Episode 41 - the age of the Universe, AI and literature reviews, and giant companions

So okay, my first paper is called Cosmic CORALS: Timing the Universe with High Redshift Clusters, and this is submitted to A&A, and it's led by Elena Tomasetti at the Universita di Bologna.

I don't know...

That was my Italian accent, by the way.

[laughs]

It might have been deeply offensive.

Sorry everybody, but, uh- [laughs]

[laughs]

Uh, so in this paper, we're asking, how do we measure the age of the universe? 'Cause this is obviously a key question, and typically the age that we always quote of about 13.7, 13.8 billion years comes from the analysis of the cosmic microwave background, so the energy left over from the Big Bang.

And that is where we get our, our most, most used age measurement from.

It's most reliable.

However, this age depends on the other cosmological parameters encoded in the CMB, so the density of matter, you know, the breakdown of matter versus dark energy and of course the Hubble value, H naught, which is measuring the expansion rate of the universe at the present day.

And herein lies a slight problem with the accuracy of this age because we have what we now know as the, the Hubble tension, which is the fact that if you measure H naught from the cosmic microwave background, you're starting to get like a, a result that is statistically different from the value of H naught you get if you use the sort of the local approximation where you use standard candles to measure distances to objects, and then you measure their recessional velocity, and you map out the ex- the expansion of the universe in that way.

So you have these two competing values of H naught which are close to each other, but not the same, and that's the Hubble tension.

Now, if you then use this to measure the age of the universe, you actually get about a one gigayear discrepancy potentially in the absolute age of the universe for a fixed value of omega matter, which is the density of matter in the universe.

And H naught and omega matter are somewhat degenerate with each other as well, so it's kind of hard to exactly back all that out.

But it means that there is some, some level of uncertainty based on which value of H naught you're using and what value of omega matter you're using.

So how can we resolve this? One way is to get inden- pe- independent measurements that don't rely on, on either of these approaches for either, you know, the age or, or for H naught.

And one way to do this is using some of the oldest objects we can observe in the local universe, which is the globular clusters.

Uh, so these are star clusters that formed very, very early on in the universe, so they're very ancient populations.

So if you measure their ages really accurately without using any cosmological models to underpin that age measurement, you can get an independent sort of limit, lower limit on how old the universe has to be to have allowed star formation to occur in globular clusters.

So that's great, but obviously if you're only using nearby objects, you're still somewhat sort of, you're in this...

You still have this degeneracy between H naught and omega matter, which prevents you from really kind of understanding the age of the universe, but you can at least get that limit.

So this paper is looking to sort of expand the use of globular clusters by measuring the ages of them over cosmic time from different epochs, which you can then use to sort of break this degeneracy between H naught and omega matter.

And this effort is part of CORALS, the, which is the Cluster of Stars as Observational Records of Cosmic Aging and Lookback Times.

That's where the S comes from at the end.