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Questions tagged [astrophysics]

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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Could there be a minimum black hole within each moon, every planet, every star?

It's the spherical aspect of these celestials bodies that makes me think about this. Could planet Earth have started itself with a tiny black hole?
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Can you have an infinite number of particles that don't form any event horizons?

If you bring two particles of matter close together at some point the combined mass will correspond to black hole with event horizon that encloses both particles. With an infinite number of particles ...
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what does the Thermal redshift mean?

I am reading a paper on UHE neutrinos, it talks about the importance of considering the thermal effects for components of cosmic neutrino background in the scattering with UHE neutrinos. and the ...
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35 views

Why do we have a upper and lower bound to the main sequence in the HR diagram?

The main sequence in the HR diagram doesn't run from infinity. So why do we have an upper bound and a lower bound? I mean mass is the defining parameter in the main sequence and higher up the sequence ...
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How to generate stars in a galaxy simulation? [closed]

There are lots of amazing videos for galaxy simulations like this. If I try to generate such a simulation, I need to create stars at the beginning. Let's say my star model is like this ...
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26 views

What does the second law of thermodynamics imply on the future of the universe? [closed]

According to the second law of thermodynamics, the difference between entropies of an isolated system are always greater than 0. If I consider the universe to be an isolated system, that means its ...
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48 views

How to determine the theoretical limit on the distance estimated by stellar parallax?

To make the question a bit more realistic let the following restrictions be assumed: the length of the mission is 50 years (roughly 1/2 human lifetime scale i.e. 50 years so that we get 30+ years to ...
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3answers
122 views

Are galaxies really structured the way they look in pictures?

Are real galaxies really structured the way they are in pictures online? I'm wondering this because if the speed limit of the universe is light speed, which means stuff we see on the sky or detected ...
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36 views

Why are there dark lines in an absorption line spectrum from the Sun? [duplicate]

Consider this image and quotations from Basics of Radio Astronomy for the Green Bank Telescope: When a continuous spectrum is viewed through some cool gas, dark spectral lines (called absorption ...
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1answer
36 views

What is meant by “stable/unstable to convection” in the context of the solar atmosphere?

In studying the Schwarzschild stability criterion (for the solar atmosphere); $$\left\lvert\frac{dP}{dr} \right\rvert\lt\frac{\gamma P}{\rho}\left\lvert\frac{d\rho}{dr}\right\rvert$$ From my notes are ...
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Radiative flux in astrophysics

The following equation is often used to describe the flux at a receiver: $$F_\nu = \int I_\nu \cos(\theta)\,\mathrm d\Omega.$$ Where $I_\nu$ is the specific intensity. Could somebody explain with ...
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Why do all the planets and stars in our solar system have such similar average densities?

This table lists the average density of all the planets in our solar system. We could also consider the Sun (average density 1.41 g/cm³) and Pluto (average density 1.88 g/cm³). The densest body (Earth)...
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Is there a chance for moon to collide with earth?

I have learned that attraction between the bodies increases when it's mass increases ,if the population increases day by day and hence it can increase the mass of earth which causes attraction ...
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1answer
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Has the Super Novae distribution maxima corresponding to generation of stars dying?

Within the Big bang model, mater appears then coalesce to form stars that in turn die. Some of them going boom in a supernova. Assuming the Universe is isotropic, one should observe maxima in the time-...
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What caused neutrinos to decouple at $t=1$ second?

Was it simply that the density and/or kinetic energy got too low, because of expansion? Or was it something about the weak force itself (which I thought gelled around $10^{-10}$s? For the CMB, ...
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Does more light from Andromeda get scattered in the atmosphere than in the entire trip to Earth?

Fires have been burning here in Northern California. Today there was just a slight haze of smoke. The sun had a slight red hue to it. As expected the lower it got the redder it became. The blue light ...
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Morphology-density relation and Morphology-radius relation

I have a sample of 500 galaxies with classification as ellipticals (E) or spirals (S). To each one of these galaxies I have the value of the radius R/R200. I want to check in this sample the ...
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30 views

Conditions for the possibility of life on a planet

For an arbitrary planet revolving around a star (assuming there are no other planets or stars around) what are the main properties to determine if that planet has life on it from an astrophysics ...
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Theoretical models of short Gamma Ray Bursts

I have recently been interested in the currently known theory behind short gamma ray burst (sGRB) models. I can't seem to find any available source which shows the theory behind the relativistic shock ...
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460 views

Arbitrary Planet Spectrum

During my revision for an astrophysics quiz, I have encountered a question where I don't know where to start because I feel like I am lacking some intuition. I would appreciate any feedback! ...
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56 views

Confusion regarding the concepts and derivation of Hydrostatic Equilibrium for a star

First and foremost I am sorry for this; in order to make the questions clear I must first upload the lecture notes from my institution $^\zeta$ for the derivation of Hydrostatic Equilibrium: $^\...
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1answer
58 views

What is the equation for the blackbody equilibrium temperature of a planet? [closed]

What is the equation for the blackbody equilibrium temperature of a planet given the albedo and semi-major axis ?
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1answer
101 views

Why does the gas in Sun's outer layer not expand?

Since in the outer part of sun it consists gases. Why don't the gases expand due to heat? This was asked by my friend. And he said that the gases are attracted by the plasma layer by a force. So the ...
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Good books on Venus?

I'm looking for good books on Venus. I need some more general and some specifically about the atmosphere and atmospheric waves. Any detailed, complete and well structured book references are welcome.
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What are the Procedures and Protocols to use with Gauss'method and personal observations?

