by Astronomers are now discovering record-breaking distant galaxies by the dozens as they sift through the treasure trove of data now being collected by the James Webb Space Telescope (JWST or Webb). Among them are several galaxies that date back to just over 200 million years after the Big Bang.
Before the launch of The James Webb Space Telescopethe most distant confirmed galaxy known was GN-z11which astronomers saw as it was about 420 million years after The big bangand gives it what astronomers call a redshift of 11.6. (Redshift describes how much the light coming from a galaxy has been stretched as univers expands. The higher the redshift, the further back in time we see a galaxy.)
Just a week after the release of first science images from JWST, astronomers reported detection of galaxies at redshift 13, corresponds to around 300 million years after the Big Bang. Now a new wave of scientific results is about to beat this record, with some astronomers reporting the detection of galaxies up to a redshift of 20. If true, then we see these galaxies as they existed about 200 million years after Big Bang.
Gallery: The James Webb Space Telescope’s first images
There’s a big if: At this stage, none of these redshift values have been confirmed. To confirm the distances to these galaxies will require spectroscopic analysis, which divides the light from an object into what scientists call a spectrum. That analysis will come later. Still, it seems clear that JWST is fully capable of detecting galaxies from this long-lost era.
The galaxies have been discovered using different techniques. Astronomers led by Haojing Yan of the University of Missouri-Columbia used gravitational lensing created by the galaxy cluster SMACS J0723 to detect 88 candidate galaxies beyond a redshift of 11, including a handful estimated to be at a redshift of 20. If validated, these galaxies would be by far the most distant ever discovered. Due to cosmic expansion, these galaxies would today be over 35 billion light years away from us.
Two other papers report finding high-redshift galaxies in patches of sky where JWST has simply taken deep exposures, without resorting to gravitational lensing. These images are part of the Cosmic Evolution Early Release Science (CEERS) survey, which consists of images of 10 different sky spots from JWST’s Near-Infrared Camera (NIRCam). JWST’s Near-infrared spectrograph (NIRSpec) joins observations of six of these spots, while the space telescope’s Mid-Infrared Instrument (MIRI) studies four.
One team of astronomers, led by Ph.D. student Callum Donnan at the University of Edinburgh, found a candidate galaxy with a redshift of 16.7, which corresponds to just 250 million years after the Big Bang. The team also found five other galaxies with a redshift greater than 12, all of which exceed the redshift record set by JWST’s predecessor and now colleague, The Hubble Space Telescope.
Meanwhile, using the same observations from CEERS, another team led by Steven Finkelstein of the University of Texas at Austin discovered a galaxy with a redshift of 14.3, placing it 280 million years after the Big Bang, which scientists have called “Maisie’s Galaxy”. after Finkelstein’s daughter. The astronomers found that this galaxy may have also been seen by the Hubble Space Telescope, but not recognized at the time. If a closer look at the archived data reveals the galaxy, Maisie’s galaxy would have to produce very bright ultraviolet light from a powerful burst of star formation for Hubble to have detected it.
In fact, all of the distant galaxy candidates show evidence of strong emission of ultraviolet light, enough to possibly settle the debate about what ionized the hydrogen gas in the universe, bringing an end to the so-called “Cosmic Dark Ages.” Over the years, astronomers have proposed causes ranging from radiation from the first stars and galaxies to outflows of radiation from the first supermassive black holes.
In their paper, Donnan’s team calculates the “galactic ultraviolet luminosity function” between redshifts of 8 and 15. This function is an average of the amount of ultraviolet light associated with galaxies at a particular epoch. The value is strongly linked to star formation, because the more hot young stars that form in a galaxy, the more ultraviolet light it emits. Donnan’s team concluded that there is more than enough ultraviolet radiation produced by the stars in these early galaxies to ionize the universe.
The abundance of high-redshift galaxies being discovered can be thought of as cosmic babies. These galaxies span only 1,000 or so light-years across and contain only tens of millions of stars; modern galaxies can host hundreds of billions of stars. Astronomers estimate that the cosmic babies are less than 100 million years old, and possibly as young as 20 million years.
Scientists have yet to identify any of the very first galaxies in the universe, which may lie at redshift 25 or higher. Nevertheless, the new detections represent generations of galaxies that followed closely behind, and which the researchers see in the early stages of development.
The amount of ultraviolet light (redshifted into the longer wavelengths of infrared light, making it visible to JWST), combined with the abundance of high-redshift galaxies it finds so early in the mission, suggests that there were many galaxies in the earliest history of the universe. Contrary to some expectations, the rate of star formation may slow down gradually the further back in time we look, rather than there being a sharp drop beyond redshift 11.
“Should follow up spectroscopy validate [these redshifts], [it means that] our universe was already illuminated by galaxies less than 300 million years after the Big Bang,” Finkelstein’s team wrote in the paper.
Now that JWST has detected these strong galaxy candidates at great distances, the next questions are how much further back in time JWST can see and whether that will be enough to detect the very first galaxies that existed, perhaps only 100 million years after the Big Bang. Such a discovery would require a large dose of luck, since it would rely on random gravitational lensing to bring primordial galaxies into view.
The Yan paper can be found here; The Donnan newspaper here; and the Finkelstein newspaper here.
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