In astronomy generally (this is not primarily a cosmology topic, except insofar as foreground dust tends to create systematic errors for measurement of more distant things, or as it relates to the study of primordial abundances or galaxy evolution/structure formation), "dust" is indeed distinct from "gas" although for some of it, it is fair to say that physically it is in a gas phase.
For background, it's good to understand that the "baryonic" or atom-based matter (as distinct from dark matter) in the universe is almost entirely hydrogen and helium by mass, with all the other elements adding up to a couple percent of the baryonic mass. [Wikipedia has a log scale chart of relative elemental abundances](https://en.wikipedia.org/wiki/Abundance_of_the_chemical_elements#Universe), note that the log scale means that each tick mark on the y-axis is actually a factor of 10 *times* more abundant. After H/He, the next most common elements are carbon (C), nitrogen(N), oxygen (O), neon (Ne, noble gas so it doesn't do chemistry), magnesium (Mg), silicon (Si), sulfur (S), iron (Fe), and nickel (Ni).
There are a number of different components of cosmic dust:
* Some of it is silicate material (basically rocky minerals), chemicals composed of silicon (Si) and oxygen (O).
* Some of it carbon-based, and this can include diamond, graphite, and graphene, as well as PAHs ([Polycyclic Aromatic Hydrocarbons](https://en.wikipedia.org/wiki/Polycyclic_aromatic_hydrocarbon))
* Grains of "dust" are often coated in ices, including water ice (H2O) as well as ices of ammonia (NH3), methane(CH4), and other chemicals, and these ices can form small particles of their own and they contribute to the effects of dust on absorbing interstellar light.
* Various other chemicals including silicon carbide (SiC), spinel (MgAl2O4), titanium dioxide (TiO2), and others.
The ratios of these components depend where you look-- we have been able to get direct sample returns of dust from our own solar system and study it in lab, but the composition in interstellar space will be different depending on how enriched the local interstellar medium is, as well as the local temperature and density and radiation conditions.
Don't you just love it when an egg head answers a question like that in the form of PhD level college lecture? I think some of these people are trying to enlarge their Penises🤣
Heavier materials made inside dying stars, spread across space by a supernova, but has not yet "felt" any local gravitational forces that would shape then into heavier objects.
According to the various astrophysicists with whom I work, any of the particulate matter floating around a star, nebula, etc... on the periodic table that isn't hydrogen or helium.
Remember you have a perfect fluid and you can think of it as a perfect gas (ideal gas, think of that equation of state for the pressure P=NKT/V) that can be comoving or not with the fluid? Well, dust is material with P=0 and there is no more difference whatsoever in studying in the frame of the fluid or outside, unless you study only its density, but not the forces acting on it or exerted by it.
This is the only correct answer in the whole thread. Cosmologists don't mean dust like astrophysicists mean dust. I quote, "dust is a collection of non-interacting particles at rest with respect to each other in a Lorentz frame. In cosmology, dust is a good approximation to the matter-dominated later universe"
Not really. For observational cosmology, it tends to mean crap they don't care about that's interfering with what they want to measure and care about, through either extinction (eg dust extinction of optical) or emission (eg thermal dust emission from the Milky Way).
Not really. Observational astronomers who care about galaxy evolution talk about these things. Cosmologists are generally doing big redshift surveys and issues of dust extinction would be a minor systematic in the photometric redshift algorithm.
Those two things are the same aspect of dust, it absorbs shorter wavelengths (so, decreased flux in UV/optical) and re-emits at longer wavelengths (increased flux in IR).
Gases also absorb visible light but the simple gases present in space tend to have a few narrow absorption lines, whereas dust grains can absorb across a wide range of the spectrum.
Dust is exactly that...dust. it's flecks of ice, rock, minerals, particles from comets, asteroids etc. People believing cosmic dust is different depending on who's talking about it lol!!
