[ExI] The New Milky Way

[Damien Broderick]

from the blog of Adam Crowl, astronomer:

<http://crowlspace.com/?p=133>The New Milky Way

June 4th, 2008

The latest view of our Galaxy, the Milky Way, can 
be found at the Spitzer Infra-Red Space Telescope’s newspages here


<http://gallery.spitzer.caltech.edu/Imagegallery/image.php?image_name=ssc2008-10b>The 
New Galaxy


seems we’re now officially a few galactic arms 
short - two arms based on old hydrogen-based maps 
aren’t evidenced by actual star-counts and thus 
were an artefact of the limitations of 
hydrogen-based radio astronomy. The Galaxy is 
still a BIG place, but it looks more like a 
pretty barred spiral galaxy than a relatively 
dull “grand-design” flocculent spiral like it did in the old maps.

But why are spiral arms the way they are? It’s a 
puzzle, but one astrophysicists have no end of 
good ideas about - and then along come some new surprises, like this one


<http://www.space.com/scienceastronomy/080602-aas-blackhole-mass.html>Black 
Hole Mass determines tightness of the Spiral


seems the heftier the central Black Hole, the 
tighter the spiral arms. In our Local Group there 
are three big Spirals - ours, M31 (in Andromeda) 
and M33 (in Triangulum) - and the central Black 
Hole masses 4 million Solar masses (for the Milky 
Way), 180 million for M31, and just 1,500 for 
M33. M33 is a pretty loose spiral, though pretty. 
Andromeda’s M31 is tightly wound, from what we 
can see as M31 is tilted away from us. SO the 
Milky Way is somewhere between the two.

But why the correlation? Dark Matter? Weird 
gravity lanes? Something in hyperspace? Who 
knows? And that’s why astronomy is both fun and worth doing