# Tag Info

## Hot answers tagged dust

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

Question: How are these images obtained? Later in the video the narrator says they took the images using ESO's VLT. 03:40 [Narrator] 14.​ Making these measurements pushed the power of ESO’s Very Large Telescope to the limits. (Source: ESO transscript) Over the whole observation period multiple telescopes and imaging instruments were used. Early ...

9

OK, having (finally) actually looked at the video, it's clear that Szymanek is looking at the center of M33. There is in fact a nuclear star cluster in the center of that galaxy; not knowing the field of view or the resolution, I can't tell how much of the central condensation is simply the unresolved, smeared-out nuclear star cluster (which is small -- you ...

8

I think that first, we have to properly appreciate the size of the Sombrero Galaxy. It is roughly 50,000 light years (15 kilo parsecs) in diameter. That might be only half of the diameter of our own Milky Way galaxy, but still makes each and every pixel on the photograph you're attaching in your question stretch more than 100 light years in distance. That's ...

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 ...

6

Thermal radiation $\neq$ blackbody radiation. Thermal radiation is radiation that comes from a system where an equilibrium has been reached, where the various energy states are occupied according to the Boltzmann distribution and the particle velocity distributions are Maxwellian at some given temperature. That does not necessarily imply that the radiation ...

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 ...

5

"Spinning dust" is a mechanism proposed to explain a particular feature in the foreground emission of CMB; a bump around $\nu\sim20\,\mathrm{GHz}$. Dust grains acquire charge through photoelectric emission and collisions with electrons and ions (Draine & Lazarian 1998). As zephyr comments, if the dust is a poor conductor, its charges will, in general, ...

5

From Genzel et al. (2010), here's part of Fig. 7.7.1: This is part of the spectral energy distribution of Sagittarius A*, a flot of $\nu$ (frequency) vs. $\nu L_{\nu}$ (frequency times luminosity). For comparison, visible light is in wavelengths from $\sim4\times10^{14}\text{ Hz}$ to $\sim8\times10^{14}\text{ Hz}$, which happens to be around the bottom of ...

5

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 bands. The comet looks red in the false-color infrared image because, relative to the 4.6 μm "W2" band, it emits less in the 3.4 μm "W1" band than stars ...

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 $\... 5 To get time on the Hubble Space Telescope is a difficult, peer-reviewed process. The time is usually about ten times oversubscribed. The scientific justification to get more images must be more than "it would make a nice movie". The submission of proposals for HST time is a confidential process; so I don't know whether the principal investigators for these ... 4 You'd probably be most interested in the results of the Lunar Dust EXperiment (LDEX). A 2015 paper states LDEX data show no evidence for an electrostaticallylofted dust component at densities greater than a few per m3 I am assuming the solar flare stuff didn't pan out, otherwise it would be mentioned in the various LDEX summary papers. In addition, ... 4 In an astronomical context, Rayleigh scattering does not take a huge place. The extinction is mostly due to absorption and scattering, from gas and dust. Its effect is to diminish the flux from the source (that is, a change in magnitude). Please, take care this depends on the observed wavelength! For simplicity, we can assume the extinction factor$Q_{ext}$... 4 What determines the Earth's orbital separation from the Sun is the total mass of the Sun and Earth, as described by Kepler's third law. The orbital radius of the Earth is increasing because the Sun is gradually losing mass both by emitting radiation and through the solar wind at a rate of around 5 million tonnes per second (e.g. Noerdlinger 2008). Any gain ... 4 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 rather than being free atoms. So the hydrogen is mostly H2 and not H. This is really important, since a cloud comprised of molecules can radiate away the heat of ... 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

I'm not an observational expert, but here's what I found. I found this object (V838 Monocerotis) on the HST data archive. https://archive.stsci.edu/hst/search.php I input the 'Target Name' as "V838 Monocerotis", clicked all 'Imagers', 'Spectrographs', and 'Other,' and searched it. (You can also do the exactly the same thing I did because this site is ...

4

Mg I does indeed mean neutral magnesium atoms, but May and his collaborators weren't observing magnesium atoms orbiting in the inner Solar System -- they were seeing absorption by magnesium atoms in the Sun's atmosphere. In the optical and near-infrared, the zodiacal light is sunlight scattered/reflected by interplanetary dust particles. Not surprisingly, ...

3

There are two primary dust populations near 1 AU, interplanetary dust (IPD) and interstellar dust (ISD) [Mann, 2010]. I also discussed dust observations in detail at https://physics.stackexchange.com/a/160627/59023. Interplanetary Dust IPD of ~1 $\mu$m size drift sunward due to Poynting-Robertson drag while following roughly Keplerian orbits [e.g., ...

3

Adaptive optics does not work (or at least did not 10+ years ago) on ground based astronomical telescopes at visible wavelengths. No images remotely comparable to HST could be obtained for faint$^*$ objects from the ground in the BVI wavebands. I checked for papers discussing adaptive optics at other wavelengths and couldn't find any. The field of view is a ...

3

The quantity you want is basically the extinction law, and is usually called $k(\lambda)$. An extinction law is a fit to several measurements of the extinction $A_\lambda$ in some direction (or an average of several directions). Cardelli et al. (1989) provides different functional forms for the mean extinction law, parametrized in their Eq. 1 as  \frac{A_\...

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

The first relevant point is that the equipartition theorem only formally applies in thermodynamic equilibrium, which requires that all temperatures be the same. Since the spinning dust only happens when there are temperature differences, holding to the analogy with a heat engine mentioned in the source, we should not expect that theorem to be the whole ...

3

If you can see the Milky Way, then in Summer through early Autumn you should be able to see the "dark rift" which runs through the middle of the milky way from Saggitarius to Deneb in Cygnus. This is a dust band in the Milky Way. If you live far enough South, you can see the Coalsack, a quite dense dust cloud near the Southern Cross, and also clearly ...

2

The answer is yes. The mass (and hence brightness) of meteorites follows some sort of power-law relationship such that there are many more small particles than big lumps of rock. This means that there are indeed many more faint meteorites than bright ones, though I am struggling to find any detailed study that goes below the magnitude range you can see with ...

2

I may just add to the excellent answer by Robert that interstellar dust particles, very much like cigarette smoke in air, hangs in the interstellar gas and interacts with it both kinematically (is dragged along with it depending on the particle size) and energetically (exchanges heat, which can result in significant cooling of the gas). Dust particles also ...

2

Puppis Window? (Neutral hydrogen observations towards the Puppis Window of the Milky Way)

2

The Lockman hole? http://en.wikipedia.org/wiki/Lockman_Hole It has a column density of neutral hydrogen of $6\times10^{19}$ cm$^{-2}$, which will correspond to very little dust. Two others I've heard of towards the Galactic bulge are known as the Sgr I and Sgr II windows. Finally, I offer "Stanek's window" towards the bulge, which has been referred to in ...

2

Dust absorbs stellar light (primarily in the ultraviolet), and is heated up. Subsequently it cools by emitting infrared, "thermal" radiation. Assuming a dust composition and grain size distribution, the amount of emitted IR light per unit dust mass can be calculated as a function of temperature. Observing the object at several different IR wavelengths, a ...

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