Starship Asterisk*

starsurfer wrote:

Ann wrote:

Click to view full size image

A spheroidal galaxy: NGC 205, satellite of M31.
Photo: Probably Adam Block.

The image of M110 isn't by Adam Block, it might be by Leonardo Orazi?

https://www.flickr.com/photos/leonardo70/6220115689/

Thanks, bystander.

Ann

I'm sure I'll be corrected if I'm not up-to-date, but it still seems to be the mainstream view that most globular clusters are amongst the oldest components of galaxies. The uncertainties in some of their age estimations, even overlap with the age of the universe. Whether GCs formed before or after the galactic discs of gas (which seem to form relatively quickly and early) there seems to be more to suggest that GCs formed within the halos/bulges (within regions of efficient star formation), rather than the discs.

Nitpicker wrote:I'm sure I'll be corrected if I'm not up-to-date, but it still seems to be the mainstream view that most globular clusters are amongst the oldest components of galaxies. The uncertainties in some of their age estimations, even overlap with the age of the universe. Whether GCs formed before or after the galactic discs of gas (which seem to form relatively quickly and early) there seems to be more to suggest that GCs formed within the halos/bulges (within regions of efficient star formation), rather than the discs.

It's absolutely true that globular clusters are believed to be among the most ancient components of galaxies, because their stars are so metal-poor. You can be sure that globulars are not older than the universe, though, and while it's true that you can still find age estimates in the range of 15 billion years for some globulars, those estimates were made before it was known that the universe is about 14 billion years old.

I'll still offer no strong opinion on how and where globular clusters were formed, but you must bear in mind that they formed at a time when the universe small and tight and almost roaring with sloshing and breaking waves of unused hydrogen. I think that this situation in itself was extremely favorable for the formation of truly huge numbers of globular clusters, perhaps all over the small observable universe, and that this led to changes in the universe itself.
The central starburst of small galaxy M82 has led to huge outflows of gas from the center of the galaxy, as large numbers of high-mass stars created in the starburst have gone supernova. This enormous outflow of gas has altered M82 itself. The disk of the galaxy is crisscrossed with broken dust lanes, but we see extremely few signs of any bright stars at all in the disk. It is as if star formation in the disk had come to a stop after so much gas has been blown out of the galaxy.

Now imagine a universe-full of M82s, all popping their tops in enormous supernova explosions going off mostly everywhere at the same time. I think that must have affected the properties of the entire universe at that time. For example, it may have stirred up the gas everywhere so much that it inhibited the formation of new globulars for a while. And by the time when the gas had cooled down and was ready for truly major star formation again, the universe had grown larger and more spread out. Also the gas of the universe would have become a lot more metal-rich after all those tremendous explosions, and it is not certain that metal-rich gas is as efficient at forming clusters as the concentrated, pristine, metal-poor gas was.

Ann

Ann wrote:while it's true that you can still find age estimates in the range of 15 billion years for some globulars, those estimates were made before it was known that the universe is about 14 billion years old.

Not so sure about that. Without linking to any papers, I was reading a recent one the other day, that gave age estimates for a list of GCs. I think the overlaps in the uncertainties of some of their ages, with the uncertainty in the age of the universe, is merely due to the different techniques for estimating the ages. No one seriously thinks that GCs are older than the universe. But it is interesting to note the error tolerances.

bystander wrote:

starsurfer wrote:

Ann wrote:

Click to view full size image

A spheroidal galaxy: NGC 205, satellite of M31.
Photo: Probably Adam Block.

The image of M110 isn't by Adam Block, it might be by Leonardo Orazi?

https://www.flickr.com/photos/leonardo70/6220115689/

Yep, that's the one!

Nitpicker wrote:

Ann wrote:while it's true that you can still find age estimates in the range of 15 billion years for some globulars, those estimates were made before it was known that the universe is about 14 billion years old.

Not so sure about that. Without linking to any papers, I was reading a recent one the other day, that gave age estimates for a list of GCs. I think the overlaps in the uncertainties of some of their ages, with the uncertainty in the age of the universe, is merely due to the different techniques for estimating the ages. No one seriously thinks that GCs are older than the universe. But it is interesting to note the error tolerances.

This is an interesting page.

astro.psu.edu/lecture 27 wrote:

Globular clusters

• They are among the oldest objects in the galaxy, provide a lower
limit on the age of the universe
– Why is it a lower limit?
– There are a fair number of uncertainties in these estimates,
including errors in measuring the distances to the GCs and
uncertainties in the isochrones used to derive ages (i.e. stellar
evolution models)
– Inputs to stellar evolution models include – oxygen abundance
[O/Fe], treatment of convection, helium abundance, reaction rates of
¹⁴N + p → ¹⁵0 + γ, helium diffusion, conversions from theoretical
temperatures and luminosities to observed colors and magnitudes,
and opacities


Recent Results for GC’s

• So the globular clusters are somewhere between ~11.7 and 14.7
Gyr old
• Since it probably takes 1-2 Gyr for galaxies to form, we need to
add that to the GC ages to get the age of the universe
• Note that older estimates were closer to 13-17 Gyr old, what
changed?
– Distances to globular clusters increased by ~10% based on the
Hipparcos calibration of the absolute magnitudes of subdwarfs
(lowers ages by ~20%)
– Inputs to stellar evolutionary models
– Younger ages more compatible with with ages estimated from
expansion of universe (phew!)

Ann

Ann wrote:
This is an interesting page.

astro.psu.edu/lecture 27 wrote:

Globular clusters

• They are among the oldest objects in the galaxy, provide a lower
limit on the age of the universe
– Why is it a lower limit?
– There are a fair number of uncertainties in these estimates,
including errors in measuring the distances to the GCs and
uncertainties in the isochrones used to derive ages (i.e. stellar
evolution models)
– Inputs to stellar evolution models include – oxygen abundance
[O/Fe], treatment of convection, helium abundance, reaction rates of
¹⁴N + p → ¹⁵0 + γ, helium diffusion, conversions from theoretical
temperatures and luminosities to observed colors and magnitudes,
and opacities


Recent Results for GC’s

• So the globular clusters are somewhere between ~11.7 and 14.7
Gyr old
• Since it probably takes 1-2 Gyr for galaxies to form, we need to
add that to the GC ages to get the age of the universe
• Note that older estimates were closer to 13-17 Gyr old, what
changed?
– Distances to globular clusters increased by ~10% based on the
Hipparcos calibration of the absolute magnitudes of subdwarfs
(lowers ages by ~20%)
– Inputs to stellar evolutionary models
– Younger ages more compatible with with ages estimated from
expansion of universe (phew!)

• So...essentially the classic paradox has mostly been due to:
  • an underestimation of luminosities/distances
    making for older GCs and a younger Universe.

I never realised it was considered classic paradox, nor that it had been conclusively resolved in the last 10 years. At least I was correct when I said someone would correct me. Thanks Ann.

Actually, on further reading, I found this article from Krauss and Chaboyer:
http://www.astro.caltech.edu/~george/ay ... er2003.pdf

... which seems to be the source of some of the material in the link you provided, Ann.

My reading of it (I don't pretend to understand it all) is that the upper limits on the age estimations of GCs, are still older than the universe, but the age estimations of both are considerably more certain than they were in the decades preceding.