 10 minutes. Binding with other nucleons stabilizes the neutrons in an atomic nucleus, but only if the fraction of ...
1
vote
1answer
361 views

How is the mass of black hole at the center of our galaxy measured?

I've been watching a video about dark mater and a lot of the mass is missing in our universe. Astronomers got to this by measuring the speed that stars orbit the center of the galaxy and when they did ...
6
votes
1answer
145 views

What prevents stars in globular clusters from merging over time to form a black hole?

Globular clusters are apparently very very old, and the density of these clusters appears to increase as one approaches the center of a cluster. Orbits are bound to be chaotic, since there is no ...
4
votes
1answer
191 views

Simulating a black hole binary system

As part of a project for my degree I am writing code to simulate N-body gravitational interactions, however I have to then use this code to investigate something. Struggling to think of ideas I ...
7
votes
3answers
2k views

Is it possible that black holes are also neutron stars, but so dark that we cannot see them?

Since the concept of the singularity in a black hole leads to infinite densities, I wonder if it is really certain that black holes exist? Is there a possibility that massive objects (which are ...
2
votes
1answer
103 views

What happens when Dark Matter comes in contact with the event horizon of a large Black Hole

Josh Hill, 9, Oakdale Elementary has always talked Theory of Relativity and Astrophysics etc., I can answer most but lately he has stumped me and has been begging me to ask a pro, so here it is.... ...
5
votes
1answer
458 views

Mass density of dark matter in solar system near us

What is the approximate mass density of dark matter in our solar system at the radius of the Earth's orbit? I would like some idea of the mass of dark matter going through each cubic meter of ...
0
votes
1answer
47 views

Multiple planets orbiting a star

One way of detecting exoplanets orbiting around a star is the Radial velocity method. Can this be used to detect multiple planets? Wouldn't the star orbit the center of mass of the whole system with ...
12
votes
1answer
1k views

Why don't the black holes appear black in color in images of galaxies taken from HST?

According to NASA a black hole is anything but empty space. Rather, it is a great amount of matter packed into a very small area According to the documentary Space Unraveling The Cosmos about ...
3
votes
1answer
141 views

What is the origin and nature of the “hydrogen envelope” located on the sun side of a comet coma?

It is tempting to assume the origin of the hydrogen is water vapor from the comet, in which case, what process "breaks up" the water molecule (or perhaps ammonia molecule?)? Is the hydrogen actually ...
1
vote
0answers
54 views

Is the Baum Framptom a valid alternative to Big Bang?

In the Baum Frampton model, proposed in 2007, because $\epsilon\lt-1$, after the Big Rip the universe starts again empty. The problem of this model is that inverting the arrow of the time, after a ...
5
votes
6answers
314 views

Are there free data available online from cosmology (or astrophysics) experiments that anyone can analyse?

One can understand a subject better in physics by trying to solve as many problems as one can from a textbook say. When it comes to experimental physics and data analysis, no book on experimental ...
19
votes
2answers
653 views

How do spiral arms form?

Why aren't all spinning galaxies shaped as discs as my young mind would expect? I understand how the innermost parts of a galaxy spin faster than the outer parts, and that could explain why some ...
2
votes
1answer
57 views

Distance from redshift

I am looking for a exact derivation of a relation between redshift $z$ and distance $d$. What I know is the definition ...
6
votes
1answer
160 views

Upper Mass Limit of Quark Stars

While there is no confirmation that quark stars exist, is there any theoretical limit analogous to (but different from) the Tolman–Oppenheimer–Volkoff limit for neutron stars? In other words, what is ...
2
votes
1answer
63 views

Stellar remnants in a state of matter denser than neutron-degenerate

When discussing the stellar life cycle, it's often stated that if the collapsing core of a star is bigger than the mass limit for a stable neutron star, it must collapse to a black hole. However, ...
8
votes
1answer
214 views

$\Delta^+$ decay in GZK process

The dominant channels in the GZK process are $$p+\gamma_{\rm CMB}\to\Delta^+\to p+\pi^0,$$ $$p+\gamma_{\rm CMB}\to\Delta^+\to n+\pi^+.$$ According to the pdg, $\Delta\to N+\pi$ makes up essentially ...