# Tag Info

31

It is not true that the particles in the interstellar medium (ISM) are only acted upon by gravity. For instance, In many cases a significant part of the ISM is ionized, in which case it interacts with magnetic field which permeates the gas and may in some cases be quite strong. In the vicinity of massive and hence luminous stars, radiation pressure may ...

23

You can stick a thermometer in space, and if it is a super-high-tech one, it might show you the temperature of the gas. But since the interstellar medium (ISM) is so dilute, a normal thermometer will radiate energy away faster than it can absorb it, and thus it won't reach thermal equilibrium with the gas. It won't cool all the way to 0 K, though, since the ...

18

Yes, metals and other elements and molecules can exist in gaseous form under the right conditions of temperature and pressure. A "gas" is simply one of the fundamental states of matter, as in solid, liquid, or gas (and a few other states outside the scope of this question). But as a gas, these substances exist entirely as either individual atoms, individual ...

12

First, consider that gravity is weak. The nearest star system to the Sun is Alpha Centauri, at a distance of about 4 light-years. Consider the acceleration due to the Sun's gravity at half that distance: $$a_S=\frac{GM_\odot}{r^2}\simeq3.7\times10^{-13}\text{ m/s}^2$$ where $M_\odot$ is the mass of the Sun. That's an incredibly small acceleration, meaning ...

11

What that ESA (European Space Agency) page titled Hot gas sloshing in a galactic cauldron that you link to describes are called WHIM (Warm–Hot Intergalactic Medium). They are not interstellar medium, but intergalactic medium gas. The difference in density is huge, with interstellar medium density at an average of $\rho ∼ 1\ ppcm$ (one proton per cubic ...

10

Yes. As has been commented, the amount of damage taken by an interstellar spaceship depends on its velocity $v$, as well as the number of gas and dust particles that it encounters on its way. This number is usually measured per area, in which case it's called column density $N$, and is equal to the total distance $d$ traveled times the particle density $n$, ...

10

Just to add to TidalWave's answer - something that is easier to simply imagine, the trivial "why". What we call Temperature on thermodynamic level is Speed on atomic level. Saying the medium has a high temperature is equivalent to saying particles of that medium move awfully fast. Well, they must be moving fast. They must be moving faster than the escape ...

10

The interstellar medium is a multiphase medium, and you can find (some references in this lecture and in this thesis manuscript (this one is in French, but numbers are international)): the hot ionized medium (HIM) with density as low as 10^-3 cc (particles per cubic centimeter); the warm ionized medium (WIM), with density of the order of 0.03 cc; the warm ...

9

Turbulence sources: There are numerous sources of turbulence in the interstellar medium, at all scales: at large scales, there is the shear from galactic rotation. One way to sustain turbulence and to couple large and small scales would be the magnetorotational instability (MRI). at large scales, gravitational instabilities can also play a significant role,...

9

The title of the question asks about interstellar space, but the body asks about the interstellar medium. These are two very different questions. The temperature of the interstellar medium varies widely, from a few kelvins to over ten million kelvins. By all accounts, the vast majority of the interstellar medium is at least "warm", where "warm" means several ...

9

Let $n$, $T$, and $x_i$ be the number density of hydrogen, the temperature of the gas, and $n_i/n$, where $n_i$ is the number density of the $i$th component of the interstellar medium. We can then write the criteria for thermal equilibrium as $$n^2\Lambda(n,T,x_i)-n\Gamma(n,T,x_i)\equiv n^2\mathcal{L}=0$$ where $\Lambda$ and $\Gamma$ and the heating and ...

7

The main effect would be that the Milky Way would become much more prominent and asymmetric. At the moment, our view into the Galactic plane is limited to around 1000-3000 parsecs by dust. If you look at the Galactic latitude distribution of naked eye (Aren't there more naked-eye-visible stars in the Milky Way plane? ) you see that most naked eye stars ...

7

In astronomy, there is no formal definition of the threshold between gas and dust. Gas can be monoatomic, diatomic, or molecular (or made of photons, in principle). Molecules can be very large, and in principle, dust particles are just very large molecules. I've seen various authors use various definitions, ranging from $\sim100$ to $\sim1000$ atoms. This ...

7

The "local bubble" is a region of the galaxy where the density of interstellar gas is lower than average. It has about 50 thousand atoms per cubic metre, compared with 500 thousand averaged over the whole of the milky way. It was probably formed by one or more supernova explosions (10-20 million years ago) physically pushing gas away. There are many such ...

6

The answer is in your question. You said there couldn't be any (meaningful) forces interacting between them to provide any sort of way to travel through it. That's the great thing about outer space. There normally aren't many particles around that could slow down a spacecraft via drag or friction. If you give something a push in outer space - somewhere ...

