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Milky Way Is Surrounded By Halo of Hot Gas 121

Posted by Unknown Lamer
from the fog-from-insufficient-rendering-power dept.
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."
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Milky Way Is Surrounded By Halo of Hot Gas

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  • Iiiii'm the CAT!

    Seriously, we're not going to get out of this galaxy alive.

    • Re:1,000,000 K ?!? (Score:5, Informative)

      by jamesh (87723) on Monday September 24, 2012 @07:20PM (#41444147)

      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)

    • by kasperd (592156)

      Seriously, we're not going to get out of this galaxy alive.

      We are not. But our descendants might. I think that gas is the least problem when leaving the galaxy. It might be hot, but if it isn't very dense, then that might not matter.

    • Great. This will be something else for our Congressmen to boast about as a "We worked hard to accomplish this."

  • Excuse me.

  • by Anonymous Coward

    that envelopes the galaxy

    Surely you meant to use the verb, i.e. "envelops".

  • retain it's 1,000,000K for 14,000,000 years?

    • by radtea (464814) on Monday September 24, 2012 @07:20PM (#41444151)

      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.

      • by Nutria (679911)

        First, that's 14,000,000,000, not 14 million.

        I realized that afterwards...

        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.

        Huh? "Temperature" isn't that much easier to write, say or think about than "average velocity".

        • by bughunter (10093) <<ten.knilhtrae> <ta> <retnuhgub>> on Monday September 24, 2012 @07:57PM (#41444453) Journal

          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.

          • by slew (2918)

            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 illuminatio

          • by Rich0 (548339)

            I don't think it has been this hot for the entire life of the universe - it actually hot hotter with time most likely. This was likely gas found in intergalactic space that fell gravitationally towards the milky way. After falling for billions of years it is moving really fast. However, the gas is so sparse that there really aren't any collisions to speak of. Sure, if a particle hits a star or planet or something that will stop it, but chances are this stuff is hitting our atmosphere all the time, but f

        • Temperature is in a way a measure of the energy in the system to be used to excite particles into higher energy states. In that way it incorporates several different forms of energy that are distributed "randomly" meaning they don't have a general direction of travel but none the less will provoke particles on the scale of atoms to move outside of their current stable equilibrium.
      • by PvtVoid (1252388)

        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 [caltech.edu], 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 wh

        • Re: (Score:3, Informative)

          by Anonymous Coward

          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.

          • by PvtVoid (1252388)

            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, [nasa.gov] 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.

      • by Shavano (2541114)
        Let's see. At the average thermal velocity of

        v = sqrt(3 kT/m) ; where m = 1.66E-27 k = 1.38E-23 T = 1E6 so v = 158 km/sec?

        What's the escape velocity of a particle in this halo?

        • Let's see. At the average thermal velocity of

          v = sqrt(3 kT/m) ;
              where m = 1.66E-27
              k = 1.38E-23
              T = 1E6
              so
                      v = 158 km/sec?

          What's the escape velocity of a particle in this halo?

          Somewhere close to the airspeed velocity of an unladen swallow (European)

          • by Shavano (2541114)

            Let's see. At the average thermal velocity of

            v = sqrt(3 kT/m) ; where m = 1.66E-27 k = 1.38E-23 T = 1E6 so v = 158 km/sec?

            What's the escape velocity of a particle in this halo?

            Somewhere close to the airspeed velocity of an unladen swallow (European)

            Yeah, that's my point. A really hot gas can't be gravitationally bound to the galaxy. It would all fly off into intergalactic space and then you wouldn't have a halo any more. I think what they're doing is regarding "temperature" as a stand-in for DENSITY. It's THIN not HOT.

      • Yeah, I'm having a few problems with the idea. Temperature actually implies thermal equilibrium, which in turn requires interaction. However, those atoms/molecules are, shall we say cosmicly non-interacting, being so dispersed that they basically form a hard vacuum. There are then a number of problems with the picture. One, why do the molecules not simply fall back into the galaxy (or if you like, why were they pushed out of the galaxy in the first place)? Several billion years accumulation of solar wi
    • Temperatures of near vacuum gasses are not the same as temperatures of gasses at higher pressures. You can't just stick a thermometer in and see what it reads. What you do is measure the kinetic energy of individual gas particles, and back-calculate to find out what temperature a regular gas would have in order that its average molecule would have the same kinetic energy. In the vacuum of intergalactic space, the individual gas particles can have tremendous kinetic energy, and they are likely to keep th
      • by Nutria (679911)

        What you do is measure the kinetic energy of individual gas particles, and back-calculate to find out what temperature a regular gas would have in order that its average molecule would have the same kinetic energy.

        That's an indirection too far to pass the smell test.

    • by nedlohs (1335013)

      By being "un-dense". How do you propose for the kinetic energy to be removed?

