APOD: NGC 6822: Barnard's Galaxy (2013 Feb 08)

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APOD: NGC 6822: Barnard's Galaxy (2013 Feb 08)

Post by APOD Robot » Fri Feb 08, 2013 5:06 am

Image NGC 6822: Barnard's Galaxy

Explanation: Grand spiral galaxies often seem to get all the glory, flaunting their young, bright, blue star clusters in beautiful, symmetric spiral arms. But small galaxies form stars too, like nearby NGC 6822, also known as Barnard's Galaxy. Beyond the rich starfields in the constellation Sagittarius, NGC 6822 is a mere 1.5 million light-years away, a member of our Local Group of galaxies. About 7,000 light-years across, the dwarf irregular galaxy is seen to be filled with young blue stars and mottled with the telltale pinkish hydrogen glow of star forming regions in the deep color composite image. Contributing to the science of LITTLE THINGS, this portrait of a small galaxy was made as part of the Lowell Amateur Research Initiative (LARI), welcoming collaborations with amateur astronomers.

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Re: APOD: NGC 6822: Barnard's Galaxy (2013 Feb 08)

Post by Ann » Fri Feb 08, 2013 5:42 am

Oh, it's that lovely little dwarf galaxy, NGC 6822! It's a very fine APOD, too. :D

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Re: APOD: NGC 6822: Barnard's Galaxy (2013 Feb 08)

Post by 500pesos » Fri Feb 08, 2013 10:55 am

Still, 7,000 light years across is a very very extremely huge place.
/NGC 6822 slaps impudent humans, who ya calling a dorf?

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Re: APOD: NGC 6822: Barnard's Galaxy (2013 Feb 08)

Post by Astronymus » Fri Feb 08, 2013 11:03 am

Picture link doesn't work.
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Re: APOD: NGC 6822: Barnard's Galaxy (2013 Feb 08)

Post by Yuriy Toropin » Fri Feb 08, 2013 11:08 am

The requested URL /apod/image/1302/NGC6822_L_HaR_GB_final.jpg was not found on this server.

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Re: APOD: NGC 6822: Barnard's Galaxy (2013 Feb 08)

Post by winstond » Fri Feb 08, 2013 12:16 pm

At what point does a globular cluster become a dwarf galaxy? Is it related to size or position (or both)?

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Re: APOD: NGC 6822: Barnard's Galaxy (2013 Feb 08)

Post by mugsy » Fri Feb 08, 2013 1:06 pm

What is the yellowish halo that seems to envelop this miniature galaxy. Mostly seen to the left around to the top of the galaxy in this picture. Is it the glow from older stars??

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Re: APOD: NGC 6822: Barnard's Galaxy (2013 Feb 08)

Post by geckzilla » Fri Feb 08, 2013 1:47 pm

Yuriy Toropin wrote:The requested URL /apod/image/1302/NGC6822_L_HaR_GB_final.jpg was not found on this server.
Astronymus wrote:Picture link doesn't work.
Uh oh. I let them know. Should be fixed as soon as they can.
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Re: APOD: NGC 6822: Barnard's Galaxy (2013 Feb 08)

Post by bystander » Fri Feb 08, 2013 2:36 pm

Yuriy Toropin wrote:The requested URL /apod/image/1302/NGC6822_L_HaR_GB_final.jpg was not found on this server.
Astronymus wrote:Picture link doesn't work.
geckzilla wrote:Uh oh. I let them know. Should be fixed as soon as they can.
Meanwhile, you can find it here.
APOD Robot wrote:color composite image
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Re: APOD: NGC 6822: Barnard's Galaxy (2013 Feb 08)

Post by eksgabe » Fri Feb 08, 2013 2:39 pm

mugsy wrote:What is the yellowish halo that seems to envelop this miniature galaxy. Mostly seen to the left around to the top of the galaxy in this picture. Is it the glow from older stars??
Considering the location in Sagittarius, my guess is that it is dust lanes from the galactic center of the Milky Way galaxy which are in the way.

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Re: APOD: NGC 6822: Barnard's Galaxy (2013 Feb 08)

Post by Psnarf » Fri Feb 08, 2013 3:02 pm


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Re: APOD: NGC 6822: Barnard's Galaxy (2013 Feb 08)

Post by Ann » Fri Feb 08, 2013 3:28 pm

mugsy wrote:What is the yellowish halo that seems to envelop this miniature galaxy. Mostly seen to the left around to the top of the galaxy in this picture. Is it the glow from older stars??
Image
© 2006 Michael R. Blanton & David W. Hogg
Yes, I think that is exactly what it is. Take a look at this picture of dwarf galaxy NGC 4449. It is a gri image, taken through green, red and infrared filters. Note the non-blue halo surrounding the bright starforming parts of the galaxy. This non-blue halo is certainly made up of old stars.

Also take a look at this Hubble image of another bright blue starforming dwarf galaxy, NGC 4214. Hubble took this image in order to look for an underlying population of old yellow stars. The red color of the old stars is exaggerated here, but you can see how numerous these old stars are. NGC 4214 really has a large halo made up mostly of old stars.

So I believe that NGC 6822, just like NGC 4449 and NGC 4214, may have a quite large underlying population of old yellow stars.

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Re: APOD: NGC 6822: Barnard's Galaxy (2013 Feb 08)

Post by lems1802 » Fri Feb 08, 2013 4:32 pm

Thanks a lot!

