My god, it's full of stars

[pokerfan]

Millions of 'em...



Image Credit & Copyright: Fred Lehman (South Florida Dark Sky Observers)

Explanation: Featured in the sharp telescopic image, globular star cluster Omega Centauri (NGC 5139) is some 15,000 light-years away and 150 light-years in diameter. Packed with about 10 million stars much older than the Sun, Omega Cen is the largest of 200 or so known globular clusters that roam the halo of our Milky Way galaxy. 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.

http://antwrp.gsfc.nasa.gov/apod/ap100331.html

As a side note, Omega Cen would certainly have been included in the Messier catalog had Charles Messier lived further south. (Its declination is -47° so if you live north of 43° latitude, it's never above the southern horizon.) I've seen it many times from Arizona and Mexico.

[tridim]

1. I always wonder what it's like to live in a solar system within a cluster

I bet it's never very dark.

[BlooInBloo]

2. (facepalm)

[tridim]

3. Hope you didn't hurt yourself.

[pokerfan]

4. Nightfall by Asimov

http://www.astro.sunysb.edu/fwalter/HON114/Nightfall.htm

[arcane1]

5. I loved that story :)

[tridim]

6. Thanks. Love Asimov.

[muriel_volestrangler]

7. diameter 150 light years, 10 million stars

volume = 4/3 * pi * 75^3 = 1.8 million cubic light years.

So less than 6 stars per cubic light year, on average. Very roughly half a light year to the nearest star on average? Maybe a bit less if the centre is more crowded, as it looks. But that's still a long way away. More calculation would be needed to compare it to the light we get from the moon at various phases, but I suspect it wouldn't be more.

[pokerfan]

8. quite a bit more crowded

The average star density in a Globular Cluster is about 0.4 stars per cubic parsec. In the dense center of the cluster, the star density can increase from 100 to 1000 per cubic parsec. However, even in the center of clusters, there is still plently of space between the stars.

http://www.astro.keele.ac.uk/workx/globulars/globulars.html

[muriel_volestrangler]

9. Not that much difference, for linear distances

1 parsec = 3.26 light years; 1 cubic parsec = 34.7 cubic light years
1000 stars/cubic parsec = 28.8 per cubic light year; or about 5 times as crowded.

So average linear distance decreases by the cube root of 5 - about 1.7. So perhaps a third of a light year between stars.

[pokerfan]

11. you're right

I didn't bother to work through exactly how many cubic lys are in a cubic parsec. :banghead:

"Could we expect to find Earth-type planets (big things with rocky/metallic compositions) around globular cluster stars?

In very low-metallicity clusters, probably not; we’d end up with Moon-sized planets at best, after boiling away all the gas; and these little things would not hold on to their atmospheres long enough for life to develop. But in high-metallicity clusters such as many of the ones in the Galactic bulge, big terrestrial planets should be able to form. However, then we need to ask where in the cluster we should look! The central parsec or so, with its frequent star-star interactions, would be a very dangerous environment for planets, which would be removed by tidal encounters. So we’ll have to stay a few parsecs out form the cluster centre, and hope that our star doesn’t have a plunging orbit that would take it through the core every few million years.

Then what would the night sky look like from our hypothetical planet? The core of the cluster would look like a huge nest of multicolored jewels, several degrees across on the sky and almost as bright in total as the full Moon. Inside the core, the main-sequence turnoff stars would be easily visible to the eye as 4th to 5th magnitude – thousands of them sitting on top of the diffuse light of the still fainter stars. But the real spectable would belong to the hundreds of horizontal-branch stars, each as bright as Spica or Altair; and best of all the additional hundreds of yellow and red giants, each shining as brightly as Venus of Jupiter. We should even be able to see the core in the daytime! Scattered more thinly across the sky – but still adding up to thousands of stars visible to the eye – would be the rest of the cluster. And, let’s not forget the Galactic bulge! We are closer to it now, and it is less obscured by dust clouds in the disk, so it would be hanging (somewhere!) in the night sky, again about as bright as the full Moon but much more diffuse. The rest of the Milky Way would stretch across the sky brighter than we see it from Earth.

All in all, a dramatic place to live! The astronomers there must be a happy crowd. And of course, it may be even more fun for us to speculate about how this view of the sky would affect the mythology, religion, and cultural history of any civilisation there.

Isaac Asimov gave a vivid – an mostly correct – answer to this question about half a century ago in one of his fiction pieces called "Nightfall", probably the most famous science-fiction short story ever written."

http://www.iac.es/gabinete/iacnoticias/winter98/xplaneta.htm

http://wildwildweather.com/forecastblog/2009/07/">
(Inside view of a globular cluster from The Harvard-Smithsonian Center for Astrophysics.)

[tridim]

12. That's about what I've imagined.

I would LOVE to live there!

[Fumesucker]

13. Astronomers Ponder Lack of Planets in Globular Cluster

I thought I remembered that a search had been done for planets in globular cluster with negative results..

http://hubblesite.org/newscenter/archive/releases/2000/33

October 31, 2000: Astronomers using the Hubble telescope made the first broad search for planets far beyond our local stellar neighborhood. They trained Hubble's "eagle eye" for eight days on a swarm of 35,000 stars in 47 Tucanae, located in the southern constellation Tucana. The researchers expected to find 17 "extrasolar" planets. To their surprise, they found none. These results may be the first evidence that conditions for planet formation and evolution are different in other regions of our Milky Way Galaxy.

[tridim]

14. From what I've read, clusters are most likely reminants of galactic collisions

If that's the case, there must be planets there by default. Planets are just a side effect of star formation.

[pokerfan]

10. delete (nt)