Half of Milky Way's mass found in million-Kelvin gas cloud Scientists have just discovered that the extreme drought bedeviling America's midsection is being caused by a gigantic halo of hot gas surrounding the Milky Way. Okay, okay... We're kidding about the cause of the drought – but not about that gas cloud, which is a few hundreds of thousands of light years in diameter, weighs …
Quick answer: no
Longer answer: This is the missing baryon content ( 'ordinary matter' contents of the universe). The dark matter is far more than double the mass of stars ;something like 5-10 times the baryon content -so more like 10-20 times the mass in stars that we see. People have been looking for this missing baryon content in hot gas for some time. That is why several groups have seen it.
A quick Google on "missing baryons" will tell you about it.
It says diffuse cloud, so I'd assume that you wouldn't hit to many of them on your way out; a bit like solar radiation or cosmic rays. It's a bit like the difference between being underwater compared to out in the rain and being scaref of drowning. Yes it's another issue to overcome because you don't want to get wet,but probably trifling compared to the problem of actually getting there (maybe like worying about the temperature in the Sahara deset when you go out for a walk - starting in Sydney)
Similar clouds have been known to surround galactic clusters, but not around our own. That is of course hard to do, and has been likened to "drawing up a map of the city whilst standing in the market square." A more accurate analogy would be "drawing up a map of the city whilst standing on a playground somewhere in the (unfashionable western) suburbs"
Thumbs up to the scientists for attempting perhaps not the impossible, but at least the very, very improbable!
Sad that Rik hasn't bothered to correct this egregious error ! One of the aspects I most appreciate about Richard Chirgwin's Reg postings on scientific matters - he actually seems to read the comments and to be willing to correct errors that are pointed out. Kudos !...
Henri
While we're nitpicking, "comprised of" as in "[...] such as protons and neutrons that are comprised of three quarks" is an error that someone claiming to be a professional writer really shouldn't make. "Composed of" would be correct here. "Comprised" means "made up of", the appending of an additional "of" is redundant.
My very slightly informed guess for why this extremely hot gas cloud was much more difficult to detect than the cold cosmic background radiation is that the black body radiation at extremely high temperatures is skewed toward the far blue end of the spectrum (so the use of X-ray detection satellites). In addition to the difficulty detecting X-rays (even using a satellite), the high energy per photon for X-rays reduces the number of photons emitted for a given energy. This cloud is also extremely diffuse, so the X-ray glow viewed from a telescope's relatively narrow cone would be relatively faint (I suspect).
How do they estimate temperature? Do they not estimate particle velocities by measuring doppler shift and then calculate temperature from the kinetic energy of the ions via the Bollzmann constant?
http://en.wikipedia.org/wiki/Bolzmann_constant
This assumes that the gas is in equilibrium, more or less like an ideal gas. Apparently it's convenient to do this so that other thermodynamic concepts can be applied.
At such high temperatures gas would indeed glow, even when quite dilute. It's actually more likely to be fast moving streams and sheets of cool partly ionised gas.
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