FloridaMike wrote:
The "blueness" of the antennae confuse me. I associate the blueness with star formation and star formation is associated with gas and dust. Can that much dusty gas be projected into a hyperbolic orbit that way? I would assume that the tidal slingshot effect is restricted to the heavier objects and only small amounts of gas dust would be carried along.... Am I misinterpreting the blue or misunderstanding basic physics?
I can't tell you about the basic physics, but I'll comment on the color of the tails.
There is clearly gas in the long tail on the left, which originates in the gas-rich galaxy on the right, NGC 4038. There are certainly a lot of pre-existing stars in that tail too, but the "squiggliness" of that tail tells us that there is also gas in it and that there has been "internal dynamics" when the gas and stars interacted. Star clusters have formed in that tail, mostly at the end of it, where the gas from the tail interacts with the surrounding intergalactic medium. To me the blue color of this tail makes very good sense. The tail contains many relatively young stars that were born already when tidal forces threw them out of their galaxy, and also it contains a good number of even younger stars that were born in the tail.
The tail that originates in the gas-poor galaxy on the left, NGC 4039, is shorter, is "elegantly shaped" with no kinks in it and it contains no clusters. Also the tail gets fainter at the end. I'd say this tail contains almost no gas at all. To me, the color of this tail seems bluer than I would have expected. But if the stars that are found in this tail were originally located in the other parts of this galaxy, then they may be younger and bluer than than the rest of the galaxy.
Take a look at Adam Block's excellent image of galaxy
NGC 6340. (There are several satellite galaxies and background galaxies in the picture as well.) The large bulge of this galaxy is yellow, but the bulge is surrounded by faint spiral arms that are bluer than the bulge. If this galaxy had been affected by tidal forces that made the galaxy "throw out" a tail of stars, then this tail would be bluer than the galactic bulge, if most of the stars in the tail came from the outer parts of the galaxy.
But I still suspect that the blue color of the tail of NGC 4039 has been somewhat enhanced.
Ann
Exploring the Antennae
