Using observations from NASA’s Hubble Space Telescope and other space- and ground-based telescopes, an international team of astronomers and physicists has witnessed the death of a star by supernova in real time—about 60 million light-years away from Earth in the constellation Virgo. The team reported its findings in the journal Monthly Notices of the Royal Astronomical Society on October 26.
Historically, astrophysicists and other scientists have analyzed supernovas after they occur. In fact, the first human record of one dates back to 185 CE. “We used to talk about supernova work like we were crime scene investigators,” said astronomer Ryan Foley, who led the new research, in a NASA press release. By making observations after the explosive event, scientists would try to figure out what happened to the star.
Foley and study co-author Samaporn Tinyanont, both of the University of California, Santa Cruz, are calling the event, formally named SN 2020fqv, “The Rosetta Stone of supernovas” because it could help inform scientists when other stars in the universe are ready to explode.
Massive stars—those much larger than our sun—explode as supernovas when they run out of fuel. During a star’s lifetime, its stable spherical shape results from the balance between heat and pressure generated by hydrogen fusion at its core, which push outward, and gravity, which pulls inward. As long as that balance is maintained, nuclear fusion can generate enough power to keep a star shining for billions of years.
But all stars eventually run out of power. And when a star about eight or more times the mass of our sun runs out of nuclear fuel and the outward pressure of heat wanes, gravity wins. It begins to pull everything inward. The star’s core becomes denser and denser, collapsing faster and faster until a final massive crunch releases a surge of heat and energy—as hot as tens of billions of degrees. This causes the outer material of the star to explode as a supernova.
“You know that saying ‘Live fast, die young’? That really applies to stars, right? So the most massive, luminous stars have the shortest lifetimes,” Harvard & Smithsonian astrophysicist Grant Tremblay tells NOVA.
SN 2020fqv is in the interacting Butterfly galaxies, a place already watched by NASA’s Transiting Exoplanet Survey Satellite (TESS). “TESS provided an image of the system every 30 minutes starting several days before the explosion, through the explosion itself, and continuing for several weeks,” NASA states in its press release. On Mar. 31, 2020, the star that became SN 2020fqv began flaring up, Emily Conover reports for Science News, eventually going supernova in April. TESS and researchers at the Zwicky Transient Facility at the Palomar Observatory in San Diego were watching. And since Hubble had been tracking the star for decades, the team was able to go back to Hubble’s observations from the 1990s onward.
In the hours and days following the first observations of the supernova, the team coordinated “a last-minute change of plans for the Hubble Space Telescope,” Conover writes, which “provided the supernova’s spectrum, an accounting of its light broken up by wavelength, at various moments after the blast.” Mere hours after the supernova, Hubble made observations of the gas, dust, and other matter, called circumstellar material, around SN 2020fqv, George Dvorsky reports for Gizmodo.
“We were able to make ultra-rapid observations with Hubble, giving unprecedented coverage of the region right next to the star that exploded," Tinyanont told NASA.
By comparing its observations of the star with theoretical models, using historical data from Hubble, and “measuring the amount of oxygen in the supernova, which is a proxy for mass,” Elizabeth Howell writes for Space.com, the team was also able to calculate the mass of the star. The results of all three methods were consistent: The star was 14 to 15 times the mass of our sun, the researchers believe.
The team hopes the finding will do more than inform them of the star’s final years and moments. It could help astronomers predict when other stars in the universe are about to explode, they say.
"Now we have this whole story about what's happening to the star in the years before it died, through the time of death, and then the aftermath of that," Foley told NASA. "This is really the most detailed view of stars like this in their last moments and how they explode."