Featured – Canadian Institute for Theoretical Astrophysics The Canadian Institute for Theoretical Astrophysics is a nationally supported research centre located at the University of Toronto that is devoted to studying the origin and evolution of the universe, and the many wonderful phenomena revealed by modern astronomy. Thu, 22 Oct 2026 01:02:33 +0000 en-US hourly 1 https://wordpress.org/?v=6.9.10 Turtles all the way down: towards a new paradigm for galaxy formation and cosmology /turtles-all-the-way-down-towards-a-new-paradigm-for-galaxy-formation-and-cosmology/ /turtles-all-the-way-down-towards-a-new-paradigm-for-galaxy-formation-and-cosmology/#respond Fri, 16 Oct 2026 19:42:40 +0000 /?p=19300 Turtles all the way down: towards a new paradigm for galaxy formation and cosmology

Seminar by Rachel Somerville, CCA, Flatiron Institute

Monday, October 19, 2026, 3 PM in MP1318A/ Zoom

A new generation of multi-tracer surveys has the potential to yield huge progress in our understanding of galaxy formation and cosmology, but only if we can overcome certain challenges. These include accurately modeling the intertwined effects of baryonic processes and the nature of dark matter and dark energy, as well as incorporating diverse types of data and observational tracers into a robust statistical framework. I will discuss how my collaborators and I are working towards building more robust, physically motivated sub-grid models for star formation, stellar feedback, and black hole formation and growth. I will describe the status of our efforts to use these new models to train accelerated forward models using machine learning, create detailed multi-probe synthetic observations, and fold all of these elements into a Simulation Based Inference pipeline, with the ultimate goal of constraining galaxy formation, cosmology, and the initial conditions that gave rise to our Universe.

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Welcoming the 2026 Cohort of CITA Fellows /welcoming-the-2026-cohort-of-cita-fellows/ /welcoming-the-2026-cohort-of-cita-fellows/#respond Fri, 16 Oct 2026 19:08:27 +0000 /?p=19292 Welcoming the 2026 Cohort of CITA Fellows

 

CITA extends a warm welcome to our incoming Fellows and National Fellows. This Fall we are joined by an unprecedented number of talented Postdoctoral and National Fellows. We are committed to providing post-doctoral training for early career researchers in the field of Theoretical Astrophysics and are excited about the contributions these outstanding researchers will bring to CITA.


Weikai Cui

Dr. Weikai Cui joined CITA as a Postdoctoral Fellow in October 2026 after earning his doctorate from the University of Virginia in 2026. His research focuses on astrochemistry, interstellar molecules, chemical processes in the interstellar medium, and reactions occurring on icy grain surfaces. His work combines theoretical and computational chemistry with astrophysical applications to understand the molecular evolution of interstellar environments and the chemical processes that precede star and planet formation.

Paul Huet

Dr. Paul Huet is joining CITA as a Postdoctoral Fellow in November 2026, after earning his doctoral degree at the Paris Observatory. His research focuses on planetary formation, planetary atmospheres, protoplanetary and debris disks, gas accretion onto planets, numerical modeling and observations, and exoplanets. His work combines numerical modeling with observations to investigate the formation and evolution of planetary systems, including the interaction between planets and their surrounding gaseous and dusty environments.

Sóley Hyman

Dr. Sóley Hyman is a CITA National Fellow at Queen’s University. She earned her Ph.D. from the University of Arizona in 2026. Her research focuses on galaxy dynamics, stellar orbits, chaos, and computational methods, with particular interest in the internal dynamics of galaxies. She studies how evolving stellar orbits drive morphological changes in galaxy simulations, including the role of chaotic stellar orbits in the evolution of bars and boxy-peanut-X (BPX) structures in disk galaxies.

Christian Kragh Jespersen

Dr. Christian Kragh Jespersen is a CITA National Fellow and Schmidt AI in Science Fellow. His research focuses on galaxy evolution, astrostatistics, machine learning, and spectroscopy. He develops statistical and machine-learning methods for studying how galaxies and dark-matter halos form and cluster, with research spanning JWST observations of early galaxies to the study of Earth’s own night-sky glow. His work combines astronomical observations with statistical and computational methods to extract physical information from large datasets.

Xuan Ji

Dr. Xuan Ji joined CITA as a Postdoctoral Fellow in October 2026, after receiving her Ph.D. in Geophysical Sciences from the University of Chicago in 2026. Her research focuses on rocky exoplanet atmospheres, climate, and habitability. She uses both low-order mathematical models and numerical simulations to study the coupled dynamics of small rocky exoplanets’ interiors, atmospheres, and orbits. At CITA, she will contribute to an international effort to develop next-generation computational frameworks that connect physics-based models of exoplanet interiors and atmospheres with limited observations.

