Observing a distant supernova is like looking back in time. The explosions offer astronomers a peek at what our universe was like billions of years in the past. Now astronomers have discovered 10 times more distant supernovae than anyone had seen before, including the oldest and farthest supernova ever observed.
The discoveries came from data captured by NASA’s James Webb Space Telescope. Announced at the American Astronomical Society meeting in Madison, Wisconsin, earlier this month, astronomers analyzed Webb images and found about 80 supernovae in just one tiny patch of the sky. Many of the supernovae are further out than those previously known, representing a time when the universe was a youthful two billion years old.
The telescope is an ideal tool to search for such distant points of light in the universe. “[Webb] is a big telescope, nearly 10 times bigger than the Hubble Space Telescope in terms of light collecting area,” says Justin Pierel, an astronomer at the Space Telescope Science Institute in Baltimore, Maryland, who worked on the new research. In addition to seeing a larger part of the sky, Webb is also more sensitive to the longer light wavelengths that indicate the presence of supernovae. “We knew these faint and far-off supernovae existed, but we were unable to see them prior,” Pierel says.
(Learn about what happens when stars explode.)
The increased size and sensitivity of Webb allowed it to pick up what other telescopes have not been able to detect. “I think it is great to see that these supernovae can be recovered in the Webb data,” says Harvard University astronomer Edo Berger, who was not involved in the new research. The new data add to a growing record of exploded stars from different times in the universe’s history. While finding around 80 distant supernovae in a small patch of sky is significant, Berger notes, “these are still a small fraction of all supernovae being discovered by wide-field and shallower surveys, in excess of 10,000 supernovae per year.” But many of those supernovae are younger and closer to Earth. The significance of the Webb finds is in uncovering supernovae that are further out, representing a much earlier time in the universe’s history.
Peek into the past
In order to find more distant and therefore more ancient supernovae, researchers compared multiple images taken by Webb over the span of a year. The astronomers looked for light sources that appeared or disappeared in the images, or what experts refer to as transients. Not only did the researchers detect dozens of supernovae, but the nature of the light indicated that the supernovae exploded billions of years before our present moment.
Webb can detect supernovae thanks to a phenomenon known as cosmological redshift. As light travels through space, its wavelength is pulled like taffy. Light’s wavelengths become longer, falling into the infrared part of the spectrum—invisible to the naked eye, but visible to a telescope with the right equipment.
Different redshift characteristics correspond to different times in the universe’s history, and the present day is redshift zero. The higher the redshift, the older the supernova is. So while a redshift of 2 indicates a supernova from when the universe was about 3.3 billion years old, one of the newly-found supernovae has a redshift of 3.6 and formed when the universe was about 1.8 billion years old. That puts the ancient supernova at 12 billion years old, the oldest ever detected. The data offers a way to get a sense of what the universe was like long before Earth even existed. “The universe is nearly 14 billion years old, but these supernovae are from a time when the universe was just a couple billion years old, the equivalent of being a teenager for humans,” Pierel says.
Early universe insights
The new data will provide a launching point for researchers to investigate the nature of the early universe, how stars formed, and what happened when they exploded. In fact, Pierel notes, distant stars are often too faint to see even with the most powerful telescopes. Exploding stars are brighter and easier to detect.
Specific types of supernovae in the sample may provide some new insights, as well. Webb detected at least one supernova that astronomers categorize as Type 1a, which means it’s particularly bright and could be used to measure long distances in space. “Finding these higher redshift supernovae is important for making cosmological measurements,” Berger says, as well as studying phenomena like dark energy.
(Learn about the mysteries surrounding Type 1a supernovae.)
Exploding stars are an essential part to the universe we live in. “If stars did not explode, life as we know it would not be possible,” Pierel says. The elements that are so essential to life on Earth were flung out of such explosions when the universe was much younger, forming the basis for our planet and life upon it. Distant as they may be from us, the supernovae are an essential part of our own story.
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