Using data from a deep survey of the early universe conducted with the Webb telescope, a team has identified ten times more distant supernovae than previously known. Some of the newly discovered exploding stars are the most distant examples of their type, including those used to measure the expansion rate of the universe. This study is the first significant step toward broader studies of ancient supernovae with the Webb telescope, according to its authors. “The Webb telescope is a supernova discovery machine,” Christa DeCoursey, a third-year graduate student at Steward Observatory and the University of Arizona in Tucson, said in a statement. “The large number of detections plus the great distances at which these supernovae are found are the two most exciting results of our study.” DeCoursey presented these findings at a press conference at the 244th meeting of the American Astronomical Society. To make these discoveries, the team analyzed image data obtained as part of JWST’s Advanced Deep Extragalactic Survey (JADES) program. The Webb is ideal for finding extremely distant supernovae because its light is stretched into longer wavelengths, a phenomenon known as cosmological redshift. Before Webb’s launch, only a handful of supernovae had been found above a redshift of 2, which corresponds to when the universe was just 3.3 billion years old, just 25% of its current age. The JADES sample contains many supernovae that exploded even further away in the past, when the universe was less than 2 billion years old. Previously, researchers used NASA’s Hubble Space Telescope to view supernovae from when the universe was in the “young adult” stage. With JADES, scientists are seeing supernovae when the universe was in its “adolescence” or “pre-adolescence.” In the future, they hope to observe the “infancy” phase of the universe. To discover supernovae, the team compared multiple images taken a year apart and looked for sources that disappeared or appeared in those images. These objects whose observed brightness varies with time are called transient objects, and supernovae are one type of transient objects. In total, the JADES Transient Survey Sample team discovered about 80 supernovae in an area of sky barely the thickness of a grain of rice held at arm’s length. “This is really our first glimpse of what the high-redshift universe looks like for the science of transient objects,” said Justin Pierel, a NASA Einstein Fellow at the Space Telescope Science Institute (STScI). “We are trying to identify whether distant supernovae are fundamentally different or very similar to what we see in the nearby universe.” Pierel and other STScI researchers provided expert analysis to determine which transient objects were actually supernovae and which were not, because they often looked very similar. The team identified several high-redshift supernovae, including the most distant one ever confirmed spectroscopically, at a redshift of 3.6. Its parent star exploded when the universe was only 1.8 billion years old. This is a so-called core collapse supernova, an explosion of a massive star. Type Ia supernovae are of particular interest to astrophysicists. These exploding stars are so predictably bright that they are used to measure distant cosmic distances and help scientists calculate the expansion rate of the universe. The team identified at least one type Ia supernova with a redshift of 2.9. Light from this explosion began traveling toward us 11.5 billion years ago, when the universe was only 2.3 billion years old. The previous distance record for a spectroscopically confirmed Type Ia supernova was a redshift of 1.95, when the universe was 3.4 billion years old. Scientists are eager to analyze Type Ia supernovae at high redshifts to see if they all have the same intrinsic brightness, regardless of distance. This is vitally important, because if their brightness varies with redshift, they would not be reliable markers for measuring the expansion rate of the universe. Pierel analyzed this type Ia supernova found at a redshift of 2.9 to determine if its intrinsic brightness was different than expected. While this is only the first object of its kind, the results indicate no evidence that type Ia brightness changes with redshift. More data is needed, but for now, Type Ia supernova-based theories about the universe’s expansion rate and its ultimate fate remain intact.
