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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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 ...
2
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1answer
104 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, \tag{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 ...
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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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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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1answer
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: ...
3
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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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0answers
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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2answers
37 views

Curvy space in and around massive objects [closed]

If space curves around massive objects, what happens to the space within the massive objects?
4
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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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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?
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46 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
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
25 views

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 ...
3
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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, ...
4
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0answers
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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1answer
37 views

Light curve analysis: how to estimate temperatures of Binary star system

I'm stuck at a binary star system lightcurve analysis. I have to set initial values for the bodies temperatures and then improve their accuracy by fitting. I know that the system type is WUMa. How ...
2
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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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2answers
64 views

How to read the following graph?

Just to give some background, the graph in the picture below shows the variation of Luminosity with the time period of Cepheid Variable Stars. In the expression $L/L_0$, $L_0$ is the Luminosity of ...
3
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4answers
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?
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2answers
838 views

How to calculate the force of gravity that wants to collapse a star?

In astrophysics, the pressure created by the outflow of energy from the interior of the star counteracts the force of gravity that wants to collapse the star. If I want to calculate this force for a ...
3
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0answers
26 views

Lense-Thirring Precession of short GRBs

Stone et al. 2014 have proposed that the jet resulting from the merger of a black hole (BH) and neutron star (NS) may precess due to Lense Thirring torques A large rotating mass e.g. the Earth, can ...
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0answers
26 views

What will be the weight of 1kg body at event horizon and then at the centre of black hole?

As we know if we go to the centre of the earth our weight will decrease gradually and at one stage we feel weightless.... Then what will happen if go to the event horizon then to the centre of black ...
3
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1answer
184 views

Calculating telescope detection rate

I am working through a paper from Inoue et al. 2013. In section 6.1, pg 18 it states, ... assuming a whole sky rate of ∼ 600 GRBs/year, a 5◦ diameter FoV and a 10% duty cycle, the telescopes ...
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0answers
31 views

Need help with determining the stellar mass using the NFW profile

My review assignment has a question that asks us to use the Navarro–Frenk–White (NFW) profile to find total mass in the galaxy using $$\rho(R)=\frac{\rho_0}{1+\frac{R}{R_c}}$$ then taking a triple ...
3
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1answer
108 views

Mach no. should be constant for existence of similarity solution

I am reading some research papers on Taylor-Sedov type self-similar solution to the blast wave problems... It is written that for the existence of similarity solutions Mach number should be ...
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1answer
30 views

Clarify difference between Peryton and Fast Radio Burst

Could someone knowledgeable in the phenomenon help me understand the difference between the class of observations called Perytons, and those called Fast Radio Bursts. I recall the "opening a microwave ...
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0answers
18 views

Relevant Archemidan Spiral Theorems: An Enquiry

Basically what I'm doing is investigating the solar wind's outflow. As part of this investigation is included a fairly crude application of a more complex outflow solution to that of basic archemidian ...
0
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1answer
22 views

If there was an object such as a bucket travelling through the atmosphere very fast could the air caught in it transition to a liquid?

The question came to me after thinking of the pressure waves in front of a spacecraft during re-entry. Would the pressure caused by the air being compressed cause the air to liquefy and if so at what ...
1
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1answer
46 views

Logarithmic Spiral arms in the Milky Way

I am trying to model the magnetic field of the inner 'disk' of the Milky Way Galaxy. I am following the model of Jansson and Farrar 2012. In section 5.1.1 of this paper they describe the Milky Way as ...
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1answer
120 views

About the LIGO result and Abhas Mitra [closed]

Well I read this article https://en.wikipedia.org/wiki/Abhas_Mitra and he has claimed that "The so-called massive Black Hole Candidates (BHCs) must be quasi-black holes rather than exact black holes" ...
2
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3answers
121 views

Gravitational wave detection and electromagnetic counterpart

Background Referring to this article on Fermi EM signal, 0.4 s after the gravitational wave detection by LIGO, FERMI detected an electromagnetic signal (poorly localized) with a false alarm ...
2
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1answer
28 views

Can a tidally locked planet have a horizontal rotational axis?