I would like to use the Gauss' method to determine the orbit of planets of solar system. () I would like to calculate there orbits with personal observations. What is the methodology/procedure/...
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A good reference on cosmic ray?

I am looking for a good reference on cosmic ray, both galactic and solar. Does anyone have any suggestion? I'm looking for a reference that covers the production and propagation of cosmic rays in a ...
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Dark matter or Misunderstanding: Is it possible that the dark matter is simply missed variables in the math?

Is it possible that the dark matter is simply missed variables in the math? I am not a physicist but examples might include: effects of planetary and galaxy rotation, electromagnetic fields, ...
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58 views

Dark matter pressure

Dark matter is suppose to form large halos of unknown yet type of particle with a specific density density profile. Does the dark matter halo can be viewed as a fluid of particles with density and non-...
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66 views

Does Big Bang predict the size of the fluctuations in the CMB? [duplicate]

From this Ethan Siegel’s article The temperature fluctuations in the CMB are only 1-part-in-30,000, thousands of times smaller than a singular Big Bang predicts. Does big bang predict the size ...
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1answer
42 views

How to handle electron-electron or proton-proton repulsion in Cosmology?

In Scott Dodleson's book, he considers that baryons are all tightly coupled. I know this can be proved by calculating the interaction time scales and comparing with Hubble's Expansion time scale. ...
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Using of optical slit for different spectrum

Here below the 3 spectrum currently used in astrophysics and illustrating Kirchhoff's laws (emission, absorption and continuous spectrums),: I just want to know : what's the utility of the optical ...
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1answer
76 views

Realistic for intelligent undergrad to build low cost muon scatter detector?

With a budget of under $2000USD, would it be possible for an undergrad student to build a muon scatter detector (drift tubes or another method)?
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What will happen if a hypernova blast occurs very near to a supermassive black hole?

I ve studied that blackholes swallow everything that comes near to them and a supernova blast is so powerful that if it occurs at one end of our solar system it will destroy whole of it . What will ...
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What effect would a supernova have on an orbiting planet?

(Not sure if this is a better fit for worldbuilding.SE...) Suppose we have an earth-like planet orbiting comfortably far from a red giant of ~10 solar masses. If the star explodes in a supernova, what ...
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High dispersion spectrum, looking at stars

What is a high dispersion spectrum? From what I understand it has to do with detecting where absorptions lines are begin generated within the star, and then using the information to adjust the ...
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1answer
30 views

Why does the accretion disc radiate energy and matter?

Jets of matter and energy are powered by accretion disc i.e., matter spiralling into the massive black hole at the galactic centre. How is this jet formed? I think that the dust particles and gases ...
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1answer
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How is the primordial abundance of Lithium measured?

I was reading about the "Lithium problem" and I came across this Physics SE post: Discrepancy problem in lithium? The answer mentioned On the other hand, measurements of the $\rm Li$ abundance ...
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1answer
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How could an alien mega structure such as a Dyson Sphere be detected? [closed]

A friend of mine was telling me that if there is an alien structure out there, we could detect it by the energy it would be producing or sending out. Im aware of hubble’s mission (RIP) and how we ...
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1answer
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When will hydrogen no longer be the most abundant nucleus?

In a recent question, we learned why hydrogen is currently the most abundant nucleon or element in the universe. Here I ask a follow-up: For how long will hydrogen be the most abundant nucleus? It ...
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Suppose the speed of individual photons reduced over time. Would that explain the apparent speeding up of distant galaxies?

The observation that distant galaxies seem to be speeding up has led to the theory of dark energy. However if the speed of individual photons actually reduced over ( very long ) periods of time wouldn'...
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39 views

How to get the Chandrasekhar Limit from a plot?

at the moment I am trying to understand, how to obtain the Chandrasekhar mass limit from a plot like shown above. Because for $n$ = 3, the mass is independent of the radius of the white dwarf. But in ...
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In extragalactic spectroscopy, what is D4000?

In relation to astronomy what is D4000? In my work I understand it is a good indicator of a stars age and I believe it is a spectral region, but I am having a hard time even finding resources to help ...
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391 views

Astronomical sources of muons

I am looking for some sources of muon particles (μ) in astronomy. By this, I mean I am interested in any astrophysical event where theoretical presence of muons is suggested. For instance, does the ...
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1answer
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Accretion disc and infrared emission

Recently I have been reading on accretion disc and came across a web site talking about methods of detecting the disc around young form stars and one of the methods is by the infrared excess that is ...
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1answer
51 views

Black Hole Pole Shift

I know that planets and stars can experience a reversal of their magnetic poles, but can a black hole also have a pole shift? And if not, why not?
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Does the neutron star collapse from the surface to the center or from the center to the surface?

I think the collapse begins at the surface because in this place the gravity is always more intense than in the center. That's right?
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1answer
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What's up with these new high energy neutrinos?

A bunch of pop science articles just popped up talking about new high-energy neutrino detection. See this article, published today, for example. The answer to this question says that the source of ...
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Why can be detecting middleweight black holes harder than the other types?

This source says that, until recently there were no middle weight (i.e. with 1000 solar-mass) black holes discovered. Astronomers had evidence of small and super-massive black holes, but not for the ...
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What is the difference between granulation and supergranulation in the Sun's photosphere?

Granulation and super granulation seem to be some sort confused topics as they are due to the heated particles coming out of the surface. What is the difference between the two?
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Speed of sound at the Sun surface [closed]

The gas velocity at the Sun's surface is subsonic and At 1 AU from the sun, the solar wind is supersonic. Like Parker wind solution. Why the velocity at the Sun's surface is subsonic? (In the ...