Ilija Medan

Dr. Ilija Medan joined CITA as a Postdoctoral Fellow in July 2026. He earned his Ph.D. from Georgia State University in 2023 under the supervision of Dr. Sébastien Lépine and subsequently served as a VIDA Postdoctoral Fellow at Vanderbilt University from 2023 to 2026 under the supervision of Dr. Keivan Stassun. His research focuses on low-mass stars, the Solar Neighborhood and stellar populations, binary stars, spectroscopic surveys, astroinformatics and astrostatistics, and Milky Way chemodynamics. At CITA, he works under the advisement of Dr. Juna Kollmeier and contributes to SDSS-V, where he serves as FPS Design Implementation Lead, Solar Neighborhood Working Group Co-Chair, and a member of the Milky Way Mapper Data Analysis team.

William McClymont

Dr. William McClymont joined CITA as a Postdoctoral Fellow in September 2026 after completing his Ph.D. at the Kavli Institute for Cosmology, University of Cambridge. His research focuses on galaxy evolution, high-redshift galaxies, star clusters, supermassive black holes, radiation-hydrodynamic simulations, and Monte Carlo radiative transfer. He combines cosmological radiation-hydrodynamic simulations with observations to investigate why galaxies formed and grew so rapidly in the early Universe and how this relates to the formation of dense star clusters, including the progenitors of globular clusters.

Maja Lujan Niemeyer

Dr. Maja Lujan Niemeyer is an incoming CITA National Fellow at the University of British Columbia, where she will work with the CHIME group. She recently completed her Ph.D. in Physics at the Max Planck Institute for Astrophysics and Ludwig-Maximilians-Universität München, under the supervision of Professor Eiichiro Komatsu. Her research focuses on line-intensity mapping, large-scale structure, and the Lyman-α emission line, using observations of diffuse emission to study galaxies, intergalactic gas, and the evolution of the early Universe. She is a member of the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) collaboration. Her recent work includes the first detection of the galaxy–Lyman-α intensity cross-power spectrum in HETDEX data, providing a precise measurement of line-intensity mapping at cosmological scales.

Catherine Psarakis

Dr. Catherine Psarakis joined CITA as a Postdoctoral Fellow in October 2026 after completing her Ph.D. in the Department of Earth, Planetary, and Space Sciences at UCLA. Her research focuses on magnetic induction, icy moons, interior modeling, planetary habitability, astrobiology, alternative solvents, and planetary geochemistry. She combines planetary-interior and magnetic-induction modeling with laboratory experiments investigating ionic liquids and deep eutectic solvents under planetary conditions. Her work includes research conducted at NASA’s Jet Propulsion Laboratory and seeks to connect planetary geophysics, geochemistry, and astrobiology in understanding where persistent liquid environments may exist within Solar System bodies and exoplanets. She is also an AAUS Scientific Diver, with interests in terrestrial analogue environments for planetary science and astrobiology.

Soumendra Kishore Roy

Dr. Soumendra Kishore Roy is a Canada Impact+ Postdoctoral Fellow and a CITA Postdoctoral Fellow, who joined CITA in July 2026. He earned his Ph.D. from Stony Brook University in 2026. His research focuses on massive stellar evolution, gravitational-wave astrophysics, and gravitational-wave cosmology, with particular interest in population and cosmological-parameter inference. His core expertise is in hierarchical Bayesian inference, which he uses to connect models of binary stellar evolution with observations of compact-binary mergers and investigate their origins. He is involved in research associated with the LIGO–Virgo–KAGRA (LVK) Collaboration.

Sabina Sagynbayeva

Dr. Sabina Sagynbayeva is a CITA National Fellow whose research spans exoplanets, stars, astrostatistics, numerical simulations, theoretical astrophysics, and data analysis. Originally from Kazakhstan, she earned her Ph.D. from Stony Brook University. Her scientific interests include planet formation, the orbital architecture of exoplanets, and stellar magnetic activity. She also maintains an interdisciplinary creative practice in acting and singing.

Hui Tong

Dr. Hui Tong is joining CITA as a Postdoctoral Fellow after receiving his doctorate from Monash University in 2026. His research focuses on gravitational-wave astronomy, compact-object mergers, black-hole populations, and Bayesian inference. His work uses gravitational-wave observations to investigate the properties and origins of merging compact objects and the astrophysical populations that produce them. He is affiliated with the LIGO–Virgo–KAGRA (LVK) Collaboration and the OzGrav ARC Centre of Excellence for Gravitational-Wave Discovery.

