What is the center of a globular clusters made of?

In summary, Globular clusters are tightly bound by gravitational attraction between the stars. Open clusters are less tightly bound and may drift apart over time.
  • #1
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
 
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  • #3
Mainly empty space.
There can be a black hole, but that is not necessary. Individual stars can stay close to the center for a while, but they are not massive enough to avoid perturbations from other stars which move them around over time.
 
  • #4
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
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.

So what keeps the globular cluster so tightly bound, for example, are there BH's at the centre?
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.

Garth
 
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  • #5
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
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 [Broken]"
 
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  • #6
Garth said:
So what keeps the globular cluster so tightly bound, for example, are there BH's at the centre?

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
 
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  • #7
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" [Broken]

interesting looking article ... will get a chance to read it soon

thanks
Dave
 
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  • #8
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
Hi davenn!

Yes, of course, however the question arises of the stability of the member stars' orbits over ~ 10Gyrs. With perturbations of many nearby neighbours mergers between members and ejections from the globular system must be common, far more so than in the galaxy at large.

Obviously they have survived and are stable over such long periods but mathematically the stability question is an interesting one.

Garth
 
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  • #9
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
Some nice stuff in that wikipedium! It pointed to something about intermediate-mass BH,
http://hubblesite.org/newscenter/archive/releases/2002/18/text/
which in turn pointed to:
http://arxiv.org/abs/astro-ph/0209314
http://arxiv.org/abs/astro-ph/0209315

http://arxiv.org/abs/astro-ph/0508251
http://arxiv.org/abs/astro-ph/0209313
 
  • #10
Is it possible, that GCs are the tidally stripped down cores, of previously larger and more distended objects?

Can individual GCs be resolved, at cosmological distances? If so, then are they larger?

Gravity causes less massive objects to be scattered outwards, whilst more massive members sink towards the center... Less massive members farther from GC center might be easier to strip off
 
  • #11
TEFLing said:
Can individual GCs be resolved at cosmological distances?

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
 
  • #12
T
davenn 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
Those would be very important observations... If so then GCs are largely intact ancient relics
 
  • #13
marcus said:
Some nice stuff in that wikipedium! It pointed to something about intermediate-mass BH,
http://hubblesite.org/newscenter/archive/releases/2002/18/text/
that 's a nice article , thanks but it didn't answer how they become the satellite of a galaxy
 
  • #14
Click here for a link from Galaxy Zoo that has some very nice images of globular clusters.

Here are some sample images.

This is Messier 53:
getjpeg.aspx?ra=198.22978905&dec=18.16794&scale=1.58448&width=512&height=512&opt=&query=.jpg


and here is NGC 5466
getjpeg.aspx?ra=211.37&dec=28.535&scale=1.58448&width=512&height=512&opt=&query=.jpg


Thanks to ElisabethB, of Galaxy Zoo, for help with this.
 
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  • #15
vrmuth said:
that 's a nice article , thanks but it didn't answer how they become the satellite of a galaxy

May I conjecture? Imagine that a swarm of globular clusters forms first, before there IS a galaxy:smile:
a swarm not only of globular clusters as we know them, but of smaller collections of various sorts: proto-galaxies, dwarf galaxies, blobs of stars and gas, etc.
then there is a kind of "bottom-up" coalescence rather than "top down".

These globular clusters, if I remember correctly, do not orbit AROUND our galaxy, they typically orbit through, they "yo-yo" through the galactic plane
When dwarf galaxies do that, they lose stars as they pass through. They get slightly disrupted. So they gradually contribute stars to the main galaxy. Outliers get shaved off.

So I am imagining that the globulars do not have to "come into" orbit or " become satellites" of a galaxy. It is the main galaxy which "becomes" in their midst. Out of a the swarm of smaller clots and curdles. With the help of the dark matter halo. they are prior.

Perhaps the globulars are the SURVIVORS of this process and look the way they do because, like pebbles, they have been worn smooth by many passes through the plane of
collective rotation.

BTW there is a Wippy Kidium on "Galaxy formation" . I don't think structure formation and galaxy formation in particular is a completely solved problem. It probably doesn't hurt to imagine various alternatives.
 
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  • #16
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.
 
  • #17
Quds 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.
yes, that's correct as can be seen by the images posted up the page :smile:

Would be an interesting place to be on a habitable planet around one of those stars

Dave
 
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  • #18
The star densities there are not good for the long-term stability of planetary orbits.

But it could give an amazing view of the milky way.
 
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  • #19
mfb said:
The star densities there are not good for the long-term stability of planetary orbits.

Yup I would suspect that

mfb said:
But it could give an amazing view of the milky way.

Uh huh, specially if in one well above the galactic plane :smile:

That made me think of the view of the MW from one of the Magellanic Clouds, would also be an awesome sight

Dave
 
  • #20
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...
 
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  • #21
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...
Something like this?...
globular-800.jpg


Inside view of a globular cluster from The Harvard-Smithsonian Center for Astrophysics.

