The James Webb Space Telescope (JWST) is an exceptional tool for investigating the explosive deaths of massive stars in the early universe. Acting as a cosmic detective, the JWST has discovered evidence of 80 new early supernovas in a small area of the sky, equivalent to the size of a grain of rice held at arm’s length.
This discovery is remarkable for two reasons. Firstly, it is ten times more supernovas than previously found in the early cosmic history. Secondly, the sample includes the earliest and most distant supernova ever observed. This particular explosion occurred when the universe was just 1.8 billion years old, dating back 13.8 billion years.
The findings were made possible by the data collected through the JWST Advanced Deep Extragalactic Survey (JADES) program. This unprecedented collection of supernovas includes Type Ia explosions, known as “standard candles,” which astronomers use to measure cosmic distances.
Prior to the launch of the JWST in the summer of 2022, only a few supernovas had been identified from when the universe was 3.3 billion years old, which is about 25% of its current age. However, the JADES sample contains numerous supernovas that exploded even further back in time, some occurring when the universe was less than 2 billion years old.
According to Christa DeCoursey, a member of the JWST team and a graduate student at the Steward Observatory and the University of Arizona, the JWST is a highly efficient machine for discovering supernovas. She stated that the survey has yielded two exciting results: the large number of detections and the vast distances to these supernovas.
Thanks to its unparalleled infrared sensitivity, the JWST is able to detect supernovas in almost every corner of the cosmos. It has become a powerful tool in the search for these cosmic explosions.
As light wavelengths traverse the vast expanse of the universe, the expansion of space itself stretches these wavelengths. This stretching effect causes the light to transition towards the red end of the electromagnetic spectrum, moving away from the blue end. This phenomenon is commonly referred to as “redshift.”
The extent of redshift experienced by light is directly proportional to the duration it has been traveling through space. Consequently, light originating from celestial bodies located approximately 12 billion light-years away, such as supernovas, undergoes significant wavelength elongation known as “cosmological redshift.”
Due to this cosmological redshift, the light emitted by these supernovas is shifted into the infrared region of the electromagnetic spectrum. This region aligns perfectly with the observational capabilities of the James Webb Space Telescope (JWST) for studying the universe.
Previously, the Hubble Space Telescope enabled astronomers to observe supernovas that existed when the universe was in its “young adult” phase. However, with the JADES and JWST projects, astronomers now have the ability to study supernovas during the cosmos’ “teens” or even “pre-teens” stage.
In the future, scientists aim to investigate the “toddler” phase of the universe, and ideally, uncover the deaths of the initial generation of massive stars during its cosmic infancy.
To gather this wealth of supernova observations, the JADES team captured multiple images of the same region of the sky over the course of a year. They then compared these images, as supernovas are transient events that brighten and fade over time. By examining the changes in the images, the scientists were able to distinguish which points of light were actually exploding stars and which were likely unrelated phenomena.
“The findings from the JADES team provide us with our first glimpse into the high-redshift universe in terms of transient science,” commented Justin Pierel, a member of the team and a NASA Einstein Fellow at the Space Telescope Science Institute (STScI) in Baltimore, Maryland. “Our objective is to determine whether distant supernovas exhibit any fundamental differences from those observed in the nearby universe.”
It is worth noting that not all of the supernovas observed by the JADES team were of the “core collapse” variety, which occur when massive stars exhaust their nuclear fusion fuel in their cores and collapse under their own gravitational pull, resulting in the formation of a black hole or a neutron star.
In addition, the team also observed Type Ia supernovas, which occur when white dwarf stars feed on material stripped from a companion star. This material accumulates on the surface of the white dwarf until a runaway thermonuclear explosion occurs, completely obliterating the white dwarf.
The brightness of these events remains constant, regardless of their distance, indicating that they can be used as reference points to measure distance in the universe. Additionally, they can help us understand the rate at which space is expanding. However, if the intrinsic brightness of Type Ia supernovas changes at high redshifts, their usefulness in measuring large cosmic distances would be limited.
The team’s observations of a Type Ia supernova that occurred approximately 11 billion years ago showed that its brightness had not changed, even though its light had undergone cosmological redshift.