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Questions tagged [astrophysics]

Questions involving the physics of the universe, especially the nature of astronomical objects, energy fields, and/or regions, rather than their positions or motions in space.

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1answer
24 views

who use the GADGET-2 pack for simulation? can I do it with my PC?

I want to do hydrodynamic simulatin for universe at vary redshifts. How can I do it? or how can I find an simulation of universe for use my work?
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0answers
14 views

Calculate rest flux density from emitted flux density derived from fits data of SDSS data tool

Say I have a spectrum of a galaxy at a redshift z, with flux density units of erg/s/cm^2/Angstrom. I'd like to convert flux density(in the same units) at z=0, i.e. at its rest it's rest emisison. How ...
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2answers
2k views

Gravitational Properties of Asteroids

How large would an asteroid have to be in order to hold a person so that the person could not escape?
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65 views

Rocket Equation from Newton’s 3rd Law, Force of Gravitation, and dp/dt

I am using the derivative of momentum (dp/dt) with Newton’s 3rd Law with the gravitational force of Earth.   $$ F - F_{gravity} = \dfrac{\mathrm{d}p}{\mathrm{d}t} \\ F - \dfrac{G \, m_e \, m_r}{...
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1answer
84 views

Where does Love's number come from in $\delta m = \frac{1}{2}k_2M_2\lbrace\frac{R_1}{r_\star}\rbrace^3$, the formula for the mass of a tidal bulge?

My question refers to page 165 of this paper. Specifically, how does one derive the equation $\delta m = \frac{1}{2}k_2M_2\lbrace\frac{R_1}{r_\star}\rbrace^3$ for the mass of a tidal bulge? A full ...
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1answer
84 views

A question related to black holes

Not a physicist just a simple guy, don't know much about physics as well. Just like to read things. I was reading about black holes and a question popped in my mind. If I understand it correctly ...
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1answer
39 views

Where can I find the previous years' International Astronomy Olympiad question papers?

I have looked at the official site but the link for previous papers isn't working.
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1answer
128 views

How much volume of gases could be added to Mars atmosphere that the planet gravity can retain?

This article Mars atmosphere states that Today Mars atmosphere is very thin, but it was not always like this. Around 3.5 billion years ago, the red planet had a thick enough atmosphere for liquid ...
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2answers
578 views

Can I see Harvest moon in India?

I just saw articles which say the Harvest moon will be visible in the US. Apart from the US, in which other country can people see it? Can I see it from India?
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1answer
83 views

By convention, when observing an exoplanet, is the observer's line of sight (on Earth) perpendicular to the plane of sky?

This is just a quick question. In this picture of the orbit of an exoplanet, is the observer's line of sight perpendicular to the plane of reference, which is in the +z direction on the diagram? In ...
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3answers
177 views

Does the universe curve in on itself?

I've read a little bit about the universe, but its not clear to me if there is a place in the universe beyond which there are no stars. For example, is there anywhere in the universe that one could ...
2
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2answers
116 views

Tallest cliffs, by falling duration

If you threw something over a certain cliff on a moon of Uranus, it would take over ten minutes to hit bottom. By this measure, local fall time rather than absolute height, what are the near ...
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0answers
36 views

Is there a way to calculate how much damage black hole merger shockwaves inflict on nearby objects?

Black hole mergers lose respective rotational energy during a merger. I understand that the energy 'emitted' is scattered as gravitational 'energy' that can henceforth be detected by gravitational ...
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1answer
132 views

Is it possible that Venus was once a rogue planet? [closed]

As Venus rotates in clockwise direction, while other planets rotate in anti clockwise direction: Is it possible that Venus was once a rogue planet?
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1answer
40 views

Maxwell stress contribution to $\nabla \cdot \mathbf{P}$ in the Navier-Stokes equation for fluid in stars

I was reading through the following extract outlining how the Maxwell stress contributes to the $\nabla \cdot \mathbf{P}$ term of the Navier-Stokes equation for fluids in a star. Here $\mathbf{P}$ is ...
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5answers
8k views

If all stars rotate, why was there a theory developed that requires non-rotating stars?

