Thousands of supernovae – exploding stars – have been spotted in our vast universe, but one that’s nearly 4 billion light years away really stood out.
Dubbed ASASSN-15lh for the All-Sky Automated Survey for Supernovae, which found the object, it’s by far the brightest supernova detected to date. Rutgers professor Saurabh W. Jha and two of his former students helped with this discovery.
“It was really exciting,” said Jha, an associate professor in the Department of Physics and Astronomy in the School of Arts and Sciences. It’s “a very strange object.”Subo Dong from Peking University in China led the discovery team, which announced its findings in the journal Science last month. Rutgers – a partner in the Southern African Large Telescope (SALT) in South Africa – played a critical role, said Jha, a member of the Rutgers astrophysics group since 2007.
Jha used observations made by SALT, one of the world’s largest telescopes, to measure the distance to the supernova, a key ingredient to determining its exceptional brightness.
A supernova is typically a massive star that’s reached the end of its life and explodes. “Most stars don’t explode,” Jha explained. “They mostly just fade away.”
Scientists have discovered thousands of supernovae in the observable universe, which is believed to be about 13.7 billion years old and consists of about 100 billion galaxies. Each galaxy has about 100 billion stars, according to Jha.
“We think in the part of the universe that we can see, there’s a supernova exploding every second,” Jha said. “It’s hard to find all of them.”
According to the Science study, ASASSN-15lh is a “highly super-luminous supernova.”
The cosmic explosion uncovered was about 200 times more powerful than a typical supernova and about 570 billion times brighter than our sun, according to a SALT statement. Indeed, it was about 20 times brighter than all of the light from the few hundred billion stars in our Milky Way galaxy.
"Not only was it so bright, but it stayed bright for a long time,” Jha said. “It stayed bright for hundreds of days, several times longer than a typical supernova. Altogether, it’s just a tremendous amount of energy that it puts out there, and so it’s straining all the models that we have for supernovae."
If scientists discover more supernovae like ASASSN-15lh, “they could be used as a probe of the very distant universe because they’re so luminous,” he said. “So that would be another great thing if we could find more of these.”
Ever since he was a graduate student at the Harvard-Smithsonian Center for Astrophysics 20 years ago, Jha’s research has focused on supernovae.
“It’s really fascinating,” he said. “Supernovae are transients. You only get a certain amount of time that you can observe them and then they go away. They’re also unpredictable. There’s always some new object to study. I like that dynamic environment.”
The two former Rutgers undergraduates on the ASASSN team at Ohio State University are Ben Shappee (Rutgers ’09) and Tom Holoien (Rutgers ‘13). Shappee and Holoien, who both graduated summa cum laude, did undergraduate research on supernovae with Jha and then enrolled in the Ph.D. program in astronomy at Ohio State. Shappee received his Ph.D. in 2014 and Holoien is a Ph.D. student.
Scientists at the following universities and organizations contributed to the discovery: Peking University; Carnegie Observatories; Universidad Diego Portales; Millennium Institute of Astrophysics; Rutgers, The State University of New Jersey; Ohio State University; Liverpool John Moores University; Coral Towers Observatory; INAF-Osservatorio Astrofisico di Catania; Association Francaise des Observateurs d’Etoiles Variables, Observatoire de Strasbourg; Harvard-Smithsonian Center for Astrophysics; Morehead State University; Variable Star Observers League in Japan; The Virtual Telescope Project; Mt. Vernon Observatory; Universidad Andres Bello; Warsaw University Astronomical Observatory; and Los Alamos National Laboratory.
For media inquiries, contact Todd B. Bates at email@example.com or 848-932-0550.