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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How well conserved is etendue in extreme gravitational lensing scenarios?

This excellent answer to Could dark matter exist in the Universe in the form of sufficiently dense objects? includes the following image and description: Light from the background galaxy circles a ...
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How do astronomers know that distant galaxies aren't actually nearby star clusters?

When reading about the recent release of data from the Dark Energy Survey, and the 'pictures' of well over 200 million distant galaxies, I got to wondering: How can they know that a small, faint, ...
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Is a Hertz ratio to 65M ☉ proof that Betelgeuse had a core collapse in 1491 from a gravitational wave on January 14, 2020? [closed]

By analysis of gravity waves GW150914 to S200114f when compared to a ratio from the Black Hole merger of 65 M ☉ at 260 Hz with Betelgeuse frequency of 64.698303 Hz the gravitational release on January ...
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Relationship between 3 quantities : Density Matter power spectrum, Density Matter angular power spectrum and Temperature angular power spectrum

I take over another post that is going to be deleted since I have none answer. Summary: I would like to go deeper in the relationship between Matter power spectrum and Angular power spectrum. From a ...
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3answers
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How can a black hole have a charge, or be charged?

So-called 'hairless' black holes (no-hair theory, or theorem?) , which is what real black holes are, can be described by just three characteristics: Mass, spin, and charge. It is easy enough to ...
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What happens to the 99.9 % of the sun-rays that do not fall on any planets or any other celestial body?

I assume that about 99.9% of the sun-rays that do not fall on any planet or any other celestial body keep on traveling farther and farther unto infinity. Apparently such rays get lost. Keeping in mind ...
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Learning astrophysics from zero

I'm a liberal arts student, an undergraduate English student who out of the blue, started getting interested in astronomy and physics, searching for facts all the time, googling about some theories, ...
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2answers
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What explains the existence of energy/matter if it cannot be created or destroyed?

If the energy/matter that was contained in the singularity before the Big Bang had always existed, and if it’s true that energy/matter cannot be created or destroyed, then what explains its existence?
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What exactly is the orbital period value of Sirius binary star system?

My Textbook An Introduction to Modern Astrophysics 2nd edition (2017), page 557 mentions that the modern value is 49.9 years. But Wikipedia mentions 50.1284±0.0043 years. Which is correct? Or, has the ...
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What are good resources to study Gravitational Waves?

I am undergraduate student having basic knowledge of Physics. I'm looking for resources (books, video lectures, research papers, etc) to study Gravitational Waves from scratch, I think initially I ...
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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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Error of bisector method

How to determine the error of bisector velocity span? I have found the article below, but I do not know what all quantities mean. What is the number of lines in the mask? How to find out x? How to ...
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Degrees of freedom in restricted circular coplanar three body problem

How many degrees of freedom does a mechanical system consisting of three bodies, the Sun, Jupiter and an asteroid, have in the restricted circular coplanar problem of the three bodies? I know that if ...
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What is the sun's maximum influence on a magnetic object?

How much magnetic repulsion could the sun's magnetic field produce on an magnetic object? Consider the object is ideal: It could be flat, to create more resistance, balanced, to stay on the opposing ...
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Role of power laws in astronomy?

I often see astronomers fitting data to power laws. What about power laws makes them so useful in astronomy? Why are so many astronomical observations well-fit by power laws? I know it's a relation ...
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How does the evolution of a solar system not break the second law of thermodynamics?

Please forgive: I am a layman when it comes to physics and cosmology, and have tried finding an answer to this that I can understand, with no luck. As I understand it, the solar system evolved from a ...
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Basic, learning examples of applications of CFD and MHD in astrophysics, and current research directions using these techniques?

I am an undergraduate in Physics, and I have an opportunity to work with a some of my seniors to learn Computational Fluid Dynamics (CFD) and Magnetohydrodynamics (MHD). I would like to choose my ...
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Is the dark matter just regular matter out of the observable universe?

Could it be that darkmatter is actually the gravitational influence of regular matter that is situated out of the observable universe?
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Looking for analytical expression of Cosmic Variance - Poisson distribution?

I have an expression of Matter Angular power spectrum which can be computed numerically by a simple rectangular integration method (see below). I make appear in this expression the spectroscopic ...
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Shot noise in cosmology : Expectation and Variance expression

I am trying to express the Shot noise in cosmology context, mostly the Shot noise expression into error on a $C_\ell$ If this would be only for myself, I would take $$\text{Variance}(Shot\,noise) = 1/...
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Why did astronomers believe most or all stellar black holes had masses no greater than 15 solar masses?

The so-called 'mass gaps' for black holes, according to theoretical models, are between 2-5 solar masses and 50 to 150 solar masses. (Actually, I have read that there is no good theoretical reason ...
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1answer
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How to isolate H$_\alpha$ from Nitrogen doublet emission lines

I am trying to find out line intensity and FWHM of H$_\alpha$6565 emission line from a quasar spectrum obtained from SDSS DR-14Q. Visual inspection of spectrum shows H$_\alpha$ being contaminated with ...
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1answer
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If Proxima Centauri goes supernova will it negatively affect the Earth? [duplicate]

Proxima Centauri is the closest star to the Earth (besides our Sun). If it went supernova, would such an event negatively affect the Earth? Can Proxima Centauri negatively affect the Earth in some ...
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1answer
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Can a neutron star ever be less than about 1.44 solar masses (the Chandrasekhar limit)? Why not?

I learned about the Chandrasekhar limit as being the UPPER limit, in terms of mass, for a white dwarf... But, I have never heard of a neutron star being BELOW that mass, so I have wondered, recently, ...
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Is our universe stable or metastable?

