Questions tagged [astrophysics]

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's the minimum possible mass of a stable neutron star? [duplicate]

What's the minimum possible mass of a stable neutron star? Let's say you have a neutron star and slowly take away it's mass, e.g., either by firing a stream of anti-neutrons or by proton decay, since ...
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How to explain why an element constantly absorbs certain wavelength of a starlight? [duplicate]

I really cannot grasp what happens to starlight that gets absorbed by an element or more. The atoms should have a capacity and in no way constantly absorb light like a sink. If that light is somehow ...
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If the inclination of a cloud of oxygen in outer space is to diffuse, then how do nebulae form?

If a cruise ship-size object in outer space were surrounded by a spherical cloud of oxygen, and there were no other bodies exerting significant gravitational force in the vicinity, would the cloud of ...
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Cosmology context - MCMC code : Recomputation of covariance matrix after each point accepted

I am working on a MCMC code (basically with Metropolis-Hastings) and I would like to understand different important points. We always mention the covariance matrix which is used in the computation of ...
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Spherical harmonics with 2 cosmological probes : considering $a_{\ell m, photo}$ as a constant and $\hat{a}_{\ell m, spectro}$ as an estimator

I am in cosmological context where the survey on which I am working has 2 probes : a photometric galaxy clustering ($GC_{ph}$) probe and a spectroscopic galaxy clustering ($GC_{sp}$ probe). We use an ...
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Can Black hole eat white hole or white hole eat black hole? [duplicate]

No light can enter black holes, but is it possible for a white hole to enter a black hole? Or vice versa? Could there be black holes inside the white holes? Or were there black holes inside them that ...
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How to test for possible negative mass of dark matter?

What is the phenomenology of how to test if dark matter has possibly a negative mass (WP negative mass) in particle physics experiments, cosmology or astrophysics? I lately came across this ...
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What implications to cosmology would it have if Webb Telescope probing the far end of our observable Universe finds out a large number of galaxies?

Since it is predicted that Cosmos is no less than 250 times that of the observable Universe (13.8 Blyrs) in size: MIT Technology Review I wondering how you can calculate any age of matter creation (...
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Does the Milky Way have any impact on Earth?

Does which galaxy we are in (Milky Way) have any impact on Sun/Earth? What I mean is: suppose our solar system was instantly teleported into a different galaxy (eg Andromeda). Apart from the stars ...
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Can Jupiter turn into a star if it radiated off enough heat?

Since a star heats up when it radiates more heat (via gravitational compression), and since that's also how protostars turn into stars, I was wondering what are the chances of Jupiter reaching the ...
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About the non-intuitive announcement at 12 May 2022 of the EHT team that spin axis of Sgr A* Black Hole facing Earth?

What is this all about?: At 12 May 2022 at the ESO official announcement live streaming event the EHT representatives claimed that the Sgr A* BH accretion disc spin axis is sort of facing Earth's ...
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Why are there three bright spots in the first picture of Sagittarius A*?

Why are there 3 distinct bright spots? The old blackhole picture had half bright and half dark, which I believe is a result of the different relative velocities of particles orbiting it, (towards or ...
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What does $C^{XY}_{\ell}$ mean when we weasure $a_{\ell m}$ in the sky?

In cosmology context, we have the general formula for the angular power spectrum $C_{\ell}$ : $$C_{\ell}=\left\langle a_{l m}^{2}\right\rangle=\frac{1}{2 \ell+1} \sum_{m=-\ell}^{\ell} a_{\ell m}^{2}=\...
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The Event Horizon Telescope collaboration will announce groundbreaking observations of our galaxy at 12 May 2022, what this announcement could be? [closed]

"Live webcasting for the ESO-hosted EHT 2022 event On 12 May 2022 at 15:00 CEST, the European Southern Observatory (ESO) will host a press conference on groundbreaking new Milky Way results from ...
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Can someone explain exactly what Bates is doing on page 42 of Fundamentals of Astrodynamics?

(See below for answer, I made a few math errors and a bad assumption about what he did) Or rather, can someone explain exactly why he's using $v=1 \frac {DU} {TU}$ when according to the first given is ...
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Why is it that Transneptunian Objects (TNOs) have colour indices that are in the red yet some are considered blue, gray, or neutral?

