# What is Clusters: Definition and 70 Discussions

Star clusters are large groups of stars. Two main types of star clusters can be distinguished: globular clusters are tight groups of hundreds to millions of old stars which are gravitationally bound, while open clusters are more loosely clustered groups of stars, generally containing fewer than a few hundred members, and are often very young. Open clusters become disrupted over time by the gravitational influence of giant molecular clouds as they move through the galaxy, but cluster members will continue to move in broadly the same direction through space even though they are no longer gravitationally bound; they are then known as a stellar association, sometimes also referred to as a moving group.
Star clusters visible to the naked eye include the Pleiades, Hyades, and 47 Tucanae.

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1. ### I The purpose of trigonometric axes in plot of electron clusters, ATLAS

I have been doing some reading on electron reconstruction from proton-proton collisions at CERN. In some of the papers I have read, plots such as the one In the figure are included. What I would like to know is why they have chosen to plot the x and y axes as cos(phi) * tan(theta) and sin(phi) *...
2. ### A Optimizing Grouping of People for Teamwork

I have a matrix of dimension 56*56, each row and column represent the compatibility of one person with the rest of the people. A sample matrix could be Alejandro Ana Beatriz Jose Juan Luz Maria Ruben...
3. ### Why globular clusters don't collapse.

I asked Bard that question and it responded (among other things) that a) globular clusters are spherical and b) that they are spinning rapidly. Aren't those two things contradictory, as in they should be flattened by centrifugal forces?
4. ### C/C++ Perform RK4 between 2 Clusters in Magnetic Field

I have a simulated data of charged particles in a magnetic field. I have selected clusters, each cluster contains a set of points(x,z) and I want to perform RK4 between the first and second clusters and fill the positions in a histogram. I have selected the clusters with the initial...
5. ### I How accurate is the distance to M4 and its stars according to different sources?

How far is M4? I have seen contradictory numbers for M4 and stars in it. How precise is Gaia in measuring the radial distances to various stars in M4? Their radial position relative to each other? Their peculiar motions? What kinds of orbits do stars in the outskirts of M4 follow? High...
6. ### A Globular clusters in SDSS data

I am searching for Globular Clusters in SDSS data. From what I have learned after sifting through documentation and the data structures, there is no identifier by which I could directly search for GCs. Nearby clusters are catalogued as individual stars with no apparent link to parent cluster...
7. ### I New Hubble Paper On Lensing In Galactic Clusters

A new report based on Hubble Space Telescope observations is a big deal because it presents a new and independent apparent disparity between the lambdaCDM predictions for dark matter phenomena in galactic clusters and what is observed via gravitational lensing. The paper and its summary and...
8. ### I Question regarding the future of galaxies within a group of clusters

Given that the galaxies within a cluster of galaxies are generally gravitationally bound, and not affected by the expanding universe, would it not also be expected that after some large number of billions of years, all of the individual galaxies would merge together to become one single very...
9. ### Virial thereom as applied to clusters of galaxies

I'd just like to comment if I may - The virial thereom is not applicable to clusters of galaxies as the numbers of member galaxies in the majority of clusters (as opposed to superclusters) are too small for the virial thereom to effectively calculate the cluster mass. There is a short article to...
10. ### B Dark matter not found in globular clusters orbiting MilkyWay

On the podcast “Skeptics Guide to the Universe”, host, Steven Novella mentioned that astronomers can tell the difference between globular clusters orbiting the Milky Way Galaxy and satellite galaxies by looking to see if there is the gravitational effects of dark matter. Why would this be? That...
11. ### I Minimal number of clusters

Hello, I am tackling a problem related to clustering, and something came up that got me quite baffled. Suppose you have N distinct objects. Each of them is associated to a list of 'descriptors'. The task is to cluster together objects that have as many descriptors as possible in common, with the...
12. ### I Why do galaxy and galaxy clusters look so colorful?

Why do galaxy and galaxy clusters look so colorful?
13. ### B Our solar system and its fellows

Hello, I am new to this forum, so be brutal :) So, I've tried to find information about Earth's origin. The nebula, cluster we are a part of etc. but i could not find the answer I was looking for. For me, it seems logical that we are a part of a cluster. How often do we find a star whos just...
14. ### I Clusters at center and periphery

An acquaintance has told me that the Sloan Digital Sky Survey found clusters of galaxies in which most of the galaxies were divided between the center and the periphery, with a smaller density of galaxies in between. Is this case, and if so, why?
15. ### I Question about Accumulation points

So we just recently did accumulation points in my maths class for chemists. I understood everything that was taught but ever since I was trying to find a reasonable explanation if the sequence an = (-1)n has 2 accumulation points (-1,1) or if it doesn't have any at all. I mean it's clear that...
16. ### I Milky Way's Globular Clusters

My question is directly towards figure 2.15 from Galaxies in the Universe, An Introduction by Sparke and Gallagher. Everything in the figure makes sense to me until the authors make the point, "Clusters with a blue horizontal branch (filled dots) are more concentrated to the center than are...
17. ### I Bullet clusters & CMB accoustic peaks dark matter

is it possible the dark matter in bullet clusters & CMB accoustic peaks were the result of black holes, originally from baryonic matter, but galaxy rotation curves are MOND. So MOND + dark matter as black holes from baryon, not dark matter particles
18. ### I Percent of stars in our galaxy that belong to clusters?

