APOD: Millions of Stars in Omega Centauri (2011 Jun 15)

APOD Robot · Post by **APOD Robot** » Wed Jun 15, 2011 4:06 am

Millions of Stars in Omega Centauri

Explanation: Featured in this sharp telescopic image, globular star cluster Omega Centauri (NGC 5139) is some 15,000 light-years away. Some 150 light-years in diameter, the cluster is 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.

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LarryPark · Post by **LarryPark** » Wed Jun 15, 2011 4:10 am

If we lived in a globular cluster, how close would the neighboring star be to ours? Seems like sending probes to nearby stars would be a LOT more practical than in our own star neighborhood...

Chris Peterson · Post by **Chris Peterson** » Wed Jun 15, 2011 4:22 am

LarryPark wrote:If we lived in a globular cluster, how close would the neighboring star be to ours? Seems like sending probes to nearby stars would be a LOT more practical than in our own star neighborhood...

The average stellar density is similar to what we have here in our part of the galaxy. But that average represents a very low density at the outside, and a very high density at the core. The problem is that once the stellar density gets up to 20 or 30 times higher than what's around us- and the core of a globular has a density hundreds of times higher- the environment is probably hostile to the existence of stable planetary systems. So the exploratory advantage of having stars much closer together seems rather offset by the problem that there's nobody to do the exploring... <g>

Guest · Post by **Guest** » Wed Jun 15, 2011 11:22 am

In fact, Omega Cen may be the remnant core of a small galaxy merging with the Milky Way.

If this is a remnant core of a galaxy would it be safe to assume there should be a black hole at the center of the cluster? And if so, would such a black hole be easier to study with so little around it?

neufer · Post by **neufer** » Wed Jun 15, 2011 11:45 am

Guest wrote:
In fact, Omega Cen may be the remnant core of a small galaxy merging with the Milky Way.

If this is a remnant core of a galaxy would it be safe to assume there should be a black hole at the center of the cluster?
And if so, would such a black hole be easier to study with so little around it?

If there was a black hole at the center it would probably look more like M15:

http://en.wikipedia.org/wiki/Messier_15 wrote:
<<Messier 15 or M15 (also designated NGC 7078) is a globular cluster in the constellation Pegasus. It was discovered by Jean-Dominique Maraldi in 1746 and included in Charles Messier's catalogue of comet-like objects in 1764. At an estimated 13.2 billion years old, it is one of the oldest known globular clusters. M15 is about 33,600 light-years from Earth. Messier 15 is one of the most densely packed globulars known in the Milky Way galaxy. Its core has undergone a contraction known as 'core collapse' and it has a central density cusp with an enormous number of stars surrounding what may be a central black hole.>>

orin stepanek · Post by **orin stepanek** » Wed Jun 15, 2011 1:04 pm

It's amazing that so many of these are floating around the halo of the Milky Way! I wonder if other galaxies have star clusters in similar conjunctions as does the Milky Way? BTW Omega Centauri is very neat!

Picture from Wikipedia

: Click to view full size image

luigi · Post by **luigi** » Wed Jun 15, 2011 2:51 pm

Fantastic Image, every star is clearly defined, millions of them!

I live in the South Hemisphere so Omega Cen is almost always high in the sky. At naked eye it looks like a blurry star, with common binoculars it's a fantastic object, quite a beautiful sight.

Thank you for this beautiful image.

rstevenson · Post by **rstevenson** » Wed Jun 15, 2011 3:46 pm

luigi wrote:Fantastic Image, every star is clearly defined, millions of them!

Yes, a beautiful image of one of my favourite kinds of objects, globular clusters. But I don't think we're seeing millions of stars in this particular image. At max resolution the image is 3735 px square, which is <14 M pixels. When I zoom in to see the individual pixels, the average star in the image occupies about 20 of them, and the image is at least half dark, so there's no more than about 35,000 stars visible in this image. (I think the stars themselves would not even be as big as a pixel at this scale, but they appear larger because their light is flooding the receptors in the CCD.)

Omega Centauri does contain several million stars; we just can't see them all very well.

Rob

kaigun · Post by **kaigun** » Wed Jun 15, 2011 4:28 pm

luigi wrote:Fantastic Image, every star is clearly defined, millions of them!

I live in the South Hemisphere so Omega Cen is almost always high in the sky. At naked eye it looks like a blurry star, with common binoculars it's a fantastic object, quite a beautiful sight.

I live too far north to see Omega Centauri now, but I have enjoyed it in the past while in the Southern Hemisphere. I found Delta Cru and Gacrux useful as pointers. I was in the Navy at time, we used 7x50 binoculars, 20x120 ship's binoculars (only useful if the sea was dead calm), and Night Vision Goggles. The NVGs did not magnify, but the light amplification was cool. The only light pollution we worried about was the Moon.

luigi · Post by **luigi** » Wed Jun 15, 2011 5:17 pm

kaigun wrote:
luigi wrote:Fantastic Image, every star is clearly defined, millions of them!

