Peering back to before the cosmic dawn: astronomers unveil first results from the JWST

A year after its launch, astronomers are revealing the secrets of the universe, as the first scientific results from observations made by the James Webb Space Telescope (JWST) are released. This month, Physics World is publishing a series of blog posts on the discoveries. This is the first post in the series.

A JWST image of the galaxy cluster Abell 2744
Magnifying lens: A JWST image of the galaxy cluster Abell 2744, the great mass of which acts as a gravitational lens, magnifying the light of high redshift galaxies. (Courtesy: NASA /ESA /CSA /Bezanson et al.)

Just under a year after this incredible mission took off, astronomers have been meeting this week to present and discuss the first scientific results from the James Webb Space Telescope (JWST). Monday 12 December marked the first day of “First Science Results from JWST” conference, transporting astronomers back in time to just before the cosmic dawn, when galaxies were young, the first supermassive black holes were awakening and the cosmic “Dark Ages” were coming to an end.

The three-day conference – which ran until 14 December at the Space Telescope Science Institute (STScI) in Baltimore, US – has been long awaited by scientists and engineers, some of whom have invested decades of their lives into getting the JWST built and into space. “It’s like we’re living in the future now,” says Susan Mullally, conference co-chair and deputy project scientist for the telescope, “I’ve been waiting for Webb to launch for my entire career.”

“We’re seeing farther away, seeing very infant galaxies that we haven’t been able to see before,” adds Mullally. Speaking before the event began, she provided Physics World with a preview of what else was to come. “I also expect to hear about our ability to look deep into exoplanetary atmospheres of worlds we’ve previously known little about. And the other thing that’s going to be interesting is the spectacular images – Webb has wonderful resolution, and as I’ve been perusing the conference posters, I’ve never seen so many beautiful images.”

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The first science results

The first day focused on the current status of the telescope – described as “phenomenal” by NASA’s Jane Rigby, the JWST’s operations project scientist – before moving on to the first science results. While some of these had been revealed previously in press releases detailing some very-high-redshift galaxies observed by the JWST, the conference presentations put some much-needed meat on the bones.

Many of the initial science results have come from the early release of data from several of the JWST’s deep surveys of the universe, including JADES, the JWST Advanced Deep Extragalactic Survey. Emma Curtis-Lake of the University of Hertfordshire, UK, kicked things off  by describing the initial findings from JADES, which has so far focused on the area of the Hubble Ultra Deep Field. Thanks to the JWST’s Near-Infrared Spectrometer (NIRSpec) – which can obtain spectra of hundreds of galaxies in the field of view simultaneously – astronomers have been able to sample thousands of galaxies.

“We’re really getting some beautiful spectra out,” said Curtis-Lake during her presentation. Among these are three galaxies with spectroscopically confirmed ultrahigh redshifts of 11.58, 12.63 and 13.20, smashing the pre-JWST record of 11.1 for the galaxy Gn-z11. These galaxies existed less than 400 million years after the Big Bang and have very low abundances of heavy elements, as expected for galaxies that have barely had any time to form stars.

NIRSpec is also finding evidence for supermassive black holes in the JADES field. Hannah Übler, of the Kavli Institute for Cosmology at the University of Cambridge, UK, revealed the presence of an active black hole hundreds of millions of times the mass of the Sun at the centre of a modestly sized galaxy at a redshift of 5.5. In fact, the galaxy almost seems too small for the black hole, upending the relationship between the stellar mass of a galaxy and the mass of its black hole.

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Feige Wang, of Steward Observatory at the University of Arizona, US, spoke on how the JWST was finding even more black holes in the early universe as part of ASPIRE (A SPectroscopic survey of biased halos In the Reionisation Era). ASPIRE is detecting quasars (active galactic nuclei powered by accretion onto a supermassive black hole) at redshifts as great as 7.5, nearly 13 billion years ago. Wang described how the JWST is able to detect the host galaxies of these distant quasars where the Hubble Space Telescope could not, and also showed evidence that these galaxies lie in “over-densities” – regions of space filled with more galaxies than on average, indicating they could be proto-galaxy clusters.

Gravitational lenses are also exploited in the hunt for high-redshift galaxies. Some of these have been identified as part of the JWST’s UNCOVER (Ultradeep NIRSpec and NIRCam ObserVations before the Epoch of Reionisation) survey, which is probing the gravitationally lensing galaxy cluster Abell 2744. The JWST has uncovered 75 new multiply lensed images, originating from 16 high-redshift background galaxies whose light has been magnified and distorted by the massive gravity of Abell 2744 in the foreground. “There’s much more still to be discovered in the data,” said Rachel Bezanson of the University of Pittsburgh in her presentation. “I can’t tell you what the most exciting thing here is, but there’s some cool stuff.”

“Something really exciting is going on”

Another survey is CEERS (Cosmic Evolution Early Release Science). Steven Finkelstein of the University of Texas at Austin, US, described the high-redshift galaxies that are being discovered in the CEERS data, including one galaxy named Maisie’s Galaxy after Finkelstein’s daughter, which is at a redshift greater than 12 (although this awaits spectroscopic confirmation).

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Intriguingly, many of these high-redshift galaxies are shining brighter in ultraviolet (UV) light than cosmologists’ simulations predict. UV light is produced largely by hot, young stars and therefore a galaxy’s UV luminosity is a measure of star formation. The expectation was that this UV luminosity function would drop off the earlier we look into the history of the universe, since early galaxies would contain fewer stars. For these galaxies to be so bright in UV means that something fundamental about how galaxies form stars was different back then.

“It’s not anything that breaks the universe,” quipped Finkelstein in response to previous social-media claims that the JWST had somehow disproven the Big Bang through this discovery. One possible explanation, he said, could be that these early galaxies hosted a greater abundance of hot, massive, UV-emitting stars as a result of the low abundance of heavy elements at these times. Calculations suggest that this could see the UV luminosity increase by as much as 2.5 times, matching what the JWST observes.

“Am I saying that’s the case? Absolutely not,” said Finkelstein. “We need a lot more data, we need spectroscopic confirmation, but it’s giving us a lot of hints that something really exciting is going on.”

  • Keith Cooper’s next blog post will report on the second day of the conference, covering the JWST’s observations of star formation and evolution, and new discoveries made on comets and planets in the solar system and beyond.

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