Today is the one-year anniversary of the death of Professor Don Backer, an astronomer at the University of California, Berkeley. I was a friend, colleague and collaborator of Don, and I never had the chance to appropriately memorialize him on that sad day a year ago.

Don was a great radio astronomer who understood both the technical details of the equipment that he used, as well as the new science enabled by that technology. He was best known for having discovered the first millisecond pulsar — a neutron star more massive than the sun and only tens of miles across, spinning at over 1000 revolutions per second.

Millisecond pulsars are exquisite clocks, comparable to the best that can be built on earth. We can use that to not only measure the properties of the pulsar itself, but also to monitor the spacetime in between the pulsar and the earth. That’s how I got to work with Don: he was interested in using pulsar timing to measure gravitational waves from the collisions of supermassive black holes at the centers of galaxies throughout the Universe, as their host galaxies merge and grow over time. We calculated the expected signal from those sources and made some predictions for how they might be detected by future pulsar observations.

Today at Imperial, on this sad anniversary, we had a talk from Professor Andrea Lommen from Franklin and Marshall College, one of Don’s former students, who has dedicated her recent career to the detection of gravitational radiation using a Pulsar Timing Array. That this field, based on Don’s original discovery as well his subsequent ideas, has grown to a world-wide effort, is testament to his energy and excellence as a science.

In addition to that energy and excellence, I remember Don as a patient mentor when I was a postdoc looking for a permanent job, as good at listening and asking questions as explaining to a naive theorist those many experimental details that he understood better than anyone. This questioning on small and large scales led him into new fields and new questions; over the last few years he became interested in the PAPER experiment, observing 21 cm radiation which can trace the evolution of gas in the Universe over billions of years.

As scientists we continue to miss his contributions to these and other fields, and as his friends we just miss him.