APOD: Edge-On Galaxy NGC 5866 (2016 Mar 09)

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APOD: Edge-On Galaxy NGC 5866 (2016 Mar 09)

Post by APOD Robot » Wed Mar 09, 2016 5:12 am

Image Edge-On Galaxy NGC 5866

Explanation: Why is this galaxy so thin? Many disk galaxies are actually just as thin as NGC 5866, pictured above, but are not seen edge-on from our vantage point. One galaxy that is situated edge-on is our own Milky Way Galaxy. Classified as a lenticular galaxy, NGC 5866 has numerous and complex dust lanes appearing dark and red, while many of the bright stars in the disk give it a more blue underlying hue. The blue disk of young stars can be seen extending past the dust in the extremely thin galactic plane, while the bulge in the disk center appears tinged more orange from the older and redder stars that likely exist there. Although similar in mass to our Milky Way Galaxy, light takes about 60,000 years to cross NGC 5866, about 30 percent less than light takes to cross our own Galaxy. In general, many disk galaxies are very thin because the gas that formed them collided with itself as it rotated about the gravitational center. Galaxy NGC 5866 lies about 50 million light years distant toward the constellation of the Dragon (Draco).

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Re: APOD: Edge-On Galaxy NGC 5866 (2016 Mar 09)

Post by Ann » Wed Mar 09, 2016 5:51 am

Oh, that's a fascinating picture of a fascinating galaxy! :D
APOD Robot wrote:
Why is this galaxy so thin?
Components of the Milky Way. Wikimedia Commons/Gaba p.
Well, that depends on what you mean by a "thin" galaxy. Clearly NGC 5866 has a big fat halo. But all disk galaxies that contain a plane of dust, including the Milky Way, have a thin disk. Our own galaxy also has a thick disk, a bulge and a halo.

I have to admit that I can't readily discern a thick disk in NGC 5866, or even a bulge. There might not actually be a bulge in this galaxy, although there is a nucleus, which is hidden by dust.

It is fascinating, nevertheless, that the thin disk of NHC 5866 is so thin. Obviously almost all star formation in this galaxy has come to an end. We can spot a very few bright spots, likely clusters, in the dust lane. My impression is that this galaxy is a lot less dusty than the Milky Way and contains far less star formation, and that its dust lane actually might be thinner.
Image
The Milky Way. Photo: Ken Croswell.
Why is the dust lane two-colored? The orange part of it is clearly blocking and reddening light coming from behind it, like the dust lane of the Milky Way. But what about the long blue stretch of dust in NGC 5866? I guess this is either the thick disk of this galaxy, which would be blue for some reason. Or else this bluish color might be a sort of galaxy-sized reflection nebula. This could be dust with embedded stars, whose light might be reflected in our direction. That would explain the blue color too, because reflections nebulas are typically bluish.

But I'm doubtful that the bluish stretch of dust is as blue as it looks in today's APOD. I get the impression that the picture has been color-balanced so that the overall color of the galaxy is neutral. In my opinion, most of the light from this galaxy - and certainly from its halo - comes from old yellowish stars, particularly old red giants.

Note that the disk of NGC 5866 extends to the upper right and lower left, even when the dust disk has come to an end. Beyond the dust the disk is made of stars only. This could be the thick disk. Note its neutral color, which suggests that the stars it is made of are old or of intermediate age.

We can see two fantastic and incredibly large dust features rising above the disk. At left is a tremendous loop, and farther to the right is a humongous arc far above the disk. These features speak of past upheavals, possibly a series of supernovas.

All in all, a fascinating picture of a fascinating galaxy!

Ann
Last edited by Ann on Wed Mar 09, 2016 7:57 am, edited 1 time in total.
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Re: APOD: Edge-On Galaxy NGC 5866 (2016 Mar 09)

Post by Boomer12k » Wed Mar 09, 2016 7:34 am

Looks to me like an Elliptical Galaxy with a ring of dust...but that could just be the appearance of the "galactic halo"....but still. It surrounds the whole thing, appearing to extend beyond the dust lane. The dust part looks tiny. It reminds me of the Sombrero Galaxy...if seen totally edge on, it may well look a bit..."thin"...and from what we see it is very thin from a more top view.

