Astronomy/Star clusters

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Expert: - 12/13/2011


Question
I was wondering specifically about the coma cluster if you had any knowledge on that in particular but my question generally is what does it mean for a star cluster to be in equilibrium? While studying the coma cluster I read that it has been thought that it is not in equalibrium and that is why Fritz Zwicky came up with dark matter using the virial theorem. The information came from spiff.rit.edu/classes/phys440/lectures/gal_clus/gal_clus.html

Answer
Hi Zach,
just from what I read on the internet, like
http://en.wikipedia.org/wiki/Coma_Cluster
(The galaxy cluster, not the open star cluster in Coma, designated Melotte 111)... this is the galaxy cluster Abell 1656, not the Coma open star cluster designated Melotte 111).

I believe equilibrium means, or is meant to mean, that since no galaxy has enough velocity and inertia to escape from the cluster, equilibrium has been achieved.  But for this to be true, over 90% of the cluster HAS to have more "gravity" than what the visible sources (over 1000 galaxies) says it has.  Thus the term, missing matter, which became "dark matter"... with the ability to hold even the fastest moving galaxy within the confines of the cluster itself.  If equilibrium was not achieved, (not enough mass in the form of dark matter)... then some fast galaxies would be escaping the cluster. But... they aren't.  "Something" is holding the cluster together, and that something, is termed dark matter.    That's how I read it.  Hope this helps,
Clear Skies,
Tom Whiting
Erie, PA  

Astronomy

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Tom Whiting

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Astronomy has been my hobby/pasttime for over 50 years.  Currently own 3 telescopes, the largest of which is a 30 inch Newtonian truss Dob that is portable.I taught Astronomy/Meteorology at the University Level for 13 years before retiring in 1995. Being retired and home most of the time, I am able to answer all questions relatively quickly, unless it's a new moon weekend with good observing conditions.  No astrology questions please, or questions about alleged UFO picture identifications.

Experience

Experience: Astronomy has been my hobby and study for over 50 years. We currently now own a 30 inch portable telescope (Updated - Pennsylvania`s largest portable telescope). It can be seen on our website at:http://www.velocity.net/~bwhiting and also attend several regional starparties during the year, and have been on 5 total solar eclipse expeditions.

Organizations: President, Erie County Mobile Observers Group for over 15 years.

Publications: Wrote the "Over Erie Skies" newspaper article in our local newspaper for 11 years (1975-86).

Education: Masters Degree- Taught at the University level for 13 years. Retired 20 years -USAF Pilot - KC-135 with 180 combat missions;  Also Eagle Scout, Philmont staff 2 Yrs, Order of Arrow Lodge Chief, Ham Radio (inactive).

Awards: two discoveries: The mini-coathanger asterism in Ursa Minor (the little dipper) And the mini-ladle- another asterism in the bowl of Ursa Minor. Clients: Currently President of the ECMOG as mentioned above.

Education/Credentials
BS  Metallurgical Engineering Grove City College, PAMaster's Degree, Gannon University, Erie, PA Also retired USAF pilot, 20 years.

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