by Ann » Thu Aug 28, 2014 4:44 am
That is indeed a gorgeous picture!
Is M21 about 8 million years old? Well, it is clearly much older than the stars of the Trifid Nebula, since there is no nebulosity around M21 at all. It is interesting, however, that there are no red giants in M21. Perhaps M21 is a more massive version of the the Pleiades cluster - we see these clusters at a time when none of their stars are massive
and old enough to be red giants. (It is interesting to think that the Pleiades may in fact have had red giants in the past, but if so, those red giants have disappered by now. And not only are the red giants themselves gone, if they were ever there in the first place, but the planetary nebulas that they must have left behind if they were there have also evaporated now.)
But the stars of the Trifid Nebula are only 300,000 years old. They are baby stars, indeed. And how brilliantly beautiful their natal cloud is!
But really, is there no connection between M20 and M21? I find that somewhat hard to believe. Of course I realize that we are not talking about triggered star formation, but still - the visual appearance of these clusters strongly suggests a connection, and if they are at the same distance from us as well, then that makes it almost too much of a coincidence that they would not be at least distantly related.
Ann
That is indeed a gorgeous picture! :D
Is M21 about 8 million years old? Well, it is clearly much older than the stars of the Trifid Nebula, since there is no nebulosity around M21 at all. It is interesting, however, that there are no red giants in M21. Perhaps M21 is a more massive version of the the Pleiades cluster - we see these clusters at a time when none of their stars are massive [i]and[/i] old enough to be red giants. (It is interesting to think that the Pleiades may in fact have had red giants in the past, but if so, those red giants have disappered by now. And not only are the red giants themselves gone, if they were ever there in the first place, but the planetary nebulas that they must have left behind if they were there have also evaporated now.)
But the stars of the Trifid Nebula are only 300,000 years old. They are baby stars, indeed. And how brilliantly beautiful their natal cloud is!
But really, is there no connection between M20 and M21? I find that somewhat hard to believe. Of course I realize that we are not talking about triggered star formation, but still - the visual appearance of these clusters strongly suggests a connection, and if they are at the same distance from us as well, then that makes it almost too much of a coincidence that they would not be at least distantly related.
Ann