Intense flashes of light, not mass, resolve the puzzle of impossible brightness
Artist conception of early starbursting galaxies. Stars and galaxies are shown in the bright white points of light, while the more diffuse dark matter and gas are shown in purples and reds. Image by Aaron M. Geller, Northwestern, CIERA + IT-RCDS
When scientists viewed the James Webb Space Telescope’s (JWST) first images of the universe’s earliest galaxies, they were shocked. The young galaxies appeared too bright, too massive and too mature to have formed so soon after the Big Bang. It would be like an infant growing into an adult within just a couple years.
The startling discovery even caused some physicists to question the standard model of cosmology, wondering whether or not it should be upended.
Using new simulations, a Northwestern University-led team of astrophysicists now has discovered that these galaxies likely are not so massive after all. Although a galaxy’s brightness is typically determined by its mass, the new findings suggest that less massive galaxies can glow just as brightly from irregular, brilliant bursts of star formation.
Not only does this finding explain why young galaxies appear deceptively massive, it also fits within the standard model of cosmology.
The research was published on October 3 in the Astrophysical Journal Letters.
“The discovery of these galaxies was a big surprise because they were substantially brighter than anticipated,” said Northwestern’s, Claude-André Faucher-Giguère, the study’s senior author. “Typically, a galaxy is bright because it’s big. But because these galaxies formed at cosmic dawn, not enough time has passed since the Big Bang. How could these massive galaxies assemble so quickly? Our simulations show that galaxies have no problem forming this brightness by cosmic dawn.”
“The key is to reproduce a sufficient amount of light in a system within a short amount of time,” added Guochao Sun, who led the study. “That can happen either because the system is really massive or because it has the ability to produce a lot of light quickly. In the latter case, a system doesn’t need to be that massive. If star formation happens in bursts, it will emit flashes of light. That is why we see several very bright galaxies.”
Faucher-Giguère is an associate professor of physics and astronomy at Northwestern’s Weinberg College of Arts and Sciences and a member of the Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA). Sun is a CIERA Postdoctoral Fellow at Northwestern.
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