“We’re essentially opening a new window on the transient universe” said Matthew Siebert of the Space Telescope Science Institute, capturing the awe that swept through the astrophysics community after the James Webb Space Telescope (JWST) revealed 80 ancient supernovae erupting just 1.9 billion years after the Big Bang. This announcement, presented at the 244th meeting of the American Astronomical Society, represents a quantum leap in humanity’s efforts to reconstruct the universe’s early stages a stretch of time that, until now, has been lost in space-age darkness.
The JWST’s JADES (JWST Advanced Deep Extragalactic Survey) program achieved what had long eluded astronomers: it filled in a 13.7-billion-year gap in the history of supernovae, and discovered stellar explosions when the universe was in its cosmic “pre-teen” years. Prior to JWST, even the Hubble Space Telescope a celebrity for its starling “Pillars of Creation” image could see only back to when the universe was a “young adult,” about 3.3 billion years old, equivalent to a redshift of 2. The JADES survey pushed that limit to redshifts as high as 3.6, with light from a core-collapse supernova that exploded when the universe was just 1.8 billion years old (the farthest ever spectroscopically confirmed).
This was made possible through the intersection of science and engineering expertise. The infrared sensitivity of JWST is tuned to the expansion of the universe: since light from distant supernovae takes billions of years to arrive, it is stretched into red, longer wavelengths a cosmological redshift. With these faint signals, JWST enables astronomers to observe and date supernovae that went off when the universe was constructing its first galaxies.
The method is as elegant as it is straightforward. The JADES scientists compared numerous images of the same region of sky, taken anywhere from a few months to a year or so later, for transients objects that appear or go away with time. Supernovae, the most dramatic of the transients, appear as new points of light that burn and then fade. In a square of sky no larger than a grain of rice held at arm’s length, the team found their 80 supernovae, each a cosmic time capsule from an era when the universe was younger than two billion years.
The scientific reward is enormous. Among the surprises was a Type Ia supernova at redshift 2.9, whose light departed 11.5 billion years ago. Type Ia supernovae are prized as “standard candles” they burn with the same intensity every time, and astronomers can use them to measure vast cosmic distances and make an estimate of the universe’s rate of expansion. JADES’ discovery extended the old record distance for a spectroscopicly confirmed Type Ia supernova by nearly a billion years. Justin Pierel, a NASA Einstein Fellow, looked at this old supernova and found “no evidence that Type Ia brightness changes with redshift,” a discovery that at least for the time being makes these cosmic yardsticks (so critical to cosmology) trustworthy.
Real excitement, though, is in variety and violence of these early explosions. First stars, Population III stars, were composed of primordial hydrogen and helium, with hardly any heavier elements. Their lives were short and their deaths spectacular. A few, with masses ranging up to 20 times that of the Sun, detonated in core-collapse supernovae of never-before-seen energy like AT 2023adsv, which “exploded with around twice the energy of the average supernova triggered by nearby massive stars,” reports David Coulter of the JADES team (giving glimpses into the chemical evolution of the early universe). These blasts seeded the universe with heavy elements, clearing the way for later generations of stars, planets, and ultimately, life.
Physicists seek the fingerprints of yet more colossal explosions. Astronomers are beginning to detect the chemical signatures of so-called “pair-instability supernovae” theoretical explosions of 150 to 300-solar-mass stars with no remnant left behind. By examining the light of distant quasars, researchers have observed clouds with incredibly high iron-to-magnesium ratios, a hallmark of such a super-supernova. “It was obvious to me that the supernova candidate for this would be a pair-instability supernova of a Population III star, in which the entire star explodes without leaving any remnant behind,” University of Tokyo astronomer Yuzuru Yoshii (with the aid of advanced spectrographic analysis) explained to us.
This relentless parade of observational astronomy is a testament to centuries of progress. From Hans Lippershey’s first telescope in 1608, through Galileo’s observations in the heavens and Kepler’s laws of planetary motion, to the launch of Hubble in 1990 and the flight of JWST, each advance in technology has pushed the boundaries of space knowledge. Now, the JWST’s ability to probe the universe’s early days is not merely an engineering achievement, but a link through time that connects the universe’s youth turmoil and its present-day complexity.
To the world of astrophysics, the JADES discovery is not a catalog of ancient explosions. It is a living history of cosmic evolution, a new chapter in the book of how the universe assembled itself from the debris of its first stars. As Siebert described it, “Historically, whenever we’ve done that, we’ve found extremely exciting things — things that we didn’t expect.” The universe, it seems, is always poised to surprise.
