Recent comments in /f/askscience

Brain_Hawk t1_je2e2eb wrote

Reply to Why are there multiple species of various life forms, but humans only have one? Are there other complex single-species organisms? by CyberOGa3

The kind of interesting question and there's been quite a few potentially interesting answers

The fundamental reason that we are the only species of our genus remaining is that we murdered and or interbreed with all the rest of them.

Some of them just couldn't compete. And some of them we basically made friends with enough of them to mix together and kill the rest. Primitive homo sapiens were not a sharing species with our cousins. At least as much as I understand early human anthropology, which is admittedly not well.

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jayprints t1_je2cyo2 wrote

Reply to How do laser measurement tools work? by Ninjewdi

I know that wind tunnel testing will use lasers to track velocity by incorporating a seed material, a very fine material that can closely follow the fluid flow. One version of it is called DPIV (Digital Particle Image Velocimetry). And if you know velocity and are willing to make some assumptions, you can get pressure and density from this.

If this isn’t what your referring to, another is a Laser Barometer. Uses laser radiation to sense the change in a gas’ refraction index. This can give you atmospheric pressure.

Schlieren photography is another good example of using light to determine the density gradients of a fluid flow. This one I don’t think is technically lasers.

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Seicair t1_je2cmmp wrote

Reply to comment by forte2718 in Is NaCl relatively common in the galaxy/universe? by PHealthy

> The second generation of stars that formed had a middling metallicity, as they formed from material that included the higher-mass elements formed from the first generation of stars.

I’d like to point out for any chemistry enthusiasts not well versed in astronomy. In astronomy, it’s hydrogen, helium, or metal.

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adamginsburg t1_je29j3x wrote

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

I think you're on the right track that L/T/Y dwarves (brown dwarves) should have cool enough atmospheres to have NaCl in them. I don't know what references to go to say for sure, though.

One of the problems isn't just that the salt molecules need to be warm to emit (that's true), but that the wavelengths at which we see their radiation are tough to observe in stars and planets. The detection we reported was in a disk - which is very, very big compared to a star or planet, and so we could see it at radio/millimeter wavelengths. We generally can only detect stars themselves at optical and infrared wavelengths, and it turns out that NaCl and KCl don't have many transitions at wavelengths we usually observe (e.g., https://ui.adsabs.harvard.edu/abs/2014MNRAS.442.1821B/abstract). Most of their strong emission/absorption lines are at >=26 microns, which is just at the edge of what JWST is capable of observing with its MIRI instrument. No other telescope has observed at these wavelengths with enough sensitivity to pick up salt molecules. I think there's some possibility JWST will detect salts in either hot jupiters or brown dwarves, though; there are weaker salt lines covering JWST's whole range. The trick is, there are lots of other molecules that could obscure the salts in an atmosphere - I'm not sure whether we'll be able to identify the molecules cleanly. It's a much easier job at radio wavelengths.

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