Jonathan Zhang

Dr. Jonathan Zhang begins his Postdoctoral Fellowship at CITA after completing his doctorate at the University of Toronto in 2026. His research focuses on fast radio bursts and high-energy astrophysical phenomena, with particular interest in the physical mechanisms that generate these short-duration radio transients and their possible connections to magnetars and extreme magnetic environments.

Saiyang Zhang

Dr. Saiyang Zhang joins CITA as a Postdoctoral Fellow after completing his Ph.D. in Physics at the University of Texas at Austin in August 2026. His research focuses on dark matter, the early Universe, primordial black holes, Population III stars, supermassive black holes, and large-scale structure, combining theoretical modelling, cosmological simulations, and computational methods to investigate the evolution of cosmic structure. His recent work has examined how primordial black holes may influence the formation of the first stars and galaxies and potentially seed the supermassive black holes observed in the early Universe, including through observations with JWST. He is also increasingly interested in machine learning and scientific discovery, including simulation-based inference and the application of large language models to cosmology and dark-matter research.

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Professor Anupam Mazumdar and the Search for Quantum Gravity in the Lab /professor-anupam-mazumdar-search-quantum-gravity-lab/ /professor-anupam-mazumdar-search-quantum-gravity-lab/#respond Mon, 14 Sep 2026 21:32:35 +0000 /professor-anupam-mazumdar-search-quantum-gravity-lab/ Professor Anupam Mazumdar and the Search for Quantum Gravity in the Lab

By Lyuba Encheva, CITA

When Anupam Mazumdar first arrived in Canada in 2002, he was a CITA National Fellow stationed at McGill University, working at the frontier where particle physics meets the early universe. More than two decades later, he is returning to the Canadian Institute for Theoretical Astrophysics (CITA) at the University of Toronto as a full professor. In the intervening years, Prof. Mazumdar has developed one of the most distinctive research programs in theoretical physics: an attempt to catch gravity itself behaving like a quantum object, not out in space, but on a tabletop.

From the early universe to the quantum nature of spacetime

Mazumdar’s career has taken him through a remarkable circuit of the world’s leading theoretical physics institutes — Imperial College London, the International Centre for Theoretical Physics in Trieste, McGill, NORDITA and Niels Bohr Institute in Copenhagen, Lancaster University, and most recently the Van Swinderen Institute at the University of Groningen. Along the way, he built a reputation across several distinct areas of theoretical physics. These include cosmic inflation and the physics of the very early universe’s phase transitions. Prof. Mazumdar is also known for his “infinite derivative” theories of gravity — modified versions of general relativity designed to avoid the singularities — such as those at the centres of black holes — that plague Einstein’s original theory.

But it is a more recent line of work that has come to define his research identity. In 2017, Mazumdar and collaborators proposed an experimental protocol to test, in a laboratory, whether gravity is fundamentally quantum in nature. The idea, known as the Quantum Gravity Induced Entanglement of Masses (QGEM) protocol, asks a deceptively simple question: if you place two small masses side by side in quantum superpositions and let them interact only through their mutual gravitational pull, will gravity be able to entangle them the way quantum particles routinely entangle through electromagnetic or other known Standard Model forces? If it can, that would be direct evidence that gravity carries information the way quantum fields do — a long-sought clue in the decades-long effort to reconcile general relativity with quantum mechanics.

It is an audacious idea precisely because gravity is so weak. Unlike collider physics, which pushes to ever-higher energies to probe fundamental interactions, Mazumdar’s approach pushes toward ever more delicate, ever more isolated quantum systems — nanocrystals cooled and levitated with enough precision that gravity’s faint pull between them might, just barely, leave a detectable quantum fingerprint. In 2022, he extended the idea further, proposing a quantum-optics analog of the classic light-bending test of general relativity. This time the intention was to test whether the exchange of a single graviton could entangle photons and matter in quantum superposition.

The envisioned hardware for the flagship QGEM experiment is as exotic as the physics it is meant to probe: nanodiamonds (10 picogram mass), embedded with nitrogen-vacancy centres — atomic-scale defects that act as controllable quantum spins — levitated above a current-carrying superconducting chip and cooled toward the quantum regime in both their internal and centre-of-mass motion. A Stern-Gerlach-type protocol would use the embedded spin to split each nanodiamond into a spatial superposition, hold it open for roughly a tenth of a second to a full second, and then look for the telltale entangling phase that only a genuinely quantum gravitational interaction could imprint. The central experimental headache is separating that faint gravitational signal from electromagnetic backgrounds, since electromagnetic effects can be shielded away but gravity cannot — turning the experiment into what amounts to a very carefully controlled game of hide-and-seek with nature.

