by Ann » Sun Aug 28, 2016 6:56 am
The remarkable elongated okra-colored background galaxy at right is, of course, the most eye-catching object in today's APOD. The
two distorted images link takes us to a page which claims that the redshift of this object is ~0.8. That means, or so I think, that the universe has become 80% larger through expansion since the light of that background galaxy was emitted. Also the distance to that background galaxy is ~10 billion light-years. Whatever.
As a color commentator, I am of course hugely interested in this object's color. We can see a very small and faint yellow center in the galaxy - it is most obvious in the center of the "swelling" near the bottom. (This may sound rude, but to me the elongated galaxy is slightly similar in shape to a
sperm swimming downwards.)
Outside the faint yellow center is what looks like spiral arms. There are some bright blue knots in those spiral arms, which are undoubtedly bright clusters of young stars. But the overall color of the galaxy is
the color of clay. Why is that?
NGC 157. Photo: Adam Block.
I can only guess. As old as it is, the lensed galaxy may nevertheless have had an interesting past. It may have undergone one or many intense bursts of star formation, which produced very many stars and a lot of dust. At the time this galaxy was lensed and "had its distorted photograph taken", the starburst was largely over, and only a few bright clusters were still forming. The stars that had formed in the intense starburst were now aging and no longer blue, but because there were so many of them their combined light was still bright. Also there might be quite a lot of dust left over from the original starburst and scattered all over the galaxy, reddening its overall light. And then, of course, the overall color of this galaxy is reddened by redshift-reddening.
In short, I'm thinking that the lensed galaxy might really look a bit like NGC 157 at left. Note the small yellow center, the bright intermediate-aged non-blue disk and arms, and the pink and blue sites of new and ongoing star formation.
Ann
[float=right][img2]http://homepages.wmich.edu/~korista/snotes106/zdist.jpg[/img2][c][size=85]Redshift versus distance.
Source: http://homepages.wmich.edu/~korista/phys106_suppnts.html[/size][/c][/float] [float=left][img2]https://cdn1.cdnme.se/cdn/9-2/449979/images/2009/abell370_hst_54014136.jpg[/img2][/float]
The remarkable elongated okra-colored background galaxy at right is, of course, the most eye-catching object in today's APOD. The [url=http://adsabs.harvard.edu/abs/1999A%26A...347...21B]two distorted images[/url] link takes us to a page which claims that the redshift of this object is ~0.8. That means, or so I think, that the universe has become 80% larger through expansion since the light of that background galaxy was emitted. Also the distance to that background galaxy is ~10 billion light-years. Whatever.
As a color commentator, I am of course hugely interested in this object's color. We can see a very small and faint yellow center in the galaxy - it is most obvious in the center of the "swelling" near the bottom. (This may sound rude, but to me the elongated galaxy is slightly similar in shape to a [url=http://previewcf.turbosquid.com/Preview/2014/05/23__14_04_51/sperm_HIGH_ANIMATED_01.png79050f98-7708-4dc9-b10b-f95bea08d732Larger.jpg]sperm[/url] swimming downwards.)
Outside the faint yellow center is what looks like spiral arms. There are some bright blue knots in those spiral arms, which are undoubtedly bright clusters of young stars. But the overall color of the galaxy is [url=http://www.dick-blick.com/items/332/05/33205-3005-art2ww-m.jpg]the color of clay[/url]. Why is that?
[float=left][img2]http://img.sponli.com/uploads/images/Gallery/150-199/ngc157.jpg[/img2][c][size=85]NGC 157. Photo: Adam Block.[/size][/c][/float]I can only guess. As old as it is, the lensed galaxy may nevertheless have had an interesting past. It may have undergone one or many intense bursts of star formation, which produced very many stars and a lot of dust. At the time this galaxy was lensed and "had its distorted photograph taken", the starburst was largely over, and only a few bright clusters were still forming. The stars that had formed in the intense starburst were now aging and no longer blue, but because there were so many of them their combined light was still bright. Also there might be quite a lot of dust left over from the original starburst and scattered all over the galaxy, reddening its overall light. And then, of course, the overall color of this galaxy is reddened by redshift-reddening.
In short, I'm thinking that the lensed galaxy might really look a bit like NGC 157 at left. Note the small yellow center, the bright intermediate-aged non-blue disk and arms, and the pink and blue sites of new and ongoing star formation.
Ann