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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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 ...
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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, ...
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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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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 ...
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50 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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91 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?
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23 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 ...
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170 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 ...
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68 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 ...
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55 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 ...
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2answers
61 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 ...
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27 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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37 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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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 ...
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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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2answers
34 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
32 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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35 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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25 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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1answer
44 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 ...
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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 ...
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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
675 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. ...
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34 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 ...
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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: ...
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1answer
106 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 ...
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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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44 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 ...
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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
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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
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Curvy space in and around massive objects [closed]

If space curves around massive objects, what happens to the space within the massive objects?
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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?
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2answers
75 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 = $\mathrm{m_0}$ ...
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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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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?
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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 ...
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29 views

I have a fits file. I need to find the brightest pixel?

When I use astropy.fits to read the data of the fits file, I get a numpy array of values of shape(64,32,32). I am not able to understand what does this array contain. Ofcourse they are not RGB values ...
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3answers
71 views

If there were a planet with oceans tall enough saturn fitted in, would it be floating around? [closed]

In this morning I read an article that claimed (translated into english, so emphasis mine) Saturn is so slight1 it would float around in an ocean. So appart the missleading wording of its ...
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1answer
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What is the possibility of using the ionosphere or van Allen belts as a source of propellant for ion engines especially for orbital station keeping?

Just like how a jet engine uses the air it moves through to propel it self forward. In this case energy for ionizing the propellant won't be needed because we already have ions. How viable is my ...
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2answers
470 views

How can a low-mass star increase its mass to 1.4 Msun?

In my astronomy class I learned that a only low-mass stars (< 0.5 Msun) will contract, and then become degenerate, until it is a white dwarf. However, we also learned about the Chandrasekhar limit, ...
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85 views

Resources in space, and their distribution

I'm making a video game in which the economics of an interstellar civilization is important. What I'm wondering is, how are resources in space distributed? Since everything ultimately comes from ...
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47 views

Rotational axes of galaxies

The spiral shape is a preferred form for galaxies due to angular momentum, and the axis of rotation indicates a locally preferable orientation for the angular momentum. Why do galaxies in Hubble ...
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3answers
360 views

How to cut a stone on a White Dwarf?

I've heard that white dwarf stars are extremely dense and hard. So, if I had a piece of white dwarf matter, would it be possible to cut it (or otherwise) into a custom shape? How could one do that?
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1answer
461 views

Gravitational binding energy of a white dwarf at Chandrasekhar limit?

I was trying to calculate the gravitational binding energy of a white dwarf just before it went on a type Ia supernova in order to calculate the kinetic energy of the ejecta, but I wasn't able to get ...
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39 views

How far inside a white dwarf Roche limit does the Earth have to be to start losing large chunks of rocks?

I have calculated that for a one solar mass white dwarf orbited by the Earth, the Roche limit is about 600,000 kilometers. I understand that any loose mass on the surface of the Earth would start ...
9
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1answer
246 views

Does matter found at densities of white dwarfs “feel” more like a solid, liquid or gas?

I'm wondering what it would be like to touch or interact with very dense degenerate matter like this found at white dwarfs. I understand that white dwarfs are initially very hot, but for the sake of ...
5
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1answer
1k views

Reason why stars do not produce elements heavier than iron

In his book "Origins", Neil deGrasse Tyson says that "if you seek to split iron nuclei apart, you must them with additional energy. On the other hand, if you combine iron atoms they will also absorb ...
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1answer
31 views

Pulsar-white dwarf binary

In the paper from Hulse & Taylor 1975 on the first discovery of a pulsar in a binary system, they conclude that the companion to the pulsar must be a compact object, probably a neutron star or ...
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76 views

Structure formation: Galaxies as different entities and stars as groups

Why do stars exist in groups like galaxies rather than individual stars, and why do galaxies exist as different entities without continuity and with large intergalactic spaces?