This is not a solo effort. Prof. Mazumdar is a co-principal investigator of the MAST-QG collaboration, which brings together University College London, Yale, Northwestern, and Warwick, and the QGEM program has drawn support from major philanthropic science funders, including the Gordon and Betty Moore Foundation and the Alfred P. Sloan Foundation. It is, in other words, an internationally resourced, multi-institution bet on a genuinely novel way of probing fundamental physics — and one that a research group at CITA now has a direct stake in.

Why CITA

CITA has long been a home for physicists who treat gravity and cosmology as an integrated whole — the origin of cosmic structure, the physics of the very early universe, gravitational waves, black holes and compact objects. Mazumdar’s work extends that tradition into a domain the Institute has not historically had in-house: table-top, laboratory tests of gravity’s quantum character. Rather than looking to the cosmos for evidence of quantum gravity’s effects, he is trying to manufacture the conditions for it in a lab on Earth — an approach that is complementary to, rather than in competition with, CITA’s traditional strengths in astrophysical gravity and cosmology.

There is also a symmetry to the appointment that is hard to overlook. Mazumdar’s first taste of Canadian science came as a CITA Fellow at McGill more than twenty years ago, at a formative stage in his career when he was still establishing himself in cosmology and particle physics. His return to CITA itself, now as a senior faculty member leading an internationally recognized experimental-theory program, closes a loop that began at the very outset of his career — and brings with it not just his own research group, but an entry point for CITA into the fast-moving, interdisciplinary field of quantum information science as it intersects with gravity.

With roughly 240 published papers, three major review articles in journals including Physics Reports and Reports on Progress in Physics, a multi-institution collaboration in MAST-QG, and philanthropic funding already secured from the Moore and Sloan foundations, Mazumdar arrives at CITA with both a substantial body of foundational work behind him and an ongoing, high-profile experimental program still very much in motion. For an institute built on the premise that some of the deepest questions in physics — the origin and fate of the universe, the nature of black holes, the unification of gravity and quantum mechanics — require sustained, focused theoretical effort, his presence adds a genuinely new avenue toward one of the oldest open problems in physics: whether gravity, like everything else we know, is quantum after all.

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New Simulations Reveal Telltale Differences Between Stars Born of Collisions and Stars Born of Mergers /new-simulations-reveal-telltale-differences-stars-born-collisions-stars-born-mergers/ /new-simulations-reveal-telltale-differences-stars-born-collisions-stars-born-mergers/#respond Wed, 09 Sep 2026 21:22:29 +0000 /new-simulations-reveal-telltale-differences-stars-born-collisions-stars-born-mergers/ New Simulations Reveal Telltale Differences Between Stars Born of Collisions and Stars Born of Mergers

Magnetohydrodynamic modelling shows that colliding and merging stars produce distinct “fingerprints,” offering a new way to trace the violent origins of unusual stars such as blue stragglers.

A study published recentlyÌýinÌýThe Astrophysical JournalÌýprovides the most detailed comparison yet of what happens when two stars collide versus when two stars in a binary system merge together — two processes long suspected of producing similar-looking, rejuvenated stars, but which turn out to leave behind different physical signatures.

The research, led by CITA Postdoctoral Fellow along with Taeho Ryu, Chen Wang, Alison Sills, and Rüdiger Pakmor, used the moving-mesh magnetohydrodynamics code AREPO to simulate collisions and mergers of main-sequence stars between five and ten times the mass of the Sun. The team then compared the internal structure, rotation, chemical mixing, and magnetic fields of the resulting objects in detail.

Collage of snapshots depicting the sequence of events during a collision, from two stars approaching each other due to a gravitational encounter (left column) to them colliding to form a single resulting star (right column). The three rows depict three quantities: mass density (top), magnetic field strength (middle), and passive scalar (right) to show material mixing. The collision product has a much larger magnetic field strength than the two initial stars and shows significant material mixing.

Two roads, two different destinations

Both stellar collisions — sudden, high-speed encounters typically occurring in the crowded cores of dense star clusters — and binary mergers — the slower coalescence of two stars after unstable mass transfer — are known to produce more massive, rapidly rotating stars with hydrogen-enriched cores. These “rejuvenated” stars are prime candidates for explaining blue stragglers, a class of stars that appear anomalously bright and hot for their host clusters, as well as other exotic objects such as magnetic massive stars.

