Astronomer Prof Simon Jeffery talks about a career spent examining rare old stars and how they fit into the tapestry of our universe.

September is a busy month for the Armagh Observatory and Planetarium. The annual British Association of Planetaria, an event which began there in 1978, took place on the 1st and 2nd of the month. This was followed by an international workshop on AM CVn binaries from the 5th to 8th September. And just last week, the 11th international conference on Hot Subdwarf Stars and Related Objects took place.

This last event was organised by senior research astronomer Prof Simon Jeffery. He says the team at Armagh has been “a world-player for over 20 years” on the topic of hot subdwarf stars.

Jeffery began his astronomical career with a stint at the Royal Observatory in Edinburgh in 1976. He went on to study for a physics degree at Imperial College London and completed a PhD at the University of St Andrews on the topic of stellar structure and evolution. Here, he discusses his research and what sparked his cosmic curiosity.

Tell us about your current research.

My major work has been on stars that are approaching the end of their lives, and that have been reborn because of a merger between two stars or an explosion within the star.

These typically have surfaces devoid of hydrogen, which is the most common substance in the universe. Instead, they are extremely helium rich and incredibly rare.

Over the last 10 years, I have led a project to discover new types of helium star using the Southern African Large Telescope (SALT). Our team includes Ted, Asish and Laura from Armagh, Brent and Itumeleng, from South Africa, Vincent from the USA and Matti from Germany.

‘Astronomy is about understanding how the universe works’

We identify potential helium stars from their brightness, distance and colour. Using the SALT, we record the spectrum of each candidate. From these, we measure the star’s temperature, size and surface chemistry.

By 2020, we had observed 100 stars. This total reached 400 in late 2022 and we are aiming for nearly 800 stars by the end of 2024.

With more time devoted to the survey, we’re discovering new helium giants, heavy-metal stars, magnetic stars and super-hot white dwarfs, to name just a few.

Why is your research important?

Astronomy is about understanding how the universe works, from the Big Bang through to the emergence of life. Those massive concepts are mediated by stars, which convert hydrogen and helium into heavier elements and transfer them to new star and planet systems.

Whilst the vast majority of stars have relatively common types, as they approach the ends of their lives, their life histories become more complex, often through interactions with other stars. We cannot normally watch stars transform from one type to another, so we must guess how different types of stars are connected – rather like joining the dots – in order to see the bigger picture.

The SALT survey is a mission of discovery. It’s about finding new classes of star, most of which are extremely rare, and filling in the missing pieces to explain how hugely different and exotic stars are connected. The results will give us a clearer picture of how double stars end their lives, and hence fill in that big tapestry of how stars behave and the universe works.

What inspired you to become a researcher?

As a small child, I was curious and asked questions like, ‘Why is the Moon?’ Both of my grandmothers were teachers and encouraged my interest in mathematics.

I recall reading a magazine article about stellar evolution when I was about 7 years old. This was in 1965 when the first computer models of red-giant stars were still very new. My grandfather was an engineer and taught me how to use machine tools and build motors.

As a teenager I was fascinated by subatomic and nuclear physics. However, the strongest driver was a friend who hired me to work at the Royal Observatory, Edinburgh, during my gap year.

There, I learnt to read papers, program computers, challenge others’ results, study for myself, listen to research seminars, and debate with other students. I also met famous scientists, and I think it was there that I determined to study stellar evolution.

What are some of the biggest challenges or misconceptions you face as a researcher in your field?

I count myself fortunate to have had a fantastic job, working with amazing people for all my career. However, the early years were extremely challenging and involved a succession of short-term contracts and associated job insecurity whilst I was raising a young family.

These pressures also apply to young scientists today and I have seen exceptional talents leave science for more secure careers.

A more general challenge is to explain just what I do. The job is so much more technical than sitting at the eyepiece of a telescope, and yet it all starts with someone building and operating amazing telescopes.

The process, from requesting an observation, to receiving the data, to building models to analyse and interpret the data, and then to finally publishing the results, can take years, if not decades!

Do you think public engagement with science has changed in recent years?

Covid-19 led to an unprecedented scientific effort to understand the disease and to find vaccines, and this has brought science into the public gaze as never before. Astronomy provides countless opportunities to showcase science in action.

The Armagh Observatory and Planetarium is the oldest scientific institution in Northern Ireland, and the longest continuously operating astronomical research institute in the United Kingdom and Ireland. Here, we are dedicated to encouraging public engagement with science and to inspiring the next generation of STEM leaders through our education and outreach programmes.

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By mrtrv