APOD: The Densest Galaxy (2013 Oct 04)

[Beyond]

I couldn't help following the pattern, though.

It's just the "zilla" part doing it's thing.

[BDanielMayfield]

Today's APOD makes me wonder if there is a clear demarcation or mass gap between the smallest dwarf elliptical galaxies and the largest globular clusters. Or are these two classes of objects the same, except for where they are located?

P. S. I wrote the above prior to seeing Anthony’s comment, which relates to my question too, since he points out another ambiguous case. Is there any difference between these objects other than size and location in or outside another galaxy?

My understanding is that the stars in a typical globular cluster are all the same very old age and have very low concentrations of elements heavier than hydrogen and helium. I.e. they're all "Population II" stars, which are older than "Population I" stars like our Sun (maintaining this arcane terminology is one way that astronomy professors torture their introductory astronomy students). When you see something that looks like a globular cluster but has stars of widely differing ages and compositions, you're probably looking at a dwarf galaxy. And if it has a central black hole, that suggests that it used to be bigger and has lost a lot of stars to tidal interaction with a larger galaxy.

If you have a clear dark sky and a good telescope, look at some globular clusters and some open clusters. The globulars have a more even mellow golden glow, because all the surviving stars are old yellow or red stars (nitpicker foil: you're not going to notice "blue stragglers" through an amateur telescope). Young open clusters look more blue and sparkly, because they still have some massive blue stars.

Thanks Anthony. The range of ages of the stars inside these objects was something that hadn't occured to me. Pop I stars inside an object would mean that it wouldn't be a globular cluster, as their stars are all extremely old.

[Ann]

BDanielMayfield wrote:
Thanks Anthony. The range of ages of the stars inside these objects was something that hadn't occured to me. Pop I stars inside an object would mean that it wouldn't be a globular cluster, as their stars are all extremely old.

That is not actually true. If you check out this topic, you can read about a Population I star that is only 190 light-years away from us. This star is extremely metal-poor, and astronomers consider it the oldest star they know. But this star is not located in a globular cluster. Although I haven't checked, I would guess that this star is a halo object, and that it is passing us by in its orbit around the center of the Milky Way.

It is true that stars in the bulge of a galaxy tend to be metal-rich even though they are old. Since they are metal-rich, they most certainly don't belong to Population I. They were born from gas that had been recycled through several generations of stars. But can we be sure that there are no Population stars in the bulges of galaxies? Normally we can't be sure of this at all. This picture shows two globular clusters that are embedded in the bulge of the Milky Way. These globulars are just passing through, but they will likely lose some stars during their crossing of the bulge. Will the "lost stars" end up in orbits that really make them true members of the bulge? I think that is unlikely.

So it is an interesting question if there are any Population I stars in M60-UCD1 or in M32. Perhaps there aren't any. If Population I are either halo objects or members of globular clusters, then there may not be any such stars in a galaxy that has been whittled down to its bulge.

Ann

[neufer]

Thanks Anthony. The range of ages of the stars inside these objects was something that hadn't occured to me. Pop I stars inside an object would mean that it wouldn't be a globular cluster, as their stars are all extremely old.

That is not actually true. If you check out this topic, you can read about a Population I star that is only 190 light-years away from us. This star is extremely metal-poor, and astronomers consider it the oldest star they know. But this star is not located in a globular cluster.

Nevertheless, it could have escaped from a globular cluster thanks to multiple gravitational interactions.

However, it would be much more unlikely that a Pop I star would actually be captured by a globular cluster during a rare flyby.

[bystander]

That is not actually true. If you check out this topic, you can read about a Population I star that is only 190 light-years away from us. This star is extremely metal-poor, and astronomers consider it the oldest star they know. But this star is not located in a globular cluster. Although I haven't checked, I would guess that this star is a halo object, and that it is passing us by in its orbit around the center of the Milky Way.

It is true that stars in the bulge of a galaxy tend to be metal-rich even though they are old. Since they are metal-rich, they most certainly don't belong to Population I. They were born from gas that had been recycled through several generations of stars. But can we be sure that there are no Population stars in the bulges of galaxies? Normally we can't be sure of this at all. This picture shows two globular clusters that are embedded in the bulge of the Milky Way. These globulars are just passing through, but they will likely lose some stars during their crossing of the bulge. Will the "lost stars" end up in orbits that really make them true members of the bulge? I think that is unlikely.

So it is an interesting question if there are any Population I stars in M60-UCD1 or in M32. Perhaps there aren't any. If Population I are either halo objects or members of globular clusters, then there may not be any such stars in a galaxy that has been whittled down to its bulge.

I think you have your populations confused. Population I stars are relatively young and metal rich, like our Sun. HD 140283 is possibly a Population III star, or no less than a Population II.

My understanding is that the stars in a typical globular cluster are all the same very old age and have very low concentrations of elements heavier than hydrogen and helium. I.e. they're all "Population II" stars, which are older than "Population I" stars like our Sun (maintaining this arcane terminology is one way that astronomy professors torture their introductory astronomy students). ...