However, it has been difficult to tell these two formation pathways apart. The new simulations identify several distinguishing features:

  • Chemical mixing: Merger products retain core hydrogen fractions up to 10% higher than collision products, reflecting differences in how thoroughly the two processes mix stellar material.
  • Magnetic field structure: Turbulent mixing dramatically amplifies magnetic fields (by nine to twelve orders of magnitude) in both scenarios, but the character of the resulting fields differs: near-head-on (small-impact-parameter) collisions generate small-scale, tangled magnetic fields likely to fade over time, while mergers and grazing (large-impact-parameter) collisions generate large-scale, ordered fields that may persist far longer.
  • Outflows: Only merger products in the study produced magnetically driven, bipolar outflows, with material streaming away at speeds up to 300 kilometers per second — a feature entirely absent from the collision products.
Collage of snapshots depicting the sequence of events during a merger, from two stars spiraling in towards each other in a close binary (left column) to them merging to form a single resulting star (right column). The three rows depict three quantities: mass density (top), magnetic field strength (middle), and passive scalar (right) to show material mixing. The merger product has a much larger magnetic field strength than the two initial stars and shows significant material mixing.

Why it matters

Distinguishing collision products from merger products has been a long-standing challenge for astronomers trying to interpret observations of blue stragglers, magnetic OB stars, and other objects thought to form through stellar interactions. Because collisions dominate in dense globular clusters while mergers are thought to be more common in sparser open clusters, being able to identify a star’s formation history from its magnetic and structural properties could sharpen models of how star clusters evolve and how exotic, highly magnetized stars, and potentially magnetars, come to be.

The authors note that the long-term evolutionary consequences of these differences, particularly whether the ordered magnetic fields in merger products survive over stellar lifetimes, warrant further study.

Publication details

Pavan Vynatheya et al 2026, “The Collision and Merger Products of Stars Do Not Look Alike: A Magnetohydrodynamics Comparison,” The Astrophysical Journal, Volume 999, Number 1. .

Media Contact:
Lyuba Encheva, Communications and Events Coordinator
Canadian Institute for Theoretical Astrophysics, University of Toronto
Email: communication@cita.utoronto.ca

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CITA Researcher Helps Distinguish Black Holes from a Type of Boson Star in New Gravitational Wave Study /cita-researcher-helps-distinguish-black-holes-type-boson-star-new-gravitational-wave-study/ /cita-researcher-helps-distinguish-black-holes-type-boson-star-new-gravitational-wave-study/#respond Tue, 25 Aug 2026 20:20:44 +0000 /cita-researcher-helps-distinguish-black-holes-type-boson-star-new-gravitational-wave-study/ CITA Researcher Helps Distinguish Black Holes from a Type of Boson Star in New Gravitational Wave Study
CITA Postdoctoral Fellow Dr. Aditya Vijaykumar – one of the three leading authors of the publication “Implications of GW241011 for Rotating Exotic Compact Objects. Phys. Rev. Lett. 137, 071402.

Are all merging compact objects that produce gravitational waves black holes, or are some of them highly convincing imposters?

A new study published on August 14, 2026 in the prestigious journal Physical Review Letters has brought scientists one step closer to answering this fundamental question. Co-led by Dr. Aditya Vijaykumar, a Postdoctoral Fellow at the Canadian Institute for Theoretical Astrophysics (CITA) at the University of Toronto, the research uses recent gravitational wave data to check for “Exotic Compact Objects” (ECOs)—hypothetical structures that mimic black holes but lack an event horizon from which nothing can escape.

The international research team focused their attention on GW241011, a massive gravitational wave event generated by a violent cosmic collision. The larger of the two colliding bodies (the “primary”) was roughly 20 times the mass of our sun and spinning incredibly fast, making it the perfect laboratory to test the laws of fundamental physics.

To determine if this object was a true black hole or an exotic imposter, the team measured its “spin-induced quadrupole moment.”

“When an object spins rapidly, it bulges at its equator. How much it bulges depends entirely on what it is made of,” explains Dr. Vijaykumar, one of the lead authors of the study. “Because the more massive object in GW241011 was spinning so fast, the gravitational wave data provided us with the tightest constraints ever recorded on this bulging effect. This allowed us to test beyond the standard realm of black holes.”

One of the leading theoretical candidates for black hole imposters is a “Boson star”—a hypothetical compact object thatÌýwould be made of a yet-to-be-discovered heavy Boson particle (like the theoretical “Axion”). Because BosonsÌýcanÌýshare the exact same space, they don’t push back the way neutrons do. They just peacefully overlap into a giant, dense, quantum fluid blob. The theoretical models of Boson stars anticipate that theirÌýshape would be distorted by rotation in a way that differs from that of a spinning black hole.

