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.

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Meteorite hunters Search for FIREBALLS

normally meteorite hunters search for fireballs....but they totally ignore meteor showers . why so? as far as i can think meteors in meteor showers are usually produced by small particles so they ...
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0answers
78 views

Chandrasekhar Limit [closed]

A white dwarf is essentially a degenerate electron gas, in which pressure of degenerate electrons supports gravitational pressure. As a simplified model of such an object, consider a spherical star of ...
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1answer
220 views

Red Giant branch and Asymptotic Giant branch

What's the difference between the RGB and the AGB? I can't seem to find an clear distinction anywhere. Thanks.
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3answers
5k views

What are good books for graduates/undergraduates in Astrophysics?

There are no book recommendations for Astrophysics here. I will write my own answer, but I am also interested in what are others' views on the question (I will NOT mark my own answer as the best one). ...
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19 views

Recommendations regarding high-energy astrophysical objects (AGNs, jets, etc.)

I know basic astronomy and I know a few good textbooks for general astrophysics (eg. "Introduction to Astrophysics" by Carroll and Ostlie). I also have a strong background in theoretical physics and ...
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1answer
74 views

How can such a wave exist at the surface of the sun?

Recently, I came across the following picture from NASA's SOHO observatory: It seems evident that this is a transverse wave (mind the ring which is bright and dark). But how can this be the case ...
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1answer
46 views

Why 21cm line observations is more helpful compared to other radiation?

Why 21cm line observations is more helpful compared to other radiation? Is it only because of its abundance in whole universe or anything else?
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2answers
78 views

When we look in different directions in the universe how do we know we're not seeing the same thing?

For my question assume: 1: Big bang happened at a point (I know it happened everywhere) but after that explosion universe started to expand in all directions so it maybe considered to happened ...
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1answer
36 views

Are galaxies “disk” shaped?

When you look a sphere from a fixed observation point, you can easily mistake it for a circle, so I was wondering: are galaxies really "disk" shaped or we just don't have the means to detect the ...
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2answers
43 views

Redshift 1+z - CMB Temperature lower?

I know that $\frac{\lambda_2}{\lambda_1} = 1 + z$ Suppose a galaxy had redshfit $z=3$. Does this mean that the wavelength becomes $4\lambda$? Then by wien's law where $\lambda \propto \frac{1}{T}$, ...
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0answers
85 views

Why did everything in space cooled out?

Through my research, I learned that; According to thermophysics, heat always moves from and area of high heat to an area of low heat. Space has no heat at all. It is extremely cold However, ...
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1answer
207 views

What interaction is responsible for the 21 cm Hydrogen line transition?

The 21 cm Hydrogen line is from the transition between the hyperfine levels of the ground state of the hydrogen atom. So, what interaction is coupling the hyperfine levels? I suspect that it is not ...
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2answers
1k views

Artificial planetary magnetic field

I wonder how difficult it is to create an artificial planetary magnetic field with generators? What power they would need? The question is inspired by thinking about possible colonization of ...
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2answers
93 views

Abundances of the light element of the Big Bang Nucleosynthesis

This question is related to the Big Bang Nucleosynthesis of light elements, more concretely I do not understand some features of the graph Why do the $^3$He and D abundances go down with ...
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2answers
452 views

What is the frequency of occurrence of stellar classifications off the HR main-sequence?

An alternative version of this question would be: "if was to pick a star from the $10^{11}$ or so in our galaxy at random, what are the probabilities of it being various kinds of star?" (and I do mean ...
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0answers
37 views

Any cheap (less than 100 euro) telescope for observing Jupiter? [closed]

The moon is not challenging. I would like to observe the big planets and their rings.
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1answer
23 views

Why is solar eclipse so important for sunlight spectrum analysis?

