They're All Full of Stars!

It's been quite a while since I did an Astronomy post. I am now back in Lexington for a month rather than in Naples. When I am in Lexington, I try to get caught up on APOD (Astronomy Picture of the Day), because in Lexington I have my desktop PC, with a 2 TB hard drive with 1.1 TB free, to which I can save as much as I like, vs my MacBook Air, with a 128 GB solid state drive, with not enough free to install the latest software update :-(

So I go through APOD from my last forward progress mark. A couple of days ago, I got to the 2023 February 20 post: "NGC 1850: Not Found in the Milky Way". OMG, what a beautiful pic, and this is possibly the largest open cluster I have ever seen! And it is not in the Milky Way, it is in the LMC (Large Magellanic Cloud), the Milky Way's largest satellite galaxy. Here's the pic:

The open cluster is rich enough that I wondered, is this not a globular cluster? But, absolutely not - the stars in the large cluster in the center top of the image are ~50 million years old - globular cluster stars are mostly > 10 billion YO. There is the smaller open cluster to the right, whose stars are only ~4 million years old - very young as stellar ages go.

So it is definitely not a globular cluster, way too young.

Note, the blue filaments to the left of the clusters are a supernova remnant (SNR). I thought that perhaps it was foreground, in our galaxy, but looking at the area in Google Sky makes it clear that the SNR is in the LMC - but I would guess that the open cluster did not form due to the shock wave associated with the SNR, the scale/timing seems wrong.

The most recent APOD pic of a globular cluster I remembered was this one, of NGC 6355, 2023 January 30:

But, this is not really a representative globular cluster. Its stars' average age is 13 billion years, what you would expect, but the description of the pic says "Globular cluster stars are concentrated toward the image center and highlighted by bright blue stars." ??? Globular clusters do contain newly created (blue) stars, but mostly are old red, orange, and yellow stars.

Globular clusters orbit the center of their galaxy, and the orbit of this particular globular cluster has brought it very close to the galactic center. So many/most of the many stars in this image are not part of the cluster. But, still, I luv this pic, so many stars!

Here is a definitive globular cluster: NGC 5139, Omega Centauri, APOD 2023 March 16. I just noticed, this is in my APOD future, I have no idea when I will catch up with this.

The cluster is packed with about 10 million stars much older than the Sun within a volume about 150 light-years in diameter. It's the largest and brightest of 200 or so known globular clusters that roam the halo of our Milky Way galaxy.

How interesting, the largest & best known globular cluster in the Milky Way might actually be different:

Though most star clusters consist of stars with the same age and composition, the enigmatic Omega Cen exhibits the presence of different stellar populations with a spread of ages and chemical abundances. In fact, Omega Cen may be the remnant core of a small galaxy merging with the Milky Way.

So no easy attributions, but, OMG, so, so many stars! FTW!