By analyzing the data from GW241011, Vijaykumar and his colleagues presented compelling evidence that the primary object in the spinning binary was not distorted enough to fit the hypothetical model of a rotating Boson star – specifically, not the kind characterized by quartic self-interactions, effectively ruling out this exotic model for this event.

Sequences of repulsive BSs in the χ − κ plane (solid lines), with different colors denoting the coupling values, λ=μ2, and dots the maximum mass solution. The dotted lines indicate dynamically unstable solutions according to our relativistic criterion (see the main text). The gray shaded region denotes the κ–χ measurement (at 95% credible level).
Exclusion regions in the mb − Λ˜ plane, where mb is the boson mass in physical units, Λ˜ ¼ ΛðℏcÞ is dimensionless, and Λ is the coupling in physical units. Gray denotes the region excluded by GW241011, yellow corresponds to stars with masses incompatible with GW241011, whereas blue contains only unstable solutions. For reference, we also overplot the Λ˜ and mb values corresponding to a hypothetical dark matter particle with cross section per unit mass of 0.1 cm2 g−1 in dashed red line.

However, the mystery of Exotic Compact Objects is far from solved. The study notes that while certain Boson stars have been eliminated, other highly dense theoretical models—specifically those with an extreme “compactness” factor greater than 0.24 (black holes have compactness value of 0.5)—are still viable contenders for what this object might have been.

“This is a thrilling era for astrophysics,” says Vijaykumar. “With the increasing sensitivity of gravitational wave detectors like LIGO, Virgo, and KAGRA, we are no longer just guessing about what exists in the deep universe. We are actively stress-testing the standard model of particle physics and general relativity in real-time.”

The paper, led by Dr. Vijaykumar along with Dr. Tamara Evstafyeva (Perimeter Institute) and Dr. NV Krishnendu (University of Birmingham), places some of the most stringent constraints on beyond-Kerr black hole physics to date and establishes a vital new framework for how scientists will analyze future gravitational wave detections.

To read the full studyÌýgo to:. Phys. Rev. Lett. 137, 071402.

½Û×ÓÊÓƵ the Canadian Institute for Theoretical Astrophysics (CITA)
Located at the University of Toronto, CITA is a globally recognized research institute dedicated to advancing our understanding of the universe. CITA researchers specialize in theoretical astrophysics, cosmology, and fundamental physics, driving innovation in our understanding of black holes, dark matter, and gravitational waves.

SCIENCE CONTACT:ÌýDr. Aditya Vijaykumar

Media Contact:
Lyuba Encheva, Communications and Events Coordinator
Canadian Institute for Theoretical Astrophysics, University of Toronto
Email: communication@cita.utoronto.ca

 

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Radio Emission from Pulsars and White Dwarfs /radio-emission-pulsars-white-dwarfs/ /radio-emission-pulsars-white-dwarfs/#respond Wed, 12 Aug 2026 20:08:19 +0000 /radio-emission-pulsars-white-dwarfs/

Radio Emission from Pulsars and White Dwarfs

Joonas Nättilä (University of Helsinki) — August 6, 2026

Abstract

Radiative plasma processes in neutron star and white dwarf magnetospheres play a central role in shaping their radio emission and high-energy variability. Magnetospheric gaps — regions of unscreened electric field — are natural sites of extreme particle acceleration, radiation, and electron–positron pair creation. They are thought to trigger pair cascades and regulate magnetospheric activity in radio pulsars, millisecond pulsars, and possibly the white-dwarf-hosting long-period transients.Their time-dependent plasma physics, however, remains poorly understood.

In this talk I will present our recent work on the radiative plasma physics of these discharges. We develop an analytical theory for the coupled evolution of electric field, particle acceleration, radiation, and pair creation in this extreme regime, and complement it with first-principles radiative particle-in-cell simulations that include exact QED processes and realistic plasma parameters, allowing us to test and validate the theoretical predictions.

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Cosmology and Astrophysics with SPHEREx /cosmology-astrophysics-spherex/ /cosmology-astrophysics-spherex/#respond Wed, 12 Aug 2026 20:01:35 +0000 /cosmology-astrophysics-spherex/

Cosmology and Astrophysics with SPHEREx

Yun-Ting Cheng (Caltech) — July 8, 2026

Abstract

SPHEREx is a NASA near-infrared satellite mission launched in March 2025, currently conducting the first all-sky near-infrared spectral survey. I will begin with a brief overview of the mission, its current status, and some early science results. Then I will introduce the main scientific goals of SPHEREx, focusing on two: 1) constraining primordial non-Gaussianity (PNG) from inflation, with a target precision of O(1) on the PNG amplitude parameter (f_NL); and 2) studying galaxy formation and evolution through intensity mapping of the extragalactic background light. I will walk through the science motivation, the analysis methodology, and our progress on these analyses within the SPHEREx science team.

