Astronomers Just Solved the Mystery of the Universe's Missing Matter
(gizmodo.com)37 points by guerrilla 13 hours ago
37 points by guerrilla 13 hours ago
Perhaps some local astrophysicists can chime in on how the gas could be characterized as "hot" - my naive assumption is that could only be relative?
So, temperature is basically a measure of the average kinetic energy of particles in a substance. When you have an extremely diffuse gas, as is the case between galaxies, the particles can be moving very fast, but energy density is still low, because there are so few particles. According to the abstract of the paper, this gas is just 10^-3 particles/cm^3 or 1000 particles per cubic meter. That is 5 orders of magnitude less than the space between planets in our solar system.
So, yes, it is hot. But it also very, very sparse. According to Wikipidia 10^5 to 10^7 K[1]. But there isn't very much of it.
As to why they are hot, from what I've been able to find, it is at least partly due to gravitational potential energy being converted to thermal energy, as it falls into filaments.
[1]: https://en.wikipedia.org/wiki/Warm%E2%80%93hot_intergalactic...
Assuming it's not a fabrication of the press release, it may be jargon. Astrophysicists call "metal" everything that is not Hydrogen or Helium, but Chemist disagree heavily.
In this case, the paper don't call it "hot" but it says that 99.99% of the Hydrogen is ionized.
To ionize one Hydrogen you need 13.6eV. The average energy is temperature*k_Boltzmann. So if the temperature is 13.6eV/k_Boltzmann ~= 160000K then the 50% of the Hydrogen is ionized and 50% not ionized.
To get only 0.01% not ionized you need to increase the temperature, IIRC -log(0.01%)~=9 times.
So the temperature is ~1400000K. Unless I'm making an horrible stupid mistake, I agree it's hot.
(I may be missing the 4.7eV of the dissociation of H2 molecules into two H atoms, that would increase the temperature like a 40%.)
Wouldn’t that be trivially the average velocity of the particles?
Average velocity of the particles if there are enough of them to collide frequently (and if you can factor out bulk motion). But you can also look at average vibrational energy.
So collisions would provide enough energy to call them hot, or is that a term of art, like calling all non-hydrogen, non-helium elements "metallic"?
I want to hear what Sabine Hossenfelder says. I trust that she will say her honest truth.
The Youtube algorithm unfortunately had the same effect on Sabine as it has on every Youtuber who depend on the platform for income
Sabine has always been a little bit on the fringe of physics (e.g. Superdeterminism has had a, let's call it, less than mainstream appeal)
But now every other video is some complete crackpot nonsense being given consideration for 5 minutes and, hastily debunked in the last minute, and with a title like Could This New Theory of Everything Solve Consciousness and Dark Energy?
Sabine's Youtube is a very different type of content than the old BackReaction days.
Perhaps I'm missing something critical.
As I understand it: when astronomers are looking at things a very long distance (measured in lightyears) away, they are looking at how things were that number of millions/billion(s) years ago.
Based on my possible misunderstanding, shouldn't any such claims be made on the basis of how things were and with no indication as to how things may have changed since?