Hidden Galaxies in Deep Universe May ‘Break Current Models’ – ryan

Astronomers peering back deep in time into the distant universe think they may have discovered a population of previous hidden galaxies that could shake up astrophysics.

The research, based on data from the Herschel Space Observatory, was undertaken by astrophysicist Chris Pearson of the Rutherford Appleton Laboratory in England and colleagues.

“This work has pushed the science with Herschel to its absolute limit, probing far below what we can normally discernibly see and potentially revealing a completely new population of galaxies that are contributing to the very faintest light we can observe in the universe,” he said in a statement.

His colleague, physicist Thomas Varnish of the Massachusetts Institute of Technology, added: “If confirmed, this new population would effectively break all of our current models of galaxy numbers and evolution.”

In their studies, the researchers analyzed observations of the distant universe made by the SPIRE instrument on the Herschel Space Observatory, a European Space Agency mission that ended in 2013.

SPIRE was tasked with observing the universe in the very longest infrared wavelengths.

“When we look at starlight through normal telescopes, we are only able to read half of the story of our universe, the other half is hidden, obscured by the intervening dust,” said Pearson.

“In fact, roughly half of the energy output of the universe is from starlight that has been absorbed by dust and reemitted as cooler infrared radiation.

“To fully understand the evolution of our universe we need to observe the sky in both optical and longer wavelength infrared light.”

Stacking 141 images on top of each other, they created the deepest ever image of the sky in the far-infrared—one that is five times deeper than the previous single Herschel observation.

The technique allowed the team to not only see some of the dustiest galaxies, where most of the cosmos’ new stars form, but also to track the contribution that galaxies of different brightness make to the total energy budget of the universe.

However, the image ended up being so deep—and revealed so many galaxies—that some of the individual objects began to merge and become indistinguishable from each other.

“We employed statistical techniques to get around this overcrowding, analyzing the blurriest parts of the image to probe and model the underlying distribution of galaxies not discernible in the original image,” said Varnish.

“What we found was possible evidence of a completely new, undiscovered population of faint galaxies hidden in the blur of the image—too faint to be detected by conventional methods in the original analysis.”

These galaxies could also provide the missing piece in the puzzle of the universe’s energy generation in the infrared, effectively accounting for all the missing sources of energy emission at these long wavelengths.

With their initial studies complete, the researchers are now hoping to confirm the existence of these “hidden” galaxies, using observations with telescopes operating at both other wavelengths, but also further observations in the far-infrared part of the spectrum.

The latter could potentially be provided by the proposed Probe far-Infrared Mission for Astrophysics (PRIMA), which is currently one of two missions short-listed for NASA’s next $1-billion probe mission. A final decision on whether PRIMA will go ahead is expected to be announced next year.

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References

Pearson, C., Varnish, T. W. O., Wu, X., Clements, D. L., Parmar, A., Davidge, H., & Pearson, M. (2025). The Herschel-SPIRE Dark Field I: The deepest Herschel image of the submillimetre Universe. Monthly Notices of the Royal Astronomical Society, 539(1), 336–346. https://doi.org/10.1093/mnras/staf335

Varnish, T. W. O., Wu, X., Pearson, C., Clements, D. L., & Parmar, A. (2025). The Herschel-SPIRE Dark Field – II. A P(D) fluctuation analysis of the deepest Herschel image of the submillimetre universe. Monthly Notices of the Royal Astronomical Society, 539(1), 347–354.