People wait for decades to catch the chance of a solar eclipse to observe the sun. Why cannot they do it every noon?
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1answer
93 views

How is dark energy calculated

This should be a very simple question. What would be the proper way to calculate Dark Energy in Joules at any point in history and that is consistent with the Standard Model? I'm thinking that ...
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4answers
2k views

Can there be Electron and/or Proton Stars?

What happens to all of the electrons and protons in the material of a neutron star? Could there ever be an electron star or a proton star?
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7answers
1k views

Mathematically possible vs physically probable outcomes

A good buddy of mine and I have had a friendly debate about the origins of the current state of our universe (namely; Earth and life on Earth) and have fundamentally disagreed in our stances with ...
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1answer
122 views

Is there a connection between exclusion principle and the speed of light?

As far as I know exotic stars are composed of degenerate matter created by the balance between gravity and pressure of exclusion principle and as the mass of the star grows it goes into more ...
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8answers
3k views

Why is absolute zero considered to be asymptotical? Wouldn't regions such as massive gaps between galaxy clusters have temperatures of absolute zero?

Why is absolute zero considered to be asymptotical? Wouldn't regions such as massive gaps between galaxy clusters have temperatures of absolute zero? I just do not see why our model must work the way ...
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2answers
83 views

Quick question on astronomical units

I'm trying to solve for $\frac{M*}{M_0}$ and $p''$ using these two equations: Here is the lecturer's working, I worked it out several times and I got a different answer! Surely when you use ...
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1answer
23 views

The Helium mass fraction from the Big Bang Nucleosynthesis

In Perkin's book Particle Astrophysics (page 144): I do not understand how one comes to the following expression (the second equality with $r$) for the Helium mass fraction due to the Big Bang ...
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2answers
47 views

Size of objects and variations in brightness?

My textbook says talking about Cygnus X-1 (the first black hole to be identified as such) has variations in brightens of the order of 0.01 seconds and that this means that it's dimeter must be on the ...
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1answer
57 views

Interpretation of the WIMP annihilation cross section graph

I have some trouble in the interpretation of the WIMP cross-section annihilation versus their mass. I understand that the lines represent a upper bound on the cross section from the observation. ...
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3answers
1k views

How do neutron stars burn? Is it decay or fusion or something else?

What makes a neutron star burn, and what kind of fusion/decay is happening there? What is supposed to happen with a neutron star in the long run? What if it cools, then what do the degenerated matter ...
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1answer
39 views

Quick question on derivation of mass of star

How do I show that for a binary star system, if one star has mass $M_s$, speed $V_s$, period $P$, the mass of the other star is given by: $$M_P^3 \approx \frac{V_s^3}{2\pi G} PM_s^2$$ I showed it ...
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1answer
55 views

Lifetime of a horizontal branch star

I'm trying to determine what the lifetime of a star on the horizontal branch of the Hertzsprung-Russell diagram would be. Some websites say $10^8$ while others said $10^7,$ so I don't know which one ...
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1answer
55 views

Quick question on parallax and parsec

I know that 1 parsec (pc) is the distance of star at which 1 AU subtends 1 arcsecond. so $1 pc = \frac{1 AU}{1"}$ Now, if two stars in a binary with a separation of 3" and have a trigonometric ...
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2answers
73 views

What is chaotic about Chaotic Inflation?

Chaos is defined as an aperiodic long-termed behavior, that is very sensitive to initial conditions. Now from this definition I can only conclude that the adjective 'chaos' is a mere analogy, since ...
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0answers
17 views

Dependence of the neutron-freeze-out temperature

What is the physical explanation for the dependence for the freeze-out temperature $T_\text{F0}$ of the neutrons as a function of the number of degrees of freedom $g^\star$? ...
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0answers
46 views

Is it true that the sun will cause very high temperatures on Earth long before the red-giant-phase?

