TORONTO, Dec. 18, 2025 – How galaxies assemble their stars and grow over billions of years remains one of the central questions in astronomy. Recent results from the James Webb Space Telescope (JWST), including reports of surprisingly massive and evolved galaxies in the early Universe, have only deepened the mystery. Understanding how our own home galaxy, the Milky Way, built itself over time provides a crucial piece of this broader cosmic puzzle.

led by 91��ɫ PhD graduate Vivian Tan, who studied under the supervision of Faculty of Science Associate Professor Adam Muzzin, provides the most detailed reconstruction yet of how the Milky Way may have evolved from its earliest phases to the structured spiral we see today. Tan and her colleagues examined 877 “Milky Way twins” — galaxies whose masses and properties closely match what astronomers expect the Milky Way would have looked like at different ages across cosmic time. By observing more distant, and therefore progressively younger examples of these galactic look-alikes, the team effectively charted a timeline of our galaxy’s life, with surprising results. Our Milky Way’s history started from a remarkably tumultuous youth before its more settled adulthood.

The findings were recently published in The Astrophysical Journal and were undertaken with the financial support of the Canadian Space Agency.

Rewinding the Milky Way’s cosmic clock

The galaxies in the sample span a remarkable range of cosmic time, from when the Universe was just 1.5 billion years old (12.3 billion years ago) to 10 billion years old (3.5 billion years ago). This period covers as far back as when the Universe was only 10 per cent its current age, a crucial epoch when galaxies transformed from small, irregular systems into the stable disk galaxies familiar today.

To carry out this work, the team combined high-resolution imaging from JWST and the Hubble Space Telescope (HST). The JWST observations come from the Canadian NIRISS Unbiased Cluster Survey (CANUCS), a major Canadian observing program that uses five massive galaxy clusters as natural gravitational lenses. These clusters magnify background galaxies, revealing faint structures that would otherwise be too distant and too dim to study in detail.

CANUCS takes advantage of Canada’s hardware contributions to the JWST mission through the Near-Infrared Imager and Slitless Spectrograph (NIRISS) instrument, built for the mission by the Canadian Space Agency in partnership with the Université de Montréal, the National Research Council Herzberg Centre for Astronomy and Astrophysics, and Honeywell. In return, Canadian astronomers received valuable guaranteed observing time on JWST, including the data that enabled this study.

Building galaxies from the inside out

JWST’s exceptional spatial resolution allowed the researchers to create detailed maps of the stellar mass and star formation activity across each galaxy. These maps show where stars were already in place and where new stars were forming at different phases in a galaxy’s life.

Across the entire sample, the results point to a clear pattern: galaxies like our Milky Way grow from the inside out. The earliest Milky Way twins are dominated by dense, compact central regions. Over time, their outer parts — the regions that will later become the disk — rapidly gain mass and become the primary sites of star formation. This gradual expansion outward creates the extended spiral structures we see in present-day galaxies.

“Astronomers have been modeling the formation of the Milky Way and other spiral galaxies for decades,” says lead author Tan. “It's amazing that with the JWST, we can test their models and map out how Milky Way progenitors grow with the Universe itself."

Turbulent teenage years

The most exciting results of the study also reveal that young Milky Way-like galaxies lived through far more chaotic conditions than their older, more evolved counterparts. The youngest, most distant systems show highly disturbed shapes, asymmetric features, and evidence of frequent galaxy–galaxy interactions and mergers. These disturbances are signatures of a dynamic environment where galaxies were constantly colliding, accreting material, and triggering intense bursts of star formation.

By contrast, the Milky Way twins at later cosmic times appear much more stable and orderly. Their structures are smoother, their star formation is more evenly distributed, and signs of major interactions become far less common. Overall, they point to a more chaotic past for our Galaxy than we had expected.

Comparing observations and simulations

Tan and her collaborators compared their observations to state-of-the-art computer simulations that track the evolution of Milky Way–like galaxies. The simulations broadly agree with the observed inside-out growth and early clumpy, merger-driven activity. However, they sometimes fail to reproduce the high central compactness seen in the earliest galaxies, and they underestimate how quickly mass accumulates in the outer regions between 8 and 11 billion years ago.

These differences provide important constraints on feedback, merger rates, and disk formation models, and highlight the need to refine theoretical predictions in the era of JWST.

Building on Webb’s early insights

This study marks a significant milestone for Canada’s growing leadership in JWST galaxy research. With NIRISS and CANUCS continuing to deliver exceptionally deep, high-resolution data, astronomers will be turning to even larger samples of Milky Way–like systems and extending their analysis to include gas content, dust, and kinematic structure.

“This study is a significant step forward in understanding the earliest stages of the formation of our Galaxy,” says Muzzin, co-author of the study. “However, this is not the deepest we have pushed the telescope yet.  In the coming years, with the combination of JWST and gravitational lensing we can move from observing Milky Way twins at 10 per cent their current age to when they are a mere 3 per cent of their current age, truly the embryonic stages of their formation.”

Other co-authors from 91��ɫ are Ghassan Sarrouh, Visal Sok, Naadiyah Jagga, and Westley Brown. Other co-authors include researchers from the University of Toronto, the University of Ljubljana, Saint Mary’s University, Kyoto University, the University of Groningen, Columbia University, Wellesley College, the Space Telescope Science Institute, and the National Research Council Herzberg Astronomy & Astrophysics Research Centre.

