ESO: A Postcard from Extragalactic Space?

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bystander
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ESO: A Postcard from Extragalactic Space?

Post by bystander » Wed Jun 01, 2011 3:01 pm

A Postcard from Extragalactic Space?
European Southern Observatory | 2011 Jun 01
ESO astronomers have used the Wide Field Imager on the MPG/ESO 2.2-metre telescope to capture an image of NGC 6744. This impressive spiral galaxy lies about 30 million light-years away in the southern constellation of Pavo (The Peacock). But this view could almost be a picture postcard of our own Milky Way, taken and sent by an extragalactic friend, as this galaxy closely resembles our own.

We see NGC 6744 almost face on, meaning we get a dramatic bird’s eye view of the galaxy’s structure. If we had the technology to escape the Milky Way and could look down on it from intergalactic space, this view is close to the one we would see — striking spiral arms wrapping around a dense, elongated nucleus and a dusty disc. There is even a distorted companion galaxy — NGC 6744A, seen here as a smudge to the lower right of NGC 6744, which is reminiscent of one of the Milky Way’s neighbouring Magellanic Clouds.

One difference between NGC 6744 and the Milky Way is their size. While our galaxy is roughly 100 000 light-years across, the galaxy pictured here extends to almost twice this diameter. Nevertheless, NGC 6744 gives us a tantalising sense of how a distant observer might see our own galactic home.

This dramatic object is one of the largest and nearest spiral galaxies. Although it has a brightness of about 60 billion Suns, its light spreads across a large area in the sky — about two thirds the width of the full Moon, making the galaxy appear as a hazy glow with a bright centre through a small telescope. Still, it is one of the most beautiful objects in the southern sky, and it can be identified by amateur astronomers as an oval shape contrasting with a rich background of stars.

With professional telescopes such as the MPG/ESO 2.2-metre telescope at La Silla, which captured this image, NGC 6744 can be seen in all its glory. The dusty spiral arms are home to many glowing star-forming regions (seen in red) and give this Milky Way look-alike its striking spiral form.

This picture was taken by the Wide Field Imager attached to the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory in Chile. The picture was created from exposures taken through four different filters that passed blue, yellow-green and red light and the glow coming from hydrogen gas. These are shown in this picture as blue, green, orange and red, respectively.
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neufer
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Re: ESO: A Postcard from Extragalactic Space?

Post by neufer » Wed Jun 01, 2011 3:34 pm

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BMAONE23
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Is NGC 6744 a visual clone of the MW?

Post by BMAONE23 » Sat Jun 04, 2011 8:31 pm

The bird's eye view of NGC 6744 gives a good idea of what our own galaxy would look like to a passing space traveller.

The spiral galaxy is around 30 million light years away in the southern constellation of Pavo, the Peacock.

In the new image from European Southern Observatory astronomers it is seen almost face on, so that the striking spiral arms are clearly visible.

NGC 6744 would almost be an identical twin of the Milky Way were it not for its size.

While our own galaxy is roughly 100,000 light years across, it has nearly twice that diameter.
Image
The large spiral galaxy named NGC 6744 Photo: ESO/PA

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Ann
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Re: Is NGC 6744 a visual clone of the MW?

Post by Ann » Sat Jun 04, 2011 9:17 pm

Interesting. Here is a larger picture of NGC 6744:

http://www.eso.org/public/archives/imag ... o1118a.jpg

Personally I'm mystified by the colors of NGC 6744. According to the ESO Catalog, NGC 6744 has a B-V index of 0.99 and a U-B index of 0.5. This is very red indeed for a galaxy, and redder when it comes to B-V than giant elliptical galaxy M87! :shock:

But according to the Principal Galaxy Catalog, NGC 6744 has an effective B-V of 0.86 and an effective U-B of 0.24. That's much bluer than what the ESO Catalog says. And according to James D Wray's Color Atlas of Galaxies, NGC 6744 has a B-V of 0.65 and a U-B of 0.00, which is of course still bluer. How confusing!

Interestingly, James D Wray's book shows NGC 6744 to be completely dominated by a bright yellow center and bar. The arm structure, which in the case of NGC 6744 James D Wray calls plume structure, is full of star formation, but it looks quite faint.

I find it interesting that the galaxy is so yellow. I also find it interesting that NGC 6744 is such a big and bright galaxy. According to Principal Galaxy Catalog, it is 2.4 times brighter than the Milky Way.

In ESO's new image the arm structure appears to dominate the galaxy. Personally I associate a multitude of rather short arms, like the ones seen in NGC 6744, with relatively lightweight and small galaxies, so it is really interesting that NGC 6744 is so big and bright.

(Of course... when I look more closely at the galaxy, I can see that there really are some long elegant arms of the kind that you hardly find anywhere else than in large galaxies.)

Ann
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