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Re: APOD: NGC 6822: Barnard's Galaxy (2013 Feb 08)

Post by quigley » Fri Feb 08, 2013 7:40 pm

This is off-subject, but I have been anxiously waiting for the subject of approaching asteroid 2012DA14 on February 15th to come up on APOD or in this discussion forum. The proximity of its travel (.09 LD) and its size (half the size of a football field!) beg to question if it will be visible as it passes by our planet? Will the earth's gravitational pull have any affect on 2012DA14's trajectory? If anyone would like to share information on the subject, it would be welcomed. :D

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Re: APOD: NGC 6822: Barnard's Galaxy (2013 Feb 08)

Post by neufer » Fri Feb 08, 2013 7:47 pm

quigley wrote:
This is off-subject, but I have been anxiously waiting for the subject of approaching asteroid 2012DA14 on February 15th to come up on APOD or in this discussion forum. The proximity of its travel (.09 LD) and its size (half the size of a football field!) beg to question if it will be visible as it passes by our planet? Will the earth's gravitational pull have any affect on 2012DA14's trajectory? If anyone would like to share information on the subject, it would be welcomed. :D
It will be visible only with binoculars from Asia & Australia.
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Re: APOD: NGC 6822: Barnard's Galaxy (2013 Feb 08)

Post by bystander » Fri Feb 08, 2013 7:52 pm

quigley wrote:This is off-subject, but I have been anxiously waiting for the subject of approaching asteroid 2012DA14 on February 15th to come up on APOD or in this discussion forum. The proximity of its travel (.09 LD) and its size (half the size of a football field!) beg to question if it will be visible as it passes by our planet? Will the earth's gravitational pull have any affect on 2012DA14's trajectory? If anyone would like to share information on the subject, it would be welcomed. :D

http://asterisk.apod.com/viewtopic.php?t=30624
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Re: APOD: NGC 6822: Barnard's Galaxy (2013 Feb 08)

Post by StarCuriousAero » Fri Feb 08, 2013 8:43 pm

Do we know if NGC 6822 has a (super)massive central black hole? It doesn't appear to...

Also, is it likely just a comparatively young but future elliptical galaxy? All the stars in this particular image look young and blue, but others it does seem to have an older appearing population of main sequence stars. Any estimates of it's age? Can't seem to find many details on this little guy, but I only tried the available links and wikipedia. What do we know/suspect about the evolution of these little blue galaxies?

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Re: APOD: NGC 6822: Barnard's Galaxy (2013 Feb 08)

Post by Anthony Barreiro » Fri Feb 08, 2013 9:56 pm

quigley wrote:This is off-subject, but I have been anxiously waiting for the subject of approaching asteroid 2012DA14 on February 15th to come up on APOD or in this discussion forum. The proximity of its travel (.09 LD) and its size (half the size of a football field!) beg to question if it will be visible as it passes by our planet? Will the earth's gravitational pull have any affect on 2012DA14's trajectory? If anyone would like to share information on the subject, it would be welcomed. :D
Sky and Telescope Magazine has a detailed observing guide in their February print edition and on their website:

http://www.skyandtelescope.com/news/hom ... 52161.html
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Re: APOD: NGC 6822: Barnard's Galaxy (2013 Feb 08)

Post by Anthony Barreiro » Fri Feb 08, 2013 10:16 pm

winstond wrote:At what point does a globular cluster become a dwarf galaxy? Is it related to size or position (or both)?
The stars in a globular cluster all formed at the same time, a long time ago, like 10 to 12 billion years ago. So if any big, bright, blue stars formed when the cluster was born, they have already burned through most of their hydrogen and turned into red giants or invisible white dwarfs. The light from the consistently old stars in a globular cluster is yellowish. (There are rare so-called "blue stragglers" in some globular clusters. The current guess is that one of these more massive, hot, blue stars could form when two smaller, cooler, older stars collide and merge into one new star.)

A dwarf galaxy like NGC 6822 has stars of widely varying ages, from old yellow stars to young blue stars to areas of current active star birth.

A globular cluster becomes a dwarf galaxy when astronomers learn enough about its population of stars to realize that it was mistakenly categorized as a globular cluster. :wink: This happened to Omega Centauri a few years ago.
Last edited by Anthony Barreiro on Fri Feb 08, 2013 11:16 pm, edited 1 time in total.
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Re: APOD: NGC 6822: Barnard's Galaxy (2013 Feb 08)

Post by Chris Peterson » Fri Feb 08, 2013 10:29 pm

StarCuriousAero wrote:Do we know if NGC 6822 has a (super)massive central black hole? It doesn't appear to...
How would you tell? Unless the central black hole was in an active phase, resulting in jets, it would be undetectable at this image scale. Central black holes are normally detected by examining the orbits of stars very near the center with a high resolution imaging system ("near the center" meaning inside one or two pixels in an image like this one).
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Re: APOD: NGC 6822: Barnard's Galaxy (2013 Feb 08)

Post by Boomer12k » Sat Feb 09, 2013 12:04 am

It looks like a spacey chicken looking at you sideways.

Odd, little galaxy, I always thought M31 was the closest GALAXY to us, not counting the Magellanic Clouds, and any other satellite objects. But evidently not.
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