starsurfer wrote:The image of M110 isn't by Adam Block, it might be by Leonardo Orazi?Ann wrote:A spheroidal galaxy: NGC 205, satellite of M31.
Photo: Probably Adam Block.
https://www.flickr.com/photos/leonardo70/6220115689/
starsurfer wrote:The image of M110 isn't by Adam Block, it might be by Leonardo Orazi?Ann wrote:A spheroidal galaxy: NGC 205, satellite of M31.
Photo: Probably Adam Block.
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.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.
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.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.
Yep, that's the one!bystander wrote:starsurfer wrote:The image of M110 isn't by Adam Block, it might be by Leonardo Orazi?Ann wrote:A spheroidal galaxy: NGC 205, satellite of M31.
Photo: Probably Adam Block.
https://www.flickr.com/photos/leonardo70/6220115689/
This is an interesting page.Nitpicker wrote: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.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.
Annastro.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 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!)