I've been reading and thinking about this subject for some time, but I can't seem to find a clear answer. After reading Q14: Aspects of the Higgs boson suggest that our Universe is only “...
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What new instruments “so sensitive that we can see (large circumgalactic winds) have only been on telescopes for a few years”?

The Rhodes College press release Prof. David Rupke and Team of Astrophysicists Make Major New Discovery About Galaxy Evolution links to Astronomy Community/Nature.com: The Making of Makani; The story ...
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What is the application of pseudorandomness in astrophysics?

What are the advantages of using pseudorandom numbers in Monte Carlo simulation instead of random numbers? What are other applications of pseudorandomness in astrophysics? Many thanks.
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Is **Voyager I’s** reduced data transmission rate as described in [this article][1] because of the distance or because its transmitter getting slower? [closed]

Is Voyager I’s reduced data transmission rate as described in this article because of the distance or because its transmitter getting older & slower?
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Any examples of a gas object temperature from Doppler broadening along one axis turning out to be wrong because velocity spread was not isotropic?

Discussions under Mass of the stellar cluster (not the whole galaxy) lead me to mention that when an actual temperature is inferred from a Doppler-broadened line profile (rather than just a linewidth ...
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Why do stars born in a cluster finally disperse?

In other words, if a group of stars born within the same nebula, e.g. the Pleiades, are initially gravitationally bound - what causes them to finally get separated and proceed individually? Is it the ...
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How to determine the age of a star using asteroseismology?

I keep reading that a standard way to determine the age of a star is asteroseismology, and I tried to learn more about it. I am wondering if somebody could help me to describe the method in simple ...
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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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Orbital Angular Momentum of a Binary Star System

Let's say you have a binary star system, consider the orbital motion of that binary star consisting of two solar-like stars separated by 20 stellar radii. How would one calculate the angular momentum ...
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1answer
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What exactly is space-time fabric?

I have heard about space-time fabric but I can't understand its definition. Is space-time fabric a physical thing or did Einstein imagine it to assist him with general relativity?
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1answer
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Spectra: What is that Supposed to Mean?

I've found this website (click here for the link), the link leads you to a problem about the velocity Andromeda is going towards the Milky way galaxy, and you can try three approaches. I like to ...
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1answer
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Virial ratio behaviour

I think I didn't understand something about virial theorem for an $N$-body system, for instance the behaviour of virial ratio $T/\Omega$, with $T$ kinetic energy and $\Omega$ gravitational potential ...
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1answer
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Resource Recommendations to systematically develop a foundation via Self study in Astrophysics/Astronomy?

I am a high school senior (Grade 12) with a passion for Astronomy/Astrophysics. I already searched quite a bit here on the other questions on resources, but I couldn't find any that shows a concise, ...
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How do scientists know that distant parts of the universe obey the physical laws exactly as we observe around us?

How do scientists know that distant parts of the universe obey the physical laws exactly as we observe around us? The question might look a bit odd but I am really stuck on my head. We know, ...
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Astrophysical particle spectroscopy; narrow-line particle sources (charged or uncharged) for things other than photons? Have any been detected?

Is Cosmic Ray Astronomy a thing? Is there an equivalent of the red shift effect for cosmic rays? have got me thinking and under this answer I've commented: That's a good point; there aren't as many ...
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What's the minimal argument I can give to reject The Geocentric Universe?

I'm new to Astrophysics, So pardon me if you find it silly to ask. I was just started reading about the basics of astrophysics. I read about the Greek Tradition, the concept of a geocentric universe. ...
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1answer
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What exactly is “the rotating lighthouse model” in the context of a double pulsar?

The introduction to Testing the rotating lighthouse model with the double pulsar system PSR J0737-3039A/B (open access) says: The double pulsar system PSR J0737-3039A/B was discovered by Burgay et al....
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1answer
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Fraction of initial mass lost (radiated) by neutron star mergers compared to black hole mergers?

GW190521 black hole merger total mass calculation and missing mass, how does this happen? notes that there are about 9 solar masses missing from the final black hole. GW170817 is the first observed ...
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How much more mass would Mars need to currently have enough pressure for liquid water and oxygen?

My question is whether Mars just about failed to meet the threshold or missed it by a lot. It's been dry for 3 billion years. How much bigger would it have needed to be to buy it that extra time? Let'...
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1answer
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Keplerian Elements

So, I've been doing endless research, and I've found a bit of information, all in different places, that is. Now, I'm getting really confused about it; I can't keep up with it all anymore, so, now, it'...
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How massive does a moon have to be to have a stable magnetic field?

Is there a minimum mass or other minimum properties necessary for a body to have a strong, stable dynamo to create a magnetic field conducive for life? For example, would it be possible for Titan to ...
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Is there software to calculate/plot decomposed rotation curves from observational data (FITS, etc)? [closed]

I have observation data of galaxies (in FITS format). From the FITS data, I want to calculate & plot the decomposed rotation curves as pictured below. Is there a software package that will do that ...
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Why isn't most hydrogen in the universe molecular (diatomic), instead of atomic (monoatomic)?

Similar questions have been asked before; but, why? Is the monoatomic hydrogen left over from the Big Bang? And hasn't had the opportunity to collide with other hydrogen atoms yet? Or are hydrogen ...
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How can astronomers pinpoint the location of the source of a neutrino?

In the popular press, in recent months, we have heard a lot about high-energy neutrinos from far outside our solar system reaching our detectors.... But I wonder... If a single neutrino from a great ...
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Has anyone back-calculated previous close encounters between the Apophis asteroid and Earth?

The Apophis asteroid was only discovered in 2004, and shares an orbit similar to Earth's orbit, leading to many close encounters on the scale of decades. Most of the stories about this asteroid are ...

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