6

You can find a neat description and some examples of the effect here. This is known as the pulsar dispersion measure. As you correctly say, waves with longer wavelength (lower energy photons) are delayed with respect to shorter wavelength radiation from the same phenomenon. When electromagnetic waves travel through a plasma, they excite currents in the free ...

6

The amount of metals locked up in planets is completely negligible compared to that of the interstellar medium (ISM). First, in a typical stellar system, the mass fraction of planets is less than 1%, and of this by far the most mass will be in gaseous planets, rather than rocky planets. For instance, in the Solar System, the mass fraction of all planets is ...

6

It should probably be added that the article includes a glaring error of the type you often see when the science writer apparently did not take an elementary astronomy class (this is why we have such classes!). When the article states that the "lost matter exists as filaments of oxygen gas", you can be sure that Michael Shull never said any such thing, ...

6

Unlike the saturated hydrocarbons in kerosene, carbynes are unsaturated carbon chains with alternating single and triple bonds. Molecules containing such chains are called polyynes, e.g. the short cyanopolyyne HC5N: H−C≡C−C≡C−C≡N Those carbon atoms readily interact, and long chains (if they form; see comments) are more ...

5

The term "optically thin" means that the optical depth is small. The optical depth is a measure of the opacity of a medium, in this case dust, experienced by light traveling through that medium, and is defined as $$\tau \equiv n \, r \, \sigma,$$ where $n$ is the density of the particles in question, $r$ is the distance traveled through the medium, and $\... 5 The collision timescale for a star in the solar neighborhood is1 $$t_c\simeq5\times10^{10}\text{ Gyr}\left(\frac{R}{R_{\odot}}\right)^{-2}\left(\frac{v}{30\text{ km s}^{-1}}\right)^{-1}\left(\frac{n}{0.1\text{ pc}^{-3}}\right)^{-1}$$ where$R$is the radius of a star,$v$is its speed relative to the stars around it, and$n$is the stellar number density. ... 5 The answer is almost certainly magnetic fields. A collisionless shock occurs when you try to propagate an increase/density in pressure through a sparse plasma at faster than the sound speed. Whilst the ions and electrons don't collide (very frequently), the magnetic fields that thread the plasma do accelerate the charged particles. In a collisionless shock ... 4 This is an area of active research. The current Cold Dark Matter (CDM) paradigm predicts bottom-up formation of halos, whereby smaller halos coalesce in to the larger halos we observe indirectly today through X-ray measurements of clusters. This suggests that small dark matter halos wouldn't survive to the present day. There has been research in to the ... 4 Not clear what the initial part of your question means. Objects can be in virial equilibrium without being in thermal equilibrium. A clear exception to the virial theorem would be any system that is gravitationally unbound. So you couldn't apply it to a supernova explosion or a dissolving cluster of stars. The examples you quote are not self-gravitating, ... 4 There may be Sednoids there. Sednoids are a hypothetical class of "inner Oort Cloud objects" named after their prototype, Sedna. Sedna's aphelion is ~936 AU, bringing it close to the inner boundary of the Oort Cloud. Sednoids may have aphelions ranging from about 100 AU to 1,000 AU. The problem is, only two Sednoids have beet detected to date, 90377 Sedna ... 4 Not noticeably darker. Assuming such a globule has a mass of 50 solar masses and a diameter of 1 light year, that would make it's average density about$2.2\times 10^{-16}\,kg\,m^{-3}$which is fairly close to not being there at all in human terms. An imaginary tube of this stuff 1 AU tall and of area 1 meter squared would contain about$3\times 10^{-5}\,...

4

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 extenting to lower and higher temperatures, it is hot enough to keep hydrogen ionized, and various metals exist as low-ionization species, such as S II, N II, and ...

3

There doesn't seem to be such a word. Interstellar space within the Solar System is still just interstellar space. There doesn't seem to be a demand for the word you're looking for either. We distinguish space by its contents; the space within the heliosphere is called the interplanetary medium (it contains solar plasma, dust, etc.), while the interstellar ...

3

As I have discovered afterwards, the described bubble exists and is in fact a known phenomenon. For those, who want to read more, here is a wiki link http://en.wikipedia.org/wiki/Local_Bubble and the links therein. Otherwise, it is an underdensity in ISM (not only dust) in the region of Orion Arm (which is a minor spiral arm). The underdensity is up to ten ...

3

They are hot in the sense of particle speed, but if you were out there, you will get freezed, since there is such a low density that any of these particles will likely impact you (and transfer you its energy, which is what you would notice as heat) while you will cold due to radiation.

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