Is it hypothetically possible for a planet to be both tidally locked, and still have a rotation "horizontally"? Where the substellar point would in effect be like the point of a top, spinning and yet ...
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2answers
52 views

Kepler Orbits: Equal areas in equal times [closed]

I've written some python code to simulate a Kepler orbit. Every 50 time-steps I draw a radial vector from the centre of the sun to the centre of the earth, as shown below. However, my ...
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2answers
55 views

What's the nature of intraction between hydrogen atoms in the interstellar medium?

Interstellar densities are about 1 atom/cm$^3$. Do these atoms even move? If they do, why do they move? What would be their average speed? (Free expansion)
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0answers
30 views

Spectroscopy: The trustworthiness of reflected, refracted, and “mixed” light sources

Spectroscopy: If spectral lines are used to determine the composition of an object, wouldn’t the reflected light (e.g., from a star) that allows us to see non-luminous objects (e.g., planets, bolides) ...
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2answers
53 views

Can solar flares affect gravity?

Can a large eruption of solar flares on our sun change the effects of its gravity ever so slightly, and is it possible to measure these changes with the equipment we have today.
3
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2answers
103 views

What would the Sagittarius A black hole look like if we were in a spaceship just outside its event horizon?

Let's pretend that our spaceship is shielded well enough that being in the presence of the black hole won't kill us with radiation. I have read that the black hole is as large as the space between the ...
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0answers
46 views

How to calculate opacity of smoggy air (astrophysics)? [closed]

The question asks what the opacity of smog in the air is if you can just barely see a city that is 60km away. There is no other information. My thinking is that "just barely visible" means I have to ...
1
vote
1answer
36 views

How is the stellar flux for exoplanets calculated?

I have noticed that in many Wikipedia articles, the stellar flux received by each planet is stated. I tried to calculate this stellar flux from the given data, but the results didn't seem to be ...
0
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1answer
27 views

Will a collapsing black hole be ensured to be in eternal equilibrium at some point?

I'm just even if at all hobbyist in this matter. I learned that stars will collapse at some point and go supernova or turn into black holes if not able to keep equilibrium. But what happens in the ...
0
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0answers
22 views

Good books to read [duplicate]

I still regard myself as a beginner in the field of physics.. And there are a lot of information I should know, I am in my second year physics, and I need to read books which are not hard to ...
2
votes
2answers
64 views

Gravitational wave of Big bang? [duplicate]

Questions about the g-wave caused by the big bang: 1)was there a g-wave produced? 2) when will it reach us? 3) will it be too weak for us to detect(atleast now?)?
1
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1answer
27 views

Relativistic blast waves in medium of non uniform density

The relativistic outflow of a gamma ray burst drives a shock into the circumburst medium. This medium could have a uniform density $n_0$ or a density profile of the form, $n(r) \propto r^{-2}$. For ...
3
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2answers
79 views

Are ergs commonly used in astrophysics? If so, is there a specific reason for it?

I was reading the recent LIGO paper and one passage stuck out to me: The system reached a peak gravitational-wave luminosity of $3.6^{+0.5}_{−0.4}× 10^{56}\:\mathrm{erg/s}$, equivalent to ...
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0answers
111 views

What are the implications of today's direct detection of gravitational waves?

Here is the announcement from today's Physical Review Letters by Abbott et al.:"On September 14, 2015 at 09:50:45 UTC the two detectors of the Laser Interferometer Gravitational-Wave Observatory ...
2
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1answer
80 views

Why do we assert Hulse–Taylor binary system's orbital decay to gravitational waves and not radiation?

From https://en.wikipedia.org/wiki/PSR_B1913%2B16#Star_system The Hulse–Taylor system's orbit has decayed since the binary system was initially discovered, in precise agreement with the loss of ...