What is globular: Definition and 27 Discussions

A globular cluster is a spheroidal conglomeration of stars. Globular clusters are bound together by gravity, with a higher concentration of stars towards their centers. They can contain anywhere from tens of thousands to many millions of member stars. Their name is derived from Latin globulus (small sphere). Globular clusters are occasionally known simply as "globulars".
Although one globular cluster, Omega Centauri, was observed in antiquity and long thought to be a star, recognition of the clusters' true nature came with the advent of telescopes in the 17th century. In early telescopic observations globular clusters appeared as fuzzy blobs, leading French astronomer Charles Messier to include many of them in his catalog of astronomical objects that he thought could be mistaken for comets. Using larger telescopes, 18th-century astronomers recognized that globular clusters are groups of many individual stars. Early in the 20th century the distribution of globular clusters in the sky was some of the first evidence that the Sun is far from the center of the Milky Way.
Globular clusters are found in nearly all galaxies. In spiral galaxies like the Milky Way they are mostly found in the outer spheroidal part of the galaxy – the galactic halo. They are the largest and most massive type of star cluster, tending to be older, denser, and composed of lower abundances of heavy elements than open clusters, which are generally found in the disks of spiral galaxies. The Milky Way has more than 150 known globulars, and there may be many more.
The origin of globular clusters and their role in galactic evolution are unclear. Some are among the oldest objects in their galaxies and even the universe, constraining estimates of the universe's age. Star clusters were formerly thought to consist of stars that all formed at the same time from one star-forming nebula, but nearly all globular clusters contain stars that formed at different times, or that have differing compositions. Some clusters may have had multiple episodes of star formation, and some may be remnants of smaller galaxies captured by larger galaxies.

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  1. J

    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?
  2. S

    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...
  3. Barbequeman

    Virial Theorem for an expanding globular cluster

    I attached a file which shows my attempt to resolve this problem with the possible two pair interaction which gives us the kinetic energy of the cluster in an expanding system, at least I think so. But to be honest I´m more or less completely stuck with this question and I would be glad if...
  4. M

    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...
  5. G

    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...
  6. ISamson

    B Chemical study of an old, metal-rich globular cluster

    Regarding a recent article from phys.org , Chilean researchers have conducted a study of an old, metal-rich cluster, NGC 5927. Interesting results are the abundance of many metals, which include sodium, aluminium, iron, oxygen and some heavy metals such as yttrium and zirconium. Thank you.
  7. Jamison Lahman

    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...
  8. J

    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...
  9. R

    Are Globular proteins red blood cells?

    So globular just means spherical, are globular proteins just red blood cells; then all red blood cells are considered globular proteins. Are all enzymes in the blood red blood cells? Are all red blood cells enzymes? What else in the blood is spherical? What is in the blood other than...
  10. Andy Resnick

    Is Stacking RAW Images the Key to High-Quality Astrophotography?

    Virgo has moved on, Hercules is now in position- from last night: This is a downsized crop. Technical deets: 800/5.6, 10s ISO 2000, 204 frames.
  11. K

    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...
  12. J

    Globular cluster luminosity function

    So I was interested in how astronomers measure the distances to other stars, galaxies, etc and I found this pdf about the subject http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1992PASP..104..599J&data_type=PDF_HIGH&whole_paper=YES&type=PRINTER&filetype=.pdf It seems to be a good...
  13. liometopum

    Black holes in the globular cluster M22 with Dr. Tom Maccarone

    Dr. Tom Maccarone is a coauthor of the paper, “Two stellar-mass black holes in the globular cluster M22”, and is Associate Professor,Department of Physics, at Texas Tech University at Lubbock Texas. The work is discussed in a popular form at "Physicists Find Black Holes In Globular Star...
  14. S

    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...
  15. liometopum

    Globular cluster ejected from M87

    In preparing a post for the globular cluster thread, I found reference to "High Velocity Globular Cluster One, or HVGC-1. This is the first globular cluster discovered to have been ejected by the interaction of two massive black holes. http://hvgc-1/ A Globular Cluster Toward M87 with a Radial...
  16. P

    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 :)
  17. vrmuth

    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
  18. T

    Determining the mass of globular cluster?

    : Estimate the mass of a globular cluster with the radius of R=20pc and root mean square velocity of stars equal to Vrms=3km/s i can apply the formula like Vrms=(root over) 3RT/M ( where R=gas constant, T= absolute temperature, M=mass of the cluster) but here the variable of the "T" is...
  19. D

    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...
  20. C

    Calculate distance between stars in a globular cluster?

    Would it be possible to calculate the approximate distance between stars in a globular cluster by doing something simple like this: Approximate distance to a cluster: 25,000 Ly Two stars in the cluster just barely resolved in my telescope (resolution about 1 arcsec) Therefore: 2pi...
  21. B

    Simulating globular clusters over blackholes with Fortran

    I suspect that the runtime simulation for a star systems containing thousands of stars , many of those stars whose mass is way beyond the solar mass to be very very long. Is it possible and cost-friendly(i.e, not expensive) to simulate a globular star system cluster over a supermassive black...
  22. L

    Difference between fibrous proteins and globular proteins

    Hey guys, can somebody helps me to understand better about fibrous vs globular protein please "So what is the main difference between fibrous proteins and globular proteins? Aside from the difference in shape (elongated vs. spheroidal) and solubility (insoluble vs. soluble), fibrous proteins...
  23. DaveC426913

    Characteristics of globular clusters

    Quick question(s): If a cluster is not "open", it's what? M62 is a what cluster? (No, not peanuty nougat). What would be the average distance between stars in a cluster like this? What would be the average orbital period? And ultimately, what would the motion patterns of stars in...
  24. S

    Why are Globular Clusters so Metal poor?

    I do not understand why Globular clusters, with ages around 10 Giga years, are so metal poor. Their stars are surely undergoing nucleosynthesis, right? Are all the stars in such cluster only of such low mass that they never explode as supernova and scatter their elements? TIA Sterling
  25. F

    How did globular clusters get their properties?

    As I understand it, the stars in a globular cluster have orbits with a whole range of eccentricities and directions of motion, giving the cluster an overall spherical shape, with a greater density of stars toward the center. How did the overall cloud out of which the globular cluster arose...
  26. E

    Should globular clusters exist?

    they are the oldest things in the galactic halo, having formed near the birth of the milky way. So with all the 10 odd billions of years of existence, i think they all should have gone supernova and destroyed the shape of the cluster. So how do they stay gloubular in their shape?
  27. B

    Gravitational field of globular clusters ?

    what does the gravitational field at the center of a globular cluster look like? it doesn't look as though there is any angular momentum - is there a 'center' of gravity inside? a black hole?