by Ann » Wed Mar 06, 2024 7:48 am
Yes, today's APOD showcases an interesting-looking galaxy!
Let's analyse it. The dust disk is thick and dark, with little blue or white flecks of either star clusters or star formation. Light brown dust bunnies rise from the disk, remnants of violent occurrences in the past, most likely supernovas. Behind the dust disk is a diffuse, bright, yellow-white light: That would be the light from the central yellow bulge.
And then there is that blue, blue light, shooting out like a
light saber from the end of the dust disk at right. The blue laser beam seems to shoot out from the dust lane handle. What is it?
Let's compare NGC 5866 (M102) with another very edge-on spiral galaxy, NGC 891:
We recognize the dark dust lanes, the dust bunnies rising from it, and the yellowish galactic bulge behind it. But the blue laser beam isn't there! Also note that the dust lane in NGC 891 is much longer than the dust lane in NGC 5866. It extends to the edge of the visible disk, which is clearly not the case for NGC 5866.
NGC 5866 reminds me of M64, the Black-Eye galaxy, which has a very small dust disk indeed:
If you look at an 1.5 MB version of the closeup of the center of M64,
here, you can see more clearly how blue stars stream away from the dust. You can also see that while you can discern individual stars or clusters in the "blue stream", the stream is mostly smooth. It appears to contain large numbers of smallish blue stars like Sirius and Vega.
Take a look at small galaxy NGC 5364:
The bright white crescent "above" the nucleus of NGC 5394
is a remnant of past star formation. It contains huge numbers of
smallish blue star like Sirius and Vega.
So, yes. The blue laser beam of NGC 5866 is actually the remnant of past star formation. It's more than that: The dust lane where the stars were born has probably receded, and the stars have been left behind. They may just have "streamed out of it", but my bet is that the dust lane has receded and the stars have been left behind.
The reason why the small blue stars like Sirius and Vega are left behind to form a light saber beam of blue light in NGC 5866 is of course that they are a lot more more long-lived than the blue behemoths that once kept them company. Also, they are much, much more numerous than the heavyweight OB stars ever were. But their light is certainly not as "electric blue" as the APOD seems to suggest.
And how about this gorgeous spiral galaxy that contains no dust lanes whatsoever except a small dust ring around the center, where we also find star formation?
Can you see the tiny blue ring around the center?
Credit: G. Fritz Benedict et al.
NGC 4314 must have contained a lot of dust in its youth, because if it didn't, I just can't see how it could have formed such a gorgeous spiral shape. Now the dust is all gone, except in a small ring. Don't ask me how it happened, although the Youtube video below just maybe will give you a clue!
Click to play embedded YouTube video.
And finally, there is the question of the flatness of many galactic disks.
APOD Robot wrote:
In general, many disk galaxies become thin because the gas that forms them collides with itself as it rotates about the gravitational center.
Like pizza dough, you mean?
Click to play embedded YouTube video.
Ann
Yes, today's APOD showcases an interesting-looking galaxy!
[img3="M102: Edge-on Disk Galaxy
Image Credit: NASA, ESA, Hubble; Processing: Ehsan Ebahimian"]https://apod.nasa.gov/apod/image/2403/M102_HubbleEbrahimian_960.jpg[/img3]
Let's analyse it. The dust disk is thick and dark, with little blue or white flecks of either star clusters or star formation. Light brown dust bunnies rise from the disk, remnants of violent occurrences in the past, most likely supernovas. Behind the dust disk is a diffuse, bright, yellow-white light: That would be the light from the central yellow bulge.
And then there is that blue, blue light, shooting out like a [url=https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcR3Obh3dJpbh8sjnS7Fq0C4WaW5qQMdd9wBPg&usqp=CAU]light saber[/url] from the end of the dust disk at right. The blue laser beam seems to shoot out from the dust lane handle. What is it?
Let's compare NGC 5866 (M102) with another very edge-on spiral galaxy, NGC 891:
[float=left][img3="NGC 891. Credit: Bernard Miller."]https://cs.astronomy.com/resized-image.ashx/__size/1000x0/__key/telligent-evolution-components-attachments/13-58-00-00-00-49-21-26/NGC891_5F00_PS1_5F00_CROP_5F00_12x12.jpg[/img3][/float][float=right][img3="NGC 891. Credit: R. Jay GaBany."]https://www.universetoday.com/wp-content/uploads/2011/01/small_gabany_ngc891_2010.jpg[/img3][/float]
[clear][/clear]
We recognize the dark dust lanes, the dust bunnies rising from it, and the yellowish galactic bulge behind it. But the blue laser beam isn't there! Also note that the dust lane in NGC 891 is much longer than the dust lane in NGC 5866. It extends to the edge of the visible disk, which is clearly not the case for NGC 5866.
