Questions tagged [interstellar-medium]

Questions about the gas that lays between stars in galaxies.

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16
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3answers
3k views

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 ...
16
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3answers
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Why is the interstellar medium so hot?

On this link, it states the following: "large assemblies of galaxies that are permeated by even larger amounts of diffuse gas. With temperatures of 10 million degrees or more". How are these ...
16
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1answer
352 views

How does interstellar matter density vary?

Answer to my question partially answers this one, about density of intergalactic matter and matter within galaxy: But it is mostly a hot, ionized void. How void? The density of the intergalactic ...
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3answers
4k views

Why isn't interstellar medium pulled in towards nearest massive object?

How does the ISM resist gravity? That's the only force acting on it, and all other particles seem to collect together to form stars. What makes the ISM so special among other particles?
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5answers
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How cold is interstellar space?

The vastness of space brings me a sense of chilliness even though I have never experienced it, although I wish to. Just how cold is interstellar space (on average)? How is this even measured? I mean ...
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1answer
508 views

Sources of Turbulence in the ISM

What sources of turbulence exist within the Interstellar medium (ISM)? Which ones are physically the most important for newly forming stellar systems?
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2answers
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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 ...
11
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2answers
667 views

Would a spaceship have to evade interstellar clouds?

Apparently, there are clouds of "dust" between the stars. Would a starship have to fly around those clouds, trying to find "tunnels" between clouds, or are the interstellar clouds harmless for a ...
10
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1answer
308 views

Why are there no ISM clouds with temperatures between 100 and 6,000K?

In the interstellar medium, there are several different diffuse phases of gas, distinguished by their density and temperature. Specifically, the cold neutral medium has temperatures from ~50-100 K and ...
9
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2answers
514 views

Gravitational waves and gamma ray burst: how were the error bars determined for this speed of gravity calculation? Was $H_0$ used?

This newly updated answer to How precise are the observational measurements for the speed of gravity? and this answer to How is the most accurate value of 𝐺 measured? cites the November 2017 arXiv ...
9
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1answer
117 views

Do we live in a galactic bubble?

I have heard a certain statement, which can be summarized succinctly into "we live in a local bubble", implying that solar system is located in an intestrellar dust underdensity region. This region ...
8
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2answers
991 views

Why is the Warm-Hot Intergalactic Medium (WHIM) so hot, and what is “collisionless shock heating”?

The Phys.org article Researchers find last of universe's missing ordinary matter says: Ordinary matter, or "baryons," make up all physical objects in existence, from stars to the cores of ...
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Lack of objects between heliopause and Oort cloud?

If we take a look at a logarithmic scale of the Solar System, there appears to be a large gap between the heliopause and the Oort cloud: Why is that? There are some objects in the gap, but why are ...
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3answers
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Can circumstances exist such that as seen from some solar system all stars are obscured?

I am mostly active on Physics Stack Exchange but a question occurred to me that I think is best submitted here. This question is about a thought experiment: whether the circumstances of the intended ...
6
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1answer
258 views

Speed of light through the ISM and Wavelength

Articles written about fast radio bursts describe the signal's short-wavelength components arriving before its longer-wavelength components, suggesting energy-dependent time delays in the interstellar ...
6
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2answers
125 views

Why is blue light extincted more strongly than red?

We know that blue light suffers extinction more strongly than red (examples include ISM, atmosphere etc.), but why? Is it a property of the shorter wavelength itself? Can someone provide a conceptual ...
6
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2answers
116 views

Do pulsar beams interact with the interstellar medium?

Pulsars are rotating objects that emit a beam in a direction that is not aligned with the axis of rotation. Because of this, we see them as a periodic pulse. If the beam isn't towards us, we don't see ...
6
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1answer
89 views

How much of a molecular cloud can end up as “starstuff”?

