Research Interests: Globular clusters, stellar populations, evolution of galaxies

William Harris and The Big Picture

My main research interests are in the earliest stages of galaxy evolution — the first few Gigayears of a galaxy’s history during which structures like its halo stars and globular clusters emerged. Their properties yield unique clues to the most active part of galaxy formation. See my webpage for more, but here’s a shortlist of projects I’m currently involved with:

Hubble Space Telescope imaging of a series of supergiant elliptical galaxies in the cosmologically “nearby” universe at distances from 40 to 200 Megaparsecs.¬† These giants have the largest globular cluster populations known (tens of thousands of clusters per galaxy) and with this data, our team is building up the biggest photometric database for globular clusters in existence.¬† With this material we are exploring patterns in the distributions of globular cluster luminosity, heavy-element enrichment, and spatial distributions in their galaxy halos — all of which are tracers of their formation epoch.

Correlations between globular cluster populations and other large-scale properties of their host galaxies, including dynamical mass, galaxy type, and (very puzzlingly) their central supermassive black holes.

Dynamics and assembly history of groups of galaxies over the redshift range z=0 to 1.

Photometry and modelling of the halo-star populations in nearby galaxies such as M33, NGC 5128, and M87.

Developing hydrodynamic modelling for the formation of massive star clusters.¬† The formation stage of “true” globular clusters (in the mass range of 0.1 to 10 million Solar masses) from their parent molecular clouds is the least well understood, but also most crucial, stage in their histories, and is likely to have produced important feedback on the larger-scale star formation history of the entire galaxy.

Research Interests: Electron systems, including high temperature superconductors, frustrated antiferromagnets, and quantum Hall systems

Catherine works in the general area of Quantum Condensed Matter Theory. Her current research is primarily on quantum magnets and novel superconductors, including high temperature superconductors and chiral superconductors that may exhibit topological order. More information about her research group and activities can be found on her website.

Art is by Pamela Davis Kivelson.

Research Interests: Development of radiation-based biomedical devices for the painless, in vivo measurement of toxic metals such as Pb, As, F, Al and Gd in bone, liver, and kidney.

Trace Toxic Elements

The main focus of my research is the development of biomedical devices based on radiation physics techniques for the in vivo measurement of trace toxic elements. In the last few years, my graduate students have built the first in vivo systems in the world for the painless, non-invasive and low dose measurement of arsenic, gadolinium and fluoride. We use two main techniques for these devices; neutron activation analysis (NAA) and x-ray fluorescence (XRF) analysis.

In addition to building biomedical systems, I apply them to studies of human health and exposure. My research has helped the understanding of human health effects from lead (Pb) exposure; my work has shown that Pb can result in elevated blood pressure and early menopause in women. Recently we discovered that people living in Hamilton have measurable levels of fluoride in their bones and a major source of exposure is tea drinking. We have been studying gadolinium and this element is used in image enhancement drugs for MRI. The Gd may be detaching from the chelate which could be potentially toxic, so we are developing systems to measure long term uptake of detached Gd in bone.

Some of the reasons I study toxic metals are explained in the Research2Reality video which can be found at http://research2reality.com/video-categories/health/ under ‘measuring health effects of metal exposure’.

Radiation Tools in Cultural Heritage

In recent years, I have used radiation tools in the study of art and cultural heritage. I was a member of a team who studied nine works of art from the McMaster Museum of Art. This resulted in an exhibition, The Unvarnished Truth: Exploring the Material History of Paintings, which is travelling across Canada until 2017. The work is also presented in the interactive website http://theunvarnishedtruth.mcmaster.ca/ .

Low Dose Radiation Effects

For the last few years, I have been collaborating with Professors Colin Seymour and Carmel Mothersill from the Department of Biology. We have been studying the effects of low level exposure to radiation types that include x- and Œ?-rays and neutrons. We have recently shown that cells, when exposed to radiation, emit a UV signal which can cause effects in nearby cells that were not exposed to the initial radiation. The UV causes a ‚Äòhalo‚Äô of effect. We are continuing to explore whether this UV signaling is an important aspect of low dose radiation effects.