Of all the stars in our galaxy, how much of them belong to clusters?? Is our sun rare in terms of not belonging to any cluster? I can't find any sources on that
19. ### B Galaxy Clusters, Masses and Radius

This is a request for a good reference. I'm doing a report on dark matter and am wondering if there's any recent references that collects a bunch of galaxy clusters, their dark masses and the radius of the cluster. Preferably in a table that I can shred or download but I'll copy if I have to...
20. ### I Are There Black Holes in Galaxy Clusters?

I know that I'm most galaxies black holes live in the center. I'm wondering if this is true for Galaxy clusters. Are there black holes in the center of galaxy clusters?
21. ### Angular distance in globular clusters

Homework Statement Go to the following web site: http://www.astro.utoronto.ca/~cclement/cat/listngc.html This is the portal to a large on-line catalog of variable stars in globular clusters. Each link is a cluster name and will take you to a simple text page that lists near the top the...
22. ### Why can't there be other Boson particle clusters

I most recently heard about the new mathematics that help predict glueballs properties better. I had the really strange question of, why can't all other bosons have a cluster particle, like the glueball. Is it due to there force strength over distance or am I missing something.
23. ### Fortran Input/Output error with error code -5

I got a problem running my FORTRAN program in high performance computer cluster. It runs well in my PC but I want to have mass production of data with different initial conditions so I put it in a cluster node with eight cores, simulate eight sets of data. The program can run without problem...
24. ### Do Galaxy Clusters follow De Vaucouleurs' Law?

If objects in the universe are built hierarchically, wouldn't one expect a Galaxy Cluster that is roughly spherical to follow the same profile as an elliptical galaxy?
25. P

### Neutral hydrogen gas in galaxy clusters

Neutral hydrogen gas in galaxy clusters Most galaxies are members of a cluster, a grouping of several to thousands of galaxies. Our Milky Way, for example, is a member of the "Local Group," a set of about fifty galaxies whose other large member is the Andromeda galaxy about 2.3 million...
26. ### Cumulative number counts of galaxy clusters

Dear all, I am trying to plot the cumulative number counts of galaxy cluster (N>S) as a function of X-ray flux. The method I am following is using the mass function and scaling relation to calculate dN/dVdz. Then I do a double integrate over the redshift range and flux range. But the plot that...
27. ### When can globular clusters be considered collisionless?

Hi all. I'd like to use a software package, that has been designed for collisionless dynamics, to investigate general globular clusters. As they are highly collisional, at least in their inner parts, this perhaps makes no sense. However, it may be meaningful for some time- or length-scales or...
28. ### Observing proposal for globular clusters in M31

Hello, As part of a course I have been asked to make a observing proposal which aims to detect globular clusters in the bulge of M31. The "virtual" observation will be conducted using the Hubble telescope and the WFC3 To begin with we aim to acquire a sample of globular clusters down to 10^6...
29. ### Calculating the distance between the clusters

Blue star 1 is 1.36 parsecs from you, and has a measured flux of 9.6×10−9Wm−2. The similar colour star in star cluster 1 has a measured flux of 9.5×10−21Wm−2. How far away (in Mega-parsecs) is star cluster 1? Can anyone tell me how to start off? I'll do the rest
30. ### Calibration cosmic distance scale on age globular clusters

Hi, Could someone enlighten me in this matter? . how the calibration of cosmic distance scale affects the determination of the age of globular star clusters? thanks a lot :)
31. ### What is the center of a globular clusters made of?

