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andrew s

Galaxy and cluster formation simulations

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Prof Nat Bastian gave a brilliant talk on Globular Clusters at Chester Astro Soc last night. He completely revised what I thought we new about them.

In his talk he showed simulations from the Eagle Project http://icc.dur.ac.uk/Eagle/downloads.php and from the E-Mosaics Project  http://www.astro.ljmu.ac.uk/~astjpfef/e-mosaics/downloads which combine his groups work on cluster formation with the cosmological evolution simulations of Eagle.

The downloads are not the exact same ones shown but if you have not seen them the they are well worth a look.

Regards Andrew

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Sorry to have missed that talk, Andrew. Was working in London.

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Ah, fantastic. I would have loved to have heard that talk. 'What are Globular Clusters?' is one of my big unanswered questions (the other one concerns the Big Bang, but I won't go into that right now!)... what did he have to say - roughly?

I'm now going to go and watch the two simulations.

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@PhotoGav very roughly our old idea that GC were old is wrong and due to selection effects prior to IR ccd and hst. There are gc of all ages and a continuum of clusters from compact gc  to open clusters. What you get depends on just how massive and dense the gas cloud they formed in. 

gc  form today in regions where galaxies are colliding and other situations triggering star bursts.  gc can be used to trace galaxy mergers as gc  with common properties come from different source galaxies. They can be used to trace the star streams from the mergers as have been done for the milkyway and other large galaxies.

Regards Andrew 

Edited by andrew s
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Hah... the only thing that doesn’t change is that everything changes! Fascinating stuff. It’s good to see that these objects are being investigated and understood a little more. I rather like telling people at outreach sessions that they are some of the oldest objects visible. I’ll have to adapt my patter slightly!

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They are Population-II old stars, that lie in, around, to the top & bottom of the nuclear halo. Yes, they are coorelated, with the Big Bang.  

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17 minutes ago, Science562h said:

They are Population-II old stars, that lie in, around, to the top & bottom of the nuclear halo. Yes, they are coorelated, with the Big Bang.  

That was what was thought to be the case but it was a selection effect. We now know as per the talk that they form throught out time and are indeed forming now.

Regards Andrew 

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That's, what my Astronomy I class teaches, right out of the text. Population II stars are old stars that were not enriched by heavy metals, yet. They are intermediate population stars. Population III stars are primordial & devoid of any metal, exccept for lithium. Therefore, if stars are forming in bound GCs, those GCs are now comprised of population I stars, within a population II cluster. Umbrella'd, as GC POP-II. However, true POP-II GCs do not have active star formations. POP-II GCs don't contain high mass main sequence stars & the clusters are doomed to burnout. GCs formed, at the same time, as OCs & traveled to our MWG or were accreted, through dwarf galaxies & mergers. 

There are exceptions, such as Westernlund 1 & in other galaxies. That's, what I think, you are referring to & I know exactly, what you meant. We can't teach that straight forward or make test questions, out of it.  

The "exceptions" are new forming Type-I globular clusters but they require mass. They are main sequence stars, in the upper left of the HR-Diagram. In contrast, POP-II GCs are not main sequnce, in the lower right. They fuse helium. Typical GCs, like M55, do not have considerable mass & the stars are -2 solar masses. They are also in the lower right of the H-R diagram.

Any gravitationally attracted stars can form in-to a globular cluster; new stars can form in-to a globular structure but they are not population-II. Those become population-I , like open clusters. The exceptions are "isolated globular clusters or just clusters." Typical aged globulers stop, at the turnoff point," about 6,000-6,500 k. 

Yes, new GCs can form but they are very young, like 5 mill yr old, giants, white, blue & hot; not like 12.8 bill yr old, dwarf & red. Anyway, those are called superstar clusters. GC exceptions are in the early stages of GC formation & are POP-I stars. They form around H-II regions of dense gas & dust, opposite of devoid POP-II GCs.. 

Like I said, 95-99% of globular clusters are old population-II stars, that formed, at the same time, after the Big Bang, along with open clusters. That's, what has to be taught first, which is why, that's all I posted. That's the actual test question, to pass, with an A. Your answer is correct, POP-I stars can form in-to a globular structure early-on but they are not POP-II. Whether it remains bound or unbound, depends on interactions. Primordial typical GCs have to be differentiated from new GCs because the stars are comprised of different populaces; yet, both have similar structure. 

Yes, but to get to get the actual test queston right, I have to say, this & then teach:

POP-I (Open Clusters)= young & hot, millions to tens of mill yr old; located inide of the nuclear bulge or disc. Metal rich. 

POP-II (Globular Clusters)= old, of the oldest & 12.8 bill yr old; lie in halo. Metal poor. NO ACTIVE STAR FORMATION.

Edited by Science562h
Grammar

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Yes, GCs can form, while being comprised of population-I stars, as type-I globular clusters but they are not population-II. To be a POP-II GC, you can't have star formations or any gas present. That's why, it's broken down in-to type-I & II. Your GC possibility is a globular cluster type-I, with population-I stars, which still makes it type-I, in everyway. GC only in structure, due to early formation, like all others. It's, like resetting spacetime & counting the age of our observable universe all over again. We already have POP-II GCs. The belief was, per book, "that all GCs were very old" (PG. 394). Obviously, that's not true; hence, we have exceptions & that isn't taught anymore. That leads to population-I stars & open clusters. 

 

Chapter 12: Test Question

1. Globular clusters are spherical shaped and __________. 

A. comprised of old bound stars located in the galactic halo  

B. normally located along the galactic disc

C. unbound group of stars located near the nuclear core

D. comprised of young and hot stars, that are tens of thousands years old 

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Prof Nat Bastian gave us an update on the latest research in this area. He clearly showed how out of date the textbooks now are.  Fortunately,  I am not studying for any exam.

Regards Andrew 

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