Astronomy scientists She spotted something unusual happening in a distant galaxy in recent images from the James Webb Space Telescope – something that wasn’t there when Hubble last looked at the same galaxy.
“We suspect it’s a supernova,” astronomer Mike Engiser From the Space Telescope Science Institute (STScI) says inverse. Finding short-lived cosmic events like supernovae isn’t what Webb was designed for, but the newly launched space telescope seems to be full of surprises. This could open the door to searching for the death pains of the first generations of massive stars.
what’s new – The bright object may have been the first supernova spotted by the Webb telescope, Engeser and colleagues say. It’s very bright compared to the rest of the galaxy, for one thing. Webb observed the galaxy, named SDSS.J141930.11 + 5251593, twice, five days apart; The object is opaque, slightly, during those five days – classic supernova behaviour.
“We’ll need more time-series data to make a decision, but the data we have matches that of a supernova, so it’s a very good candidate,” Engiser says.
The galaxy, which we won’t repeat its unwieldy astronomical name, is between 3 and 4 billion light-years away, so astronomers see the slowly fading light of an explosion 3 to 4 billion years ago. The actual death of a star takes a split second, but the resulting fireball takes days to grow and shine, then gradually fades over the next few months. This is a snapshot of astronomical time, so it is fortunate that Webb discovered this supernova shortly after it reached its peak brightness.
“In the first place, it’s exciting because we’ve shown that we’re able to find and detect new transients using Webb, something that JWST wasn’t designed to do,” Engesser says. “But it’s one of the things we’re showing that we can do in a kind of customized way.”
Although versatile, Webb is not the type of telescope that astronomers typically use to search for short-lived objects such as supernovae. Most of the time, this work is done by ground-based telescopes here on Earth, which visualize large swaths of the sky every night.
On the other hand, Webb appears much deeper in smaller patches of sky. The telescope’s first deep-field image, released on July 12, covers an area of the sky that you can cover with a grain of sand held at arm’s length.
“So the actual probability that you’ll find a temporary item in the field you’re looking for is fairly small — or at least we thought it would be small,” Engeser says. “But as you’ve probably heard, every JWST field is a deep field at this point, so there are galaxies all over the place, and now we’re thinking, Oh, we might have a really good chance of spotting supernovae all the time.”
Here’s the background – Ground-based telescopes that usually search for supernovae take pictures of the same wide areas of the sky every few nights. Their data processing software compares each new image to previous images of the same area, looking for anything that might have changed.
To do the same with space telescopes, Engesser and colleagues compared the new data from Webb’s NIRCam instrument to Hubble images from the same region. They used software to look for any differences that might reveal what astronomers call “transients,” things that appear, fade, light up, or dim on a timescale that we can actually see in real time.
This is how the team found the supernova. It’s also how to locate a supernova that erupted into life in 2013. Astronomers knew it, called 2013 EJ, but the once bright ball of fire faded away so long ago that most telescopes couldn’t see it.
“There are a lot of questions about this particular object and what kind of star it was, and its environment – like how dusty is it? It seems very dusty,” Engiser says.
Because supernovae tend to fade within a few months, astronomers usually don’t get to see their much later stages, and they could provide more clues about what type of star exploded, along with the physics of that starburst. Webb’s deep view of the universe could make tracking the effects of a supernova like 2013 EJ easier even after several years.
“So observing this now with Webb is really cool as a way to explore the very late environment around big, bright supernovae like this,” Engesser says. “We get new insights that we couldn’t get before.”
Ingeser describes both discoveries—the newly discovered supernova and the vanishing supernova that scientists have lost—as proof of concept. He and colleagues are part of the Transient Science @ Space Telescope research team, led by astrophysicist Ori Fox at STScI. Fox’s team wants to use Webb to search for supernovae in the oldest and most distant galaxies in the universe, the kind that even Hubble has a hard time seeing.
“If we can discover new things, it allows us to do this kind of goal of a very quick turnaround of opportunity proposals, where we discover something and then we can say, ‘OK, interrupt everything else. We want to notice this thing now; This is time sensitive,” Engiser explains. “Once we have good ammo [of supernovae] We could say, “Well, it’s very useful to have these time-sensitive observations of super redshift supernovae.”
why does it matter – Old and distant supernovae could help astronomers better understand the fabric of the universe and how it expands and expands over time. Most physicists now agree that the universe is expanding, and that expansion is accelerating. That’s thanks to a 1998 study that used a specific type of supernova to help measure distances between objects in the universe. These supernovae, called Type Ia supernovae, occur when a white dwarf star in a binary star system steals so much material from its companion star that the greedy white dwarf collapses under its own mass.
Since a Type Ia supernova is always the same brightness, astronomers can measure how bright a supernova is in order to calculate its distance and host galaxy. Astronomers call objects of known brightness “standard candles”.
“By looking at the redshift of these supernovae, you can measure how quickly they are moving away from you, as well as how far away they are,” Engiser explains. “So one of the things we want to be able to do with Webb is to discover extremely redshift supernovae to further constrain the cosmic nature of the universe and how it changes over time.”
The oldest supernovae in the universe also contain clues about the short life and violent death of the first generation of very massive stars in the universe. Perhaps those ancient giant stars were very different from the giant stars in the nearby universe, which is the modern universe more familiar to us.
“We think the stars in the first few million years were essentially, almost entirely, of hydrogen and helium, unlike the kinds of stars we have now. They would have been massive – 200 to 300 times the mass of our sun, and they would certainly have lived in some sort of style “Live fast, die young,” says Engeser. “Seeing these kinds of explosions is something we haven’t done yet.”
What’s Next – Engeser and his team have yet to decide whether to take a second look at the supernova they’ve discovered.
“Supernovae in the grand scheme of things are actually fairly common,” he says. “This supernova is as interesting as Webb was the first to find it, which is amazing. In and of itself, it might not all be that interesting. We are still looking at whether or not we want to make any follow-up observations of this thing.”
If astronomers decide to study the newly discovered supernova further, they can answer some specific questions. Watching how the supernova’s light dims over time can reveal the type of supernova — such as Type Ia — that Engiser and colleagues found. Spectrophotometry from a supernova can reveal which chemical elements make up the parent star, and thus what kind of star exploded violently.
But in the meantime, Engesser and his colleagues are focused on finding more transient bright spots in Webb’s deep views of the universe.
This story was updated on July 28, 2022 to include the last five paragraphs.
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