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CITA marks 40th anniversary with global gathering at the University of Toronto. /cita-marks-40th-anniversary-global-gathering-university-toronto/ /cita-marks-40th-anniversary-global-gathering-university-toronto/#respond Mon, 13 Jul 2026 15:31:26 +0000 /cita-marks-40th-anniversary-global-gathering-university-toronto/ CITA marks 40th anniversary with global gathering at the University of Toronto.

Originally published by .

The Canadian Institute for Theoretical Astrophysics (CITA) marked its 40th anniversary at the University of Toronto at the end of May, bringing together astrophysicists from around the world for a three-day conference celebrating four decades of research, training and collaboration.

More than 160 participants attended in person, with hundreds more joining online.

The conference featured 87 speakers from 15 countries — including many former CITA postdoctoral fellows and graduate students who returned to share new research and reconnect with colleagues.

A recurring theme throughout the celebratory event was the importance of academic community — with many attendees describing CITA as both a research hub and a formative “home” during their early academic careers. Words like “family” and “homecoming” were scattered through narratives of youthful times, full of enthusiasm for science and fun with friends.

Melanie Woodin addresses attendees.
U of T President Melanie Woodin addresses attendees on the opening day of CITA’s 40th anniversary conference.

, CITA’s director and a professor of astrophysics at Western University, opened the conference by welcoming participants and reflecting on the institute’s history. He noted that this meeting “brings together the three pillars of CITA: members of CITA the flagship in Toronto, the national network of affiliate faculty, and the global network of CITA alumni.”

U of T President Melanie Woodin highlighted CITA’s global reputation and paid tribute to the leadership of its founders, Professors Richard Henriksen and Peter Martin, as well as its first directors, Scott Tremaine and Dick Bond.

Early CITA postdoctoral fellows and faculty members.
Early CITA postdoctoral fellows and faculty members reconnect at the anniversary banquet, sharing memories and celebrating four decades of impact.

Woodin said it is rare for her to travel without hearing about “CITA’s outstanding success and legacy of scientific discovery,” adding that U of T was chosen to host the institute because of its commitment to leadership and fundamental science.

Stephen Wright, dean of the Faculty of Arts & Science, congratulated CITA on four decades of “training the next generation of explorers and leaders in the field of astrophysics.”

Attendees and faculty members.
Attendees and faculty members engage in opening-day presentations at CITA’s global anniversary gathering.

Nobel laureate — and guest of honour — said, “Over the years, it has been an education for me to interact with CITA researchers and friends, and I am very pleased to be here for their anniversary.”

McDonald, co-recipient of the for his work on neutrinos and a professor emeritus at Queen’s University, shared the prize for research demonstrating that neutrinos have mass, a discovery that reshaped understanding of fundamental particle physics.

Peter Martin presents during the conference.
CITA co-founder and University of Toronto professor Peter Martin presents during the institute’s 40th anniversary conference.

Founded in 1984 to address a gap in Canada’s research landscape — at a time when the country had strong observational astronomy but no centralized hub for theory — CITA is administered by the Faculty of Arts & Science and operates both as a University of Toronto department and as an independent national research corporation.

Richard Henriksen, a co-founder and former chair of the CITA Council, recalled early efforts to strengthen Canada’s theoretical astronomy. Working with Peter Martin, he helped lead the successful campaign — officially endorsed in 1983 — to establish a national institute at U of T, formally created on June 21, 1984, with NSERC support.

From the very beginning, CITA adopted a distinctive model focused on postdoctoral training.

Rather than building a large permanent faculty, the institute emphasized recruiting top early-career researchers from around the world for fixed-term appointments, creating a dynamic research environment with a constant influx of new ideas.

Richard Henriksen speaks during the conference.
CITA co-founder and former chair of the CITA Council Richard (Dick) Henriksen speaks during the 40th anniversary conference.

Scott Tremaine, recruited from MIT as CITA’s first director in 1985, said the model was a major attraction. He described the institute as unique both as a national centre for theoretical astrophysics and for its emphasis on postdoctoral researchers at a pivotal early-career stage.

CITA’s research scope has evolved alongside major developments in astrophysics. Early work focused on galaxy formation, star formation and planetary dynamics, supported by increasingly sophisticated computational tools.