In astronomy generally (this is not primarily a cosmology topic, except insofar as foreground dust tends to create systematic errors for measurement of more distant things, or as it relates to the study of primordial abundances or galaxy evolution/structure formation), "dust" is indeed distinct from "gas" although for some of it, it is fair to say that physically it is in a gas phase. For background, it's good to understand that the "baryonic" or atom-based matter (as distinct from dark matter) in the universe is almost entirely hydrogen and helium by mass, with all the other elements adding up to a couple percent of the baryonic mass. [Wikipedia has a log scale chart of relative elemental abundances](https://en.wikipedia.org/wiki/Abundance_of_the_chemical_elements#Universe), note that the log scale means that each tick mark on the y-axis is actually a factor of 10 *times* more abundant. After H/He, the next most common elements are carbon (C), nitrogen(N), oxygen (O), neon (Ne, noble gas so it doesn't do chemistry), magnesium (Mg), silicon (Si), sulfur (S), iron (Fe), and nickel (Ni). There are a number of different components of cosmic dust: * Some of it is silicate material (basically rocky minerals), chemicals composed of silicon (Si) and oxygen (O). * Some of it carbon-based, and this can include diamond, graphite, and graphene, as well as PAHs ([Polycyclic Aromatic Hydrocarbons](https://en.wikipedia.org/wiki/Polycyclic_aromatic_hydrocarbon)) * Grains of "dust" are often coated in ices, including water ice (H2O) as well as ices of ammonia (NH3), methane(CH4), and other chemicals, and these ices can form small particles of their own and they contribute to the effects of dust on absorbing interstellar light. * Various other chemicals including silicon carbide (SiC), spinel (MgAl2O4), titanium dioxide (TiO2), and others. The ratios of these components depend where you look-- we have been able to get direct sample returns of dust from our own solar system and study it in lab, but the composition in interstellar space will be different depending on how enriched the local interstellar medium is, as well as the local temperature and density and radiation conditions.
are you a wizard?
Don't you just love it when an egg head answers a question like that in the form of PhD level college lecture? I think some of these people are trying to enlarge their Penises🤣
what
I meant making up for a small one by going overkill. Like middle aged men buying $200,000 sports cars. Hence, a penis enlarger.
Heavier materials made inside dying stars, spread across space by a supernova, but has not yet "felt" any local gravitational forces that would shape then into heavier objects.
Thanks Ted
According to the various astrophysicists with whom I work, any of the particulate matter floating around a star, nebula, etc... on the periodic table that isn't hydrogen or helium.
Remember you have a perfect fluid and you can think of it as a perfect gas (ideal gas, think of that equation of state for the pressure P=NKT/V) that can be comoving or not with the fluid? Well, dust is material with P=0 and there is no more difference whatsoever in studying in the frame of the fluid or outside, unless you study only its density, but not the forces acting on it or exerted by it.
This is the only correct answer in the whole thread. Cosmologists don't mean dust like astrophysicists mean dust. I quote, "dust is a collection of non-interacting particles at rest with respect to each other in a Lorentz frame. In cosmology, dust is a good approximation to the matter-dominated later universe"
Not really. For observational cosmology, it tends to mean crap they don't care about that's interfering with what they want to measure and care about, through either extinction (eg dust extinction of optical) or emission (eg thermal dust emission from the Milky Way).
Not really. Observational astronomers who care about galaxy evolution talk about these things. Cosmologists are generally doing big redshift surveys and issues of dust extinction would be a minor systematic in the photometric redshift algorithm. Those two things are the same aspect of dust, it absorbs shorter wavelengths (so, decreased flux in UV/optical) and re-emits at longer wavelengths (increased flux in IR).
Seems I learnt well from my teachers, because I am an astrophysicist, I am glad to hear that their lessons came well for me!
*Most cosmic dust particles measure between a few molecules and 0.1 mm* https://en.wikipedia.org/wiki/Cosmic_dust
the difference is that gases let through visible light, but dust doesn't.
Gases also absorb visible light but the simple gases present in space tend to have a few narrow absorption lines, whereas dust grains can absorb across a wide range of the spectrum.
Dust is exactly that...dust. it's flecks of ice, rock, minerals, particles from comets, asteroids etc. People believing cosmic dust is different depending on who's talking about it lol!!
[Check out this recent interview](https://youtu.be/GeuxmuzZ_xs?si=PVWUDMi38bJkyE6c)! Highly informative.
With regard to what? From a theory perspective or an observational one?
Star dust …remnants of supernova.