Swift has been keeping a close eye on the possible supernova (Image: NASA/GSFC)

The supernova world has a new brightness champ. A supernova discovered on 14 June appears to shine more than 400 billion times brighter than the sun would if they sat next to each other.

An ordinary supernova usually marks the death of a massive star, but a so-called superluminous supernova shines at least 10 times brighter and has more mysterious origins. The newly found explosion, called ASASSN-15lh, is at least 2.5 times brighter than any superluminous supernova seen before.


The All-Sky Automated Survey for Supernovae (ASAS-SN), a suite of automated 14-centimetre telescopes that scour the sky for stellar explosions, discovered the bright object in the southern constellation of Indus.

Over the next few weeks, Subo Dong of The Kavli Institute for Astronomy and Astrophysics at Peking University in Beijing, China, and colleagues looked toward the supernova with several larger telescopes to determine how far away it is, what its peak brightness was and to check that it was indeed a supernova. NASA’s Swift space telescope also started observing it in ultraviolet light on 30 June.

Dong’s team found that the supernova was discovered nine days after its peak brightness, and that its light took more than 2.8 billion years to get to Earth. That means its luminosity is about 100 times brighter than normal supernovae and several times higher than any previous superluminous supernova found. The team posted a summary of their observations on The Astronomer’s Telegram website on 8 July.

Classification confusion

Not everyone is convinced that ASASSN-15lh is a superluminous supernova, however. “We don’t even really know that this is a supernova,” says Robert Quimby of San Diego State University in California, who discovered the first superluminous supernova a decade ago.

That’s because this blast’s light has only just started to lessen. As it fades, it will reveal more information about the explosion, which will help to confirm ASASSN-15lh’s true nature. But this will take time: extra bright supernovae take about 100 days to fade, a few times longer than regular supernovae.

Quimby points out that some objects can initially look like superluminous supernovae, but turn out to be something else. The most common impostors are stars that pass too near a black hole and get ripped apart. “Or we’ve got some new class of objects,” he adds. “That could be even more exciting.”

If it is a superluminous supernova, observing it could help illuminate a different kind of burst. Some astronomers are investigating a connection between these supernovae and huge blasts of gamma rays that signal the end of a massive star’s life, called gamma-ray bursts. A recent study further connects a superluminous supernova to a gamma-ray burst that shone for hours – adding more fuel to the idea’s bright fire.

References: The Astronomer’s Telegram #7774; Nature, DOI: 10.1038/nature14579

Update, 14 June 2015: Dong’s team have now published their work on arxiv.org