Holiday Glitter With Omega Centauri
Written by Nancy Atkinson
Omega Centauri. Credit: ESO
A new image of Omega Centauri shows the globular cluster glittering away as one of the finest jewels of the southern hemisphere night sky. It contains millions of stars and is located about 17,000 light-years from Earth in the constellation of Centaurus, and sparkles at magnitude 3.7, appearing nearly as large as the full moon on the southern night sky. Visible with the unaided eye from a clear, dark observing site, when seen through even a modest amateur telescope, the Omega Centauri can be seen as incredible, densely packed sphere of glittering stars. But when astronomers use a professional telescopes, they are able to uncover amazing secrets of this beautiful globular cluster.
This new image is based on data collected with the Wide Field Imager (WFI), mounted on the 2.2-metre diameter Max-Planck/ESO telescope, located at ESO's La Silla observatory, high up in the arid mountains of the southern Atacama Desert in Chile. Omega Centauri is about 150 light-years across and is the most massive of all the Milky Way's globular clusters. It is thought to contain some ten million stars!
Recent research into this intriguing celestial giant suggests that there is a medium sized black hole sitting at its center. Observations made with the Hubble Space Telescope and the Gemini Observatory showed that stars at the cluster's center were moving around at an unusual rate — the cause, astronomers concluded, was the gravitational effect of a massive black hole with a mass of roughly 40,000 times that of the Sun.
The presence of this black hole is just one of the reasons why some astronomers suspect Omega Centauri to be an imposter. Some believe that it is in fact the heart of a dwarf galaxy that was largely destroyed in an encounter with the Milky Way. Other evidence (see here and here) points to the several generations of stars present in the cluster — something unexpected in a typical globular cluster, which is thought to contain only stars formed at one time. Whatever the truth, this dazzling celestial object provides professional and amateur astronomers alike with an incredible view on clear dark nights.
Source: ESO
Filed under: Astronomy, Observatories
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December 2nd, 2008 at 3:56 pm
"Whatever the truth, this dazzling celestial object provides professional and amateur astronomers alike with an incredible view on clear dark nights."
Can't argue with that. Omega Cen is one of the very finest objects in the entire sky through any aperture.
December 2nd, 2008 at 4:57 pm
what does it mean: "astronomers suspect Omega Centauri to be an imposter."
does it mean it's not really there? i wonder if some of the stars we see today are really not there anymore since light takes thousands of years to reach the Earth…. Is there a part of astronomy that deals with stars being "gone" from the sky?
December 2nd, 2008 at 5:03 pm
Beautiful! And nearly the size of the full moon!
i vote we move it to the northern hemisphere so more people can enjoy it.
On second thought, we've got too much light pollution up here. It probably looks better where it is.
P.S. the links in the last paragraph — "(see here and here}" don't work.
December 2nd, 2008 at 10:23 pm
# jose Says:
December 2nd, 2008 at 4:57 pm
"what does it mean: "astronomers suspect Omega Centauri to be an imposter."
does it mean it's not really there? i wonder if some of the stars we see today are really not there anymore since light takes thousands of years to reach the Earth…. Is there a part of astronomy that deals with stars being "gone" from the sky?"
Omega Cen is referred to as an imposter here because astronomers have strong suspicions that it is not in fact a 'globular cluster' as it was always assumed to be. Due to a number of reasons, not least of all it's sheer mass, astronomers suspect that it may in fact be a dwarf galaxy that has been stripped of a large number of it's stars, and only appears to be a globular now that only the core of the original galaxy is left. Hence, you could say that Omega Cen is in some sense masquerading as a globular – an imposter if you like, if an inanimate object can be said to 'masquerade'.
And yes, there are likely many stars in the (deep) sky that are 'gone' in the sense that if you could instantaneously transport yourself to that point in the universe, the star may have aged sufficiently to die, or may have moved a great distance from that location due to it's motion through space. Such stars are highly unlikely to be visible to the naked eye though – stars bright enough to be visible to the naked eye would, for the most part, be too close to age appreciably in the time it takes light to reach us from them. There are, or course, a few notable exceptions. Many stars move quickly enough through space to be able to shift position considerably in the time it would take their light to reach Earth though. For some of these, if you could instantly transport to the point you believed they were at as derived by visual sighting, they would be long gone.
