[extropy-chat] the galaxy's fifth leg

[Damien Broderick]

http://www.theaustralian.news.com.au/printpage/0,5942,9483846,00.html

Aussie astronomers redraw the galaxy
 From AFP
06may04

A 50-year-old map of the Milky Way will have to be redrawn after Australian 
astronomers made the astonishing discovery that our spiral galaxy has a 
huge, outflung arm, New Scientist reports in next Saturday's issue.

The vast gassy limb comprises an arc of hydrogen 77,000 light years long 
and several thousand light years thick, running along the Milky Way's 
outermost edge and sweeping around the four main arms that swirl out from 
the galaxy's core.

As it is not in the visible part of the light spectrum, it cannot be seen 
by ordinary telescopes.

Astronomers at the Australia National Telescope Facility made the discovery 
in a project to map the distribution of hydrogen gas across the galaxy.

Most of the Milky Way is obscured by interstellar dust, but hydrogen emits 
radio waves which pass through the dust clouds and which thus make it 
detectable by radio telescope.

"We see it over a huge area of sky," lead astronomer Naomi 
McClure-Griffiths said.

She speculates the arm is a long gaseous tendril that was once joined up 
with another spiral limb but became detached.

The study will be published in Astrophysical Journal Letters.

Astronomers are amazed that the feature had been overlooked, New Scientist 
says.

"I was absolutely flabbergasted, it was quite clearly seen in some of the 
previous surveys but it was never pointed out or given a name," said Tom 
Dame at the Harvard-Smithsonian Center for Astrophysics in Massachusetts.

AFP

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