Tuesday, October 2, 2012

halo around the milky way galaxy

all the light in the universe that our eyes can see comes from stars.

but stars are only one constituent of our milky way galaxy, which also has gas and dust and a lot of other stuff that i've described before. we use wavelengths of light that our eyes are not sensitive to (X-rays, infrared, radio, etc...) in order to detect some of this other stuff. 

it's much more challenging to detect stuff in the universe that doesnt produce light that we know how to see.  for instance, dark matter makes up 25% of all the stuff in the universe, but we dont know exactly what it is yet because we dont know how to "see" it (although we can infer its presence in other ways).

all the "normal" stuff in the universe (planets, stars, gas, trees, humans, etc...) is made of what we call baryons, and it only makes up about 4% of all the stuff in the universe.    the problem is that we havent actually found all the baryons that our otherwise very successful theories tell us there should be.  this has been referred to as the "missing baryon problem" and has been studied for a while.

recent results released by NASA using the chandra x-ray telescope suggest that new observations may help solve this mystery, by detecting a hot halo of gas that surrounds our milky way galaxy. 

above is an artist's illustration of the results (since we cant yet fly away to get an outside perspective of our cosmic home, unfortunately).   the blue color shows a very diffuse, and therefore very difficult to detect, cloud of hot gas surrounding our milky way galaxy and our nearest neighboring galaxies, the small and large magellanic clouds.

if all galaxies are embedded in such diffuse clouds, this could account for much of the previously missing baryons.  the results will have to be verified with some other technique before they are completely believable, but this is a nice start!

1 comment:

Greybeard said...

As you say, we can't get an outside perspective of the Milky way to try and detect such a halo - but why would it harder to detect it from the inside looking out?

If that is not possible, then why not try to detect it around M31, our nearest spiral neighbour, using a segmented imaging technique (like PAndAS)? It's not that far away (and it's getting closer!) and it's bigger than us so it's likely to have more of the stuff.

Nice post.