This team and several international teams already have future JWST observations scheduled to do this. Combined with updated simulations, they will help determine precisely when galaxies like our Milky Way settle into stable disks, how long turbulent phases last, and what physical processes drive the transition between them. By expanding this work, the team aims to build an increasingly complete picture of how galaxies like our own assembled their stars and evolved from the early Universe to the present day.

-30-

91��ɫ is a modern, multi-campus, urban university located in Toronto, Ontario. Backed by a diverse group of students, faculty, staff, alumni and partners, we bring a uniquely global perspective to help solve societal challenges, drive positive change, and prepare our students for success. 91��ɫ's fully bilingual Glendon Campus is home to Southern Ontario's Centre of Excellence for French Language and Bilingual Postsecondary Education. 91��ɫ’s campuses in Costa Rica and India offer students exceptional transnational learning opportunities and innovative programs. Together, we can make things right for our communities, our planet, and our future.

Media Contact:

Emina Gamulin, 91��ɫ Media Relations, 437-217-6362, egamulin@yorku.ca

Nathalie Ouellette, JWST Outreach Scientist, Université de Montréal,  nathalie@astro.umontreal.ca

The post Canadian astronomers use Webb to uncover Milky Way’s turbulent youth through galactic twins appeared first on News@91��ɫ.

91��ɫ-led findings show astronauts can safely assess distances in weightless environment

TORONTO, March 25 2024 – New research led by 91��ɫ finds .

The findings of the study, done in collaboration with the Canadian Space Agency and NASA, have implications for crew safety in space and could potentially give clues to how aging affects people’s balance systems here on Earth, says the study’s lead Faculty of Health Professor .

“It has been repeatedly shown that the perception of gravity influences perceptual skill. The most profound way of looking at the influence of gravity is to take it away, which is why we took our research into space,” says Harris, an expert on vision and the perception of motion who also heads up the Multisensory Integration Lab and is the former director of the at 91��ɫ.

“We’ve had a steady presence for close to a quarter century in space and with space efforts only increasing as we plan to go back to the moon and beyond, answering health-and-safety questions only becomes more important. Based on our findings it seems as though humans are surprisingly able to compensate adequately for the lack of an Earth-normal environment using vision.”

Harris and collaborators – who include Lassonde School of Engineering professors Robert Allison and Michael Jenkin, and two generations of 91��ɫ post docs and graduate students Björn Jörges, Nils Bury, Meaghan McManus and Ambika Bansal – studied a dozen astronauts aboard the International Space Station, which orbits about 400 kilometres from the Earth’s surface. Here, Earth's gravity is approximately cancelled out by centrifugal force generated by the orbiting of the station. In the resulting microgravity, the way people move is more like flying, says Harris.

“People have previously anecdotally reported that they felt they were moving faster or further than they really were in space, so this provided some motivation to actually record this,” he explains.

The researchers compared the performance of a dozen astronauts – six men and six women – before, during, and after their year-long missions to the space station and found that their sense of how far they travelled remained largely intact.

Space missions are busy endeavours and it took the researchers several days to connect with the astronauts once they arrived at the space station. Harris says that it’s possible their research was unable to capture early adaptation that may have occurred in those first few days, “it's still a good news message because it says that whatever adaptation happens, happens very quickly.”

Space missions are not without risk. As the ISS orbits the Earth it is sometimes hit with small objects that could penetrate the vessel requiring astronauts to move to safety.

“On a number of occasions during our experiment, the ISS had to perform evasive maneuvers,” recalls Harris. “Astronauts need to be able to go to safe places or escape hatches on the ISS quickly and efficiently in an emergency. So, it was very reassuring to find that they were actually able to do this quite precisely.”

The study, published recently in npj Microgravity, has been a decade in the making, and represents the first of three papers that will emerge from the research investigating the effects of microgravity exposure on different perceptual skills including the estimation of body tilt, travelled distance, and object size.

Harris says research shows exposure to microgravity mimics the aging process on a largely physiological level  – wasting of bones and muscles, changes in hormonal functioning and increased susceptibility to infection  – but this paper finds that self-motion is largely unaffected, suggesting the balance issues that frequently come from old age may not be related to the vestibular system.

“It suggests that the mechanism for the perception of movement in older people should be relatively unaffected, and that the issues involved in falling may not be so much in terms of the perception of how far they've moved, but perhaps more to do with how they're able to convert that into a balance reflex.”

About 91��ɫ

91��ɫ is a modern, multi-campus, urban university located in Toronto, Ontario. Backed by a diverse group of students, faculty, staff, alumni and partners, we bring a uniquely global perspective to help solve societal challenges, drive positive change, and prepare our students for success. 91��ɫ’s fully bilingual Glendon Campus is home to Southern Ontario’s Centre of Excellence for French Language and Bilingual Postsecondary Education. 91��ɫ’s campuses in Costa Rica and India offer students exceptional transnational learning opportunities and innovative programs. Together, we can make things right for our communities, our planet, and our future.

Media Contacts: Emina Gamulin, 91��ɫ Media Relations and External Communications, 437-217-6362, egamulin@yorku.ca

The post Astronauts have surprising ability to know how far they ‘fly’ in space appeared first on News@91��ɫ.