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29 votes
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Starting a fire in a cold planet that was full of flammable gas

The outer parts of Neptune are mostly hydrogen and helium. There are small amounts of other gases such as methane, ammonia and water vapour. However, there is no oxygen at all. If you took some of ...
James K's user avatar
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29 votes
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How are we observing the newly discovered "dark galaxy" J0613+52, if it has no stars and is so far away from other galaxies?

The low surface brightness survey at the GBT is looking for H(I) emission, i.e. emission from neutral hydrogen atoms (for example see O'Neil 2023). The most obvious signature they use is the 21 cm ...
ProfRob's user avatar
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13 votes
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Is there any way to detect the three-dimensional distribution of baryonic gas in our Universe?

Yes! The cosmic web Matter in the Universe is distributed not uniformly, but in the so-called cosmic web. This large-scale structure consists of sheets and filament of dark matter, baryonic gas, and ...
pela's user avatar
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6 votes
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What would the pressure and temperature of gas be, right above Jupiter's gas/liquid boundary?

Technically there isn't really a gas-liquid boundary because temperatures are well above the critical point of hydrogen (33K and about 18bar). It's a supercritical fluid. There are important changes ...
Steve Linton's user avatar
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6 votes
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How do astronomers detect gases that are in the atmosphere of exoplanets?

It is only possible to detect gases in transiting Exoplanets. The spectrum of the star is taken when the Exoplanet is not in transit and again when in transit. The differences between the spectrums is ...
James Screech's user avatar
6 votes
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Are gas giants supported by thermal pressure?

I am not sure what you mean by "thermal" pressure. Jupiter is supported by pressure, just like all objects that are in (approximate) hydrostatic equilibrium. That pressure is provided by your ...
ProfRob's user avatar
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5 votes
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What is the diffuse ionized gas?

The "diffuse ionized gas" (DIG) is another term for the phase of the interstellar medium (ISM) usually called the warm ionized medium (WIM). With a temperature of the order $10^4\,\mathrm{K}$, but ...
pela's user avatar
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5 votes
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Why is the "green" comet C/2014 Q2 (Lovejoy) red in this picture?

Mainzer et al. 2014 characterize the performance of the reactivated NEOWISE. Having run out of cryogenic coolant for the original WISE's 12 and 22 μm bands, it only detects in the 3.4 and 4.6 μm ...
Mike G's user avatar
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5 votes
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Why is it safe to assume that K = 3/2kT in a self-gravitating gas

I will use some concepts form statistical mechanics, I hope you are familiar with some of the concepts. Consider a gas of $N$ particles of mass $m$ with Hamiltonian function $$H(\bar{q}, \bar{p}) = \...
Prallax's user avatar
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4 votes

How does gas in accretion disks of supermassive black holes create orbital torques on smaller black holes within the disks causing them to migrate?

Not really my area, but this question is probably related to the planetary migration in circumstellar disks. In this case, the migration is caused by gravitational interactions between the planet and ...
Pablo Lemos's user avatar
4 votes

Would a spacecraft just go "through" a gas giant?

In short, No. Side detail: Uranus and Neptune consist likely of 20% gas and 80% rock, coming from simple density considerations. They have large inner cores with masses around $\rm 12-14 \; m_{earth} ...
AtmosphericPrisonEscape's user avatar
4 votes

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

There are a few reasons molecular hydrogen (H2) is hard to detect depending on what band you are looking. In the UV, it can be detected in absorption of the electronically excited Lyman–Werner bands, ...
Kyle's user avatar
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4 votes
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What are the so called clouds of dust and gas made of?

The clouds of gas and dust that form stars are usually what are called Molecular Clouds and Giant Molecular Clouds (GMCs). The "Molecular" means that most of the atoms are combined into molecules ...
Mark Olson's user avatar
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3 votes
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How is interstellar gas density mapped from GAIA data?

Two techniques immediately spring to mind. For the stars you detect, you can compare their colours and luminosities (Gaia provides photometric colours and distances) with what you expect for a star ...
ProfRob's user avatar
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3 votes
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Why are Bok globules so cold?