Garth
 
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  • #22
Nice : ) I'd have thought the colors would look less saturated, like those of stars seen from earth, but maybe that's incorrect ?
 
  • #23
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 ?
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...:wink:

Garth
 
  • #24
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...:wink:

Garth
Ah yes good point... Now I wonder how Antares would look like if it had the apparent size of the Sun..
Edit : blinding of course: ) Somewhat farther so we can look at it with full color vision instead
Edit2 : quite white it seems. From Wikipedia article on thermal radiation anything above ~1700K is whitish, and Antares is 3400K
 
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  • #25
wabbit said:
Edit2 : quite white it seems. From Wikipedia article on thermal radiation anything above ~1700K is whitish, and Antares is 3400K

Antares, Betelgeuse, Aldebaran, Arcturus and others are red giants and can be seen with a distinctly reddish hue to the naked eye. (Surface temps ~ 3,500 K)

Rigel is a blue white supergiant with a bluish hue, (Surface temp ~12,000 K+), whereas if you want a pure white star you can do no better than good old Sirius. (Surface temp ~10,000 K)

Our own Sun of course is yellowish with a surface temp of ~5,800K.

Each star radiates more or less as a Black Body and the colour is determined by the photosphere temperature.

Garth
 
  • #26
Hmm our sun is white by definition of white no ? I thought the yellowish tint was due to the atmosphere (the counterpart of that being the sky is blue)
 
  • #27
wabbit said:
Hmm our sun is white by definition of white no ?

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
 
  • #28
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
Right but white is in the middle of the range (red white blue), and I don't see how the spectrum depends on distance.
What I meant was "white" is a human perception of a neutral balance of colors, and I assume sunlight is pretty much what we mean by that.
But maybe I'm missing something ?

Edit : if you look at the sun in a telescope thru a neutral filter say mylar it is very white indeed. Warning: Never view the Sun without proper safety precautions, you could seriously damage your eyesight
 
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  • #29
wabbit said:
Right but white is in the middle of the range (red white blue),

not sure where you get that from ?
wabbit said:
and I don't see how the spectrum depends on distance.

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
 
  • #30
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
I don't think so. Look at the sun through a solar filter.
 
  • #31
wabbit said:
Look at the sun through a solar filter.
solar filters come in all variations of colour renditions ... that's a very poor comparison
 
  • #32
see where the sun is on the standard H-R diagram ...

H-R%20Diagram1.jpg
 
  • #33
davenn said:
solar filters come in all variations of colour renditions ... that's a very poor comparison
Yes but good ones have a flat transmission curve. See for instance http://www.alpineastro.com/Solar_Observation/Images/DERF_Curve_Lg.jpg
 
  • #34
davenn said:
see where the sun is on the standard H-R diagram ...

View attachment 79343
Yes G2 star. The colors on his chart are illustrative,not accurate.
 
  • #35
accurate enough to give a good indication compared to the other stars in the sequence and you will find that is the description in most places
 
<h2>1. What is a globular cluster?</h2><p>A globular cluster is a spherical collection of stars that are held together by gravity. They typically contain hundreds of thousands to millions of stars and are found in the outer regions of galaxies.</p><h2>2. What is the center of a globular cluster?</h2><p>The center of a globular cluster is the point at which the majority of the stars in the cluster are concentrated. It is often referred to as the core of the cluster.</p><h2>3. What is the center of a globular cluster made of?</h2><p>The center of a globular cluster is primarily made up of old, low-mass stars. These stars have burned through most of their fuel and have a reddish color. There may also be a small number of brighter, more massive stars in the center.</p><h2>4. How are globular clusters formed?</h2><p>Globular clusters are thought to have formed early in the history of the universe, around 10-13 billion years ago. They are believed to have originated from large clouds of gas and dust that collapsed under their own gravity, forming dense clusters of stars.</p><h2>5. Why do globular clusters have a spherical shape?</h2><p>Globular clusters have a spherical shape due to the strong gravitational forces that hold them together. As the stars orbit around the center, their paths become randomized, resulting in a spherical distribution of stars.</p>

1. What is a globular cluster?

A globular cluster is a spherical collection of stars that are held together by gravity. They typically contain hundreds of thousands to millions of stars and are found in the outer regions of galaxies.

2. What is the center of a globular cluster?

The center of a globular cluster is the point at which the majority of the stars in the cluster are concentrated. It is often referred to as the core of the cluster.

3. What is the center of a globular cluster made of?

The center of a globular cluster is primarily made up of old, low-mass stars. These stars have burned through most of their fuel and have a reddish color. There may also be a small number of brighter, more massive stars in the center.

4. How are globular clusters formed?

Globular clusters are thought to have formed early in the history of the universe, around 10-13 billion years ago. They are believed to have originated from large clouds of gas and dust that collapsed under their own gravity, forming dense clusters of stars.

5. Why do globular clusters have a spherical shape?

Globular clusters have a spherical shape due to the strong gravitational forces that hold them together. As the stars orbit around the center, their paths become randomized, resulting in a spherical distribution of stars.

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