NGC 5866 reminds me of M64, the Black-Eye galaxy, which has a very small dust disk indeed:
[float=left][img3="The inner dust disk of M64. Note the star formation in the dust, and also note the blue stars that seem to 'stream away' from the dust out into the mostly stellar disk. Credit: NASA/Judy Schmidt."]https://upload.wikimedia.org/wikipedia/commons/thumb/e/e8/NGC_4826_-_HST.png/450px-NGC_4826_-_HST.png[/img3][/float][float=right][img3="M64. Note how small the inner dusk disk is, and how little dust there is in the outer disk. Also note that just outside the dark 'eye', the disk is bluish. Credit: NGC 1535."]https://upload.wikimedia.org/wikipedia/commons/9/9f/M64_Blackeye_Galaxy_from_the_Mount_Lemmon_SkyCenter_Schulman_Telescope_courtesy_Adam_Block.jpg[/img3][/float]
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If you look at an 1.5 MB version of the closeup of the center of M64, [url=https://upload.wikimedia.org/wikipedia/commons/thumb/e/e8/NGC_4826_-_HST.png/1024px-NGC_4826_-_HST.png]here[/url], you can see more clearly how blue stars stream away from the dust. You can also see that while you can discern individual stars or clusters in the "blue stream", the stream is mostly smooth. It appears to contain large numbers of smallish blue stars like Sirius and Vega.
Take a look at small galaxy NGC 5364:
[float=left][img3="NGC 5394. Credit: NSF'S NATIONAL OPTICAL-INFRARED ASTRONOMY RESEARCH LABORATORY/GEMINI OBSERVATORY/AURA"]https://i.ytimg.com/vi/HfuWNqvCYXQ/maxresdefault.jpg[/img3][/float][float=right][attachment=1]NGC 5394 Gemini Observatory annotated.png[/attachment][c][size=85][color=#0040FF]The bright white crescent "above" the nucleus of NGC 5394
is a remnant of past star formation. It contains huge numbers of
smallish blue star like Sirius and Vega.[/color][/size][/c][/float]
[clear][/clear]
So, yes. The blue laser beam of NGC 5866 is actually the remnant of past star formation. It's more than that: The dust lane where the stars were born has probably receded, and the stars have been left behind. They may just have "streamed out of it", but my bet is that the dust lane has receded and the stars have been left behind.
The reason why the small blue stars like Sirius and Vega are left behind to form a light saber beam of blue light in NGC 5866 is of course that they are a lot more more long-lived than the blue behemoths that once kept them company. Also, they are much, much more numerous than the heavyweight OB stars ever were. But their light is certainly not as "electric blue" as the APOD seems to suggest.
And how about this gorgeous spiral galaxy that contains no dust lanes whatsoever except a small dust ring around the center, where we also find star formation?
[float=left][attachment=0]NGC 4314 G Fritz Benedict Andrew Howell Inger Jorgensen David Chapell Jeffery Kenney Beverly J Smith and NASA.png[/attachment][c][size=85][color=#0040FF]Can you see the tiny blue ring around the center?
Credit: G. Fritz Benedict et al.[/color][/size][/c][/float][float=right][img3="Closeup of the starforming ring of NGC 4314. Note the blue stars streaming out of the ring."]https://cdn.sci.esa.int/documents/34247/35306/1567219515721-i_screenimage_16985.jpg[/img3][/float]
[clear][/clear]
NGC 4314 must have contained a lot of dust in its youth, because if it didn't, I just can't see how it could have formed such a gorgeous spiral shape. Now the dust is all gone, except in a small ring. Don't ask me how it happened, although the Youtube video below just maybe will give you a clue!
[youtube]https://www.youtube.com/watch?v=9YVRxAX6fwg[/youtube]
And finally, there is the question of the flatness of many galactic disks.
[quote]APOD Robot wrote:
In general, many disk galaxies become thin because the gas that forms them collides with itself as it rotates about the gravitational center.[/quote]
Like pizza dough, you mean?
[youtube]https://www.youtube.com/watch?v=i2Qc3KR6XVQ[/youtube]
Ann