Webb telescope just saw more galaxies in a snapshot than Hubble's deepest look

A project to map the earliest structures of the universe has found 15,000 more galaxies in its first snapshot than captured in an entire deep field survey conducted 20 years ago.

The James Webb Space Telescope, the new preeminent observatory in the sky, saw about 25,000 galaxies in that single image, dramatically surpassing the nearly 10,000 shown in the Hubble Space Telescope's Ultra Deep Field Survey. Scientists say that little piece of the space pie represents just four percent of the data they'll discover from the new Webb survey by the time it's completed next year.

"When it is finished, this deep field will be astoundingly large and overwhelmingly beautiful," said Caitlin Casey, a University of Texas at Austin astronomer co-leading the investigation, in a statement.

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Before Webb even became operational in July 2022, scientists at NASA, the European Space Agency, and the Canadian Space Agency promised the telescope would go deeper into space than humans had ever seen before. In astronomy, looking farther translates into observing the past because light and other forms of radiation take longer to reach us.

A deep field image is much like drilling deep into Earth to take a core sample: It's a narrow but distant view of the cosmos, revealing layers of history by cutting across billions of light-years. In Hubble's deep field, the oldest visible galaxies dated back to the first 800 million years after the Big Bang. That's an incredibly early period relative to the universe’s estimated age of 13.8 billion-with-a-B years.

But Webb was built to see an even earlier period, using a much larger primary mirror than Hubble's — 21 feet in diameter versus just under eight feet — and detecting invisible light at infrared wavelengths. In short, a lot of dust and gas in space obscures the view to extremely distant and inherently dim light sources, but infrared waves can penetrate through the clouds. One Webb scientist said the telescope is so sensitive, it could detect the heat of a bumblebee on the moon.

"The initial goal for this mission was to see the first stars and galaxies," said Eric Smith, Webb's program scientist, last year, "not the first light of the universe but to watch the universe turn the lights on for the first time."

Researchers involved in the new survey, called COSMOS-Web, released mosaic images taken in January by Webb's Near-infrared Camera and Mid-Infrared Instrument. A paper providing the scope and outlook for the project is available on the ArXiv preprint server now and will be published in The Astrophysical Journal.

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The first images from COSMOS-Web, the largest program in Webb's first year, show a rich variety of structures, teeming with spiral galaxies, gravitational lensing, and galaxy mergers. Furthermore, hundreds of galaxies that were previously identified by Hubble are getting reclassified with different characteristics after being shown in more detail with Webb.

Scientists say the purpose of the probe is to learn more about the so-called Reionization Era, which occurred about 200,000 to 1 billion years after the Big Bang. They'll also seek to identify massive galaxies from the first 2 billion years and study how dark matter, invisible space material suspected to exist throughout the universe, has evolved.

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Over 255 hours of observation, the COSMOS-Web team wants to map 0.6 square degrees of the sky with NIRCam — roughly the size of three full moons — and 0.2 square degrees with MIRI. Nearly 100 astronomers from around the world are involved.

So far the sharpness and clarity of the data are even better than expected, said Jeyhan Kartaltepe, an astrophysicist at Rochester Institute of Technology co-leading the project, in a statement.

"This is just a drop in the bucket of what’s to come,” she said.