[Ann]

Bystander wrote:
I think you have your populations confused. Population I stars are relatively young and metal rich, like our Sun. HD 140283 is possibly a Population III star, or no less than a Population II.

You are right. Thanks for correcting me.

Ann

[BDanielMayfield]

BDanielMayfield wrote:
Thanks Anthony. The range of ages of the stars inside these objects was something that hadn't occured to me. Pop I stars inside an object would mean that it wouldn't be a globular cluster, as their stars are all extremely old.

That is not actually true. If you check out this topic, you can read about a Population I star that is only 190 light-years away from us. This star is extremely metal-poor, and astronomers consider it the oldest star they know. But this star is not located in a globular cluster. Although I haven't checked, I would guess that this star is a halo object, and that it is passing us by in its orbit around the center of the Milky Way.

It is true that stars in the bulge of a galaxy tend to be metal-rich even though they are old. Since they are metal-rich, they most certainly don't belong to Population I. They were born from gas that had been recycled through several generations of stars. But can we be sure that there are no Population stars in the bulges of galaxies? Normally we can't be sure of this at all. This picture shows two globular clusters that are embedded in the bulge of the Milky Way. These globulars are just passing through, but they will likely lose some stars during their crossing of the bulge. Will the "lost stars" end up in orbits that really make them true members of the bulge? I think that is unlikely.

So it is an interesting question if there are any Population I stars in M60-UCD1 or in M32. Perhaps there aren't any. If Population I are either halo objects or members of globular clusters, then there may not be any such stars in a galaxy that has been whittled down to its bulge.

Ann

Bystander wrote:
I think you have your populations confused. Population I stars are relatively young and metal rich, like our Sun. HD 140283 is possibly a Population III star, or no less than a Population II.

You are right. Thanks for correcting me.

Ann

Howdy y’all. I just noticed the additional comments about the question I raised and Anthony answered re the distinctions between dwarf elliptical galaxies and large globular clusters. Just to be clear, it was these two objects alone that I was referring to in my last comment.

And Ann, please don’t feel too bad ‘bout yer a gettin’ yer stellar populations all reversed and all. Long standing astronomical tradition has got us all locked into a confusing, kinda backassward nomenclatural convention here, hasn’t it? (Pop I young, Pop II old, and Pop III so ancient that da ain’t no mo’.)

And Ann, while I’m truly obliged fer yer a linkin’ ta dis here,‘bout that thar Methuselar star; (‘cus it was, in my ENORMOUSLY humble opinion, one of the best threads ever, and I’m so glad you both started it and recalled it to our attention), I’m just a tad mifftified as well. Did ya really think that I needed schoolin’ ‘bout dis here subject, when we had such an interesting conversation at the end of it?

Bruce, an armchair nuclear astrophysist, who (according to my wife) can’t pronounce the word nuclear (along with other notable Texans). There’s only two syllables in nuclear, right?

My apologies to any school marms who may have been offended.

[Beyond]

One way to pronuncicate nuclear in inglish is-->new clee er. Anudder way is-->nu cle er. nuclear, an easy woid to pronucicate, if you don't stop to think about it. Just say it.

[geckzilla]

There's always three syllables in nuclear but how, exactly, it gets pronounced varies quite a bit, with the noo-kyuh-luhr one being controversial. I thought this was a very good article on the phenomenon, clearly explaining metathesis and showing us that the nucular example isn't the first time it's happened.
http://www.nytimes.com/2002/10/13/weeki ... ation.html

[Beyond]

For me, NOO-kyuh-luhr seems about impossible to say. I don't know how to pronounce the "kyuh". Of course, IF the whole nuclear thing blows up, who's gonna be left to say it

[BDanielMayfield]

There's always three syllables in nuclear but how, exactly, it gets pronounced varies quite a bit, with the noo-kyuh-luhr one being controversial. I thought this was a very good article on the phenomenon, clearly explaining metathesis and showing us that the nucular example isn't the first time it's happened.
http://www.nytimes.com/2002/10/13/weeki ... ation.html

So, it really is pronounced with three syllables? How inefficient. But nay I drawl, why use 3 when 2 will suffice? So I stubbornly prefer the deep Texican NEUK-luhr. I mean, how many syllables do y’all use when saying the word “clear”?

Well, if 3 syllables must be used, and according to Geckzilla’s helpful link “NOO-kyuh-luhr is so frowned upon, then I think my next preference might be Jimmy Carter’s ''NOO-kee-yer''. After all, not only was he once the US President, wasn’t he once a nuclear engineer too?

[Beyond]

And, wasn't he also a peanut farmer

[neufer]

Click to play embedded YouTube video.

And, wasn't he also a peanut farmer

• Goober peas, please!

NEUF-fuhr (who learned how to pronounce nuclear from IKE)

[Beyond]

Gee, i always thought that goober peas were just a variation of peas. But they're not peas at all. They're peanuts.

NEUF-fuhr. NOT to be confused with Abominable Snowman fur, or any other kind of fur.