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Milky Way Is Surrounded By Halo of Hot Gas
New submitter kelk1 writes "If the size and mass of this gas halo is confirmed, it also could be an explanation for what is known as the 'missing baryon' problem for the galaxy [...] a census of the baryons present in stars and gas in our galaxy and nearby galaxies shows at least half the baryons are unaccounted for [...] Although there are uncertainties, the work by Gupta and colleagues provides the best evidence yet that the galaxy's missing baryons have been hiding in a halo of million-kelvin gas that envelopes the galaxy."
that envelopes the galaxy
Surely you meant to use the verb, i.e. "envelops".
These insignificant lumps came together to form the first union, our sun, the heating system. And about this glowing gas bag, rotated the Earth, a cat's eye among aggies, blinking in astonishment across the face of time.
"Flyin' in just a sweet place,
Never been known to fail..."
Well, we were covered with a molten scum of rocks, bobbing on the surface like rats. Later, when there was less heat, these giant rock groups settled down among the land masses. During this extinct time, our Earth was like a steam room, and no one, not even man, could get in. However, the oceans and the sewers were simmering with a rich protein stew, and the mountains moved in to surround and protect them. They didn't know then that living as we know it was already taking over.
"Flyin' in just a sweet place,
Never been known to fail..."
Animals without backbones hid from each other, or fell down. Clamosaurs and oysterettes appeared as appetizers. Then came the sponges, which sucked up about 10% of all life. Hundreds of years later, in the Late Devouring Period, fish became obnoxious. Trailerbites, chiggerbites, and muskquitoes collided aimlessly in the dense gas. Finally, tiny, edible plants sprang up in rows, giving birth to generations of insecticides and other small, dying creatures.
"Flyin' in just a sweet place,
Never been known to fail..."
here in the technical vastness of The Future, we can guess that surely, the past was very different. We know for certain, for instance, that for some reason, for some time in the beginning, there were hot lumps. Cold and lonely, they whirled noiselessly through the black holes of space.
This is making me feel like there's a big game going on.
You'll never escape gravity!
OK, you escaped gravity, but you'll never survive the Van Allen Radiation Belt!
OK, you passed through the Van Allen Radiation Belt, but you'll never make it through the Asteroid belt!
OK, you successfully navigated the Asteroid belt, but you'll never make it through the Kuiper belt!
Dang, you made it through the Kuiper belt, but you'll never, ever make it through the Baryon Halo! Muah ha ha ha haaaah!
A feeling of having made the same mistake before: Deja Foobar
Millions of months passed, and, 28 days later, the moon appeared. This small change was reflected best, perhaps, in the sand dollar, which shrank to almost nothing at the bottom of the pool, where even dumb amphibians like catfish laid their eggs in the boiling waters, only to be gobbled up every three minutes by the giant sea orphans and jungle bunnies, which scared everybody. And so, IN FEAR AND HOT WATER, MAN IS BORN!!!
"Flyin' in just a sweet place,
Never been known to fail..."
http://en.memory-alpha.org/wiki/Galactic_barrier
more cowbell
"No, Mr. Bond. I expect you to die."
-- Auric Goldfinger
"Flyin' in just a sweet place,
Never been known to fail..."
Depends on how dense it is. If you immerse yourself in water at 100C (boiling point for you imperial scumdogs :) you won't last long at all, but in dry air at 100C you can survive for substantially longer. If the gas was so sparse that you might only hit a molecule every few seconds or so then the temperature might not matter so much. The article hints that the density is low "The estimated density of this halo is so low that similar halos around other galaxies would have escaped detection." but that doesn't really help in absolute terms.
(or maybe you're making a joke... i don't get the reference in the first line you posted)
retain it's 1,000,000K for 14,000,000 years?
First, that's 14,000,000,000, not 14 million.
The key is how undense it is. When a physicist talks about "temperature" in this context it's just short-hand for "average velocity"... it doesn't necessarily imply thermal equilibrium, even. So 1e6K means a high average velocity. Now, if it were a dense gas there might be collisions that would do things like excite electrons into higher states, which would then decay by emitting photons (light), and so the gas would lose thermal-kinetic energy over time.
In a sufficiently diffuse gas, loss processes like this are very slow because the chances of collision are very slow, so it can stay "hot" (that is, have a high average velocity) for a long, long time.
Blasphemy is a human right. Blasphemophobia kills.
Hold on a second... so they just discovered the Galaxy is surrounded by gas that's the same temperature as the surface of the sun, and is 300,000 lightyears across... possibly extending far into other galaxies... I'm going to take a wild stab here and say that, if that's true it probably pervades the entire universe... Isn't this the biggest scientific discovery in the past decade? What effect does this have on Dark Matter, Dark Energy, etc... etc...
Sorry, that was me. BIG burrito last night.
Where No Man Has Gone Before
What are you talking about, Bozo?