I live in the South Hemisphere so Omega Cen is almost always high in the sky. At naked eye it looks like a blurry star, with common binoculars it's a fantastic object, quite a beautiful sight.
I live too far north to see Omega Centauri now, but I have enjoyed it in the past while in the Southern Hemisphere. I found Delta Cru and Gacrux useful as pointers. I was in the Navy at time, we used 7x50 binoculars, 20x120 ship's binoculars (only useful if the sea was dead calm), and Night Vision Goggles. The NVGs did not magnify, but the light amplification was cool. The only light pollution we worried about was the Moon.

Omega can be seen from some northern places I think even 40 degrees North. It's just spectacular with binos rising above the horizon in a dark place. Right now from my location is almost at the Zenit (75 degrees at 9pm).
Boomer it's raining for today's eclipse. I'm so so so mad about that

Wolf Kotenberg · Post by **Wolf Kotenberg** » Wed Jun 15, 2011 5:40 pm

there is an area in the Pacific ocean where the floating garbage collects and makes a giant circle of solid stuff. I never personally seen it so i rely on newsmedia to tell the news consumer to be telling the facts. Is this the same kind of principle that could cause a globular cluster to form ? Al,kl the magnetic lines of force point to a place in this giant Universe .

Chris Peterson · Post by **Chris Peterson** » Wed Jun 15, 2011 5:45 pm

Wolf Kotenberg wrote:there is an area in the Pacific ocean where the floating garbage collects and makes a giant circle of solid stuff. I never personally seen it so i rely on newsmedia to tell the news consumer to be telling the facts. Is this the same kind of principle that could cause a globular cluster to form ? Al,kl the magnetic lines of force point to a place in this giant Universe .

Magnetic forces play almost no role in the Universe on any sort of large scales (outside of stellar environments) because they are simply too small.

It seems likely that the processes involved in forming globular clusters are similar to those involved in forming galaxies, and that these are dynamical interactions involving gravity.

neufer · Post by **neufer** » Wed Jun 15, 2011 6:40 pm

Chris Peterson wrote:
It seems likely that the processes involved in forming globular clusters are similar to those involved in forming galaxies, and that these are dynamical interactions involving gravity.

Then how do you explain the spherical symmetry of globular clusters

Chris Peterson · Post by **Chris Peterson** » Wed Jun 15, 2011 6:47 pm

neufer wrote:Then how do you explain the spherical symmetry of globular clusters :?:

Spherical symmetry doesn't argue against gravitational forces being the primary factor in the formation of a many-star body, whether a galaxy (and there are spherical galaxies) or a cluster.

I'm not trying to describe any detail about how galaxies or clusters form (it's an area of active research, of course), only arguing that in the broadest of terms, gravity is probably the dominant force involved.

Joe · Post by **Joe** » Wed Jun 15, 2011 7:14 pm

I still remember the first globular cluster I saw with my telescope. What an amazing site. They still are my favorite objects to look at. Great image today and thank you Chris for enlightening me about the density of the clusters. I assumed that they were way more dense than this area of the galaxy, but it would make sense that they are less dense on the outer regions and get extremely dense on the way in.

Joe Stieber · Post by **Joe Stieber** » Wed Jun 15, 2011 11:04 pm

luigi wrote: Omega can be seen from some northern places I think even 40 degrees North. It's just spectacular with binos rising above the horizon in a dark place. Right now from my location is almost at the Zenit (75 degrees at 9pm).
Boomer it's raining for today's eclipse. I'm so so so mad about that

At a declination of -47.5 degrees, Omega Centauri would just reach the horizon at +42.5 degrees latitude (actually, it would be slightly higher because of atmospheric refraction). I've seen it at a bit more than 3 degrees altitude from a latitude of +39.25 degrees in southern New Jersey, USA, looking over the Delaware Bay. Even at that low altitude, it's impressive on a clear night. I can only imagine what it looks like at a favorable altitude.

Ann · Post by **Ann** » Thu Jun 16, 2011 4:09 am

What is it about globular clusters that makes me find them so much less interesting than most spiral galaxies? I think it is entropy. Globular clusters strike me as systems with a very high degree of entropy, where everything is very well mixed, and few obvious structures can be seen. Compare globular clusters with spiral galaxies, which often walk on the wild side and have amazing personalities. This is NGC 1087:

Infrared NGC 1097 by Spitzer.

: Click to view full size image

Visual NGC 1097, by R. Jay GaBany.