Most of my information is sourced from here: https://apod.nasa.gov/apod/ap990511.html To summarize the source, Bok globules are extremely cold because of their composition -- they're generally just ...
Cloudy7's user avatar
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3 votes

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

The light that we receive from space contains a lot of information. Specifically, because of quantum nature of molecules and atoms, theses small species absorb light at very specific wavelengths.Each ...
Shamaz's user avatar
  • 264
3 votes
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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?

They know there's molecular gas because they observed emission from the CO molecule in two of the previously identified (atomic-hydrogen-emitting) gas clouds. From the paper: ... we targeted two ...
Peter Erwin's user avatar
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3 votes
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Galactic winds/outflows: why and how are they detected via blueshifted absorption lines in spectra?

Yes, a blueshift here would mean relative to the systemic velocity of the galaxy - which means that, relative to the galaxy, the material is moving at least partly in the direction of Earth. In many ...
Eric Jensen's user avatar
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2 votes
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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?

A gravitating object in a disk creates a wake on the inner edge of its orbit as well on the outer edge of its orbit. The inner wake is the leading wake, while the outer wake is trailing. The torques ...
planetmaker's user avatar
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2 votes
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Can we get the gas compositions from a gas planets?

Yes. It's certainly feasible to obtain a sample from Jupiter or Saturn, effectively getting gas from the planet, but it's not easy. Massive planets, as a byproduct of their high mass, create large ...
userLTK's user avatar
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2 votes
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What is the equation of state for a relativistic fluid/gas?

Your equations seem correct. Note, you can also get $v$ without having to differentiate, from $E=\gamma mc^2$ and $p=\gamma mv$. Here are some notes on relativistic fluids as related to stellar ...
cnosam's user avatar
  • 106
2 votes

Using Saha's equation knowing the overall pressure

The pressure of a gas depends on the number density of particles and the temperature. There is therefore no unique relationship between $P_g$ and $N_{I+1}/N_I$.
ProfRob's user avatar
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2 votes
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Weight of a gas measured in Space and other planets of Solar System

Weight is a property of mass which you can experience only when on the solid surface of a gravitating body - but not when you are in free fall. Yet even in free fall you retain your mass. Weight is ...
planetmaker's user avatar
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1 vote
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What does it mean for cold clouds to be in pressure equilibrium with a diffuse hot medium?

Pressure equilibrium means that the pressure of the hot component and the pressure of the cold component are equal at their interface, so that neither expands nor contracts relative to the other. The ...
Peter Erwin's user avatar
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1 vote

What is the condition for the number density of a gas to be ultra-relativistic or non-relativistic and degenerate or ideal

This is fairly standard bookwork that I am not going to reproduce and you should understand that the lines on your diagram are "fuzzy" in the sense that they mark the loci where you can neither use ...
ProfRob's user avatar
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1 vote
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Is this gas cloud or lens effect?

This particular object I tracked down by comparing the visual with the infrared image of the sky. It was a little tricky because no very bright star appears at that location. But after making ...
James K's user avatar
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1 vote

Is this gas cloud or lens effect?

As the comments have said, this is simply a camera effect known as a lens flare If you look around at the various bright stars, you can see this in multiple places, e.g.: (source: snag.gy) and also:
Beta Decay's user avatar
1 vote
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How to show that the Jeans Criterion for Mass, Radius and Density are equivalent?

What you want to do is use the relation between Mass, Radius, and Density. The proper expression should be $$\rho_c = \frac{M_c}{(4/3) \pi R_c^3}$$ Your three Jeans conditions are $M_c > M_J$, $...
zephyr's user avatar
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1 vote

What will happen when landing on Jupiter?

It's worth noting that a probe entering Jupiter's atmosphere is NOT hypothetical: The orbiter carried a small probe that became the first to sample the atmosphere of a gas planet. The probe measured ...
giardia's user avatar
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