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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35 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
19 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
147 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?
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3answers
107 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 ...
11
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1answer
584 views
+100

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 ...
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2answers
53 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 ...
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1answer
46 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 ...
20
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2answers
859 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
50 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
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1answer
116 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
27 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 ...
3
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1answer
41 views

Will stars disappear from the sky when their particle horizon is outside the event horizon

Given that the universe is expanding at an accelerated rate, will there be a point where stars visible in the night sky will simply disappear from view when their particle horizon is outside the event ...
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0answers
12 views

Why Free-Free emission is regarded as Thermal emission?

I read that thermal emission/radiation are the ones whose spectra is similar to that of a Black body radiation. Also thermal radiation depends solely on the temperature of the object. How can we ...
4
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1answer
87 views

Gravitational waves from neutron star - neutron star merger

How is neutron star-neutron star merger different from Black Hole-Black Hole merger and what information can be extracted from gravitational waves emitted by these processes?
3
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0answers
18 views

Relationship between oscillator strength and cross section

In the context of absorption of photons by atoms, I have come across two seemingly very related quantities, cross section and oscillator strength. In the book Physics of the Interstellar and ...
1
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1answer
158 views

Crab pulsar radiation

Regarding the radiation from the Crab pulsar and nebula, some reading leads me to the following conclusions. The rotation energy of the neutron star is the source of the non-thermal electromagnetic ...
5
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1answer
65 views

What's the evidence, if any, for some local concentration(s) of dark matter in some region(s) smaller than a galaxy?

What's the evidence, if any, for some local concentration(s) of dark matter in some region(s) smaller than a galaxy? Galactic-sized - or larger - gravitating halos seem to get all the attention. I'm ...
6
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1answer
49 views

Why is the white-dwarf mass distribution highly peaked?

I am doing an undergraduate course in astrophysics. The lecturer mentions that observed white dwarfs have a mass distribution that peaks at around 0.6 solar masses. Consider the plot from ...
4
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2answers
47 views

Why is the distribution of Cosmic Rays isotropic?

We observe that cosmic rays (CRs) are isotropic on the sky, i.e. they come from all directions with no apparent preference. I understand this is related to the deflection of these CRs by the magnetic ...
3
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1answer
23 views

What is a quasar flux ratio anomaly?

In the context of strongly lensed, multiply-imaged quasar observations, I sometimes hear about "flux ratio anomalies". What are these? Why are they important?
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0answers
36 views

Gravity Theory Question [closed]

Three Questions: Is the Modern Five Dimension Theory of gravity an adaptation of Einstein's relativity theory? If so, can it allow us to accurately predict the movement, speed and direction of ...
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0answers
37 views

Is it true that in a black hole there is a point where there is no attraction of gravitational pull?

If so how is this possible because the black hole containing so much gravitational power might not have such faults in it
10
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1answer
1k views

If matter and antimatter repel, how do we know other galaxies aren't made of antimatter? [duplicate]

Wikipedia's article on antimatter says this: There is considerable speculation as to why the observable universe is composed almost entirely of ordinary matter, as opposed to a more even mixture ...
2
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1answer
68 views
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3answers
3k 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 ...
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0answers
48 views

Can the energy released from a black hole be calculated at the time of birth?

this might be a stupid question but when a black hole is formed it releases a lot of energy our satellites just catch the gamma rays and X rays released by the black hole. can we estimate the amount ...
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2answers
31 views

How to calculate the mass of the orbiting body given only its orbital information

A question asks the following: Using Newton’s Law of Gravity, show that the mass of a planet can be written: $$M = \frac{4\pi^2a^3}{ GP^3}$$ where $a$ is the semi-major axis and $P$ is the orbital ...
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1answer
31 views

How do black holes join each other? [duplicate]

If black holes can swallow any object, and can radiate energy, then how could black holes join each other and can form bigger black holes?
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0answers
28 views

Is there a direct/indirect detection for the homogeneity of the Universe?