Ultraviolet NGC 1097, by GALEX.

: Click to view full size image

Circumnuclear ring of star formation in NGC 1097, by Hubble.

Wow, you know. But I have to admit that Omega Centauri looks better than NGC 1097 through an amateur telescope!

Ann

kaigun · Post by **kaigun** » Thu Jun 16, 2011 4:17 am

Omega can be seen from some northern places I think even 40 degrees North. It's just spectacular with binos rising above the horizon in a dark place. Right now from my location is almost at the Zenit (75 degrees at 9pm).

Unfortunately (for viewing Omega Cen) I live at 61 degrees N, in Alaska. I missed that planetary line up earlier, too.

owlice · Post by **owlice** » Thu Jun 16, 2011 9:45 am

Ann wrote:What is it about globular clusters that makes me find them so much less interesting than most spiral galaxies? I think it is entropy. Globular clusters strike me as systems with a very high degree of entropy, where everything is very well mixed, and few obvious structures can be seen. Compare globular clusters with spiral galaxies, which often walk on the wild side and have amazing personalities. This is NGC 1087:

Infrared NGC 1097 by Spitzer.

Click to view full size image
Visual NGC 1097, by R. Jay GaBany.

Ultraviolet NGC 1097, by GALEX.

Click to view full size image
Circumnuclear ring of star formation in NGC 1097, by Hubble.

Wow, you know. But I have to admit that Omega Centauri looks better than NGC 1097 through an amateur telescope!

Ann

Ann,

I'm not getting the connection between all these images of galaxies and the topic of this thread; what am I missing here? Please enlighten me; thanks!

Owlice

neufer · Post by **neufer** » Thu Jun 16, 2011 2:04 pm

owlice wrote:
Ann wrote:
What is it about globular clusters that makes me find them so much less interesting than most spiral galaxies? I think it is entropy. Globular clusters strike me as systems with a very high degree of entropy, where everything is very well mixed, and few obvious structures can be seen. Compare globular clusters with spiral galaxies, which often walk on the wild side and have amazing personalities.
I'm not getting the connection between all these images of galaxies and the topic of this thread; what am I missing here?

Because unlike globular clusters
Ann's galaxies have got personality;
Walk with personality;
Talk with personality;
Smile with personality;
Charm with personality;
Love with personality;
Plus they've got so much less en-tro-py.

rstevenson · Post by **rstevenson** » Thu Jun 16, 2011 2:33 pm

Unlike galaxies, globular clusters have sublety. Those brazen galaxies are just showing off, waving their skirts all over the place, flaring and glaring at us. Give me a quiet old cluster any day.

Rob

Chris Peterson · Post by **Chris Peterson** » Thu Jun 16, 2011 2:40 pm

rstevenson wrote:Unlike galaxies, globular clusters have sublety. Those brazen galaxies are just showing off, waving their skirts all over the place, flaring and glaring at us. Give me a quiet old cluster any day.

Hmmm... I have now constructed slightly richer (although possible wrong!) images in my mind of both Ann and yourself. <g>

neufer · Post by **neufer** » Thu Jun 16, 2011 2:50 pm

rstevenson wrote:
Unlike galaxies, globular clusters have sublety.

sublet: Property leased by one lessee to another.

Anagrams: bluest, bustle, subtle

rstevenson wrote:
Those brazen galaxies are just showing off, waving their skirts all over the place, flaring and glaring at us.

http://asterisk.apod.com/viewtopic.php? ... 60#p150520

rstevenson wrote:
Give me a quiet old cluster any day.

- Coriolanus Act 4, Scene 6
MENENIUS: We loved him but, like beasts
- And cowardly nobles, gave way unto your clusters,

owlice · Post by **owlice** » Thu Jun 16, 2011 3:13 pm

Yes, yes, I know globular clusters are unlike galaxies; that was the point of my question! Sheeesh!! Why are images of galaxies and discussion thereof posted on a thread about a (gorgeous!) image of a (lovely!) globular cluster? What's the connection between Ann's post and the thread's topic? I'm trying to understand why she posted what she posted, because I'm not getting it and I hope she will enlighten me! Was yesterday opposite day or some such?

Ann · Post by **Ann** » Thu Jun 16, 2011 3:16 pm

rstevenson wrote:Unlike galaxies, globular clusters have sublety. Those brazen galaxies are just showing off, waving their skirts all over the place, flaring and glaring at us. Give me a quiet old cluster any day.

Rob

Thanks for setting me straight with subtlety, Rob! (Hmmm... sounds like a song, doesn't it?)

Ann

P.S. Now I know what I was thinking of. "Killing me softly with his song", that's it.

Click to play embedded YouTube video.

Starship Asterisk*