See my journal for slashdot ID's by year. Mine created in 2005. http://slashdot.org/journal/289875/slashdot-ids-by-year
And if that doesn't work, at least we can keep you humans confined by the whole speed of light thing.
See my journal for slashdot ID's by year. Mine created in 2005. http://slashdot.org/journal/289875/slashdot-ids-by-year
As a plasma physicist, I'm not bothered or concerned about them calling it gas. When interacting with the general public to discuss plasma related research, sometimes you find yourself having to make a choice between trying to teach a person what a plasma is, or teaching them what you are doing with it. Attention spans, and time/space are sometimes limited with such interactions and you have to choose your priorities.
When a physicist talks about "temperature" in this context it's just short-hand for "average velocity"... it doesn't necessarily imply thermal equilibrium, even. So 1e6K means a high average velocity. Now, if it were a dense gas there might be collisions that would do things like excite electrons into higher states, which would then decay by emitting photons (light), and so the gas would lose thermal-kinetic energy over time. In a sufficiently diffuse gas, loss processes like this are very slow because the chances of collision are very slow, so it can stay "hot" (that is, have a high average velocity) for a long, long time.
Uh, no. If the collision rate weren't high enough to excite electrons into higher states, it wouldn't be radiating X-rays, which is how Chandra detects the gas. Not a whole lot is known about gas in halos like the Milky Way's, but clusters have been extensively studied, and the gas is pretty close to thermal equilibrium, but not exactly. Hot cluster halos are ubiquitous, and it's not terribly surprising that more isolated galaxies have hot halos as well. The gas heats from loss of gravitational potential when it falls into the halo, and it stays hot because there are few cooling mechanisms, and because subsequent infall repleneshes it.
Temperature (in Kelvin) is actually more useful in astrophysics and thermodynamics of plasmas. It wraps up a bunch of messy real world constants into one number, and also neatly describes the behavior of the volume of gas as a whole, rather than forcing the analyst to perform a lot of messy integrating and averaging of distributions of actual velocities in three dimensions.
Think about it this way. No one is really interested in how fast a specific particle is moving. They're more interested in how the Thermal Energy of the gas couples with other systems.
A galactic halo would be coupled very, very, (very^18) poorly with other systems, at least conductively. And probably even worse convectively, given the scales involved. Radiatively, I don't know near enough about the behavior of these particles to talk about why, but if it's stayed that hot for the life of the universe, effectivelt, then apparently its either not coupled to another system, coupled far more strongly to itself than anything else, or somehow not stimulated to emit blackbody radiation... or all three of the above.
I can see the fnords!
If the collision rate weren't high enough to excite electrons into higher states, it wouldn't be radiating X-rays, which is how Chandra detects the gas.
Chandra isn't seeing X-ray emissions from the gas, it's seeing X-rays being absorbed by the gas. Specifically, observing 8 X-ray sources hundreds of millions of light-years beyond the gas, it was discovered that some of the X-rays from those sources were being absorbed, and it was possible to deduce the temperature of the absorbing gas.
This just accounting for regular own (baryonic) matter. The Halo is still mostly "Dark" matter, which is non-interacting. (It may be WIMPs, i.e., non-baryonic, or it may be quark nuggets, i.e., baryonic, but either way it is non-interacting.)
Chandra isn't seeing X-ray emissions from the gas, it's seeing X-rays being absorbed by the gas. Specifically, observing 8 X-ray sources hundreds of millions of light-years beyond the gas, it was discovered that some of the X-rays from those sources were being absorbed, and it was possible to deduce the temperature of the absorbing gas.
Whoops. My bad, But my point still stands: the light is being absorbed by oxygen ions at a temperature of a million Kelvin: what do you think is ionizing them?
When people refer to temperatures in a galactic halo, they absolutely mean to imply that the halo is somewhere close to thermal equilibrium.
...has Rush Limbaugh really gotten that big?
On the other hand Temperature (e.g., in Kelvin) is only marginally useful in describing the distribution of a phenomena that isn't in thermal equilibrium (say non-blackbody radiation)...
For example, people used to grade lightbulbs by their color Temperature, but that didn't say much about the quality of illumination from said lightbulb. Now they use CRI (color rendering index) for lightbulbs which give some information about the actual distribution instead of the really poor assumption that the illumination was comparable to black-body radiation distribution.
It's not clear (to me) that a galactic halo would necessarily be in thermal equilibrium, except only approximatly over a long time horizon. The real interesting observable phenomena is likely a result of this not being true (e.g. http://arxiv.org/abs/1106.4816 )
It's relative warmth in the 100,000 K and up club it's rather difficult to keep track because once you've boiled away Rhenium, there's not much meaning in additional units of heat.
https://en.wikipedia.org/wiki/Rhenium :)
The more you know...
Do what thou wilt shall be the whole of the Law
but if it isn't very dense, then that might not matter.
That was perhaps the best worst pun ever.
For large sets, this will be our guide even unto death, for the LORD will work for each type of data it is applied to...