I know that for mathematical simplicity the Universe is assumed to be isotropic and homogeneous (the cosmological principle). The isotropy of the universe, and correct me if I'm wrong, is confirmed ...
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0answers
20 views

What happens when we use the Virial Theorem iteratively?

Say I want to model the formation of structure in the Universe as a series of events whereby already virialised systems are brought together to create a larger virialised system. I will take the ...
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0answers
17 views

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, ...
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0answers
4 views

Dependence of low res spectrum of binary system on phase

How much a low resolution spectrum of a binary star system depends on the phase of the system? i.e., what's the difference in the spectrum if star1 is ahead of star2 or star2 is ahead of star1 or ...
1
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1answer
41 views

Are there star systems orbited by stars? [closed]

I never really heard about such occurencies and now asked my self if this could be possible. So could there be systems with a star (or black hole) that is so heavy that other less heavy stars are ...
1
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0answers
26 views

How is it possible to have such massive black holes? [duplicate]

Recent observations discovered really massive black holes, up to $20-40$ billions Solar masses. Now, according to an recent study and various computer simulations (I'm sorry, I don't have any ...
5
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0answers
38 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 ...
20
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2answers
3k views

Why is the cut off mass for massive stars 8 solar masses? Why can't it be 10-11 solar masses or so?

I know that stars having a mass greater than or equal to 8 solar masses are termed "massive stars". But why is the cut-off 8 solar masses?
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2answers
656 views

What are the demographics of stars visible to the naked eye?

Of the stars that can be seen with the naked eye, what are the distributions of each type? For example, how many are main sequence? how many are Super Red giants/white dwarfs/neutron stars...etc. ...
0
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1answer
33 views

Angular momentum, its conservation and Nebula theory

I am carrying out a research work and I am stuck at the first page where there is an introduction to the angular momentum and its relationship in the formation of the solar system. According to that ...
1
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1answer
41 views

What size of object does the peak of the cosmological power spectrum correspond to?

The title almost says it all, but to flesh it out more, what is the size a sphere corresponding to the peak in the cosmological power spectrum (Figure 2: ...
3
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1answer
91 views

What causes the differential rotation of the Sun?

I have read the explanation in Wikipedia, but the problem is that because I'm a beginner in physics, I don't quite understand what more than half of the words mean! Here is the explanation from ...
14
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1answer
2k 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 ...
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0answers
43 views

How can the energy of a spinning black hole be converted into magnetic field?

I've read about the Blandford-Znajek process, and what I understood is that the black hole is treated as if it were a conducting sphere spinning rapidly with an accretion disk around it, and the ...
8
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2answers
3k views

What would happen to a teaspoon of neutron star material if released on Earth?

I've read on NASA's page on neutron star that one teaspoonful of that star would weigh over 20 billion tonnes on Earth. If it was somehow possible to bring it to earth would it: Burn and disappear ...
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4answers
12k 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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2answers
36 views

Curvy space in and around massive objects [closed]

If space curves around massive objects, what happens to the space within the massive objects?
3
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1answer
3k 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?
4
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2answers
72 views

If we increase the mass of a black hole by a factor of $k$, by what factor will the surface area of the event horizon change?

If we increase the mass of a black hole by a factor of $k$, by what factor will the surface area of the event horizon change? Given any number of identical black holes each with mass = $\mathrm{m_0}$ ...
0
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0answers
25 views

Time and light and the expansion of space , the effects?

Here is my question : Space is expanding at an accelerating rate and apparently at the far reaches approaches the speed of light and then as it exceeds the speed of light to effectively be removed ...
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0answers
64 views

What is the metric at the center of a star? [duplicate]

If there is only one star in the universe then is the metric at the center of the star flat?
4
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2answers
3k views

How long does it take a black hole to eat a star?

I presume the answer is that it depends on the mass and size of the star and black hole and how they approach either other, but I was wondering if somebody could provide some rough bounds (e.g. hours ...