Comments on: Ho hum, another boring gorgeous sparkling beehive of stars

By: Messier Tidy Upper

Messier Tidy Upper — Sun, 13 May 2012 05:36:17 +0000

@8. kat wagner asked : "wait, is there a black hole in the middle of that cluster too?" No Intermediate Mass central Black Hole in Messier 55 from all I've been able to find in a quick~ish web search through quite a few pages on it. Messier 54 (wiki-link in my name here) apparently does have such an IMBH but Messier *55* does not - or at least not that we've found so far and not that I'm aware of yet. There could well be stellar mass black holes in Messier 55 too naturally - although there's also no mention of them that I could find.

By: Jon Hanford

Jon Hanford — Fri, 11 May 2012 15:59:11 +0000

@7 John,

ESO has a large number of mounted images on sale, check here for selection: http://www.eso.org/public/products/mountedimages/

By: Mike

Mike — Fri, 11 May 2012 01:57:56 +0000

Something else about M55 — you can detect the tidal arms of the Sagittarius dwarf in the background.

By: þorfinn

þorfinn — Fri, 11 May 2012 01:49:11 +0000

What is the orange stripe on the top+right side of the cluster, on the 3k*3k image Gimp read 2290,1190 as the co-ordinates.
The objects at (2560,1735) (0708,2790) (1055,2120) & (0520,0950) are all background galaxies to the main image.
þ

By: BCFD36

BCFD36 — Thu, 10 May 2012 19:20:05 +0000

So we know that all the stars in a globular cluster are moving. Over a period of time, have we been able to see the stars actually change position or has there not yet been enough time?

I have the same question about some of the nebulae… over the time we have been photographing them, have we seen changes, like in the Crab or the Eagle?

D. Scruggs

By: Jess Tauber

Jess Tauber — Thu, 10 May 2012 17:50:31 +0000

Open clusters are the nurseries of stars. Globulars are the retirement facilities.

By: kat wagner

kat wagner — Thu, 10 May 2012 17:31:48 +0000

wait, is there a black hole in the middle of that cluster too? I read about black holes til two in the morning the other night and I could hardly go to sleep – I was trying to wrap my brain around all that weird bat guano. so anytime you want to chat up black holes, well I’m all over it.

By: John

John — Thu, 10 May 2012 16:32:47 +0000

anyone know a good source to purchase prints, framed or unframed, of images like the one linked in this post?

Thanks!

By: Chris

Chris — Thu, 10 May 2012 15:10:05 +0000

@2 davem

Why don’t they collapse because of the gravity? Because they are moving around. The gravitational potential wants to collapse things, but the kinetic energy wants to blow them apart. In the cluster, the two are in balance. Unless two stars collide they’ll keep on orbiting the cluster’s center of mass. Now stars will be ejected and when that happens the other star will go closer to the center. That’s why the cluster is denser in the center and diffuse on the edges.

By: Chris A.

Chris A. — Thu, 10 May 2012 14:50:10 +0000

@davem:
In a sense, they are mini-galaxies, of the E0 elliptical type (i.e. with near zero ellipticity). In other words, the stars all orbit their common center of mass–there’s just no organization to their motions like you find in a spiral galaxy, with most of the stars going in more or less the same direction. So, they don’t collapse for the same reason that our solar system doesn’t collapse: angular momentum.

That being said, some globulars (about 1 in 5) do collapse, in their cores, anyway (called core-collapse globulars, unsurprisingly). What it really means is that the more massive stars tend to “sink” to the inner regions, while the less massive stars migrate outward. Crudely put, it’s a bit like the heavy bits sinking and the light bits floating. In the end, the cluster’s star density peaks sharply toward the center (as opposed to a “normal” globular, whose density plateaus in the inner region).