Brightest Supernova Baffles Astronomers

The most luminous supernova ever discovered, ASASSN-15lh, challenges a popular theory for blazingly bright exploding stars.
The left image shows the yellow-orange host galaxy prior to the supernova’s discovery, captured by the Dark Energy Camera. The righthand image, from Las Cumbres Observatory Global Network, shows the supernova, whose blue light outshines its host. The Dark Energy Survey / B. Shappee / The ASAS-SN Team
About six months ago, we alerted readers to the discovery of the most luminous supernova ever. Now the discovery team is releasing additional information, and it strains even the most extreme physical scenarios.
The explosion of light initially appeared in June 2015 as the faintest of dots in automated images taken by the All-Sky Automated Survey for Supernovae (ASAS-SN), which repeatedly observes the same areas of sky to look for ephemeral bursts of light. Sophisticated software spotted the sudden but subtle influx of light, prompting astronomers to go fishing for follow-up observations at several telescopes. They soon found that the light from the source, dubbed ASASSN-15lh, had traveled for 2.8 billion years to reach Earth.
Due to its distance, ASASSN-15lh only reached about 17th magnitude at its brightest, but its luminosity outshone any supernova yet discovered. Even months later, this single object continues to emit more energy per second than all the stars in the Milky Way.
This image shows two of the 14-cm telescopes used in the All-Sky Automated Survey for SuperNovae that discovered ASASSN-15lh. Wayne Rosing
Subo Dong (Peking University, China) and colleagues released an update to the discovery data in January 15th’s Science. Following a spate of follow-up spectra, the team continued to track the supernova’s goings-on using the Las Cumbres Observatory Global Telescope Network (LCOGT; see the October 2012 issue of Sky & Telescope for more on this ambitious project) and the Swift space telescope. The light curves