Finland (University of Helsinki) How does ordinary matter behave when it is compressed without limit?

What are your research topics?

I study how ordinary atomic matter behaves when it is compressed without limit. This seemingly childish question is highly relevant in the study of neutron stars, the remnants of supernova explosions that occur when an old hydrogen-burning star reaches the end of its life cycle. Inside neutron stars, even atoms have collapsed due to the star’s immense gravitational field.

In the cores of the most massive neutron stars, the density of matter greatly exceeds that of individual nucleons, which may be sufficient for the formation of an entirely new state of matter – cold and dense quark matter, composed of individual quarks and gluons.

Where and how does the topic of your research have an impact?

My research belongs to the field of theoretical particle physics and represents purely curiosity-driven research in the sense that our findings are very unlikely to have any direct impact on our everyday lives.

At the same time, such curiosity-driven research has, sometimes through happenstance, led to many of the most useful discoveries from penicillin to the world wide web. Needless to say, I can’t promise such results from my own research, but at least my research group constantly produces talented young theoretical physicists with a solid foundation in mathematical problem-solving.

In addition, the research questions of particle physics are of course interesting in their own right, and answering them improves our understanding of how Nature works at its smallest length scales.

What is particularly inspiring in your field right now?

The physics of neutron stars is an extremely hot topic right now thanks to a number of recent observational results that have largely revolutionised the field. The most famous of these is a gravitational wave signal from a neutron star merger that originated over 100 million years ago and was observed on Earth by the LIGO and Virgo collaborations in 2017.

From more recent observations, the most useful one is perhaps the accurate measurements of the mass and radius of one particularly heavy neutron star by the NICER collaboration in 2021. Thanks to it, we now know that the radius of a neutron star with a mass slightly above two solar masses is very likely between 12 and 13 kilometres.

The main goal of my own current research is showing that the cores of the heaviest stable neutron stars contain quark matter, which we pursue by comparing state-of-the-art particle and nuclear theory predictions with the latest astrophysical observations.