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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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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65 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 the ...
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78 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
842 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 ...
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27 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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28 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 ...
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1answer
186 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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1answer
57 views

Need help with determining the total 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 ...
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1answer
112 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 constant.....
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1answer
33 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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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 ...
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1answer
23 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 ...
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57 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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126 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" ...
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3answers
143 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 ...
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1answer
31 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
58 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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31 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
61 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.
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2answers
108 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
50 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 ...
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1answer
45 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 ...
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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 ...
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24 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 ...
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2answers
68 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?)?
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28 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 ...
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2answers
83 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 $200^{+...
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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 ...
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1answer
87 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 ...
3
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1answer
36 views

Question about the Blandford–Znajek process

I've been trying to understand the Blandford–Znajek process which explains how Gamma Ray Bursts form, but it's still not clear to me how it works. In this article, several theories about the formation ...
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3answers
112 views

How do we determine the pressure at the surface of a star?

Is there any means to do so? I know there are some means to determine the surface temperature.
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71 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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161 views

Why do stellar boundaries exist?

What theorems or insights are available to decide wether a star with some given interdependence between its density, pressure and temperature distributions ought to have a boundary at a finite ...
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2answers
121 views

Is there a natural source of Antimatter in this universe?

I was just asking if there is an natural source of Antimatter in this universe capable of creating simple molecules/compounds? So, any good answers?
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0answers
51 views

Why do some stars actually produce “Gamma ray bursts”?

I looked it up but I haven't found any explanation as to why some stars produce them, I understand that collapsing and merging stars produce them, but my question is why is the energy concentrated in ...
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0answers
27 views

What are these cycles in orbital eccentricity called?

I have created a simulator for planetary systems. When I run it with our own solar system and plot the eccentricity, aphelion and perihelion of the orbit of Earth i get these cycles. Do these ...
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3answers
112 views

is the potential energy of a black hole infinity

It appears like black holes posses an escape velocity greater than the velocity of light. It takes an atom infinity energy to travel at speed of light.Do black holes posses that energy to retain light ...
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1answer
112 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 case?...
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3answers
89 views

Measuring Rotation of Sun

If the sun had a uniform surface (i.e., if there were no sunspots to look at), is there a practical way to measure its rotation? In other words, if some external force flipped the sun's spin suddenly,...
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38 views

Could a satelite be pulled away by gravity while the object it was orbiting keeps unaffected in its own orbit?

I'm asking this, since I try to educate my self a bit in the field of astrophysics. From my point of knowledge the by title given scenario could occur. But I haven't yet read anything that sounded ...
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0answers
30 views

How do modern particle detectors identify and segregate different particles

What is the specific particle detector technology used at CERN or similar Institutions. Is it essentially a big digital camera? When said particles are detected, how are they segregated, How does this ...
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1answer
94 views

Special Relativity problem - proper time interval

The supernova 1987A explosion in the Large Magellanic Cloud 170 000 light years from Earth produced a burst of anti-neutrinos ν ̄e which were observed in terrestrial detectors. If the anti-neutrinos ...
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2answers
63 views

Is there a doppler effect on the images of stars around rotating black holes?

I'm an illustrator working on a project involving rotating black holes like those discussed in "Gravitational Lensing by Spinning Black Holes in Astrophysics, and in the Movie Interstellar" by James, ...
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1answer
77 views

What is the invisible mass in the universe?

According to scientists, currently the edge of observable universe from the earth is about 14 billion parsec. This means that the diameter of the universe is nearly 91 billion light years. If we ...
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1answer
64 views

Where do astrophysical neutrinos come from?

What I really do not get about them is collisions of cosmic rays with light produces high energy neutrinoes but cosmic rays have a little energy maybe less than a 5000 electron volt. How do high ...
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0answers
50 views

Nucleosynthesis: other than big bang and supernova

According to many texts, hydrogen and helium and traces of lithium-7 were created in a brief period after the big bang; helium is created through fusion (pp, CNO) in main sequence stars; elements like ...
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1answer
49 views

A question on Jeans's instability

I am a Physics student and I'd really appreciate if anybody could help me with an exercise my professor gave me a couple of weeks ago. It goes like this: Let us consider a spherical symmetrical gas ...
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1answer
101 views

Second order Fermi mechanism. Is there a mistake in the Claus Grupen book?

The second order Fermi mechanism describes the interaction of charged particles with magnetic clouds. This model leads to a collision-less acceleration of cosmic rays up to ultra high energies. A ...
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1answer
82 views

How does Planet 9's perihelion and aphelion affect the Kuiper belt objects?

Assuming that the existence of Planet 9 is confirmed and it really exists, how does it affect the orbits of the Kuiper belt objects? My understanding is that the discovery came in part from the ...