Using Webb, Canadian team maps the Milky Way's turbulent youth.

A Canadian team used JWST and Hubble imaging of 877 'Milky Way twin' galaxies to reconstruct the Galaxy's evolution and found a merger-rich, turbulent early phase followed by later inside-out disk growth.

A team of Canadian astronomers led by Dr. Vivian Tan used high-resolution images from the James Webb Space Telescope and the Hubble Space Telescope to map how galaxies like the Milky Way evolved. They assembled a sample of 877 galaxies selected as close analogs to expected Milky Way progenitors, spanning times when the Universe was about 1.5 to 10 billion years old (roughly 12.3 to 3.5 billion years ago). The Webb observations came from the CANUCS program using NIRISS, combined with visible-light data from Hubble. The paper describing the results was published in The Astrophysical Journal and reports a notably turbulent early history for Milky Way-like galaxies before later settling into disk structures. Key findings: - The sample included 877 galaxies identified as Milky Way analogs across a wide range of cosmic time. - Data came from JWST NIRISS within the CANUCS program and complementary Hubble imaging. - Resolved stellar-mass and star-formation-rate maps show that these systems grew from the inside out between about 3 and 4 billion years after the Big Bang. - Many early progenitors appear disturbed and asymmetric, consistent with frequent mergers and intense star formation in their youth. - Numerical simulations broadly support inside-out growth but do not fully reproduce the strong central concentrations and rapid outer mass build-up seen in some objects. - The results offer constraints on processes such as merger rates, feedback, and disk formation that shape galaxy evolution. Summary: The study provides a detailed visual timeline of how Milky Way-like galaxies evolved, showing a merger-rich, turbulent early phase followed by calmer, more extended disk growth. The CANUCS team plans to expand the work with deeper lensing and JWST data and updated simulations to probe earlier stages and refine when and how such galaxies settled into stable disks.