The thing is, astronomers don't really deal with such hypothetical situations. This is because nothing can travel faster than light (as we understand the laws of physics at the moment, anyway), and hence it is meaningless to speculate on what may or may not have happened to any given object while the light it emits is in transit to Earth.
It is important to note though that astronomy does deal with stars being 'gone from the sky' in terms of the physics of stellar lifetimes, how stars age, and how they die. We can predict what will happen to a given star to a certain extent in the future, but not know what has happened to a given star before the light from the object can reach us and let us know directly…
December 3rd, 2008 at 12:54 am
"Other evidence (see here and here) points to the several generations of stars present in the cluster — something unexpected in a typical globular cluster, which is thought to contain only stars formed at one time."
Would this tend to confirm (or infirm) the dwarf galaxy hypothesis?
December 3rd, 2008 at 2:10 am
If it is a galaxy the it must have a central black hole and I wonder how globular clusters can form without a black hole. Do they all have one?
December 3rd, 2008 at 5:35 am
I've always wondered if the stars in a globular cluster are too close together to have planets orbiting them, even habitable planets, or they just seem too close because we see them from far away and they could, and most probably have, planetary systems orbiting them.
December 3rd, 2008 at 5:59 am
I just read the exact same article on another site… Weird. Is Universe Today selling articles or buying them??! (maybe just paraphrasing them?)
Either way, I am a big fan of this site and have been lurking here for years…. Was just wondering?
I would love to see the Sky from a planet in one of these Clusters!!
December 3rd, 2008 at 6:02 am
Sorry… I just went back to check the first article I read… and they ARE different.
I guess there's not a lot of new things to say about something that's been around for 12 billion yrs
December 3rd, 2008 at 7:34 am
12 Billion years is twice the time of our solar systems creation. That means that any solar systems in the globular cluster, with a little bit of luck, could be 2x as advanced as us. So, how seriously are they looking at clusters for exoplanets? I only found one instance of a binary system in a cluster.
December 3rd, 2008 at 11:47 am
Hard to believe that with millions of stars packed into a 150LY sphere that the central black hole is not actively munching down on a star or two. Does anyone know if such activity has been detected? Could this thing actually be at equilibrium if it's indeed the core of an old captured dwarf galaxy? Does it orbit the Milky Way along the elliptic, or on an inclined path?
December 3rd, 2008 at 1:28 pm
With stars this tightly packed why haven't they all long since fallen into the center of mass of the cluster and been swallowed up in a black hole? If they are orbiting the center of mass in random orbital trajectories why aren't they smashing into each all the time? IF they are all orbiting in unison why haven't they flattened out into a disk?
Could one of you experts enlighten me? Thanks
December 3rd, 2008 at 4:56 pm
Mark,
Black holes do not suck things in from their surroundings like some vacuum cleaner. If the sun were a black hole, the earth would continue along in its orbit right on schedule. Only the comets would have a chance of crossing the event horizon and being ripped to shreds by the tidal forces. So the globular cluster is only influenced by the BH and there are many elliptical orbits that do not cross the event horizon.
Secondly, the stars in a globular cluster very seldom collide. When Andromeda eventually does collide with the MW galaxy, very few stars will collide. Many will likely form into binaries but most will not. Those stars are very far apart and only appear to be in great proximity. Our distance from them is simply that great.
Lastly, they are not all orbiting in a disc because they did not all form from the same rotating dust cloud as our solar system did.
December 3rd, 2008 at 4:59 pm
I need to edit that last statement I made. One sentence should read "Those stars are very far apart and only appear to be in CLOSE proximity.
Someszheimers on my part.
December 3rd, 2008 at 7:02 pm
Thanks for the reply bob!
Here's what I'm having trouble with:
Back of the envelope calcs on the numbers given in the article say that in the central regions of the cluster the stars are very close together – comparable to the distances that the planets in our solar system are to the sun (or each other). This kind of environment would play havoc on any orbits that the stars might try to have, so instead of orbiting they should just be free falling towards each other and towards the overall center of mass of the cluster. How are they going to survive very long at all in that kind of environment? The cluster is supposed to be almost as old as the universe (the article says 12 billion years old), during that time many cycles of star formation and supernova and then reformation are supposed to have occurred through gravity. Why doesn't gravity compactify the whole shebang in that amount of time?
December 4th, 2008 at 12:47 pm
The appeal of Argentina for vacation just keeps growing. I would love to see this.