Performing at the Gates of Dawn
Since the James Webb Space Telescope went into service two years ago, astronomers have been using it to leap millions of years into the past, back to the moment they call cosmic dawn, when the first stars and galaxies formed.
Last month, an international team conducting research as the JWST Advanced Deep Extragalactic Survey, or JADES, said it had identified the earliest, most distant galaxy yet — a banana-shaped smudge of color 1,600 light-years across. It shone with intense starlight when the universe was still in its relative infancy, at just 290 million years old, the astronomers said.
The new galaxy, known as JADES-GS-z14-0, is part of a series of Webb discoveries, including early galaxies and black holes, that challenge conventional models of the formation of the first stars and galaxies.
“This discovery proves that luminous galaxies already existed 300 million years after the Big Bang and were more common than expected,” the researchers said. wrote in a paper posted in an online physics archive.
“Models of galaxy formation will have to account for the existence of such large and bright galaxies so early in cosmic history,” said the authors, who were led by Stefano Carniani, a professor at the Scuola Normale Superiore University in Pisa, Italy.
The galaxy was first spotted during a deep-space survey using Webb’s Near Infrared Camera, one of the telescope’s workhorse instruments. Within a patch of southern sky known as the Jades Origin Field, about a quarter the size of a full moon, scientists found 11 galaxies that appeared to date back to when the universe was less than 400 million years old — far more than currently expected.
Follow-up studies by Dr. Carniani and his colleagues using the telescope’s infrared spectrograph revealed that the wavelength of light from JADES-GS-z14-0 had been stretched by more than 15 times due to the expansion of the Universe (a redshift of 14, to use astronomical jargon), similar to the way the pitch of a siren decreases as it drives away. That means the light has been coming toward us for 13.5 billion years, since shortly after the Universe began. (According to cosmological calculations, the Universe is about 13.8 billion years old.)
The Milky Way’s light is spread across a diffuse region, indicating that the glow came from stars and not from the esophagus of a black hole. Its brightness was equivalent to the production of hundreds of millions of suns, an astonishing number that formed and assembled in just 290 million years.
The starlight also contained spectral signatures of oxygen, which did not exist when the universe was first born. That means the stars in that galaxy have already undergone several cycles of birth, death and rebirth, which have enriched the universe with the heavy elements we need to evolve and exist.
How that happened in such a short time is a mystery, a riddle in a sky full of them. Some astronomers have suggested that supermassive black holes – formed by the collapse of primordial gas clouds – could have served as seeds for galaxies.
In a blog postDr. Carniani and Kevin Hainline of the University of Arizona, another member of the JADES team, wrote: “It is likely that astronomers will find many such luminous galaxies with Webb in the next decade, possibly even sooner. We are thrilled to see the extraordinary diversity of galaxies that existed at Cosmic Dawn!”