I heard at least three claims about the development of the heat of the sun. In an old book, I read, that nothing dramatically will happen in the next few billion years. Wikipedia states, that the ...
5
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1answer
107 views

Hubble time and its derivation? [duplicate]

I know the derivation of Hubble time goes something like this (I am an a-level student so this may not be the actual derivation): Two galaxy that is moving away from each other at speed v are now D ...
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1answer
47 views

The initial conditions of the CMB spectrum

The CMB spectrum shows the intensity of fluctuation at a certain angular scale: The achievement is the correspondence between the predicted power spectrum and the observed one. My question is as ...
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1answer
33 views

No tremendous neutrino-flux for SNIa?

Why do neutrino account for 99% of the energy release for a SN II, while it is not expected to be the case for SN Ia? Is it because the densities are not high enough to induce inverse beta-decay? ...
2
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1answer
58 views

Could the Earth be ejected when the sun burns out?

My younger brother came home from school today and told us at the dinner table that when the sun burns out the Earth could be ejected from its orbit. Skeptical, I asked his source. He quoted his ...
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2answers
28 views

Are combined masses in space, such as galaxies, considered to be uniform bodies? *In addition, a related question about force

If we were to calculate the force that one galaxy exerted onto another, would we consider the individual masses within the galaxies, or the masses of the galaxies as a whole? Do the individual stars ...
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1answer
51 views

Consequences of inverse square law with vast distances (Gravity); (in addition, is light speed broken)? [duplicate]

As is well known, the gravitational force between two masses is dependent on the spatial distance between them. Therefore, even at vast distances, the masses exert equal and opposite forces on one ...
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0answers
33 views

Why are other universes in the picture of Dark Flow?

It seems to me that the popular suggestive explanation of dark flow is another universe interacting with ours. Isn't there other alternative explanations?
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2answers
85 views

Smolin on Cosmological selection and neutron stars

Regarding the cosmological selection hypothesis and testable predictions, Lee Smolin asserted the following: "Smolin: I did make two predictions which were eminently checkable by astrophysical ...
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1answer
40 views

Pulsars with accreting disk in binary system

Following this line, I am wondering about the following question. Accreting pulsars in binary systems are usually thought to accrete from a prograde disk, so increasing their spin in the process. ...
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1answer
80 views

Inward Pressure of Gravity

We are looking at White Dwarfs in Quantum and specifically how they are stabilized between gravitation pressure inwards balanced by the Fermi pressure due to electrons. To start the problem off ...
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5answers
213 views

Is dark matter around the Milky Way spread in a spiral shape (or, in a different shape)?

Dark matter doesn't interact with electromagnetic radiation, but it, at least, participates in gravitational interactions as known from the discovery of dark matter. But does dark matter exist in a ...
7
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2answers
311 views

Neutron stars and black holes

The official limits for a neutron star is $1.4 - 3.2\;M_\odot$. But I read that the limit depends on the particular structure of a star to estimate which mass it must have. I also read that neutron ...
4
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1answer
32 views

Galaxy velocity curve

When deriving the relation between velocity of a star and its distance $r$ from the center of the galaxy, one assumes that the masses outside $r$ have no contribution and those inside $r$ give a force ...
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3answers
95 views

Is the solar energy Infinite?

Is the solar energy coming from the sun infinite and will continue to be radiated to our earth forever? (discarding any outer factors) what's the sun's fuel?
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6answers
7k views

Why are some galaxies flat?

What is the explanation for the flatness of some galaxies? (If it's due to their rotation then why they are rotating, why some other galaxies are not flat etc., I would like to hear a nice and ...
3
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1answer
47 views

Is it known what causes the “knee” in the observed Cosmic Ray spectrum?

I've seen many versions of the figure shown below -- the famous Swordy plot. They tend to explicitly point out two features in the CR spectrum, the knee and the ankle. I know that the source of ...
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2answers
1k views

What will happen if the solar system leaves the milky way galaxy? [closed]

Is the milky way galaxy meaningful to us? Will any bad thing happen if the solar system just leaves the galaxy?