ta152h0 wrote:If all the light being produced by each individual; star would arrive on Earth at the same time, what would a galaxy look like ?
G'day mates,
It would look the same as now. There are two arguments for this statement:
- 1) The lifetime of stars is long compared to the difference in time for light from the most far away parts of a galaxy.
2) The formation of stars in a galaxy is more or less a continuous process, dying stars regenerate clouds of gas into new stars.
Ad 1) A simple analogon. Suppose we have a family. Mother and the children live in New York, father works in Seatle. Now we take pictures of father and of mother and her children, put these pictures in envelopes and send these via surface mail (boat) to Europe. A picture from Seatle has to cross the Pacific, Indian Ocean, around the Cape and via the Atlantic to Europe. A picture of the mother only has to cross the Altantic and arives a month earlier than a picture of the father. So we take the picture of the father one month earlier than the picture of the mother and her children. We send the picture of the father one month earlier, so both pictures arrive at the same day in Europe. Nevertheless, when we combine all pictures, we see just a normal family: the father is not extremely young compared to the mother, or even younger than his children. The time difference (one month) in delivery is short compared to the human average lifetime (75 years). In a similar way is the time difference of maybe 50 kyears short compared to the lifetime of a star, 1 Gyears.
Ad 2) One could argue that the bright short-living stars in the far regions of the galaxy not yet died when the photons of these stars left tfor our eyes, whereas similar stars in the close regions of the galaxy have died in the meanwhile. Stars are continuously generated, see APODs numerous photo's of the star forming areas of the last month or so.
The 3rd galaxy, a lumb of stars 'at 12 o'clock', is IMHO a fluctuation in density of stars. If you visit the Galcrash website,
http://burro.cwru.edu/JavaLab/GalCrashWeb/ you can see a similar lumb of stars when the two galaxies cross each other. This lumb is rather short lived, visible at the 6 o'clock position.
You would see a galaxy with two supernovae, instead of one at a time. I'm not sure why you would think this situation is so special. Supernovae are local events; the galaxy as a whole isn't that much affected by it. Supernovae dim down in weeks or months. After that time they are hard to detect in far away galaxies.
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