Questions tagged [gas]

Questions regarding matter in its gaseous state, and how it behaves in astronomy (e.g. forming stars in giant molecular clouds).

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Using Saha's equation knowing the overall pressure

Knowing the pressure, $P_g$, how can I calculate $\frac{N_{I+1}}{N_I}$ using Saha's equation? If I assume that $P_g=(n_e+n_{H^+}+n_H)K_B T$ and that $n_e=n_{H^+}$, I can find the electronic pressure, $...
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2 votes
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Specific impulse of cometary outgassing?

Note: This question is related to Average DeltaV applied to a comet during outgassing? Rocket engines have a parameter called "specific impulse," which is the measurement (in seconds) of how ...
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4 votes
1 answer
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Why is it safe to assume that K = 3/2kT in a self-gravitating gas

I encountered a question: "Find the ratio of Kinetic Energy and Total Energy of a star, made out of a monoatomic ideal gas, You may not consider density to be uniform. Kinetic energy is the ...
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What does it mean for cold clouds to be in pressure equilibrium with a diffuse hot medium?

I often read about cold objects (namely cold clouds in the Galactic halo or cold filaments accreting into high-redshift galaxies) being in pressure equilibrium with the diffuse hot ambient gas. What ...
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Weight of a gas measured in Space and other planets of Solar System

I searched for how measure gas weight and about gases in space https://www.shutterstock.com/search/space+gases https://education.seattlepi.com/gases-found-outer-space-5888.html Will the weight of gas ...
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2 votes
0 answers
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Are there gas clouds in space so dense that we couldn't see out of them if one where to be inside it?

The images of telescopes capturing gas clouds are quite intriguing to me, which keeps me wondering about visibility inside them. Are there gas clouds in space so dense that we couldn't see out of them ...
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shape of gas and shape of stars

How does the shape of the gas and shape of stars change as the galaxy ages? Does there exists any such formula which relates the shape/volume with the time?
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7 votes
2 answers
387 views

Why is molecular hydrogen (H2) so difficult for astronomers to detect?

I am reading a great deal about the various forms of hydrogen throughout the universe, and I keep reading that 'molecular hydrogen is notoriously difficult to detect', and other sentiments along those ...
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How do they know the newly-spotted gas near the center of our galaxy is molecular without knowing what gas it is?

Phys.org's Mystery gas discovered near center of Milky Way links to Teodoro et al 2020 in Nature Cold gas in the Milky Way’s nuclear wind who's abstract is shown below. Question: My reading of the ...
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3 votes
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Surface of the Sun, or Jupiter, etc [duplicate]

I keep hearing and reading statements that refer to the "surface of the Sun" (how hot the surface of the sun is) or the "surface of Jupiter" (when the Shoemaker comets hit Jupiter)....
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3 votes
1 answer
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Galactic winds/outflows: why and how are they detected via blueshifted absorption lines in spectra?

I know that galaxies can eject gas due to supernovae, accreting black holes, etc. These galactic "winds/outflows" are often defined/detected observationally using blueshifted absorption ...
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2 answers
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How does gas in accretion disks of supermassive black holes create orbital torques on smaller black holes within the disks causing them to migrate?

This answer to What enhances the capture and merge rates of pairs of small black holes orbiting around supermassive black holes? links to Migration Traps in Disks Around Supermassive Black Holes which ...
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6 votes
1 answer
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Starting a fire in a cold planet that was full of flammable gas

What would happen to a cold planet that has a large amount of flammable gas, like Neptune, if we throw some fire into it? Will it burn, or would the flame be extinguished due to the cold?
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3 votes
1 answer
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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 ...
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Can we get the gas compositions from a gas planets? [closed]

Is it possible to get some gases like hydrogen from gas planets (Saturn, Jupiter, Uranus or Neptune)?
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1 answer
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Is there a plausible causal mechanism to explain why the Sun would be heating up faster/ sooner than we thought? Question for a novel [closed]

I am writing a novel about what it will be like on earth 500 or so years before the death of our Sun. The Sun is heating up gradually and one day that will negatively affect life on Earth. I know that ...
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2 answers
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What is the diffuse ionized gas?

I've been trying to find a clean definition what people mean by when they talk about diffuse ionized gas in the interstellar medium, but I couldn't find anything so far. Apparently it's supposed to be ...
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What are the so called clouds of dust and gas made of?

We constantly read about "clouds of dust and gas" surrounding a (or being the initial state of a) star, but what elements constitute such dust and gas?
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How is interstellar gas density mapped from GAIA data?