Maybe it was Elliptical, but had a small merger...thus the dust... more mergers, more dust, larger thicker hub and arms, and broader profile...


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Re: APOD: Edge-On Galaxy NGC 5866 (2016 Mar 09)

Post by geckzilla » Wed Mar 09, 2016 9:50 am

Boomer12k wrote:Looks to me like an Elliptical Galaxy with a ring of dust...but that could just be the appearance of the "galactic halo"....but still. It surrounds the whole thing, appearing to extend beyond the dust lane. The dust part looks tiny. It reminds me of the Sombrero Galaxy...if seen totally edge on, it may well look a bit..."thin"...and from what we see it is very thin from a more top view.

Maybe it was Elliptical, but had a small merger...thus the dust... more mergers, more dust, larger thicker hub and arms, and broader profile...
The Sombrero is also classified as a lenticular galaxy. Lenticular galaxies are probably a transitional phase between spiral and elliptical galaxy evolution.
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Re: APOD: Edge-On Galaxy NGC 5866 (2016 Mar 09)

Post by Guest » Wed Mar 09, 2016 11:52 am

The extra fascination to me is the liberal sprinkling of dozens of other galaxies in the background. Makes foe a humbling fascination. Wish all dictators were interested in astronomy ......

KCTJ

Re: APOD: Edge-On Galaxy NGC 5866 (2016 Mar 09)

Post by KCTJ » Wed Mar 09, 2016 12:07 pm

I was also fascinated by the other galaxies and stars in this picture,the star in the top right corner shows many dark spots left to right. Would these be planets, moons.?

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Re: APOD: Edge-On Galaxy NGC 5866 (2016 Mar 09)

Post by geckzilla » Wed Mar 09, 2016 12:57 pm

KCTJ wrote:I was also fascinated by the other galaxies and stars in this picture,the star in the top right corner shows many dark spots left to right. Would these be planets, moons.?
It's just a charge bleed with some empty black pixels inside. Nearly all of the foreground stars have them because they saturated the sensor and some of the "buckets" which hold electrons overflow up and down the sensor in two directions but they don't flow to the sides, so it forms a bright white linear feature. The black spots are some weirdo empty pixels that I don't know the exact details for why or how they got that way.

Anyway, even if there were planets around any of those stars, it's likely that the star itself and its entire system of planets would occupy only a single pixel.
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Re: APOD: Edge-On Galaxy NGC 5866 (2016 Mar 09)

Post by neufer » Wed Mar 09, 2016 2:01 pm

Ann wrote:
APOD Robot wrote:
Why is this galaxy so thin?
Well, that depends on what you mean by a "thin" galaxy. Clearly NGC 5866 has a big fat halo. But all disk galaxies that contain a plane of dust, including the Milky Way, have a thin disk. Our own galaxy also has a thick disk, a bulge and a halo.
The gases that formed the galaxy are just another type of accretion disk.

The initial conditions and mechanisms are not entirely understood.
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Re: APOD: Edge-On Galaxy NGC 5866 (2016 Mar 09)

Post by Fred the Cat » Wed Mar 09, 2016 3:41 pm

Guess it just takes a while to get things moving - galactically speaking? :wink:

How can we type galaxies by age – look further back in the universe?
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Re: APOD: Edge-On Galaxy NGC 5866 (2016 Mar 09)

Post by starsurfer » Wed Mar 09, 2016 6:03 pm

Ann wrote:Oh, that's a fascinating picture of a fascinating galaxy! :D
APOD Robot wrote:
Why is this galaxy so thin?
Components of the Milky Way. Wikimedia Commons/Gaba p.
Well, that depends on what you mean by a "thin" galaxy. Clearly NGC 5866 has a big fat halo. But all disk galaxies that contain a plane of dust, including the Milky Way, have a thin disk. Our own galaxy also has a thick disk, a bulge and a halo.