Stars form within molecular clouds. These clouds can be up to 6 millions solar masses. When the cloud collapses into stars, is it possible to know a rough figure for how much of this material actually ...
6
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1answer
157 views

Does the sun blow a bubble into the interstellar medium?

I once read that the solar wind is more or less blowing a "bubble" into the interstellar medium. However, the numbers I found while trying to verify this don't give me a clear picture yet: The ...
6
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2answers
196 views

Can dark matter decrease the Jeans length?

I am wondering if there are any models of interstellar cloud collapse out there which take dark matter into account. If dark matter has local perturbations or density fluctuations, then that may be ...
6
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1answer
79 views

Voyager 1 and 2 detected a 20-fold increase in plasma density, significantly different refractive index?

As reported by Nature.com, Voyager 1 and 2 detected a 20-fold increase in plasma density going from the heliosphere out to interstellar space. Does that 20-fold difference in density imply a ...
5
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2answers
943 views

Interstellar Dust properties

While practicing for an upcoming examination, I ran into this problem: Which of the following best describes dust grains in the interstellar medium: They are a few hundred nanometers in size (size ...
5
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1answer
444 views

What would the night sky look like if the interstellar medium didn't exist to absorb or block light?

I was curious about how much brighter it would be and how much further we could see.
5
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2answers
370 views

What is the word for space that is in the solar system, but outside the heliopause?

Wikipedia says the definition of interplanetary space is the region dominated by the interplanetary medium, which extends out to the heliopause where the influence of the galactic environment ...
5
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1answer
312 views

Do liquids exist in the interstellar medium?

Am not asking about planetary/meteorite surfaces and am restricting myself to the interstellar medium edit: by interstellar medium I mean, the following: "Interstellar medium (ISM) is the matter ...
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1answer
132 views

What is the distribution of organic compounds in the Milky Way Galaxy?

I imagine the answer is unknown for the entire galaxy, but I would appreciate a notion of the scales and locations of regions where astronomers have ventured at least a guess to the distribution of ...
5
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1answer
168 views

Potential formation mechanisms of the interstellar asteroid 'Oumuamua

NASA recently discovered 'Oumuamua, an interstellar asteroid that appears to have a very elongated shape, unseen in solar system asteroids. What physical mechanisms, in the progenitor stellar system ...
4
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1answer
128 views

Local Bubble in space

Is the Local Bubble alone in space or is there another bubble similar to the Local Bubble in space, i.e., do we live in a special place or is this a more general phenomenon?
4
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1answer
161 views

Why do these astronomers say that “Carbon chains with more than nine atoms are unstable”?

The Phys.org article Interstellar iron isn't missing, it's just hiding in plain sight links to the paywalled article On the Structure, Magnetic Properties, and Infrared Spectra of Iron Pseudocarbynes ...
4
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1answer
112 views

Metals and dust locked into planets

I wonder what is the contribution of metals and dust locked into planets, with respect to the amount in the interstellar medium (ISM). In other words, when we measure the metallicity and the dust mass ...
4
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1answer
280 views

Why dust is optically thin in Far Infrared wavelengths?

What is the actual meaning of the statement 'Dust is optically thin in the Far Infrared (FIR) over most of the Galaxy'? Kindly Help
4
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1answer
36 views

Interaction of stellar winds in binary star systems

Binary star systems are fairly common but I am unable to find any information on how the stars interact with one another on aspects other than gravitational affects. Using Alpha Centauri as the ...
4
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1answer
792 views

Why is [O III] a good density probe in interstellar medium?

