Dr. Cole Johnston

Hello and welcome to my ramblings about stars, which are objectively the best part of astronomy.

Stellar evolution

Stars are the cosmic engines of the Universe. Understanding how stars evolve and provide chemical and dynamical feedback to their local environments is fundamental to all fields of astronomy.

However, there are a lot of physics that go into how stars evolve, including rotation, convective overshooting, tides, magnetism, etc. I work on figuring out how to best implement these physics into models of stellar evolution!

Johnston C. 2021


Just like how the Earth has earthquakes, stars have starquakes. And analogously to how the size, shape, and composition of a bell determines the frequency with which a bell rings — the size, shape, and composition of a star determines how the star rings, or pulsates. Using the frequencies of stellar pulsations in order to investigate the interiors of stars is known as asteroseismology. I use asteroseismology to help calibrate different physics in stellar evolution models!

Aerts et al. 2010

Multiple systems

It turns out that most stars actually come in pairs, triples, or larger groups! Something like ~30% of stars like our Sun have a companion. But, we actually think that more massive stars always come in pairs or even in groups of several stars.

This is actually really important because pairs of stars, otherwise known as binary stars can do some really weird things, like cause each other to spin faster and even transfer mass to one another. Processes such as these are thought to be really important for producing exotic things such as black-hole binaries and their progenitors. I study these stars to understand how massive binaries can produce extreme systems such as black-hole binaries.

Eisner et al. 2022


BlackGEM is an array of telescopes located in Chile that are tying to find the optical counterparts to gravitational-wave events! In order to search for these rare events, BlackGEM has to scan the entire Southern night sky every night. Because of this, there is a TON of data on stars! I use these data to hunt for pulsating stars, binaries, and other weird star systems such as compact objects.