- In 1987, astronomers recorded the only supernova visible to the naked eye in the last 400 years.
- Astronomers have since wondered about what the massive explosion left behind in its wake.
- Using JWST, astronomers finally have the answer to the question they've been chasing for decades.
In a nearby galaxy, 160,000 light years away, a massive star exploded in a brilliant supernova, spewing its guts across the universe. The explosion was so bright that humans could see it with the naked eye.
That was 37 years ago, and astronomers have been studying that same patch of sky ever since, chasing down the answer to a single question: What's left?
There are two possible scenarios for what went down after the explosion. Now, armed with James Webb, the most powerful telescope ever built, scientists finally think they know what happened.
Research published today in the peer-reviewed journal Science has settled the decades-long mystery. It offers the most compelling evidence, to date, that what lurks behind the clouds of residual gas and debris is one of the densest objects in the universe — a neutron star.
A neutron star is the collapsed core of a supergiant star that's gone supernova. It's essentially a city-sized sphere of densely-packed neutrons, co-author Patrick Kavanagh, an experimental physicist from Maynooth University, said during a press briefing on Sunday at the American Association for the Advancement of Science conference.
"It's more massive than the sun. A teaspoon of it weighs more than Mount Everest," he said.
If the supernova of 1987, aka SN 1987A, hadn't created a neutron star, the other possible scenario was that it produced a black hole. But Kavanagh seemed pleased with the outcome.
Identifying the neutron star left behind by SN 1987A, he said in the briefing, will now give astronomers a once-in-a-lifetime opportunity to study one in the early stages of its life.
"It feels absolutely amazing," Kavanagh said.
The most studied supernova in history
Explosions like SN 1987A don't happen often. The last time Earth witnessed such a brilliant cosmic event was about 400 years ago.
So, when SN1987A lit up the skies, astronomers studied it with as many instruments as they could including Hubble, Chandra, ALMA, and much more.
Eventually, SN 1987A became known as the most studied supernova in history.
"It's the gift that keeps on giving," Kavanagh said in the briefing.
Studying SN 1987A has deepened astronomers' understanding of supernovae and the role they play in our ever-evolving universe.
For example, SN 1987A's proximity to Earth allowed astronomers to track the remnant molecules and dust that are essential for the formation of life-sustaining planets like Earth, Kavanagh said.
But all those years of observation were limited by the technology of the time. Before JWST, astronomers lacked a telescope powerful enough to observe the compact object that SN 1987A left behind.
Hunting for a neutron star
To discover what lies at the center of SN 1987A, astronomers needed a telescope big enough and advanced enough to detect evidence of radiation from a hidden neutron star.
Enter the James Webb Space Telescope: the largest, most powerful telescope ever launched into space that is already revolutionizing our understanding of the universe within its first two years of operation.
With JWST, researchers led by astronomer Claes Fransson of Stockholm University were finally able to see past SN 1987A's gas and debris at infrared wavelengths, using spectroscopy to examine the composition and movement of the gas cloud surrounding its center.
"During the initial scan through the data, a bright feature right in the center of 1987A jumped off the screen," Kavanagh said. It was radiation emission lines from argon gas.
The presence of these emission lines could only be explained by a neutron star, not a black hole, Kavanagh said.
"We interpreted this as being conclusive evidence that the emission lines we were seeing were the result of radiation from the neutron center," Kavanagh said.
Supernovae happen about every 50-100 years, or so, in our galaxy. And they need to happen close enough to Earth for astronomers to be able to observe their remnants.
"Our great hope is that these observations and future observations will simulate more developed and detailed models for supernovae," Kavanagh said.