# Questions tagged [star-clusters]

For questions concerning clusters of stars such as open clusters or globular clusters. Do not use for questions about galaxies, which belong to a distinct classification.

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### Why are globular clusters always denser in the core?

Stars falling towards the core speed up--thus, the amount of time they spend in any given volume goes down. Stars out near the edge move more slowly, thus their residence times in outer volumes should ...
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### Difference between the softening parameter in a Plummer model of a star cluster vs. the softening parameter in a softened gravitational potential

I am doing a gravitational N-body simulation of a star cluster. I set up my initial conditions using the Plummer model, which has potential $$\Phi_P = -\frac{G M}{\sqrt{r^2 + a^2}},\tag{1}$$ where $M$ ...
1 vote
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### RMS Radius of $N$-Body Simulation

I am trying to simulate a globular cluster and investigating the root-mean-square radius of the system as it evolves. I want to ignore particles which are "lost" from the system. However, ...
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### Calculating RMS Radius of a Globular Cluster

I am coding a simulation of a globular cluster in python, starting with particles of the same mass and $0$ initial velocity in a random spherical distribution. I am trying to investigate the root-mean-...
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### M3 globular cluster: simple age determination

For my pre-university pupils I would like to find a simple way to determine the age of the globular cluster M3 using a colour-magnitude diagram (CMD, B-V horizontal axis and apparent visual magnitude ...
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### How can I deduce a probability using a Kroupa IMF and a set of observed stars along a model isochrone?

I’m plotting a colour magnitude diagram for an open cluster and setting it against a few model isochrones. I want to deduce the probability that the cluster belongs to one or the other isochrone, but ...
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### Population II star orbits

Ok so they are usually found in globular clusters and can consider orbits in a static spherically symmetric gravitational field. The orbits are randomly scattered. Would these be considered to be ...
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### How to identify binary stars in $N$-body simulation?

Binary stars constitute a significant portion of the stars of a globular cluster. I would like to verify that this is true in my $N$-body simulation, but I don't know how to decide whether a star in ...
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### Why is the specific frequency of globular clusters in cD galaxies so high?

I understand that cD galaxies, very large and bright galaxies, have more globular clusters than other galaxies. For example, by calculating the specific frequency for a cD galaxy, the number is ...
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### Why are the absolute magnitudes in M5 galaxy so puny?

Wikipedia gives the following as the HR diagram for M5: The stars at the base of the red giant branch have absolute visual magnitudes of 15? That seems way, way too dim. The sun's absolute ...
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### How to find the current age of a star as a function of its luminosity

In my recent research, I have found the need to find an age of a star. But instead, I have found information telling me on how to calculate the age of a star cluster. Hence I wonder is there a formula ...
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### Do gravitational many-body systems fall apart eventually?

Imagine an $N$-body problem with lots of particles of identical mass (billions of them). I saw several simulations on the Internet, where the particles first form small clumps, then bigger clumps, ...
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### Gross "temperature" of a globular cluster

Globular clusters can be very large, which means we can do statistics about the stars in them. And that means we can try matching their star-as-particle potential/kinetic energy distribution against ...
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### Gravothermal catastrophe: looking for simple explanation

I am beginning to try to understand the gravothermal catastrophe. I was hoping someone could provide an explanation to help me understand what the gravothermal catastrophe is and why it is important, ...
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### Why do some stars have a negative parallax?

I am constructing a Hertzsprung-Russell diagram for stars within some radius around Pleiades and have repeatedly come across stars that have negative parallaxes. For example, http://vizier.u-strasbg....
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### What sets the lower mass limit for dark matter dominated structures?

Large galaxies appear to be dominated by dark matter, as do dwarf spheroidal galaxies with masses of perhaps $10^6 {\rm M}_{\odot}$. But (as far as I'm aware) there is no evidence for dark matter in ...
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### What is the most commonly used density model for globular clusters?

It is possible to model a globular cluster using a number of different density models: Plummer model King model Isothermal sphere . . . They all have advantages and disadvantages, depending on ...
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### Why are stellar clusters useful for developing stellar evolution models?

I know that for globular clusters it can be assumed that their stars developed around the same time and thus their initial chemical compositions are roughly the same. My question is how does this tell ...
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### Did dark matter cause the formation of the Solar System?