I have to admit that I can't readily discern a thick disk in NGC 5866, or even a bulge. There might not actually be a bulge in this galaxy, although there is a nucleus, which is hidden by dust.

It is fascinating, nevertheless, that the thin disk of NHC 5866 is so thin. Obviously almost all star formation in this galaxy has come to an end. We can spot a very few bright spots, likely clusters, in the dust lane. My impression is that this galaxy is a lot less dusty than the Milky Way and contains far less star formation, and that its dust lane actually might be thinner.
Image
The Milky Way. Photo: Ken Croswell.
Why is the dust lane two-colored? The orange part of it is clearly blocking and reddening light coming from behind it, like the dust lane of the Milky Way. But what about the long blue stretch of dust in NGC 5866? I guess this is either the thick disk of this galaxy, which would be blue for some reason. Or else this bluish color might be a sort of galaxy-sized reflection nebula. This could be dust with embedded stars, whose light might be reflected in our direction. That would explain the blue color too, because reflections nebulas are typically bluish.

But I'm doubtful that the bluish stretch of dust is as blue as it looks in today's APOD. I get the impression that the picture has been color-balanced so that the overall color of the galaxy is neutral. In my opinion, most of the light from this galaxy - and certainly from its halo - comes from old yellowish stars, particularly old red giants.

Note that the disk of NGC 5866 extends to the upper right and lower left, even when the dust disk has come to an end. Beyond the dust the disk is made of stars only. This could be the thick disk. Note its neutral color, which suggests that the stars it is made of are old or of intermediate age.

We can see two fantastic and incredibly large dust features rising above the disk. At left is a tremendous loop, and farther to the right is a humongous arc far above the disk. These features speak of past upheavals, possibly a series of supernovas.

All in all, a fascinating picture of a fascinating galaxy!

Ann
I would like to see a similar illustration of the Milky Way that shows its many tidal streams. Maybe there is one out there?

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Re: APOD: Edge-On Galaxy NGC 5866 (2016 Mar 09)

Post by Fred the Cat » Wed Mar 09, 2016 6:54 pm

starsurfer wrote:I would like to see a similar illustration of the Milky Way that shows its many tidal streams. Maybe there is one out there?
Lots out there! That's for sure :ssmile:
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Re: APOD: Edge-On Galaxy NGC 5866 (2016 Mar 09)

Post by Ann » Thu Mar 10, 2016 1:05 am

Thanks for your links, Fred!

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Re: APOD: Edge-On Galaxy NGC 5866 (2016 Mar 09)

Post by starsurfer » Thu Mar 10, 2016 7:20 pm

Fred the Cat wrote:
starsurfer wrote:I would like to see a similar illustration of the Milky Way that shows its many tidal streams. Maybe there is one out there?
Lots out there! That's for sure :ssmile:
Thanks for the links! The first link has a nice illustration but I would love to see a more updated version.

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Re: APOD: Edge-On Galaxy NGC 5866 (2016 Mar 09)

Post by MarkBour » Thu Mar 10, 2016 8:33 pm

Is there a publicly-accessible "large" database of galaxies?
One that would show estimated distance, mass, type, orientation, etc. ?
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Re: APOD: Edge-On Galaxy NGC 5866 (2016 Mar 09)

Post by geckzilla » Thu Mar 10, 2016 10:59 pm

MarkBour wrote:Is there a publicly-accessible "large" database of galaxies?
One that would show estimated distance, mass, type, orientation, etc. ?
There are a few. SIMBAD and NED are quite popular. Note that the more distant and smaller a galaxy is, the lower the sample size or quality of available data may be. Everything with an NGC number will probably be accurate, though.
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