APOD: NGC 253: The Silver Coin Galaxy (2020 Apr 14)

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APOD: NGC 253: The Silver Coin Galaxy (2020 Apr 14)

Post by APOD Robot » Tue Apr 14, 2020 4:06 am

Image NGC 253: The Silver Coin Galaxy

Explanation: NGC 253 is one of the brightest spiral galaxies visible, but also one of the dustiest. Dubbed the Silver Coin for its appearance in smalltelescopes, it is more formally known as the Sculptor Galaxy for its location within the boundaries of the southern constellation Sculptor. Discovered in 1783 by mathematician and astronomer Caroline Herschel, the dusty island universe lies a mere 10 million light-years away. About 70 thousand light-years across, NGC 253, pictured, is the largest member of the Sculptor Group of Galaxies, the nearest to our own Local Group of galaxies. In addition to its spiral dust lanes, tendrils of dust seem to be rising from a galactic disk laced with young star clusters and star forming regions in this sharp color image. The high dust content accompanies frantic star formation, earning NGC 253 the designation of a starburst galaxy. NGC 253 is also known to be a strong source of high-energy x-rays and gamma rays, likely due to massive black holes near the galaxy's center. Take a trip through extragalactic space in this short video flyby of NGC 253.

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Ann
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Re: APOD: NGC 253: The Silver Coin Galaxy (2020 Apr 14)

Post by Ann » Tue Apr 14, 2020 6:47 am

NGC 253 is not one of my favorite galaxies, because - you knew it - its appearance does not appeal to me. Why not?
























To me, NGC 253 is boring. Nothing seems to happen in it when you look at it - or at least, very little seems to happen in it when I look at it!

Note how almost perfectly regular this galaxy's perimeter is. And note that, even though one of the filters for the ESO picture of NGC 253 was an H-alpha one, there are relatively few and quite small pink spots visible in it. Compare the appearance of NGC 253 with the appearance of M61, in a picture that was also produced by ESO with a very similar set of filters. Most striking is the wildly distorted shape of M61, but you can also see that M61 is full of big and small pink emission nebulas. The profusion of pink nebulas in M61 makes NGC 253 look quite poor in pink gas clouds.


















I would guess that the Star Shadows Remote Observatory and PROMPT/CTIO picture of NGC 253 was made without the use of an Hα filter. Note that we can only see one obvious pink spot in the entire galaxy, although there are hints of pink elsewhere, too. But note above all the messy dust structures permeating the disk. Dark lines of dust seem to rise perpendicular from the disk everywhere, cutting right through the spiral dust lanes that I would expect to see in a spiral galaxy and making the whole interior of NGC 253 look like a hopeless mess of chaotic dust.

To make sense of the dust disorder in NGC 253, take a look at the Hubble picture of edge-on spiral galaxy NGC 891. You can see the galaxy's thin disk, which is the galaxy's central dark dust lane peppered with young stars. You can see the thick disk, which is the bright whitish quite regular structure enveloping the thin disk. And you can see the halo of stars fading into space.

Note, however, all the dust columns rising from the thin disk of NGC 891. They are called chimneys, and it is surmised that they are remnants of supernova explosions. I think the messy interior structure of NGC 253 is due to a profusion of such dust chimneys.

Finally, why is NGC 253 called a starburst galaxy, when we see so few pink emission nebulas in its disk? The answer is that the starburst takes place in the galaxy's core.
Wikipedia wrote:

NGC 253's starburst has created several super star clusters on NGC 253's center (discovered with the aid of the Hubble Space Telescope): one with a mass of 1.5*106 solar masses, and absolute magnitude of at least -15, and two others with 5*104 solar masses and absolute magnitudes around -11;[13] later studies have discovered an even more massive cluster heavily obscured by NGC 253's interstellar dust with a mass of 1.4*107 solar masses, an age of around 5.7*106 years, and rich in Wolf-Rayet stars.
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orin stepanek
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Re: APOD: NGC 253: The Silver Coin Galaxy (2020 Apr 14)

Post by orin stepanek » Tue Apr 14, 2020 1:29 pm

NGC253_HstSubaruEsoNew_960.jpg
NGC 253 is a perfect shaped Galaxy! Life there is probably peaceful! :mrgreen: Actually Ann; I kinda like it! 8-)
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Re: APOD: NGC 253: The Silver Coin Galaxy (2020 Apr 14)

Post by Chris Peterson » Tue Apr 14, 2020 1:39 pm

orin stepanek wrote: Tue Apr 14, 2020 1:29 pm NGC253_HstSubaruEsoNew_960.jpg

NGC 253 is a perfect shaped Galaxy! Life there is probably peaceful! :mrgreen: Actually Ann; I kinda like it! 8-)
I don't know... there's a heck of a lot of star formation going on. More than in most galaxies. It's a very active place... kind of the opposite of "peaceful".
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Re: APOD: NGC 253: The Silver Coin Galaxy (2020 Apr 14)

Post by orin stepanek » Tue Apr 14, 2020 2:55 pm

Chris Peterson wrote: Tue Apr 14, 2020 1:39 pm
orin stepanek wrote: Tue Apr 14, 2020 1:29 pm NGC253_HstSubaruEsoNew_960.jpg

NGC 253 is a perfect shaped Galaxy! Life there is probably peaceful! Actually Ann; I kinda like it!
I don't know... there's a heck of a lot of star formation going on. More than in most galaxies. It's a very active place... kind of the opposite of "peaceful".


I was referring to shape: flat; no bulges; just nice and round! Activity can be peaceful if done without a lot of commotion! :oops: After I blow it up; I guess there are a lot of billowy clouds! Oh well; I still like it!
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