The B-V (Blue-Visual) colour index for Orcus is .64, for Eris is .78, for Makemake is .83, for Quaoar is .94. This is all in +, which indicates red and cold, as in red stars, and - indicates blue, as ...
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Which type of star is most effective for solar power?

I'm working on a worldbuilding game, and the subject of stars has come up. Imagine you're a species, chilling in the Goldilocks zone of some alien planet, orbiting an alien star. Your people stumble ...
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Help in understanding how general relativity describes space-time near black hole poles that emit astrophysical jets

I am aware that General relativity does not explicitly deal with 'expanding' or growing and due to that reason 'cosmologically pressurised' aether (proposed by the 'Theory of a river flow' but that ...
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1 vote
1 answer
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What is the largest hollow structure that could be made before gravity becomes a problem?

Assume realistic strength of materials, like that of steel or stone, or even something with "good" properties like carbon fiber, or advanced ceramics. If one was to put together a hollow ...
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Does the HD1 Quasar explain how Super Massive Black Holes Form?

The galaxy HD1 has a 150M SM BH at its core. HD1 formed SUPER early in the universal history. It is 13.5B LY away (basically 330 M years after the big bang)... So does this show that the clumpiness ...
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What determines the black hole accretion rate?

There is clearly a natural timescale to accrete matter around a black hole given by the balance of pressure and gravity, known as the Eddington luminosity. However, as I understand it, this is really ...
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Does magnetism play a role in the formation of galaxies?

Forgive my ignorance as I know next to nothing about physics. From my layperson's understanding, galaxies are formed primarily by the interaction of gravitational forces of stars and planets, however, ...
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4 answers
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Have solar wind particles escaped the Sun's gravity or will they eventually return back?

I've read that solar wind consists of hydrogen atoms that are, near the Earth, travelling at about 450 km/s. This is only 3/4 of the Sun's escape velocity, but then the Earth is also 150 million km ...
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How can a pulsar slow down?

I saw in some astronomy textbooks that pulsars gradually slow down due to the loss of energy by its radiation. I wonder why this is possible? Although the radiation is now not thermal but in the form ...
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Latest textbooks on computational thermal analysis

I want to simulate the heat caused by planetary collision and I want a textbook about computational thermal analysis that explain the heat simulation
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How do BAOs provide evidence for dark matter?

So far my understanding of BAOs is that they are a relic of the old universe formed by the freezing of acoustic density waves in baryonic matter as the universe entered the recombination epoch. These ...
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Does pressure increasing or decreasing due to temperature have an impact on the Sun Core's "Thermostat"?

Firstly, thank you for reading this post. I have a question regarding how the Sun regulates its nuclear fusion rate in its core. This is commonly known as the Sun's thermostat. This is a homework ...
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1 vote
2 answers
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Could anything ever be brighter than the sun in our sky?

Is there anything that could explode or exist that would appear brighter than the sun in our sky? There was that meteor in Russia in 2013 where it appears brighter than the sun. However, is there a ...
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Colours of the sky if sun was blue?

What would be the colours of the sky at different points of the day if the sun was a blue star? This is assuming that our earth is at a similar distance away from the surface of the blue sun as it is ...
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How much percent of the speed of rotation of the solar surface at the equator is due to frame dragging effect? [closed]

Frame dagging effect is interesting and my particular interest is does this rotation could be compared with the law of motion of planets in a system similar to our Solar system and also can we measure ...
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Apparent diameter of Sun

The light ray grazing the surface of a massive sphere of coordinate radius $r > \frac{3 GM}{c^2}$ will arrive at infinity with the impact parameter $b=r\left (\frac{1}{1-\frac{2GM}{rc^2}}\right)^{1/...
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Fusion Rate and Luminosity in Stellar Model

In astrophysics textbooks one of the differential equations to solve in stellar model is $$\frac{dL}{dr}=4\pi r^2 \epsilon$$ where $L(r)$ and $\epsilon (r)$ are the luminosity and fusion rate per unit ...
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What is the shape of a Kerr black Hole, like in Schwarzschild BH we know it is just a spherical distribution of mass $M$?