According to Draine in his book "Physics of the interstellar and intergalactic medium" (page 210/211) and Caltech [O III] line ratio's (amongst others) are a good density probe, but I cannot really ...
4
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1answer
78 views

Population of excited H levels in a Strömgren Sphere

In chapter 2.2 of Astrophysics of Gaseous Nebulae and AGN Ostriker and Ferland claim that, as far as ionization is concerned, one can assume all atoms to be in the ground state in a Strömgren Sphere ...
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0answers
57 views

Significantly blueshifted Lyman-$\alpha$

Lyman-$\alpha$ line in galaxies is notably known to show a double peaked profile, mainly due to its scattering in a moving medium, see e.g., the very recent Matthee et al. 2021, The X-SHOOTER Lyman-α ...
3
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2answers
285 views

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 ...
3
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1answer
48 views

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 ...
3
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2answers
115 views

Are there examples of the effect of shock waves on chemical evolution in of interstellar medium or circumstellar medium?

Are there any examples of calculations or observations of suspected effects of shock waves on chemical evolution in interstellar medium or circumstellar medium?
3
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0answers
77 views

Hydrogen Frost Line? Where, if anywhere, is it cold enough for Oort Cloud objects or rogue planets to have solid hydrogen on their surfaces?

I like the idea of Oort Cloud objects all being crusted with a thin layer of hydrogen snow, though what little information I've managed to find on the topic seems to imply that that is unlikely, ...
3
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0answers
72 views

What is the specific heat capacity of interstellar clouds?

Star forming molecular clouds and especially Bok globules are low temperature $\sim 10 $ K environments with density on the order of $10^{-18}$ kg/m$^3$, mostly hydroogen with about 1% dust. What is ...
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0answers
92 views

For chemical reactions occurring in the interstellar medium, which involve metal-ions, will the metal ions be solvated or not?

Usually, metal-ions in terrestrial chemistry will be solvated - either by gas-phase solvent molecules or by liquid-phase solvent molecules. But the interstellar medium (ISM) is never in local ...
3
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0answers
75 views

How do people derive ionized gas mass from optical emission lines in a galaxy spectrum?

Suppose you had an optical spectrum of a galaxy, and you unambiguously detected emission lines from cooling ionized gas -- both forbidden lines like [O II] 3727AA and [O III] 4959,5007AA, as well as ...
2
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1answer
136 views

How dark would the sun become if we traversed a Bok globule?

Bart Bok gave his name to dust clouds of 2-50 solar masses, which by their darkness may be 100 times more frequent than telescopes can detect. If the solar system traversed a Bok Globule, how dark ...
2
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1answer
112 views

Examples of astrophysical objects NOT in virial equilibrium?

Astronomers always talk about astrophysical objects being in virial equilibrium (e.g., a stellar system, or a disk of gas within a galaxy, etc.). But I never hear about thermodynamical equilibrium. ...
2
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2answers
81 views

Dust mass-loss rate from a massive star given a set of parameters?

I've been looking for examples at how mass-loss rates are determined. I'm studying a circumstellar dust shell ejected from a Wolf-Rayet star. I have some parameters like, expansion velocity of the ...
2
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1answer
53 views

What do these statements about interstellar magnetic fields really mean?

Quanta Magazine's The Hidden Magnetic Universe Begins to Come Into View is a fascinating review of a rapidly evolving field in astronomy. It contains some statements that I feel are important to ...
2
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1answer
64 views

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 ...
2
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1answer
99 views

carbonaceous content of galaxies?

There is a phrase in a Science Daily article which appears to be wrong: The Milky Way has a very high content of carbonaceous dust, which has been shown to be very rare in other galaxies. Is there ...
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0answers
38 views

What “long chain of carbon chemistry” in the interstellar medium produces cyclopropenylidene? (C3H2)

Wikipedia's Cyclopropenylidene; Titan (Moon of Saturn); Formationsays: The major formation reaction of c-C3H2 is the dissociative recombination of c-C3H3+. C3H3+ + e− → C3H2 + H c-C3H3+ is a product ...
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0answers
22 views

Software for simulating/calculating a known EMW pulse propagating in ISM, including dispersion, scattering, etc

Could you please let me know, if there is any software/code/tool for simulating/calculating the result of a short EMW pulse (waveform is exactly known) propagating in the ISM for long distance, ...