Orion constellation – Betelgeuse is the bright orange-colored star. [Voice of Denton, credit: Hubble European Space Agency]

European AstroFest in 2021 is Worldwide AstroFest. The venue isn't Kensington, London as in the past, but rather the World Wide Web. In An Evening with the Stars, we learned about the hunt for the Universe's first stars, what the stars have meant to humanity, and what was up with Betelgeuse in November 2019.

Once again Lucie Green and Stuart Clark hosted the event, with Stuart playing a dual role in this stellar event.

First Light
From the Big Bang to the appearance of the first stars, the Universe was dark. What were those first stars like as they began to illuminate the cosmos that would grow into the one we know? Dr. Emma Chapman, a Royal Society research fellow at Imperial College London, is involved in building and using radio telescopes to try to find out.

We know some things about the very first stars (known as Population III stars). They would have been enormous, extremely hot, metal-free and with short lives. How do we know this?

1. The elements formed in the Big Bang were about 75% hydrogen and 25% helium.
2. Astronomers, unlike chemists, count all elements heavier than helium as metals. Traces of lithium and beryllium were also made in the Big Bang, but essentially metals aren't made until there are stars to make them.
3. The first stars had to be big and hot to get the temperature to fuse heavier elements, because hydrogen and helium aren't as efficient as metals for stellar fusion.
4. Big stars have short lives and go out with a bang, leaving behind the elements they made.

The next generations of stars (Population II) were metal poor, but seeded the Universe to provide the metal rich stars (Population I) that we have now.

Telescopes let astronomers look back in time. However, the light of early stars is too faint for optical telescopes. This is why Emma's work involves radio telescopes. The most promising radio array is a massive international project, the Square Kilometre Array (SKA) which is due to be built in South Africa and Australia. Emma noted that “the people who will be running it when it comes to the end of its lifetime aren't born yet.”

Beneath the night
Dr Stuart Clark is an award-winning author and journalist whose books have been translated into more than 20 languages. 

His latest book, Beneath the Night, explores the fascination with the night sky and the way it has influenced many aspects of human culture. His AstroFest presentation dealt with some aspects of this story, starting with astronomical evidence from prehistory. Stars and other celestial objects have been used for timekeeping for thousands of years, and medieval people saw the human body mirrored in the Universe. Based on this idea, they used astrology to treat illness.

But the scientific revolution needed proof, not just stories, and Stuart took us through the steps of providing it. Kepler's work – based on Tycho Brahe's observations – was able to describe the orbits of the planets. Newton's work showed that gravity made sense of the orbits. Halley used Newton's ideas to predict the return of a comet.

AstroFest described the presentation in the terms of the book description:
What’s up with Betelgeuse?
Dr Meridith Joyce is a Postdoctoral Fellow at the Australian National University in Canberra, Australia. Her work focuses on precision modelling of stars using the stellar structure and evolution software MESA, of which she is a developer.

Betelgeuse is a well known star. It's in Orion, an easily recognizable constellation, and it's bright and red-orange. You can see a photo in the header image.

There's also popular interest in Betelgeuse because it's the nearest star to us likely to go supernova, an event that would be a splendid spectacle. So when, in November 2019, Betelgeuse began very noticeably to dim, it got a lot of attention.

Meridith led a research team that investigated the dimming events, the original strong one and a later smaller one. Using observation and precision modelling techniques, they found out some interesting things about the star.

Betelgeuse is burning helium in the core. This means its demise as a supernova is more likely to be 100,000 years off than 10,000 years, let alone any time soon.

The final conclusion of the research was that the large dimming event was caused by a dust cloud. However, the team couldn't tell whether the cloud was self-generated by the star or came from elsewhere. The smaller brightness variations appeared to be stellar pulsations – these are pressure waves generated by the star itself.

As a bonus, the researchers also found out that Betelgeuse is smaller and with a slightly lower mass than had usually been cited. It's often been suggested that it could be bigger than the orbit of Jupiter, but the study's results say it's about two-thirds of that size. At 530 light years distance, Betelgeuse also turned out to be about 25% closer to us than previously thought.