An image like this one is hugely interesting, and it is very good that the Hubble telescope is being used for purposes like this.
I found this part of the caption a little confusing:
the Hubble Space Telescope has just finished taking the eXtreme Deep Field (XDF), the deepest image of the universe ever taken in visible light
So what does "visible light" mean here? You can find out what filters were used for this image here
. The filters were F105W (Y)
, F125W (J)
, and F160W (H)
As you can see if you follow the links, the Y, J and H filters are all infrared filters. So you might think that the filters don't actually track visible light. But because the galaxies are so distant, the photons detected by these filters were originally emitted as visible light and have been redshifted into the infrared part of the spectrum by the expansion of the universe.
Even so, I think it is quite difficult to "read" the colors of the galaxies. All of the largest spirals look blue, but the largest of them all at 9 o'clock is far from the bluest of the lot. At the same time, its somewhat ragged shape suggests that the galaxy is nevertheless quite full of hot young stars. So why is its blue color diluted with yellow? Could it be that this is a fairly mature galaxy, so that it has an established yellow bulge just like modern spiral galaxies? To me, this galaxy resembles the large Virgo spiral galaxy M61
Speaking of blue galaxies, there are three very blue and quite large galaxies in the upper left quadrant of the picture. Could they be strongly dominated by star formation, like modern-day NGC 3310
There are, on the other hand, tiny blue dots and squiggles scattered everywhere all over the picture. They are likely very early and small starforming dwarf galaxies.
A few very red spirals or disk galaxies interest me. At 7 o'clock is a very red smallish spiral which resembles spiral galaxies M95
. Both M95 and M96 are mature spiral galaxies dominated by old yellow stars, and it is fascinating that there might be counterparts to them that are ten billion years old or so.
A very red edge-on spiral or disk galaxy is seen at 1 o'clock. Could its red color be due to copious amounts of dust?
This is indeed a fascinating picture. I wonder how professional astronomers interpret the colors and shapes of the galaxies we see here.