According to Penrose's research, a non-rotating star would end up, after gravitational collapse, as a perfectly spherical black hole. However, every star in the universe has some kind of angular ...
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0answers
97 views

What is the meaning of ellipticity of a galaxy being more than 1?

I was recently doing a project on calculating ellipticities of galaxies using SDSS data. I downloaded the stokes parameter values (q and u) from data $e = 1 - \frac{b}{a} = 1 - \frac{1 - \sqrt{Q^2 + ...
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2answers
89 views

Could anyone recommend a good book about the basics of astrophysics? [closed]

I am sorry if a similar question has been asked before. I look at other questions but was not entirely satisfied. So, I am a Psychology student who would like to know more about the basics of ...
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0answers
96 views

What decides the shape of a galaxy?

As I know, most galaxies are spiral, some elliptical, and a rare type is ring-shaped. What causes a galaxy to become a specific shape (i.e. ring vs spiral)?
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1answer
64 views

What is the significance of minus sign in the expression of apparent magnitude?

The apparent magnitude of a distant object in the sky is measured as m=(-)2.5 log (I/I0) Where I is the intensity of the object whose apparent magnitude is to be measured and I0 is the reference ...
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1answer
94 views

When and where are we exposed to most cosmic radiation?

I understand the mechanical dynamics of being faced away from the Sun at night, having a lower altitude, not being in the weak points at the poles in the atmosphere, being in a valley and others ...
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4answers
118 views

Tilting cycle vs orbital cycle of earth

Common sense tells us a year is conveniently divided exactly into four seasons. I'm wondering whether that means the earth's tilting cycle is equal to its orbital cycle. If so, there must be a reason. ...
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2answers
127 views

What is the effect of this expanding universe on the energy density of it?

We know that our universe is expanding i.e. volume of the universe is getting larger with time with total energy being conserved. My question is whether the energy density is getting smaller with ...
2
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1answer
110 views

Does nucleosynthesis happen near a black hole or during its formation?

During its lifetime, a star can synthesize elements to iron because of the pressure and temperature. A neutron star is composed of iron nuclei 56 and up to krypton 118. According to that, a black ...
2
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0answers
28 views

Fermi-LAT gamma ray spectrum too high [closed]

I am extracting gamma ray spectrum from Fermi-LAT data. My spectrum is a lot higher than the ones on previous studies of the same object. What could cause a spectrum to go too high?
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0answers
69 views

Any good books to read for complete beginners? [closed]

Currently, I am a Ph.D. student(mathematics) but always loved the field of astronomy hence I would like to read something on the "side" in this field along with my work. So is there any good ...
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0answers
19 views

How to convert magnitude to spectral luminosity? [duplicate]

In the Gaia catalogue I have the magnitude of several stars in the G band. I also have the distances to these stars (parallax is known). Additionally, I oftentimes have the effective temperature in ...
2
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0answers
34 views

Cosmology : Formula for the bias of galaxies

first I have posted originally on the physics stackexchange but I have not had answers about my question, so I try my luck on this specific forum (if forums leaders want to delete the original post on ...
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1answer
173 views

What is the time dilation less a magnetic field?

Does time dilation drop off like a gravity or does resemble a magnetic field model? Could a smaller body with a magnetic field have more time dilation then a larger body without and to what degree?
2
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1answer
102 views

How to deal with data that's billions of years old?

We look at galaxies that are billions of light years distant and draw conclusions based on the red shift of the light. How is the age of the light accounted for. We see the reality of a galaxy perhaps ...
3
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2answers
118 views

Book recommendation

I'm looking for a modern astrophysics text. I've had Barbara Ryden's book Foundations of Astrophysics recommended to me and it sounds okay, but the only review of it I've seen slagged off the problem ...
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1answer
170 views

If space is negative energy and matter is positive energy then does that mean the universe is finite?

I was reading a book by Stephen Hawking, it was written that universe is made up of 2 ingredients,i.e., space and energy and space was the negative energy, so they add up to 0. But since space is ...
22
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4answers
11k views

Why can't we feel the Earth's revolution?

