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vrmuth
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what's the center of a globular cluster , is it a star or can it be a black hole ? how are they formed and bound to gravitational pull of the milky way
Globular clusters have a very high star density, and therefore close interactions and near-collisions of stars occur relatively often. Due to these chance encounters, some exotic classes of stars, such as blue stragglers, millisecond pulsars and low-mass X-ray binaries, are much more common in globular clusters. A blue straggler is formed from the merger of two stars, possibly as a result of an encounter with a binary system. The resulting star has a higher temperature than comparable stars in the cluster with the same luminosity, and thus differs from the main sequence stars formed at the beginning of the cluster.Globular cluster M15 may have an intermediate-mass black hole at its core.
Astronomers have searched for black holes within globular clusters since the 1970s. The resolution requirements for this task, however, are exacting, and it is only with the Hubble space telescope that the first confirmed discoveries have been made. In independent programs, a 4,000 M☉ intermediate-mass black hole has been suggested to exist based on HST observations in the globular cluster M15 and a 20,000 M☉ black hole in the Mayall II cluster in the Andromeda Galaxy.[44] Both x-ray and radio emissions from Mayall II appear to be consistent with an intermediate-mass black hole.
These are of particular interest because they are the first black holes discovered that were intermediate in mass between the conventional stellar-mass black hole and the supermassive black holes discovered at the cores of galaxies. The mass of these intermediate mass black holes is proportional to the mass of the clusters, following a pattern previously discovered between supermassive black holes and their surrounding galaxies.
Globular clusters are beautiful and weird. There are many mind boggling questions associated with them. This was the best text answering many of those questions -including yours- I have read so far. "A Thousand Blazing Suns: The Inner Life of Globular Clusters http://www.astrosociety.org/pubs/mercury/9904/murphy.html "vrmuth said:what's the center of a globular cluster , is it a star or can it be a black hole ? how are they formed and bound to gravitational pull of the milky way
Garth said:So what keeps the globular cluster so tightly bound, for example, are there BH's at the centre?
Safak Mert said:Globular clusters are beautiful and weird. There are many mind boggling questions associated with them. This was the best text answering many of those questions -including yours- I have read so far. "A Thousand Blazing Suns: The Inner Life of Globular Clusters http://www.astrosociety.org/pubs/mercury/9904/murphy.html"
Hi davenn!davenn said:The first obvious choice would be mutual gravitational attraction between the members of the globular cluster
Since there are vastly many more stars in a CG than in an open cluster. The gravitational attraction would be more substantial
As mfb said, there may be a BH at the core of some of them, but it wouldn't be necessary to keep the GC compact.
Open clusters, on the other hand, are generally likely to be less than a couple of 100 stars, with many much less than that, a few dozen or so.
They are also spread out over a larger area meaning mutual gravitational attraction is going to be lower and this would allow for
members of the OC to drift apart over time.
Dave
Some nice stuff in that wikipedium! It pointed to something about intermediate-mass BH,Garth said:One question of course is that of the internal orbital mechanics; once formed how do globular clusters remain so tightly bound for nearly the age of the universe? Open clusters have lifetimes < 100Myrs. or so.
Globular Cluster
So what keeps the globular cluster so tightly bound, for example, are there BH's at the centre?
Garth
TEFLing said:Can individual GCs be resolved at cosmological distances?
Those would be very important observations... If so then GCs are largely intact ancient relicsdavenn said:yes, tho I haven't found any images or info on if the individual stars in the GC's can be resolved
There are many images showing GC's around other galaxies
that 's a nice article , thanks but it didn't answer how they become the satellite of a galaxymarcus said:Some nice stuff in that wikipedium! It pointed to something about intermediate-mass BH,
http://hubblesite.org/newscenter/archive/releases/2002/18/text/
vrmuth said:that 's a nice article , thanks but it didn't answer how they become the satellite of a galaxy
yes, that's correct as can be seen by the images posted up the pageQuds Akbar said:A globular cluster is a group of stars bound together by gravitational effects which only increases as you approach the center and the number of stars per a given area increases too.
mfb said:The star densities there are not good for the long-term stability of planetary orbits.
mfb said:But it could give an amazing view of the milky way.
You'd need to be in its remote suburbs though, otherwise I suspect the sky would be so bright from all the nearby stars surrounding you that you wouldn't see the milky way at all. Which would be quite a sight in its own right...mfb said:But it could give an amazing view of the milky way.
Something like this?...wabbit said:You'd need to be in its remote suburbs though, otherwise I suspect the sky would be so bright from all the nearby stars surrounding you that you wouldn't see the milky way at all. Which would be quite a sight in its own right...
Inside view of a globular cluster from The Harvard-Smithsonian Center for Astrophysics.
Well it is only an artist's impression...wabbit said:Nice : ) I'd have thought the colors would look less saturated, like those of stars seen from earth, but maybe that's incorrect ?
Ah yes good point... Now I wonder how Antares would look like if it had the apparent size of the Sun..Garth said:Well it is only an artist's impression...
Our night vision (detected by the rod cells of the retina) is basically insensitive to colour, so colour perception improves with brightness. The nearer stars within a globular cluster will be brighter and therefore the colours will be more noticeable to human vision.
Assuming, of course, that there are humans there to see the view...
Garth
wabbit said:Edit2 : quite white it seems. From Wikipedia article on thermal radiation anything above ~1700K is whitish, and Antares is 3400K
wabbit said:Hmm our sun is white by definition of white no ?
Right but white is in the middle of the range (red white blue), and I don't see how the spectrum depends on distance.davenn said:only from our optical point of view ... we are so close to it
If you could get a decent distance from it, it wouldn't be the white/ blue-white of the high temperature stars
As Garth say, its a mid temp star compared to the full range of stellar colours/temperatures
wabbit said:Right but white is in the middle of the range (red white blue),
wabbit said:and I don't see how the spectrum depends on distance.
I don't think so. Look at the sun through a solar filter.davenn said:it doesn't ... but our perception does
as I said, with the sun so close, its a blinding white light, put at a few lightyears distance and you will see it for the real colour it is
solar filters come in all variations of colour renditions ... that's a very poor comparisonwabbit said:Look at the sun through a solar filter.
Yes but good ones have a flat transmission curve. See for instance http://www.alpineastro.com/Solar_Observation/Images/DERF_Curve_Lg.jpgdavenn said:solar filters come in all variations of colour renditions ... that's a very poor comparison
Yes G2 star. The colors on his chart are illustrative,not accurate.davenn said: