Jonathan Tan
​Jonathan Tan, Professor in Astrophysics at the Department of Space, Earth and Environment, one of two astronomers at Chalmers who has been awarded the prestigious ERC Advanced Grant in 2018. ​​
​Photo: Johan Bodell. 

A star is born - but how?

Jonathan Tan, professor in Astrophysics, is one of two astronomers at Chalmers University of Technology to be awarded an ERC Advanced Grant for €2,5 million, in 2018. His research group will focus on massive star formation – in current times, as well as in the very early days of the Universe. 
– Without massive stars, life as we know it would not be possible, since many important chemical elements are created in massive stars and released into space when they ultimately explode in supernovae. We hope to answer some of the numerous open questions about the birth of massive stars in this project, says Jonathan Tan, at the department of Space, Earth and Environment at Chalmers. 
The project, which will be funded by ERC, the European Research Council for five years, is called MSTAR - Massive star formation through the universe, and while it is focused on how massive stars are born, Jonathan 
hopes his group will be able to use their results to better understand the complete life cycle of stars, star clusters and the interstellar medium in galaxies. 
 
The life cycle of a star is determined by its mass. While our Sun will eventually end up as a so called white dwarf, a massive star – with eight times the mass of the sun or more – will evolve into a nuclear fusion “factory”, which produces heavier and heavier elements in its core until it ultimately explodes as a supernova, releasing the elements into the interstellar medium. 

– The oxygen that we breath and the iron in our blood have been made in previous generations of massive stars. About 4.6 billion years ago these elements were incorporated into the Earth and eventually into our bodies. This is just a couple of examples of how without massive stars, life would not have been possible, and thus one of the main reasons why we are interested in studying these stars. 

Models and observations
Jonathan’s group will develop models of the evolutionary sequence of how massive stars form and then make observations from several telescopes to test the modeled sequence – and develop it further to test formation theories.

– Theoretical modelling is an essential part, since we will never have a chance to see the birth process or evolution of a single star in our lifetime. Then, observationally we will choose a demographic approach and sample many sources that are forming in our Galaxy. 

And like a demographer would understand a human population by seeing how many young kids there are, how many middle aged and so on, the astronomers will do the same to different populations of massive stars in varying stages, to get an understanding of the life cycle. 

– The creation and life cycle of a massive star is a very complicated process, but if we develop the models properly we can obtain a good understanding of reality.  

New and powerful telescopes, like the ALMA telescope in Chile and the forthcoming James Webb Space Telescope, will make observations that can test the models and also help understanding if the life cycles of massive stars vary in different galactic environments. 

The project will also explore new theoretical models for how the very first stars in the universe were formed. One theory is that very early supermassive stars (with a mass of one million times the sun) could be the origin of supermassive black holes – like the one in the center of the Milky Way – one of the key unsolved problems in astrophysics.  

Supermassive black holes are also in focus for the other astronomy project at Chalmers project to receive funding from ERC this year. Susanne Aalto, professor and head of the division Astronomy and Plasma Physics, will lead the research project HIDDeN, which will explore how supermassive black holes – like the one in the middle of the Milky Way – grow together with their host galaxies. (Read more about Susanne Aalto's project HIDDeN​). 

A continuing team effort
The ERC grant for MSTAR will be used to expand Jonathan’s research group by recruiting PhD students and post doctoral researchers. It will also allow the researchers at Chalmers to expand their network in the world of astronomers. Apart from an international conference hosted by Jonathan’s group at Chalmers next year, there will also be a visitor’s program for international researchers coming to Chalmers and Onsala Space Observatory.

– It is not possible for one group to answer all the questions we are aiming for. We will build a core team here at Chalmers, but already in writing the proposal we involved many collaborators from around the world, so this will be a team effort all the way.  

And while on the subject of teamwork, Jonathan has also started an interdisciplinary initiative on Cosmic Origins which will be a collaborative effort between Chalmers and the University of Virginia in the  USA. 

– We are building up a group in each university and are trying to link the two together. It’s mostly involving astronomers, but also chemists, and environmental, computational and material scientists. The goal is to investigate all processes that relate to Cosmic Origins, by which we mean the formation of galaxies, stars, planets and even molecules – with the long-term goal of trying to understand the origins of life in the universe. (Read more on the Chalmers & Virginia Initiatives on Cosmic Origins)

Text: Christian Löwhagen. 

Published: Thu 05 Apr 2018. Modified: Fri 06 Apr 2018