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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Determining Mass of Spectroscopic Binaries

I know that the mass of a binary star system is given by Kepler's Law: $$\mathrm{m_1 + m_2 = \frac{4 \pi^2 r^3}{GT^2}}$$ Further we know that: $$\frac{r_2}{r_1} = \frac{v_2}{v_1} = \frac{m_1}{m_2}$$ ...
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38 views

Great Void negative gravity [on hold]

According Integrated Sachs–Wolfe effect on light, Great Void should have relatively negative gravity - it just push mater out, and maybe even light. What is cosmic speed hypothetical spaceship should ...
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1answer
31 views

Formula for cosmic variance

I was reading this page: Sample and Cosmic Variance. The section states that The multipoles $C_\ell$ can be related to the expected value of the spherical harmonic coefficients by $$ \Bigg\...
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0answers
27 views

Is there a scientific centers of support special research? [on hold]

I'm Dr Mustafa , an astrophysics researcher from Egypt I've written a Scientific paper about a possible new fundamental universal force,But it did not publish it yet. Because I want to prove ...
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1answer
417 views

Why is the spectrum of old stellar populations characterized by broad lines?

I'm taking a course in astrophysics and my teacher said that old stellar populations have broad lines whereas young populations have narrow emission lines. My first thought was to consider then case ...
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2k views

Can elements heavier than Iron be present in a star's core?

My understanding is that elements heavier than Iron and Nickel are not formed in a star but, can heavy elements such as lead and others be present/found in a star's core ? I ask because the following ...
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3answers
89 views

Doppler's effect in light is not fully accurate [closed]

We all know that universe is expanding faster than the speed of light $c=299792458 m/s$ so we can't apply his formula to all celestial bodies what if the relative velocity between source and observer ...
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1answer
30 views

What is exactly the “progenitor bias”?

I am taking a course in astrophysics and my teacher mentioned different biases that are present when taking a sample of galaxies: the progenitor bias and the Malmquist bias. I understand very well the ...
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1answer
79 views

Is cosmological constant really constant?

As the Universe expands, the dark energy in it also increases. I heard that the cosmological constant $\Lambda$ represents dark energy, so that constant must change as time passes, right? Correct me ...
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5answers
4k views

Why is the Sun called an “average star”?

This is a statement (presumably in mass, longevity, energy output) many people that I've met have heard in school, and it is known in pop culture. However, according to Wikipedia, about 75% of the ...
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3answers
162 views

Why are some stars very large (i.e., $r \geq 1000 \ R_{\odot}$) but not super massive?

Background While I was in graduate school, I put together some cartoon-like comparisons of multiple stars to show the order of magnitude differences in radii. At the time, VY Canis Majoris was the ...
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23 views

Data offset (radial velocity) [on hold]

To work out an estimate for the period, I need something called the data offset. My data is measured radial velocity for certain times. What's the data offset and how do I work this out? They're ...
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2answers
46 views

Does mass determine gravity or is it a predetermined quantity

If Earth were to gain large enough mass, would it have enough gravitational force to hold the extra mass, or is there a predetermined magnitude of gravitational force for earth due to its location in ...
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20 views

Online rotation curve data search

I would like to know how to find rotation curve data online. I know there are online data bases like hyperleda, ned, simbad, etc. but how to look inside those projects for the rotation curve data?
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0answers
15 views

How to estimate period of sinusoidal (exoplanet radial velocity) data?

I have an exoplanet's noisy radial velocity data collected over a period of time. I want to write python code that will determine an estimate for the period of this data. I've heard of ...
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0answers
35 views

Ultra-cold gas giant atmospheres

In the troposphere, which has the bulk of the atmospheric mass, it's colder at higher altitudes due to adiabatic lapse. Gas giants have several different chemicals that condense into cloud decks at ...
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1answer
42 views

Is it possible that cosmic ray particles and neutrinos account for a significant portion of dark matter?

Sounds a bit naive but I read somewhere that neutrinos were thought to account for dark matter to an extent and I think Zwicki came up with the idea before cosmic rays were announced (not sure though)....
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1answer
43 views

Do satellite galaxies have the same proportion of dark matter as “ordinary” galaxies

My question is relatively straightforward: Do we know if satellite/ dwarf galaxies contain the same proportion of dark matter to ordinary matter as "regular" sized galaxies? The Milky Way, for ...
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2answers
71 views

What is the pressure that supports boson star?

What is the pressure that supports boson star? I noticed that for a Bose-Einstein condensate $$ p = k_BT\frac{g}{\lambda^3}\zeta(5/2) $$ where $g$ is the degeneracy and $\lambda$ is the thermal ...
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2answers
59 views

Is it possible that there are stars working on fission?

Most/all stars are getting their energy from fusion of small atoms like our sun. But is it possible according to the laws of physics that there are stars getting their energy from fission fe with ...
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1answer
34 views

Is it possible that propagation of acustic waves leads to emission of radiation?

Question: Consider large cloud of gas. Assume it is electrically neutral (but as always, matter is composed of smaller things which are actually charged). Is it possible that propagation of sound ...
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1answer
119 views

How much noise is in the Cosmic Background Radiation, especially from Cosmic Rays

Do we have an estimate of how much noise, if any, say caused by cosmic rays in particular, is present in the CMB datasets and the maps based upon them? Can we extrapolate a figure from the cosmic ray ...
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1answer
20 views

Translational Velocity

Is the translation velocity equivalent to its real velocity or radial velocity? Online sites and textbook are saying different things, So Im not too sure what is going on
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1answer
32 views

Do AGN produce protons that are relativistic enough to collide with the CMB and make pions?