Research Interests: Star formation, planet formation, astrobiology

I am a theoretical astrophysicist and my research focuses on star and planet formation. I completed my undergraduate studies at UBC in mathematics and physics. I then moved to the University of Toronto for my M. Sc. (in theoretical physics). I returned to UBC to do my Ph.D. in astrophysics under the supervision of Greg Fahlman, completing it in 1980. I took up an NSERC Postdoctoral Fellowship at the Institute of Astronomy in Cambridge (England). I went on to further postdoctoral research with Chris McKee and Jon Arons at the Astronomy Dept. at Berkeley, and with Colin Norman at the Johns Hopkins University. I joined the faculty at McMaster in 1986. Research Leaves and Fellowships over the subsequent years have taken me to many outstanding research centres including the Observatoire de Grenoble (1988, 1992), the Max-Planck Inst. for Astronomy in Heidelberg (1993), the Harvard-Smithsonian Center for Astrophysics (1993), the Max-Planck Institute for Astrophysics in Munich (1997), the Canadian Institute for Theoretical Astrophysics (CITA) in Toronto (1990 and 1997), Caltech (2001), and the Kavli Institute for Theoretical Physics (KITP) in Santa Barbara (2007/08).

I have been involved in many aspects of Canadian as well as international astronomy and astrophysics, having served on Time Allocation Committees (CFHT and JCMT), NRC Science Advisory Committees (Gemini, JWST), Visiting Committees (U.S. NRAO), Advisory Boards (HIA, CITA Council), and review committees. I chaired Canada’s decadal survey of Astronomy and Astrophysics – the NRC-NSERC Long Range Planning Panel (1998/2000) – and was the principal author of the LRP report; “The Origins of Structure in the Universe”. The LRP is playing the central role in guiding the development of Canadian astronomy in this decade and beyond, having involved Canada in ALMA, JWST, TMT, SKA, and several other important space and ground based telescopes and observatories.

Most recently, I spear-headed and am the founding (2004) Director of McMaster’s Origins Institute (OI). Its scientific mission is to engage in fundamental transdisciplinary research on the origin of structure and life in the cosmos. The scientific themes of the OI cover 6 broad themes in science: the origin of space and time (cosmology, early universe), structure in the universe (planets, stars and galaxies), the elements, life (astrobiology), species and biodiversity, and humanity. In addition to its research foci, the OI has developed a novel OI Undergraduate Research specialization. The OI is committed to public outreach and education through its award winning OI Public Lecture series and played an important role in the creation of the McMaster 3D theatre. The OI has also run major international annual scientific conferences on some of the most important questions in contemporary science.

Supervisor Letter:

Ralph Pudritz
Department of Physics & Astronomy
McMaster University

Dear Prospective Research Students:
My research focuses on the theoretical and computational study of star and planet formation, and astrophysical and planetary aspects of the origin of life including experimental work in our Origins of Life Lab. Star formation impacts a huge range of astophysics – from planet formation to galaxy formation and evolution and cosmology. Stars and planets form in protostellar disks and there are very deep connections between these subjects through them. The discovery of over 4000 exoplanets is driving a major revolution in astrophysics as we try to develop new theoretical models that can explain the wealth of new data and planetary populations ‚Äì such as the dominant SuperEarths. The characterization of the composition of the atmospheres of rocky exoplanets is one of the main drivers for our search for life in the universe. Members of my group perform a wide range of state of the art, high performance computing simulations of star formation ‚Äì from galaxy scales down to individual stars forming in their protostellar disks; planet formation and the properties of exosolar planets and their atmospheres; and work on early Earth and prebiotic physics and chemistry that lead to the origins of RNA. We connect our work with exciting observations from new observatories such as the James Webb Space Telescope, as well as the ALMA millimeter observatory https://www.eso.org/public/teles-instr/alma/ allow us to connect the work with new observations. I am also the Co-Investigator for our Origins of Life Laboratory in McMaster’s Origins Institute https://origins.mcmaster.ca/research/origins-of-life-laboratory/

There are many exciting research opportunities in my group. In addition to individual meetings, I have regular group meetings every week in which everyone discusses their results and ideas. Students and postdocs at all levels are well connected to one another as well as with the many external collaborators across the world, that we work with.

