Recent comments in /f/askscience

KarmaScope t1_je226jr wrote

Reply to comment by Practice_NO_with_me in Where do rumen bacteria come from? by ryum1503

I did the audiobook. There is quite a bit of science jargon in a lot of places, so sometimes I missed out on absorbing that well by not seeing the letters. But I am a visual learner mostly anyway for that type of stuff. But I got the big picture and it was very fascinating. Was my morning commute audiobook for a few weeks.

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adamginsburg t1_je20zq7 wrote

Reply to comment by adamginsburg in Is NaCl relatively common in the galaxy/universe? by PHealthy

Someone had asked a question about "Don't we detect salt in the Orion Nebula with microwave radiation", then deleted it - I had already written an answer, so I'll share:

Sort of. The article OP linked is talking about NaCl detected with millimeter-wave spectroscopy in the disk around a star that is immediately behind M42 (the Orion Nebula). Since they're along the line of sight, we often say that this object (Orion Source I) is "in" the nebula, but we have pretty good evidence that it's actually behind the nebula. The nebula itself is made of ionized (very hot, ~10,000 K) gas; Source I sits in the Orion Molecular Cloud, which is much cooler (~few hundred K; still warm by molecular standards).

I'm not aware of any microwave detections of NaCl toward the Orion Nebula itself, but I have an observing program ongoing that should pick it up if it's there. Maybe.

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adamginsburg t1_je20qy1 wrote

Reply to comment by I_eat_staplers in Is NaCl relatively common in the galaxy/universe? by PHealthy

That's the boiling point at atmospheric pressure. The NaCl we observed is likely not that hot - probably only ~100K but maybe 1000K (fig 6 of https://ui.adsabs.harvard.edu/abs/2019ApJ...872...54G/abstract shows that there's some ambiguity - we measure two temperatures and are not sure how to reconcile them!). We observe NaCl in an effective vacuum, so the boiling point (more likely sublimation point) is much lower. That said, it's possible that non-thermal mechanisms are responsible for releasing the NaCl into the gas phase - in other words, the gas isn't at the boiling point, but something knocked the NaCl molecules off the dust grains. Another possibility is that individual dust grains got very hot briefly, hot enough to vaporize, but again the gas isn't all that hot. We don't know for sure; we haven't yet come up with a consistent model to explain all the observations.

Just to give you a sense of boiling points: water transitions to gas at 373 K at atmospheric pressure. In the interstellar medium, it sublimates at closer to 100-150K.

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pewpewbrrrrrrt t1_je1zbl7 wrote

Reply to comment by mfb- in How does an ideal vacuum have a dielectric breakdown voltage of 10^12 MV/m? If there is nothing there, then how can electricity pass through it? by skovalen

I'm sorry if this is stupid, my understanding of what space/time is would mean there's no way to not have an electric field. Even if you made a vacuum with no charge you would have to use an electric field to make the vacuum inside have no charge therefore there would always be an electric field.

Is that a flawed understanding?

Is an ideal vacuum a theoretical or mathematical concept that is technically impossible in our understanding of physics?

Thank you for any clarification, I think I have a good idea of high school level math + a high level of modern physics concepts so ELI16?

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adamginsburg t1_je1wwcd wrote

Reply to comment by AuDHDiego in Is NaCl relatively common in the galaxy/universe? by PHealthy

There actually is a decent amount expelled in gigantic jets, but the jets from quasars are relativistic (i.e., travel at a significant fraction of the speed of light) and escape the galaxy. Google "radio galaxies" and look at those images: they show jets shooting to megaparsec size scales (i.e., 10-100x bigger than galaxies), so that material totally escapes the galaxy.

That said, there is probably some material from quasars that gets mixed back into the galaxy - I think not that much, but honestly there's a lot unknown about gas cycling in the vicinity of rapidly accreting black holes. Nevertheless, even if all the accretion disk material got fed back into the galaxy, it would represent a truly tiny fraction of the galaxy's mass, much less than the material made by supernovae (our black hole is 10^6 solar masses, our galaxy is ~10^12 solar masses, of which ~10^11 is baryonic - so the black hole is a tiny fraction of the galaxy, and the accretion disk is a tiny fraction of that. my numbers here are super rough)

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tidderred t1_je1vi30 wrote

Reply to comment by Paaaaap in Is NaCl relatively common in the galaxy/universe? by PHealthy

(Have read through the first few chapters of Stars and Their Spectra by James Kaler, so most of what I will say is explained in more detail there.)

On the topic of chemical composition of stars, only cool stars, like M dwarfs or L and T type ultra-cool brown dwarfs can have complex molecules survive in their cores. If the star is any hotter (which is the result of a lot of other variables) only pure elements or hardy molecules with strong bonds can survive that chaotic environment without being ripped apart. For example L-T stars can be identified if their chronosphere contains TiO, which is a) a molecule and b) has titanium, which is heavier than sodium or chloride, so somewhere out there NaCl should exist.

But as far as we know L-T stars along with white dwarves and type 0 stars make up about 5% of stars in the universe, so not a lot of NaCl should exist in stars both in quantity and spatial spread.

Like you said, detecting chemicals on exoplanets is much more challenging, where NaCl can exist in greater quantities, without being disturbed by immense heat and pressure stellar cores have. We just cannot know for sure, but it is fun to think about! (Which is a very non-sciency way of saying we should be looking into this.)

EDIT: After an experienced scientist chimed in I realized my answer didn't take into account the fact that the molecule itself needs to radiate some energy for us to detect it, or it should absorb some energy from the envelope to create noticeable dips in the spectrum. In either case, it will heat up, not so much to break the molecule, but not as cold as L-T stars would require (about a few hundred kelvin at most). I also didn't base my speculation on any real detection, just wanted to chime in since what I learned about seemed to coincide with this topic. Still leaving this up in case anyone wants to take this info and go on their own rabbit hole. Also, just saw JWST detected some silicate dust in a what looks to be a hot jupiter (VHS 1256 b), so exoplanets being challenging to study might already be changing with JWST's observations.

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