About Me

Portugal, 2012.
Portugal, 2012.

I’m an astronomer at the Harvard-Smithsonian Center for Astrophysics. These days I spend most of my time studying “extrasolar magnetospheres” — the magnetic fields of cool bodies beyond the Solar System. My work has shown that very small stars and also “brown dwarfs,” the balls of gas that are between stars and planets in size, have magnetic fields that are quite similar to the ones we find planets around Earth and Jupiter — they’re just hundreds of times stronger! These magnetic fields drive a rich phenomenology of space plasma physics and tell us about the internal structure of these bodies.

It’s usually hard to detect a magnetic field from afar, but extrasolar magnetospheres are commonly associated with “auroral” processes that are exactly what they sound like: scaled-up versions of our own Northern and Southern Lights. We can’t detect visible light from these processes, but it turns out that they also produce distinctive bursts of radio emission that are so intense that we can detect them at interstellar distances (the Earth analog is called AKR). My core scientific training is in the field of radio astronomy and I have long been involved in the broader radio astronomical community.

One of the most exciting trends in this area is the push to be able to study smaller and smaller bodies, with the goal of studying the magnetic fields of planets around other stars. We really have no idea what other planets’ magnetic fields might look like, but they mediate the interaction between planets’ atmospheres and their host stars’ winds, so understanding exoplanetary magnetic fields is a key element of understanding habitability. We expect the radio bursts from bona fide planets to come at relatively low radio frequencies, so I have become the lead time-domain scientist of the Hydrogen Epoch of Reionization Array, HERA, a low-frequency radio telescope under construction in South Africa. While HERA’s main scientific goal is literally about probing the other end of the Universe, HERA also has the right attributes to be an amazing planetary magnetometer.

Studying the magnetic fields of very small stars also sheds light on some broader features of stellar astrophysics. I investigate the aging and internal structures of the smallest stars by combining my radio observations with data in the infrared, optical, ultraviolet, and X-ray taken with a whole host of observatories, from Hubble to Chandra to ALMA.

I got into this work through the field of “time-domain radio astronomy,” the general study of changes in the radio sky. We have long known that the radio sky is a dynamic place, sometimes with Nobel-prize-worthy consequences, but the technological developments of the past couple of decades have transformed our ability to study it. One of the most exciting breakthroughs in this area is the unexpected discovery of Fast Radio Bursts (FRBs), extremely bright and rapid pulses of radio emission that have signatures suggesting they come from well across the Universe. I’m working to pin down the origins of FRBs by understanding the astrophysical context in which they arise.

Finally, I’ve always been interested in computers, scientific communication, and especially the intersection between the two. I write my talks in HTML which allows me to include fancy interactive animations. I have spent more time in the guts of TeX than any person really ought to, including launching the Tectonic Project, which extends and reworks TeX in some key ways with the goal of providing the 21st-century typesetting system for technical documents — both print and electronic — that scientists, engineers, and in fact everyone deserves.

Because there are a lot of P. Williamses out there, I try to go by Peter K. G. Williams in my publications.

I also do things that aren’t science! But this isn’t the website for talking about that.


My CfA office is Perkin 327. My work email address is pwilliams@cfa.harvard.edu (though it just forwards to my personal address, peter@newton.cx). My postal address and phone number are listed on my CV.