I found the image below in Space.com's article This 3D Color Map of 1.7 Billion Stars in the Milky Way Is the Best Ever Made. The caption for this image reads: The Gaia spacecraft gathered ...
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3 votes
1 answer
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What would the pressure and temperature of gas be, right above Jupiter's gas/liquid boundary?

Older pages like this "Exploration of the Solar System" course page describe the transition as being a few hundred kilometers down. More recent findings seem to put the boundary deeper. See The ...
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Would a spacecraft just go "through" a gas giant?

From my understanding of the word gas giant, it is a planet composed of entirely a gaseous atmosphere, and so planets Jupiter and onwards fall in this category. That being said, what would stop a ...
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What is the condition for the number density of a gas to be ultra-relativistic or non-relativistic and degenerate or ideal

What is the condition for the number density ($n$) of a gas to be ultra-relativistic or non-relativistic and degenerate or ideal? I found problems in this subject when I was reading about White-...
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2 votes
2 answers
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Is this gas cloud or lens effect?

I was going through the zoomable image of Milky way and after zooming to this particular location, we can see a reddish area on the left side of a probably large star. Here is a screenshot I took ...
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Are gas giants supported by thermal pressure?

I've heard gas giants are supported because there is an equilibrium between thermal pressure and gravity. That is, if Jupiter were to suddenly begin compressing, temperatures would increase to the ...
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3 votes
1 answer
161 views

Why is the "green" comet C/2014 Q2 (Lovejoy) red in this picture?

In this nice NYTimes 'survey article' "Our Vast Solar System and Its Many Explorers" there is a NEOWISE image of Comet C/2014 Q2 (Lovejoy). See here also. The NASA description of the image says: ...
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How to show that the Jeans Criterion for Mass, Radius and Density are equivalent?

The gravitational collapse of a gas cloud can be described by the Jeans Criterion for mass, radius and density of the gas cloud, which is (c stands for cloud): $$M_J = (\frac{5kT}{G \mu m_H})^{3/2} (...
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3 votes
1 answer
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How do astronomers detect gases that are in the atmosphere of exoplanets? [duplicate]

Exoplanets are planets that are located outside our solar system - whether that be orbiting a star or drifting past one. Now, the closest star to us is Alpha Centauri which is just over four light-...
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2 votes
1 answer
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What is the equation of state for a relativistic fluid/gas?

Say we have a relativistic fluid/gas, as we have in some astrophyical systems. Now let us write: $e$ - energy density in the fluid's rest frame. $P$ - pressure in the fluid's rest frame. $n$ - ...
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12 votes
2 answers
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Why argon instead of another noble gas?

I noticed that the atmospheres of Earth and Mars have a little bit of argon in them (1% to 2%). I checked Venus, too, which has 0.007% argon, but that's still more than any other noble gas in the ...
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3 votes
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When is it a good aproximation to consider a star to be an ideal gas?

I am currently taking a first course on stellar astrophysics, and I noticed that in some cases we use the ideal gas equation of state for stars, so we also use $\gamma =5/3$. Of course it can only be ...
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5 votes
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Gas halo of our Milky Way Galaxy

This question relates to a diffuse hot gas halo of our Milky Galaxy. I've read that there is a hot diffuse halo of gas surrounding our Galaxy (NED, Caltech) I was wondering why such a halo can exist? ...
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2 votes
1 answer
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What is a typical value for core-to-star efficiency?

I was reading Unfolding the Laws of Star Formation: The Density Distribution of Molecular Clouds by Kainulainen et al., which discusses star formation rates and efficiencies. One variable used is $\...
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2 votes
1 answer
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Can asteroids contain atmosphere?

Gas is abundance in the universe, can a massive asteroid draws in these gas forming a thin atmosphere?
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13 votes
2 answers
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What will happen when landing on Jupiter?

Jupiter is a gas giant, so landing on it will not be like landing on Earth, our Moon or Mars etc., as it does not have a solid surface like these. If we have a hypothetical spaceship or probe landing ...
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2 votes
1 answer
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Beta profile fit of Virgo cluster gas?

I'm looking for the parameters $r_c$, $\rho_0$ and $\beta$ in a $\beta$-profile fit of the Virgo cluster's ICM density. I just can't find a reference for it. Unlike for Coma (Abell 1656) where it's in ...
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3 votes
1 answer
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What is the physics of a gas mass subject to gravity in space?

There are many formulas for atmospheric pressure on earth, but how does gas behave in free space? I am thinking about why stars form. I am guessing that the gas density will influence pressure, as ...
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17 votes
3 answers
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What is the difference between gas and dust in astronomy?

Is there a strict difference between gas and dust? In Earthly environment most things become gaseous if heated enough. The temperature of interstellar medium seems to range mostly between 10 and 10 ...
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