Today's APOD is a golden oldie, and I'm glad to see it again.
Massive young cluster Westerlund 2. Photo:
NASA, ESA, the Hubble Heritage Team (STScI/AURA),
A. Nota (ESA/STScI), and the Westerlund 2 Science Team
The Milky Way is very far from a starburst galaxy, but our own "island universe
" nevertheless contains some really massive young clusters. One of them is Westerlund 2
R136a in the
Large Magellanic Cloud. Photo: NASA.
In spite of the impressive mass and sparkle of Westerlund 2, it pales compared with the largest cluster in the Large Magellanic Cloud, R136a. Even at a glance, we can see that R136a is more massive than Westerlund 2. That is because R136a contains a large, spherical, compact core of brilliant stars, whereas the core of Westerlund 2 is more elongated.
Does NGC 3603 contain a spherical, compact core of brilliant stars, located in a more scattered "halo" of stars? It does indeed.
Core of NGC 3603. Credit: NASA, ESA and Wolfgang Brandner (MPIA),
Boyke Rochau (MPIA) and Andrea Stolte (University of Cologne)
wrote about NGC 3603:
The central star cluster is the densest concentration of very massive stars known in the galaxy.
Core of R136a. Credit: Paul Crowther, Chris Evans, VLT, ESO
Although it is very hard to compare the density of these cluster cores based on photographs, bearing in mind that R136a is about eight times farther away than NGC 3603, the best pictures of of the core of R136a don't suggest that it is a lot more compact and dense than the core of NGC 3603.
Of course, it could well be that the core of R136a is so
dense that it is almost impossible to resolve it. Actually resolving it may automatically make it look less compact than it really is, at least compared with NGC 3603.