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
32. ### Clusters of non-vaccinated children

A study in California has shown that non-vaccinated children are clustered geographically thus increasing the severity of outbreaks of preventable diseases. http://pediatrics.aappublications.org/gca?submit=Get+All+Checked+Abstracts&gca=pediatrics%3Bpeds.2014-2715v1 Apparently California has a...
33. ### Unidentified emission line in Galaxy Clusters

I could not find a thread about this (and I hope I don't start a duplicate one :smile:). I got a mail from a friend today about this: Detection of An Unidentified Emission Line in the Stacked X-ray spectrum of Galaxy Clusters Esra Bulbul, Maxim Markevitch, Adam Foster, Randall K. Smith...
34. ### Possible webpage title: Exploring the Fascinating World of Star Clusters

Hello, I would like to know if there is any book or any useful links about star clusters, dealing with the following topics :[ formation, evolution, types (open, globular), etc...]. It is very difficult to find an organized document from google results, so if anyone is familiar with the...
35. ### Angular momentum of galaxies in galactic clusters

Hi, I was wondering if the stars in a galaxy are orbiting its centre with (for example) 'anticlockwise' angular momentum. Then would you expect the orbits of the galaxy around the centre of a galactic cluster (if it's in one) to be 'clockwise' or 'anticlockwise' or will it not make much...
36. ### M67 Cluster Study: Books & Articles on Dynamics & Open Clusters

Hi, I am looking to do a study on the M67 cluster, and I would appreciate suggestions on books and articles on the topic and a little bit on open clusters in general. I have found very little information on how M67 affects the dynamics of the galaxy (part of the galaxy neighborhood). There are...
37. ### Why space expansion is limited to scales larger than galaxy clusters?

Hello everyone, I have a question about metric expansion of space. According to Wikipedia (ok probably is not the best source, but I have only a qualitative understanding of physics) the expansion occurs only at scales larger than galaxy clusters...
38. ### Network Motifs vs Clusters: Exploring Network Sub-Communities

Could someone explain what network motifs are and how they are different from clusters because wherever I've searched, both are defined as sub-communities within a network.
39. ### Dark Matter in Galaxies/Star Clusters

Has dark matter been observed to exist in quantities that correlate with the apparent observed mass or overal volume of gallexy/ star clusters? I'm wondering if dark matter is distributed in relative even amounts based on given characteristics or if it is thought to be random/unknown.
40. ### 3D Potts/Ising model. How to identify boundaries of clusters?

I am currently working on the 3D potts model in a temperature gradient to identify the critical temperature and critical exponent. I use the Swendsen-Wang algorithm to simulate the dynamics of the system, and I use the Hoshen-Kopelman algorithm to identify the clusters of spins. The problem...

42. ### Is there any gravitationally unbound' galactic clusters in observable universe

is there any "gravitationally unbound' galactic clusters in observable universe my hunch is that everything in the universe is gravitationally tugged on each other ..we can say moon is connected to andromeda galaxy in a way moon->earth->sun->milkyway->andromeda even the slightest imbalance...
43. ### Parallel universe attracting galactic clusters

On the Science Channel, US cable TV (7/11/2011): A NASA astronomer has discovered that a number of galactic clusters are all UNEXPECTEDLY drifting in a uniform manner (not directly away from earth) suggesting that something is attracting them all in a particular direction. [The astronomer was...
44. ### Question: Can elements above iron actually be clusters of smaller elements?

Hello, I would like to ask if elements of higher atomic number than iron might actually be clusters made up of smaller elements? Is there any evidence that rules out this possibility? The reason I am guessing that elements below iron are discrete is because of the theory that iron has its...
45. ### Some questions about glob. clusters and dark matter

A friend called my attention to an interesting paper by Abe Loeb and David Spergel and somebody else. It seemed to raise unresolved issues about the DM and globular clusters. Does anybody know the current mainstream thinking about this? In case anyone is new to this, Loeb and Spergel are...
46. ### Are modern galaxies found in ancient galaxy clusters?

Hi, can someone help me understand this with the concordance model? http://esciencenews.com/articles/2010/05/12/ancient.galaxy.cluster.contains.modern.galaxies
47. ### What is the diameter of star clusters?

Maybe this is stupid question, but I am not sure how to get the diameter of the star cluster, I assume from the RA and Dec. I googled it and tried to come with a realtion between the RA , Dec and Diameter from Andrea's proposal but couldn't figure the correct answer This is all I find (see...
48. ### Exploring Star Clusters: What Can Age, U-B, B-V, V Data Tell Us?

Hi, Let's say that you had the following information (age with errors, U-B, B-V, V) for 100 star clusters, what would you do with it? What can it be useful for? Just wondering...
49. ### The formation of Galaxy Clusters from density fluctuations in the early Universe

Hello!:wink: May I ask for a little assistance in filling in the gaps of my understanding? :S I understand that the current large scale structure of the Universe is thought to be the result of early fluctuations in density which have been stretched out in the expansion of the Universe. I...
50. ### Globular clusters cylindrical polar coordinates

Homework Statement Two globular clusters A and B have cylindrical polar coordinates relative to the centre of the galaxy (r, z, Ø) given by A = (5,2,15°) and B= (4.6,65°), where the r and z coordinates are in kiloparsecs. Homework Equations Find a and b the position vectors of each...