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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Are there formulae for calculating stellar luminosity and effective temperature as a function of age?

Is there a manageable formula or set of formulas or simple algorithms that approximate stellar luminosity and effective temperature (or radius) as a function of stellar age? I'm aware that accurate ...
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0answers
15 views

K-Correction of Photometric Data [on hold]

How do I achieve the K-correction with the Photometric data of type Ia Supernovae ? Basically, I want the corrected magnitude and following is the sort of data I have : ...
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3answers
2k views

How does one measure Earth's speed of revolution around the sun?

I know that there are several formulae that one can plug numbers into to arrive an estimate of Earth's speed around the sun (Kepler's third law for instance), but I'm wondering how these things are ...
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0answers
13 views

de-rotation of the cosmic microwave background polarization? [duplicate]

What is the estimator that used to de-rotation of cosmic microwave background polarization for Planck?
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1answer
48 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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0answers
37 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 ...
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1answer
109 views

Was the matter-energy content of our universe always distributed in the same ratios?

Currently, Dark energy (68.3%) and Dark matter (26.8%) together constitute about 95.1% total matter-energy content of the universe while only 4.9% is ordinary baryonic matter. Was this always the ...
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0answers
42 views

Antimatter in the solar system, Charge of the sun, and Annihilation

Since the sun is creating a lot of helium at once, and one of the protons has to undergo beta plus decay, Shouldn't there be at least a little bit of antimatter orbiting the sun? I know most of the ...
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1answer
96 views
+50

Potential of an axisymmetric disc with constant rotation velocity

I am having trouble understanding why the form of the 3D potential for a disc with a constant rotation velocity for circular orbits of stars within the disc \begin{equation} v(R) = v_0, \tag{1} ...
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3answers
53 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
57 views

Can we determine the surface temperature of stars other than the sun by using the black body radiation theory?

It is well known that the surface temperature of the sun can be determined by fitting the solar spectrum to the black body radiation spectrum. Is this scheme feasible for other stars? Possibly the ...
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2answers
29 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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3answers
6k views

Why did the asteroid belt between Mars and Jupiter form as it did?

I'm curious about why the asteroid belt wasn't pulled by Mars's or Jupiter's gravity or formed into either moons or planets. Why did it form into an asteroid belt instead?
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2answers
215 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 ...
1
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1answer
25 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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0answers
24 views

How to de-rotate the cosmic microwave background polarization?

the polarization of CMB is rotated by effect of cosmological birefringence. then to remove this rotation of polarization, we need to de-rotate this polarization. but I know about this de-rotating ...
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1answer
25 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
19 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 ...
1
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1answer
28 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 ...
1
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2answers
59 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
63 views

For gravitational wave from twin stars, how was the tidal effect counted?

As the primary indirect evidence, the work on calculating the rotational slow down earned the 1993 Nobel prize. However, I cannot find any where mention how the work deal with the tidal effect. Are ...
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1answer
25 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 ...
0
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1answer
42 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 ...
4
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1answer
42 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 ...
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3answers
45 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 ...
3
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1answer
200 views

Pulsar beam radiant intensity distribution

I'm curious about the radiant intensity distribution of pulsars: what's the general dependence of intensity on angle, and what are typical angular beam widths? How much does the beam width vary ...
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1answer
34 views
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1answer
42 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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3answers
4k 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 ...
9
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2answers
771 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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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 $150Mpc$. ...
10
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1answer
530 views

What would the collision between a (large) solid planet and a gas giant be like?

Assuming a Jupiter-like planet and an Earth-like planet (Except, say... half the mass of Jupiter), what would happen when the two collide? For clarification: What would the actual collision be like? ...
2
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1answer
1k views

What would happen if a hydrogen bomb were to explode in Saturn's atmosphere?

Purely hypothetical since any kind of testing in atmosphere/space is banned by international legislation/agreement. The humans have already bombed Luna so ... what could be expected to happen on ...
5
votes
2answers
153 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 ...
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1answer
1k views

What is the electric charge of the Sun and its corona?

What is the net electric charge (in magnitude and sign) of the Sun and its corona?
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3answers
7k 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 ...
7
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0answers
45 views

Are there any models for distribution of asteroid sizes in a belt?

Question: Is there any function that can describe the distribution* of asteroid diameters expected within an*' asteroid belt? *: distribution as frequency of occurrence within the asteroid belt or ...
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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
32 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 ...
4
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2answers
65 views

A question about the Fermi acceleration

In high school physics, we know that a charged particle cannot gain energy from a magnetic field. But, it seems that in the so-called Fermi acceleration, the particle is accelerated by the magnetic ...
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0answers
23 views

What is an overview of secondary school astronomy textbooks for students who have taken some calculus?

I teach mathematics at the secondary level. This year my students have founded an astronomy club. Most have finished two semesters of "college-level" calculus and are familiar with the derivative, ...
4
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1answer
231 views

What is the difference between the Big Bang Model and the Λ-CDM Model?

If I'm going to write about "The Consensus Model of Cosmology" should I include Big Bang Model or should I go with just the $\Lambda$-CDM Model?
8
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3answers
114 views

Gross “temperature” of a globular cluster

Globular clusters can be very large, which means we can do statistics about the stars in them. And that means we can try matching their star-as-particle potential/kinetic energy distribution against ...
15
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1answer
633 views

Do supernovae produce an appreciable amount of lithium?

David Z's answer to this question got me wondering - is any appreciable amount of lithium produced as the result of a supernova explosion, either by fusion (which seems unlikely to me, but I don't ...
3
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2answers
66 views

Why are they building eLISA and what implications would it have?

I understand that the next step after LIGO is to plan and build eLISA, I understand that out in space there are a lot less interferences compared to Earth which makes it a good way to detect things we ...
2
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1answer
59 views

Cosmic inflation and space flatness

I am new here, an avid Physics reader, but have lots of questions and doubts on which I'd like to get the help of a pro physicist. Here goes some about the theory of Inflation: a) after the first ...
22
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2answers
882 views

Do intergalactic magnetic fields imply an Open Universe?

According to a paper on the arXiv (now published in Phys Rev D), they do. How credible is this result? The abstract says: The detection of magnetic fields at high redshifts, and in empty ...
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2answers
62 views

Utilising Black Holes as a potential energy source

I'm aware of the Penrose process and the basic physics behind that. Also, I know that the Blandford-Zjanek process (That is potentially responsible for the relativistic jets). Aside from these two, ...
1
vote
1answer
118 views

Type II supernovae explosions

I'm quite confused about the explosion of a Type II supernova. As far as I understand, when the Fe-56 core has been created, and the star has all the other layers around it, it starts to collapse, ...
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0answers
28 views

How is mass of observable universe calculated? [duplicate]

How is even mass of earth known ? How do we get to know them? Whilst I was studying about dark matter it was listed about 'mass of observable universe' and density and so on...so what is the ...