Research topics in my group:
Star Formation explores a wide range of interconnected problems starting from the scale of the formation of molecular clouds in galaxies, down to filamentary structure of molecular clouds, to the formation of star clusters within them, to the collapse of individual gas “cores” within such clustered environments (to form single or binary stars), and on down to the physics of protostellar disks through which gas accretes onto their central stars and from which highly collimated jets are launched. Much of the research involves state of the art 3D numerical simulations, most recently using the RAMSES Adaptive Mesh Refinement code. We are currently using RAMSES for multiscale galaxy simulations that allow us to trace star formation in magnetized galaxies all the way from cloud formation on many kpc scales, through to star clusters and over the next year or two ‚Äì down to the 100 AU scales needed to study massive star formation in clusters. See recent articles:

-Star formation in filamentary molecular clouds and a new paradigm for star formation: see our review Andr?® et al, (2014): https://arxiv.org/pdf/1312.6232.pdf
– The formation of massive stars: Klassen, Pudritz et al (2016):
https://arxiv.org/pdf/1603.07345.pdf
– The formation of star clusters: Howard, Pudritz, & Harris ( 2018):
https://arxiv.org/ftp/arxiv/papers/1808/1808.07080.pdf
-Theory and simulations of protostellar jets and outflows: see review Pudritz and Ray (2019):
https://arxiv.org/pdf/1912.05605.pdf

Planet Formation: is arguably one of the hottest topics in astrophysics, and indeed science, today. In my group we are investigating all aspects of planet formation, connection how planets form in protostellar disks, to their final orbits and chemical compositions. This “end-to-end” approach can be used to predict the composition of exoplanet atmospheres, which will be observed for the first time with JWST. This research involves theoretical work, as well as extensive use of astrochemistry codes and population synthesis simulations. Some recent papers in my group include:

• ‚Ä¢ A theory for planet traps and the migration of forming planets in disks (2011): https://arxiv.org/pdf/1105.4015.pdf
  • Linking the composition of atmospheres to planet formation (2016): https://arxiv.org/pdf/1605.09407.pdf
  • The combined effects of disk winds and turbulence for planet formation and composition (2022): https://arxiv.org/pdf/2207.01626.pdf
  • Bifurcation of planet formation histories (2022): https://arxiv.org/pdf/2111.01798.pdf

Origins of life: focuses on the connection between protostellar disks, and the properties of pre-biotic chemistry on newly formed habitable planets. Nucleobases, amino acids, and fatty acids are found in meteorites and can be synthesized in 100 km parent bodies – planetesimals – which are also the building blocks of terrestrial planets. We have done calculations to show how these molecules are synthesized within planetesimals. Recent work focuses on understanding how meteoritic delivered biomolecules evolve on early planetary conditions, to result in the formation of RNA polymers – the first genetic materials. See our recent article:
• Fate of nucleobases in warm little ponds, upon delivery by meteorites to the Early Earth, see our Cozzarrelli prize paper; (2017): https://arxiv.org/pdf/1710.00434.pdf
• HCN synthesis in early Earth atmospheres leading to biomolecule formation (2022): https://arxiv.org/pdf/2201.00829.pdf

I have many interesting research projects within this broad set of themes. I will be happy to discuss these with you. If you are interested, please send me e-mail at pudritz@physics.mcmaster.ca or consult my departmental home page. I look forward to hearing from you!

With best wishes,
Ralph Pudritz

Research Interests: Light Echoes from luminous transient events like supernovae

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.”

Supervisor Letter:

Dear Prospective Graduate Student,

I am not in a position to recruit additional graduate students for the academic year beginning September 1, 2024. Nonetheless, should you be accepted at that time and your primary supervisor sees value in my knowledge and expertise, I may be available to serve on your supervisory committee.

Since you have read this far, I will take this opportunity to introduce myself more completely! 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, members of 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.

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 was then 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 was Brendan Sinnott whose Ph.D. thesis topic was determining the degree of asymmetry in the supernova SN 1987A from light echo spectroscopy.

In the last few years, I have been working on machine learning techniques to detect light echoes from large, wide-field survey facilities, including MegaCam on the Canada-France-Hawaii Telescope, DECam on NOIRLab’s Blanco 4-meter telescope at Cerro Tololo in Chile, and the Dragonfly Telephoto Array – a special-purpose facility located at New Mexico Skies which has the best low surface brightness sensitivity in the world.

Best regards,
Doug