[LINK] O/t: Our galaxy a bent Z

[stephen at melbpc.org.au]

For something completely different ..

Apparently our Milky Way Galaxy is shaped like a "Z" .. with a bar.

Supposedly it looks like this: http://en.wikipedia.org/wiki/NGC_1365

But also one arm (the other one) is bent, so it's not in the galactic 
plane but slightly above it. So, apparently, it looks like a coil :-)


http://www.technologyreview.com/blog/arxiv/26763

"In 1852, Stephen Alexander, an astronomer at the College of New Jersey, 
put forward the radical suggestion that the Milky Way galaxy is a spiral. 

But while today's astronomers agree on this general shape, they disagree 
over the precise structure of the spiral and in particular on the number 
of arms. 

Astronomers have named at least 6 arms and in the 1990s, evidence emerged 
that the galaxy had a central bar. The uncertainty is easy to understand. 
Our view of the galaxy shows the nearer stars superimposed on the ones 
that are further away. And much of the opposite side of the Milky Way 
galaxy is obscured entirely by the central mass of stars at the centre.

Recently, however, a clearer picture has begun to emerge. The growing 
consensus is that the Milky Way has a central bar with two main arms, 
called the Perseus Arm, which passes with a few kiloparsecs of the Sun, 
and the Scutum-Centaurus Arm. (The other arms are now thought to be minor 
structures made up largely of gas.)

Today, Thomas Dame and Patrick Thaddeus at the Harvard-Smithsonian Center 
for Astrophysics in Cambridge provide further evidence of this 2-arm 
structure but with a twist that explains why astronomers have previously 
been unable to see it clearly.

Astronomers traditionally study the Milky Way's structure by measuring the 
movement of large clouds of hydrogen and carbon monoxide gas within it 
(the velocity of distant stars being too difficult to pin down). 

The new evidence that Dame and Thaddeus have accumulated shows the 
existence of a new arm on the other side of the Milky Way, but further 
from the centre than we are. The new arm is 18 kpc long and so stretches 
some 50 degrees across the sky. 

Dame and Thaddeus conclude that this arm is an extension of the Scutum-
Centaurus Arm, the rest of which is obscured behind the galactic middle.

That makes sense. The Perseus arm, which we can see more clearly, wraps 
300 degrees around the galactic centre. If Dame and Thaddeus are correct, 
the Scutum-Centaurus Arm must be exactly symmetrical with this. That makes 
the Milky Way similar to the Great Barred Spiral, a barred, twin spiral 
some 56 million light years from here. 

But why has it taken astronomers so long to find the end of this arm? The 
reason, says Dame and Thaddeus, is that this arm is bent. Sot it's not in 
the galactic plane but slightly above it. 

Which means the Milky Way is warped, like the cap from a freshly-opened 
beer bottle."

Ref: arxiv.org/abs/1105.2523: A Molecular Spiral Arm in the Far Outer 
Galaxy
--

Cheers,
Stephen