    • by Rich0 (548339)

      It likely only got hotter with time - as it fell towards the galaxy and picked up speed. In order to lose temperature the gas molecules have to actually interact with something. There isn't anything for them to interact with - these things are flying through intergalactic space basically flying around the galaxy.

      Put hot water in a thermos and it stays hot for a while. Put hot water in intergalactic space and it stays hot for much longer. However, the water molecules still interact and release photons ou

  • Galactic Barrier (Score:5, Interesting)

    by wonderboss (952111) on Monday September 24, 2012 @07:11PM (#41444071)
  • ...I think you guys just like saying the word "baryon".

  • by Charliemopps (1157495) on Monday September 24, 2012 @07:21PM (#41444157)
    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...
    • Re:Wait (Score:5, Informative)

      by PvtVoid (1252388) on Monday September 24, 2012 @08:01PM (#41444471)

      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...

      It has been known for a long time that the intergalactic medium is hot enough to be ionized [ua.edu]. That part is not news. The thing that's news is that the hot gas makes it possible to account for the baryons in the Milky Way halo, which were previously undetected.

      • Re:Wait (Score:5, Interesting)

        by waveclaw (43274) on Tuesday September 25, 2012 @12:12AM (#41446165) Homepage Journal

        The thing that's news is that the hot gas makes it possible to account for the baryons in the Milky Way halo, which were previously undetected.

        The thought that we're just the 0.1% of the dirty precipitate at the bottom of the gravity well is a tad humbling. Not that much isn't when you look up from the T.V. to a clear night sky.

        Galaxies are apparently quite dynamic things: a rain of in-falling gas to make new stars, pressure from new stars pushing back, dust build up from all this nucleosynthesis, blackhole cores that cycle on and off. One paper I read even claims this is the beginning of the 'green' period for the Milky Way. The conditions for life will be come more abundant: the number of long-burning dwarf stars like the sun continue to rise as a fraction of the stellar population while the dust percentage (you know, planets) rises at the same time a lot of the big super- and hyper- novae are over with.

        However, longer term prospects seem bleak if the dynamic gas is all consumed or blown away. Eventually stellar production would grind to a halt. The green galaxy would give way to white and red dwarfs floating amid other stellar corpses and thinned gas.

        I have to wonder if the temperature and environmental coupling of this gas is enough to become a future raw star material resource? I mean, we're talking about 99.9% of the matter here and it's already gravitationally bound. Could someone model long-term in-fall of this ionized matter? Could it cool fast enough or even at all to beat the predicted 'big rip' from dark energy and give the galaxy a 2nd, 3rd, etc. childhood?

    • by Tom (822)

      and is 300,000 lightyears across... possibly extending far into other galaxies...

      You are vastly underestimating galactic distances. Our closest neighbor, Andromeda, is over 2 million light years away.

      • by tehcyder (746570)

        and is 300,000 lightyears across... possibly extending far into other galaxies...

        You are vastly underestimating galactic distances. Our closest neighbor, Andromeda, is over 2 million light years away.

        Yeah, and we don't even get on that well.

  • Sorry, that was me. BIG burrito last night.
  • by Bomarc (306716) on Monday September 24, 2012 @07:26PM (#41444213) Homepage
    • by Anonymous Coward
      No. The Galactic Barrier is a (fictional) force field around our galaxy, preventing matter to get out or in (supposedly placed there by some higher intelligence).

      The real thing is a very sparse cloud of ionized gas. It doesn't work like a barrier at all.
      • by tehcyder (746570)

        No. The Galactic Barrier is a (fictional) force field around our galaxy, preventing matter to get out or in (supposedly placed there by some higher intelligence). The real thing is a very sparse cloud of ionized gas. It doesn't work like a barrier at all.

        You really are a bundle of fucking laughs aren't you?

  • by Anonymous Coward
    Of course every time a story comes up about missing matter being found, people want to know the impact on the need for dark matter. There is evidence that suggest how much matter in the universe is made out of baryonic matter (protons and neutrons... essentially anything made of atoms), and how much is made out of non-baryonic matter. The latter category is dark matter. In addition to the missing non-baryonic matter, there is also a bunch of missing baryonic matter, which what is being found by studies l
  • by mbone (558574) on Monday September 24, 2012 @08:18PM (#41444625)

    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.)

  • Wow... (Score:5, Funny)

    by luckymutt (996573) on Monday September 24, 2012 @08:45PM (#41444825)
    ...has Rush Limbaugh really gotten that big?
  • The previous story is the Romney-Ryan Space Policy.

  • There is a barrier [memory-alpha.org] surrounding the galaxy!

  • Everyone knows a Milky Way is surrounded by a halo of milk chocolate.
  • Surrounded by a halo of hot gas... The Milky Way Galaxy and Washington D.C.

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