We know that the Schwarzschild solution pictures the outside region of a spherical distribution of mass $M$, which is also non-rotating, charge-free and spherically symmetric. We can begin to describe ...
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6 votes
3 answers
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What does "hard tail" mean in the context of astronomical spectra?

I am currently reading about neutron stars and came across this sentence: "Often the radius is underestimated because only a hot spot emits or the spectrum contains a hard tail." I can find ...
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How can they estimate exoplanet radial velocities using Doppler considering spectrograph resolving power?

I read that spectrograph resolving powers, the ratio of wavelength uncertainty to wavelength are like 1000 or 10000. Plugging this into the non relativistic Doppler formula gives a velocity ...
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How do you integrate by parts when you have a triple integral?

I'm studying how particles of equal mass behave in a spherical cluster held intact by gravity. I will assume that the mass density $\rho(R)$ of the cluster is a function of the magnitude of the ...
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Gravitational Lensing equation?

Consider the notion of Gravitational lensing. Gravitational Lensing is when light bends around a distortion in spacetime. According to this article, the angle of deflection in terms of curved ...
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Non-Comulative nature of Mass-Radius curves of Neutron Stars

For finding the mass-radius curve of neutron stars, we can solve TOV Equations which are constraint equations got by solving Einsteins equations. The boundary conditions are $m(r=0)=0$ and $\rho(r=0)=\...
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2 votes
1 answer
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Reversal of the psychological arrow of time on the contraction of the universe [closed]

In Brief History of Time, it says that the people living in a contracting phase (although unsuitable for living or even existence itself, but lets assume) would remember the future but not the past. ...
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Prove this Relation of Chirp Mass [closed]

In my astrophysics homework, I was asked to prove this equation of chirp mass $$\frac{(m_1m_2)^{3/5}}{(m_1+m_2)^{1/5}} = \left[\frac{-5}{192\pi}\frac{\mathrm{d}T}{\mathrm{d}t}\right]^{3/5}\frac{c^3T}{...
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A question regarding intensity of electromagnetic waves

Consider a source of electromagnetic radiation in vacuum why does the intensity of electromagnetic radiation reduce with the square of the distance(1/r^2).Since there is no medium there is no loss of ...
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How can the potential energy be found for a three body system with a co-rotating frame of reference?

I am currently studying this text about the lagrange points. I am struggling to understand equation 5 and 6, especially how the coriolis and centrifugal force can be described as potential energy. ...
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So what do we really see in the image of the black hole?

I have already read this question - Orange ring in a black hole image And also have seen several videos about it (Specificaly one from Veritasium -https://www.youtube.com/watch?v=zUyH3XhpLTo&...
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How do you estimate the core temperature of a star?

Given a star's mass, radius and average composition (e.g. 90% H, 10% He), is there a formula to estimate the core temperature of that star? I only found one for a lower bound but that wasn't very ...
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Rosseland mean of the free-free opacity in terms of fundamental constants

I'm currently trying to compute the Rosseland mean of the free-free opacity but am consistently off by a numerical factor. To keep things simple, we will take the non-relativistic limit, and roughly ...
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1 vote
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Notation question: what is $N_A$?

I'm reading some literature on stellar opacity, and there is some notation that I don't understand. In particular, they write that the total density $\rho$ is related to the electron number density $...
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Rotating black hole

I know that everything that is shaped from gravity force is rotating, and gravity is a central force. but I want to know how can we detect that a black hole has an angular momentum? By which ...
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1 answer
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Is the transit technique for exoplanet detections part of the "Wide-Field Precision Photometry Revolution"?

In a exoplanet focused lecture I was informed that the two main techniques for the detection of exoplanets were: radial velocity (VR) and transit. These were very briefly explained to us. When ...
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4 votes
2 answers
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Why does Jupiter have so many moons?

The usual explanations one finds just say that Jupiter has a strong gravitational field, thereby being able to catch moons easier, and then they stop there. But this seems far from a satisfactory ...
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4 votes
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Improving physics simulation of black hole accretion disk?

I have recently been working on software which uses ray tracing/marching to render a black hole in the Schwarzchild metric. I've implemented most everything that I originally set out to do, and I am ...
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