Over time, the institute developed advanced simulation capabilities that significantly contributed to the expansion of Canada’s supercomputing infrastructure.

In recent years, CITA researchers have been involved in emerging areas such as multi-messenger astrophysics, fast radio bursts and . The institute has contributed to projects including the CHIME telescope in British Columbia and has expanded into fields such as exoplanet research and early-universe cosmology.

Despite its incredible scientific impact, speakers at the anniversary celebration emphasized that CITA’s long-term success is closely tied to its supportive and collaborative culture. Former postdoctoral fellows described an environment characterized by intellectual freedom, trust and strong professional and personal connections.

Philip Armitage, now a professor at Stony Brook University and a research scientist at the Flatiron Institute, reflected on his time at CITA, highlighting both the academic opportunities and the supportive atmosphere.

Doug Johnstone, now science adviser to the president of the National Research Council of Canada, said in a video greeting that the “support of the CITA family” played a key role in his decision to remain in astrophysics.

Today, more than 130 CITA alumni hold tenured positions at institutions around the world, underscoring the institute’s global influence. Many of them returned to Toronto for the anniversary, reconnecting with colleagues and reflecting on the institute’s role in shaping their careers.

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Planet formation and evolution around misaligned circumbinary disks /planet-formation-evolution-around-misaligned-circumbinary-disks/ /planet-formation-evolution-around-misaligned-circumbinary-disks/#respond Wed, 24 Jun 2026 14:16:17 +0000 /planet-formation-evolution-around-misaligned-circumbinary-disks/

Planet formation and evolution around misaligned circumbinary disks

Cheng Chen (Bishop's University) — May 25, 2026

Abstract

Recent observations have revealed that circumbinary disks that are misaligned to the binary orbit could be common in the universe. Dissipation in the disk causes it to move either towards coplanar alignment or polar alignment. Since planets form inside disks, circumbinary planets may also form misaligned to the binary orbit. We explore the orbital evolution of the binary with the misaligned circumbinary disk. The disk-binary interaction leads to the evolution of the binary’s orbit, which could either shrink over time due to the loss of its angular momentum via resonances or expand due to the acquirement of specific angular momentum via accretion. We explore diverse parameter domains of circumbinary systems with polar and retrograde disks. Our results have implications in a variety of astrophysical objects, including the orbital evolution of stellar binaries and the evolution of both stellar and supermassive black hole binaries.

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50 Years of Exploring the Cosmos: The Incredible Legacy of Dick Bond /50-years-exploring-cosmos-incredible-legacy-dick-bond/ /50-years-exploring-cosmos-incredible-legacy-dick-bond/#respond Wed, 03 Jun 2026 22:14:21 +0000 /50-years-exploring-cosmos-incredible-legacy-dick-bond/ 50 Years of Exploring the Cosmos: The Incredible Legacy of Dick Bond
Dick Bond, a University Professor in U of T’s David A. Dunlap department of astronomy and astrophysics and the Canadian Institute for Theoretical Astrophyics (CITA), is best known for his leading work on the cosmic microwave background (photo by Polina Teif)

How do you map out the entire universe? For University of Toronto astrophysicist Dick Bond, you do it with five decades of passion, groundbreaking math, and a healthy dose of curiosity.

A fascinating new feature by the University of Toronto looks back at Bond’s legendary 50-year career—and his massive role in putting Canada on the global astrophysics map.

If you’ve ever heard the terms “cosmic web” or “gastrophysics” (how gas clouds transform into stars and planets), you have Bond to thank; he coined them. Decades ago, his theoretical models predicted the age, shape, and composition of our universe long before satellite technology could actually prove him right.

Beyond his equations, the article highlights Bond’s incredible impact as a mentor to over 200 researchers and his long-time leadership at the Canadian Institute for Theoretical Astrophysics (CITA), which celebrates its 40th anniversary this year.

At 75, Bond says he’s still making progress—and his best work is yet to come.

Read the full profile on Ìýto dive into his journey, his thoughts on the future of quantum physics, and his advice for the next generation of scientists.

Find more information on the history of the Cold Dark Matter (CDM) paradigm in this VIDEO by the.

The recording features talks by five scientists who played key roles in the early development and establishment of the Cold Dark Matter (CDM) paradigm.ÌýRichard Bond,ÌýKen Freeman,ÌýJim Peebles,ÌýJoel Primack, andÌýMike TurnerÌýcame together for this panel discussion at theÌý2018 Physics of Galaxy Scaling Relations and the Nature of Dark Matter ConferenceÌýheld atÌýQueen’s University. The discussion provides a valuable first-hand account of the origins, development, and early reception of CDM.

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