Astroseismology: using stellar pulsations to look inside stars.

Tuesday 18th April, 2017

Our speaker was Dr Amanda Doyle from Warwick University who had come to talk to us about "Asteroseismology: using stellar pulsations to look inside stars". She explained that for her doctoral thesis she had studied how stars like our own Sun pulsate and became quite fascinated by the subject. She said that she first became interested in astronomy from around the age of twelve and when she is not researching the various properties of stars she works as a freelance science writer. Many of her articles have been published in astronomy magazines such as "Astronomy Now" and "Sky at Night" and she is also editor of "Popular Astronomy" magazine.

Dr Doyle began by saying that the word astroseismology is derived from two ancient Greek words — "aster" meaning star and "seismos" meaning a shaking. For, just as geologists can study the internal structure of the Earth by analysing the various waves given off by earthquakes so she can understand the structure of stars by looking at their vibrations. In fact the stellar pulsations are sometimes referred to as "starquakes".

She noted that it is more straightforward for the geologists as they can just place measuring equipment directly on the Earth's surface but it is not possible to place any instruments of the Sun's surface. However, a star's internal vibrations do affect the light that it emits and so a star's internal pulsations can still be revealed by studying its starlight.

She explained that the first dedicated spacecraft to study stellar pulsations was Canadian and called "MOST" (Microvariability and Oscillations of Stars). This small satellite, the size of a large suitcase, was launched in 2003 into an orbit around the Earth and its mission lasted another 11 years. Then in 2006 The French space agency (CNES) with help from the European Space Agency (ESA) launched the CoRoT spacecraft (COnvection ROtation et Transits planétaires). Although one of its main science objectives was to discover distant planets around other stars (i.e. exoplanets) it also looked at how the stars oscillated. Unfortunately, the spacecraft suffered a critical malfunction in 2012 and ended up being deorbited, burning up in the Earth's atmosphere.

Dr Doyle then said that it was NASA's Kepler spacecraft, launched in 2009, that had really expanded our knowledge of stars' interiors and their properties. Like CoRoT, its main aim was to search for exoplanets but it was also capable of studying starquakes. By carefully studying the light from a star scientists can accurately measure the star's radius and mass as well as its age and chemical composition.

There are a couple of upcoming missions that will further our knowledge of stars and their behaviour. The first is a spacecraft named TESS (Transiting Exoplanet Survey Satellite) which is scheduled to launch in March 2018. Its primary science goal is to find and study exoplanets by noticing the drop in light as they cross their parent star but data from the starlight can be examined to see the star pulsating. The other mission is called PLATO (Planetary Transits and Oscillations of stars) and has a proposed launch date of 2025. Again, its first objective is to search out and study exoplanets but it will also be able to examine the central star's oscillations.