I googled it and checked a few Q&A and there's only things about "Earth's rotation". But why can't we feel the revolution? They say we can't feel the rotation because the Earth spins at a ...
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0answers
83 views

Three Body Problem

I tried to solve the three body problem numerically. While after 1000 time steps the system looks stable (See Fig.1) it is completely unstable after 10000 time steps (See Fig.2). Is that an intrinsic ...
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0answers
44 views

How to write a normalized, dimensionless form of Binet's relativistic equation?

$$\frac{\delta^2 u}{\delta \theta^2} + u = \frac{\mu}{h^2} + 3 \mu u^2$$ This is Binet's relativistic equation. Here $u = 1/r$ where $r$ is the radial distance, and $\mu$ is the reduced mass of the ...
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0answers
73 views

To show perihelion precession motion of Mercury in Python with matplotlib

I'm trying to make it more general code so I can trace even a parabola or hyperbola for $e=1, E=0$ and $e>1, E>0$ respectively. And after achieving that general code I want to make the same code ...
2
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2answers
221 views

Can I learn astrophysics and astronomy with my basic math?

I want to learn astrophysics and astronomy, I'm very interested in it because there are many questions that popped up in my head, and really curious about things, but I'm afraid of a little bit on ...
2
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1answer
52 views

Given a star's mass, age, and composition, how do I calculate the rest of its properties?

If I'm given a star's starting mass, starting composition (metallicity), and its current age, How do I calculate the star's luminosity, current mass, and radius? I want to know how to do this for any ...
3
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1answer
74 views

Why are Bok globules so cold?

I have recently read a bit a out Bok globules. One thing, that is repeatedly emphasised is that they are among the coldest objects in space, with a temperature of ~3 K. Why is that so? Naively, I ...
2
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1answer
38 views

Astrophysics of Supernovae - Energy over Distance?

I need this for worldbuilding, but it is a physics question. I want to be able calculate the energy over distance from a hypernova of a variable star like Eta Carinae. Understanding what energy levels ...
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0answers
44 views

How is “surface brightness dimming” derived from redshift in the NED extragalactic database

I have several questions regarding “Surface Brightness Dimming” in the “Quantities Derived from Redshift” section of the Nasa/ipac Extragalactic Database. As an example, please use quasar IRAS F08279+...
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1answer
73 views

Law of Conservation of Information?

I read about Hawking and Leonard Susskind and their debates about whether information is destroyed or not if it falls into a black hole. It was resolved in favor of information always being conserved,...
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1answer
23 views

How to convert the observed magnitude of a Quasar to it's bolometric luminosity?

How can I convert the observed magnitude to Bolometric Luminosity? I know the relation for the star but should it be same for a Quasar? Basically I want to convert the X-axis of this plot to ...
3
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1answer
97 views

What happens if I were to add angular momentum to a maximally spinning black hole? [duplicate]

I am aware that a "naked singularity" is not possible. However, what would happen if I added angular momentum to a black hole near the maximal angular momentum limit? Does it asymptote?
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1answer
121 views

What is the farthest we can see into the universe?

Is there a limit in which the mass in space obscure the ability to detect anything farther even as technology progresses? Related: Can the range of the observable universe be extended through an ...
5
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1answer
149 views

Superscript-subscript uncertainty notation

While reading publications in astrophysics I've encountered this kind of notation (fictitious example): $$M = 6.1^{+0.6}_{-0.1} \times 10^{30} \textrm{ kg}.$$ Several examples are here, p. 2. I ...
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1answer
87 views

M87. What was the black hole before?

10 seconds before the M87 black hole was a black hole, what was it? A star 10 times the size of our solar system?
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1answer
33 views

Non-thermal Sunyaev-Zel'dovich effect

Exactly what is the non-thermal Sunyaev-Zel'dovich effect? From what I understand from reading several papers by Mark Birkinshaw and Sergio Colafrancesco, I get the rough idea that the non-thermal SZ ...
3
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3answers
42 views

Does coronal mass ejection include radiation at optical wavelengths?

It is known that during Solar/Stellar Flare, plasma from the corona of the star is released into the space, and travels comparatively slowly. In an hypothetical situation, does the coronal mass also ...
2
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2answers
101 views

Why does the Sun show different colour at midday and at morning?

As we see every day in the morning the sun shows a red-orange colour but at midday has a blue-white like colour why? Is it concerned with the distance from the earth or about intensity? How do you ...