And yes, the sky must look spectacular from inside a GC! I’m sure people must have simulated the sky from a hypothetical GC planet before, but I don’t think I’ve ever seen it.

What did this (or any other) cluster look like 70,000,000 years ago, and what will it look like 35,000,000 years from now? Can you tell?

Well, some globular clusters (“globs”) – Omega Centauri being a notable example – may have been dwarf galaxies in their own right in the very distant past – and boasted more stars which were subsequently stripped away. It seems that Kapteyn’s star which is now a mere 13 light years from us was a past member of Omega Centauri which is now 15,800 light years distant.

Globular clusters are made of stars which evolve over time so logically enough, globs would have been full of brighter early spectral class (types O-B-A) stars which have since perished and will, logically, dim as they become increasingly dominated by fainter mid to late spectral class stars (F-G-K-M) plus “stellar corpses” such as neutron stars and white dwarfs. Although as their stars evolve there will always be a fair number of red and orange giants dominating their light output. (No supergiants though with a perhaps the odd exception for blue stragglers since those high-mass short-lived stars burnt out earlier.)

Over billennia these ornage and red giants will, I think, gradually get fainter because as less massive stars end up producing smaller and dimmer giants. (this might be wwrong but) At some point, the lowest mass ornage or red dwarf stars cease to become giants at all instead they circulate all their fuel internally and consume it rather than having distinct layers so ending up simply “fading out” into degenerate black dwarfs rather than ballonning into gianst although this willonlyu occur after trillions of years have passed. I’m not qite sure where that cut-off point is. (Trivia fact via Kaler’s 100 Greatest Stars book no star wiwitha spectral type less massive than G8 has yet died!)

Globular clusters also undergo processes of core collapse – where they become very compact in the centre as most massive stars wind up there and lighter ones get thrown to their outskirts – and erosion as passes near and through the galactic spiral arms strip away stars from the outer regions, effectively “evapourating” them out into the Galactic halo region. (As again, Katpteyn’s star is an example.)

I gather we have detected young very bright globulars even still forming ones in other galaxies and that even many of the milky Way’s globs are different in ages, but I could be mistaken. I am pretty sure that insome of the larger globulars – Omega Centauri for one – there have been at leats two different star forming bursts.

All of which I guess doesn’t quite answer your *specific* question there but I hope its interesting & helpful anyhow. There’s always wikipedia and the various astronomy magazine sand websites if you want more & perhaps get a more specific answer too!

See also :

http://en.wikipedia.org/wiki/Blue_straggler

&

http://en.wikipedia.org/wiki/Contact_binaries

&

http://blogs.discovermagazine.com/badastronomy/2010/02/18/dwarf-merging-makes-for-an-explosive-combo/

for more. Hope this is interesting / helpful for you.

PS. Also seconding what (#18.) KC has written too.

http://stars.astro.illinois.edu/sow/peg-t.html

for it via Kaler’s marvellous website which also has a page on M15 here :

http://stars.astro.illinois.edu/sow/m15-p.html

[I was about to post those links last night when the power went out - and stayed out. ]

@11. eyesoars :

I was hoping it was a ‘blue straggler’. Do we know of any historical instances of star star collisions? How would/could these compare with supernovae? Could we tell the difference.

We think that at least some type Ia supernova (there are a couple of models both of which may be right in different cases) are indeed produced by star-star collisions – specifically two white dwarfs that orbit closely and end up spiralling into collision with each other.

Tycho’s supernova :

http://en.wikipedia.org/wiki/Tycho%27s_Supernova

which was seen in 1572 by the great astronomer Tycho Brahe & revolutionised our understanding of the sky was one notable example.

Short gamma-ray bursts are thought to be the result of neutron star collisions. I believe some type Ia supernova are thought to be the collision of two white dwarfs.

Edit: That wasn’t a question, was it. Ok, question: How can the Hubble take IR images without a fancy cooling system?

The HST only goes a little ways into the infrared, which is why a dedicated IR telescope like Spitzer had to be launched. It’s only at deeper infrared wavelengths that the fancy cooling is needed.

The difference as far as cooling requirements is all about black body radiation. Bodies emit radiation, and the quantity and wavelengths depend on its temperature, with the peak wavelength moving to shorter and shorter wavelengths as the temperature increases. The longer the IR wavelengths you want to observe, the more the observatory’s own radiation will drown out cosmic sources unless it’s cooled.

So for Spitzer, this is a big problem, while for Hubble it’s not because Hubble isn’t trying to observe at those wavelengths. Also, this is why WISE was able to continue making observations using a small subset of instruments even after it ran out of coolant.

This is my understanding of the reason; hopefully it’s accurate and helpful.

I do have a question for y’all, though: I keep seeing references to infrared images captured by the Hubble (apparently infrared capability was added on one of the maintenance missions). But I thought infrared telescopes had to be cold? The Spitzer IR telescope ended its service life when it’s liquid helium coolant was exhausted, and the upcoming James Webb telescope has that impressive layered sun-shade to keep it cool. Hubble doesn’t have anything like that, though, right? I don’t get it.
Edit: That wasn’t a question, was it. Ok, question: How can the Hubble take IR images without a fancy cooling system?

Oh, question number 2: Are globular clusters anything like dwarf galaxies? Do they form independently, or are they simply what’s left of dense star-forming regions within a galaxy?

Where I grew up, the driveway was too flooded with light. The backyard was the only place good enough for observations. *sigh*

Anyway, beautiful picture!