Doug Welch's first glimpse of Saturn through a low-tech telescope when he was eight years old was all it took to inspire a lifelong fascination with astronomy. He is now a professor in the Department of Physics and Astronomy at McMaster University, where he studies the faint reflected light of exploding stars, known as supernova light echoes, and other cosmological phenomena.

"A supernova is one of the most influential events in the universe," said Welch. "The vast majority of elements more massive than helium are created by massive star supernovae. These elements make up much of our own bodies. Supernovae change how quickly new stars can form, and they can actually trigger the formation of new stars when they blow up." 

When certain stars die, they go out with a bang. There are two ways in which supernovae occur: one is a massive star that can no longer produce energy through nuclear fusion and collapses; the other is a white dwarf, which siphons off mass from an orbiting companion star. When the mass of a white dwarf reaches a certain level, it becomes unstable and blows up, producing a very distinct mix of elements.

In a given galaxy, supernovae are rare occurrences (only six have been observed in the past 2,000 years in the part of our galaxy which is visible from the position of the sun), but they can provide a wealth of information about the universe. Although hundreds of years have passed since the last supernova visible to the unaided eye exploded in our galaxy in 1604, astronomers can still study supernova light echoes, which are produced by light from the outbursts that are scattered toward Earth by interstellar dust. The longer path taken by the scattered light allows astronomers to study these centuries-old supernova outbursts with modern instruments.

"The supernova light echoes were the result of a dark matter search where we found a source of noise that we initially couldn't understand," Welch explained. "That 'noise' ended up being light echoes from ancient supernovae."

Welch shares his interest in astronomy through public outreach. He coordinated the purchase of new projectors for the William J. McCallion Planetarium, which hosts public astronomy shows for children and adults. He is also part of the Slacker Astronomy podcast available on iTunes (www.slackerastronomy.org).

The department is "very much a community of like-minded people," said Welch. "The thing that makes academic jobs fantastically better than most other jobs is that you're always bumping into new people, new ideas and you're always learning." He credits his undergraduate and graduate students with keeping him on his toes. "You're always being challenged in a way that never gets old."

Light Echoes from luminous transient events like supernovae

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Dear Prospective Graduate Student,

I am an observational astronomer who studies supernovae light echoes and variable stars. I have also been a member of the Science Team of the MACHO Project and SuperMACHO Project whose goals have been to determine the fraction of dark matter in massive, compact objects. The SuperMACHO Project discovered light echoes around centuries-old supernova remnants in the Large Magellanic Cloud - a finding that has made it possible to link remnants with supernova outburst light classifications. Since that time, my group and I have been working in collaboration with Armin Rest (STScI) to locate and study supernova light echoes from historical supernovae in the Milky Way and to study pre-supernova candidates such as eta Carinae.

I am looking for one or two M.Sc. or Ph.D. students to begin in September 2016.

My approach to supervision is one where my students are encouraged to enter the research arena as early as possible. My former Ph.D. students have been very successful at applying for large telescope time for their thesis observations as Principal Investigators ("PIs"). In addition, I send my students to as many relevant meetings as possible - as long as they have a publishable result to present! I attempt to ensure that any worthwhile research program which can convince a time allocation committee will be financially supported. I make it my policy to not stand in the way of good students with good ideas!

My first two Ph.D. students were Phil Fischer and Patrick Cote. Phil obtained an NSERC PDF which he took at AT&T Bell Labs with Tony Tyson. Subsequently, he was awarded a NASA Hubble Postdoctoral Fellowship which he took at the Department of Astronomy at the University of Michigan at Ann Arbor. He worked as a research associate at CITA thereafter, and is currently employed by ScotiaCapital in the Trade Floor Risk Management Department. After defending his Ph.D. thesis, Pat became a Research Associate at the National Research Council's Dominion Astrophysical Observatory in Victoria, BC. He, too, was offered a NASA Hubble Postdoctoral Fellowship but turned it down in favor of a Sherman Fairchild Prize Fellowship at Caltech. He then became a tenure-track Assistant Professor at Rutgers. In July 2004, he moved to the Dominion Astrophysical Observatory of the National Research Council's Herzberg Institute of Astrophysics where he is now a Senior Research Officer.

My most recently-graduated Ph.D. student is Brendan Sinnott whose Ph.D. thesis topic was determining the degree of asymmetry in the supernova SN 1987A from light echo spectroscopy.

Please contact me at welch@physics.mcmaster.ca if you think your research interests overlap with mine or if you have other questions.

Best regards,
Doug