This question is related to my previous question on Solar System Formation and is a pure thought experiment, with as few as possible assumptions made. From my previous question, I learned that stars ...
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### Possible intergalactic celestial objects

We know there are rouge stars floating in intergalactic space, thought to be caused by galactic collision. What other other classes of celestial object could be found floating around in intergalactic ...
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### Velocity distribution in Plummer's models and others mass distributions

The Plummer's sphere is an model for the mass density in a globular cluster of stars. For an $N$-body simulation I have initialized the position of $N$ masses with a Monte-Carlo technique but cannot ...
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### Why the galaxies form 2D planes (or spiral-like) instead of 3D balls (or spherical-like)?

Question: As we know, (1) the macroscopic spatial dimension of our universe is 3 dimension, and (2) gravity attracts massive objects together and the gravitational force is isotropic without ...
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### What is the frequency of occurrence of stellar classifications off the HR main-sequence?

An alternative version of this question would be: "if was to pick a star from the $10^{11}$ or so in our galaxy at random, what are the probabilities of it being various kinds of star?" (and I do mean ...
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### Triangulation for astronomical distances

How can triangulation be used to calculate the approximate distance to very distant celestial bodies like stars, globular clusters, etc.? And can it be used to measure the distance to a black hole?
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### Galaxies and projected radius vs arcmins

I have two sets of data (globular clusters), one for the Andromeda Galaxy and one for the Milky Way. I want to compare the distribution of globular clusters between the two galaxies according to ...
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### What prevents stars in globular clusters from merging over time to form a black hole?

Globular clusters are apparently very very old, and the density of these clusters appears to increase as one approaches the center of a cluster. Orbits are bound to be chaotic, since there is no ...
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### Existing photometry data of the open star cluster Cepheus OB3?

I am doing research with my teacher on photometry of the open star cluster Cepheus OB3, and we are trying to find research papers so we can target stars in the photos we took. Are there any existing ...
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### Why does Omega Centauri have a distinct chemical signature from the rest of the Milky Way?

In answering a question about the orbital path of Omega Centauri, I learned that it has a distinct chemical signature from the rest of the Milky Way. Basically, it is very rich in s-process elements, ...
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### What is the orbital path of Omega Centauri?

I was under the impression the only objects relatively close to our Milky Way but not yet a part of it were the Sagittarius Dwarf and Large and Small Magellanic Clouds and then much further out, but ...
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### Could a viable solar system work with a cluster of dwarf stars in center? And would it last longer than a single stellar mass star?

So, I was watching various sci channel shows, and they touch on how extremely massive stars live only 100k years, vs the sun which lives ~10 billion years, and dwarf stars live some unspecified time ...
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### How do I find the time for Pleiades to be at Zenith today

I am looking for a way find the time when: Pleiades will be at the Zenith today (11th November 2011) Pleiades will conjunct with the Moon The Moon will be at the Zenith today How do I find those out?...
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### What's the most accepted theory for Blue Stragglers These Days?

I'm working on a post against a recent creationism article about blue stragglers. From when I was in undergrad, the general explanation was that they were likely second generation stars within ...
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### Why do clusters of stars eventually dissipate?

Why don't the stars in a star cluster attract each other gravitationally, forming one big star? What causes a cluster to disperse the stars in it?
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### Pleiades through a 15x 76 mm telescope

How clearly can the stars of the Pleiades cluster be seen through a 15x telescope (for example, FunScope)?
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### Why don't stars in globular clusters all orbit in the same plane?

Globular clusters like Omega Centauri certainly don't seem to be very coplanar at all. In other words, why doesn't the explanation at Why are our planets in the solar system all on the same disc/...
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### What objects/states of objects with absolute magnitude do we know of?

For measuring distances the knowledge of absolute magnitude or luminosity is often crucial, especially for very big distances. Unfortunately we can't measure the diameter of far distant objects and ...
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### Applying the Maxwell–Boltzmann statistics to astrophysical objects

Quoting Wikipedia: In statistical mechanics, Maxwell–Boltzmann statistics describes the statistical distribution of material particles over various energy states in thermal equilibrium, when the ...
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### What if our Sun were located in the middle of a globular cluster?

Say you took our current solar system and relocated it deep in the heart of a globular cluster such as Omega Centauri. What would the night sky look like? Would the starshine of nearby stars be enough ...
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### What latitude is needed before you can reliably see Omega Centauri?

What latitude is needed before you can reliably see the globular cluster Omega Centauri, say it reaches 20 degrees above the horizon? What about if you are up on a hill looking down, what's the ...
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