Star Cluster Gravity: Impact on Forces

In summary, the forces of gravity and orbital forces of stars in a star cluster are influenced by the gravity of the largest star and the mutual attraction between the stars. This can result in irregular orbits for objects within the cluster. The cluster's evolution is determined by the initial motions of the stars and external interactions, such as with nearby galaxies.
  • #1
DB
501
0
What happens to the forces of gravity and orbital forces of stars when they are so close together in a star cluster?
 
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  • #2
The gravity of the largest star would attract objects, with the gravity of the surrounding stars slightly interfering with an object's orbit, I suppose.
 
  • #3
They orbit the center of mass of the cluster. I'm not sure, but I think a star cluster needs one body to be much more massive than the other bodies or the whole thing files apart. Perhaps every star cluster has a parent black hole.
 
  • #4
Well, if the type of clusters is an open cluster, then all the stars have mutual attraction to each other. Then the orbit of an object would be quite irregular.

Look at this model of a star cluster:


http://img126.exs.cx/img126/6231/starcluster.gif


The stars are red, and their gravitational fields are the blue rings. Now imagine an object in the orbit of one of those stars, the object would hit another star's gravity field and would jerk around.

EDIT: The stars would probably move, as they would be attracted to each other. Just as Jupiter's gravity moves the sun around.
 
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  • #5
A belated welcome to Physics Forums DB!

Whether there are just two massive objects or trillions, gravity is still the same. For star clusters, Newtonian gravity provides pretty good answers (some exceptions, of course) ... inverse square, m1 x m2, etc ... between all pairs. Not possible to derive a complete analytical solution to the equations of motion (hey, even the general 3-body problem isn't soluble!), but with good computer codes, and lots of memory, your own PC will do a pretty nice job of simulating what happens.

In the absence of external masses (e.g. a nearby galaxy ... OK, pretty unrealistic) ... the answer is quite simple: the 'cluster' will 'evaporate' unless the initial motions of the stars are insufficient for them to escape the combined gravity of the whole cluster. The cluster's evolution then becomes largely determined by how much 'cooling' it can undergo ... e.g. close encounters of a tight binary by a lone star may result in one star being flung out of the cluster (and all the other stars responding accordingly); or a collision which results in a merger and subsequent supernova (some gas may be expelled from the cluster, resulting in a loss of mass).

However, the evolution of most clusters are probably determined more by interactions with galaxies than internal dynamics ... (there's a lovely SDSS result showing a small globular on the outskirts of our Milky Way being shredded by 'tidal interaction' with the mother ship; too, a recent SDSS finding of a strange, halo object that might be a very low density cluster left over from MW formation times).
 

1. What is a star cluster?

A star cluster is a group of stars that are held together by their mutual gravitational attraction.

2. How does gravity impact star clusters?

Gravity is the force that holds star clusters together. It determines how the stars move and interact with each other within the cluster.

3. What is the gravitational force within a star cluster?

The gravitational force within a star cluster is directly proportional to the mass of the stars and inversely proportional to the distance between them. This means that the more massive and closer the stars are, the stronger the gravitational force between them.

4. How does the gravitational force affect the movements of stars within a cluster?

The gravitational force within a star cluster causes the stars to orbit around a common center of mass. This can lead to the formation of binary or multiple star systems, as well as the ejection of some stars from the cluster through interactions with other stars.

5. Can the gravitational force within a star cluster change over time?

Yes, the gravitational force within a star cluster can change over time as stars within the cluster move and interact with each other. This can also be influenced by external factors such as the gravitational pull of neighboring galaxies.

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