AGN (Active Galactic Nuclei) produce protons in their jets and they are relativistic. I was reading about photo-pion production, where a proton and photon annihilate to produce a pion. Could this ...
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0answers
63 views

Mass of star from Lane-Emden equation

Suppose we have equation of state $p=K\rho^{1+\frac{1}{n}},$ where $\gamma=1+\frac{1}{n}$ for some star. Then by standard calculations we obtain equation for enthalpy $h$: $$\Delta h+4\pi G\left(\frac{...
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3answers
62 views

How do we get images of galaxies?

First of all a very basic question upon which my main question is based. "Are the pictures of milkyway galaxy we see on books/mags are real ? ". If they are real then my question is, how we have taken ...
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2answers
32 views

Different width of spectral lines for different groups of stars

As seen in an HR-diagram, a certain stellar classification can correspond to more than one group/sequence of stars (G5 could for instance be either a giant, main sequence star or a white dwarf and so ...
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2answers
221 views

Could planets survive their star becoming a black hole? [duplicate]

Would the supernova responsible for its formation destroy them. The question becomes one of how destructive the supernova event is to its own solar system - does it completely evaporate all planets up ...
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1answer
33 views

Gamma Ray Burst data

I wanted to know if there was some database for gamma ray burst (GRB) data. I would like to get the luminosity and duration of recorded GRBs. So far, I have come across this website, but since I do ...
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1answer
26 views

Stellar classifiaction and metals

I have recently started to study astronomy and there is a thing with stellar classifications I can't get my head around: The colder the star the more absorption lines from metals are present in its ...
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0answers
20 views

Event horizon at moments of formation of black hole [duplicate]

As I understand it, the event horizon of a black hole body, has a diameter depending on the mass. So, if an existing black hole grows through infalling matter the event horizon radius increases. I'm ...
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1answer
32 views

If a meteor breaks apart in the atmosphere, how far apart could the impact craters be realistically?

Currently, my assumption is that the meteor only splits into two. The meteors could potentially land on anywhere on a whole half of a planet. How can I improve this mental model? If the meteor is ...
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1answer
26 views

scaling law of gravitational waves and consequences

With which power law of distance is decreasing the amplitude of the distortion caused by a gravitational wave ? $r^{-1}$ ? $r^{-2}$ ? something else ? -> The coalescence between 2 black holes about a ...
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3answers
79 views

Can black holes grow via accretion of dark matter particles?

I'm assuming that the answer to the question in the title is a resounding yes. Since Baryonic matter and dark matter interact via gravitational forces. If this is the case how is information not lost ...
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1answer
47 views

What is the difference between habitable and Goldilocks zone?

If I am right, Habitable Zone means that a planet is on such a distance from its Star which makes it good candidate for supporting some sort of life. But then what is Goldilocks zone and how is it ...
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1answer
44 views

Measuring the size of the core of the sun with multiple neutrino detectors

Back in 1998, researchers at the Super-Kamiokande neutrino detector released this image: of the sun using their neutrino detector using approximately 500 days of data. This picture covered 90x90 ...
4
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1answer
68 views

Hubble time and age of the universe

I'm having trouble with the following derivation of the 'age of the universe': http://imgur.com/gRvLWX8 The parts I'm struggling to conceptualize is what a 'universe expanding' means, and also why ...
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3answers
52 views

Why are pulsar's radiation beams collimated?

Every picture of a pulsar a see shows a very collimated radiation beam. What is the mechanism generating such a collimation? Note: I am not talking about "relativistic jets". I am talking about ...
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1answer
35 views

What do different frequencies in astrophysics data file mean? [closed]

I have a data file, with the first part looking like this. ...
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1answer
44 views

Surface brightness

I have to compute the surface brightness as a function of the radius from the following set of data: {right ascension ($\alpha$), declination ($\delta$), magnitude (m)}. I also know the center of the ...
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1answer
17 views

Baryon Acoustic oscillations - simple confusion about length scales

I am confused about length scales and baryon acoustic oscillations. I am clearly missing something very simple. The length scale found in the $SDSS$ and $2dF$ data is quoted as being $150Mpc$. ...
5
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2answers
156 views

How does the inclusion of vacuum energy modify Newtonian gravity equation of motion?

The equation of motion (in the center of mass frame) due only to gravitational forces between two point masses is: $$\frac{d^2r}{dt^2} = -\frac{GM}{r^2}$$ How does the equation get modified when a ...
9
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2answers
784 views

Do stars remain electrically neutral? [duplicate]

How electrically neutral do stars remain through their lifetime? As an example, I could imagine processes such as coronal mass ejections leaving the Sun in a slightly charged state. Are there such ...
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0answers
53 views

The reason for the fading of galaxies?

Galaxies that are greater than a distance of c/H metres from Earth have recessional velocities exceeding the speed of light and begin to fade. Thus, theoretical astronomers 3 trillion years the future ...
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0answers
36 views

Any method to determine the gravitational constant $G$ from observations in cosmological scale?

By the observations in cosmological scale, I mean observations by astrophysicists like motions of quasars in far distance from us, relative motions of our galaxy to others, etc. I know the famous ...