Brightest supernova ever seen shocks astronomers

15 Jan 2016

This is an artist's impression of the record-breakingly powerful, super-luminous supernova ASASSN-15lh as it would appear from an exoplanet located about 10,000 light years away – we are 3.8bn further light years away – in the host galaxy of the supernova, via Beijing Planetarium/Jin Ma

The largest supernova ever witnessed by astronomers is underway, above your head, as you read this. The radiation spewing out equates to that of “hundreds of billions of suns”.

Magnetar. Nothing? Nope, me neither. It turns out that’s the name of an incredibly rare type of star that packs a punch so powerful that it hits the extreme limits of what we believe the laws of physics to be.

Right now, some astronomers reckon a magnetar, just 10 miles in diameter, is the cause of a massive ball of hot gas spewing into space 3.8bn light years from Earth.

The result is what they believe to be the brightest supernova ever seen.

Okay, how big is it?

Some scale? Okay, well ASASSN-15lh, as it is known, is 200 times more powerful than the average supernova, 570 billion times brighter than our sun, and 20 times brighter than all the stars in our Milky Way galaxy combined.

Publishing a paper in this week’s issue of Science, researchers from both Ohio State and Peking University – led by Krzysztof Stanek and Subo Dong – said they are still in shock about what they are witnessing, referencing an eponymous scene from Spinal Tap to describe the scene.

“If it really is a magnetar, it’s as if nature took everything we know about magnetars and turned it up to 11,” Stanek said.


These are pseudo-colour images showing the host galaxy before the explosion of ASASSN-15lh taken by the Dark Energy Camera (DECam), and the supernova by the Las Cumbres Observatory Global Telescope Network (LCOGT) one-metre telescope network, via The Dark Energy Survey, B. Shappee and the ASAS-SN team

A bit of a mystery

To be honest, even these scientists can’t be 100pc sure of what they are witnessing, but one thing they do know is it’s very, very bright.

“We have to ask, how is that even possible?” said Stanek, professor of astronomy at Ohio State. “It takes a lot of energy to shine that bright, and that energy has to come from somewhere.”

One of the magnetar explanations put forward by Stanek and Dong’s team is that of a “millisecond magnetstar” a rapidly spinning and very dense star with a very strong magnetic field.

For that to happen, though, the magnestar in question would need to spin 1,000 times a second at the very least, converting all the resulting rotational energy with an incredibly high proficiency.

“Given those constraints,” said Todd Thompson, professor of astronomy at Ohio State, “will we ever see anything more luminous than this? If it truly is a magnetar, then the answer is basically no.”

Wait, Hubble can help

Despite the size of the supernova, and obvious excited nature of its discoverers, it can’t be seen by the naked eye as it’s perhaps 3.8bn light years away. For scale, last year’s headline-grabbing Earth 2.0 is 1,400 light years away and Pluto is five light hours away.

The exact galaxy it is in is not yet known, nor the exact distance, with the Hubble Telescope giving a dig out later this year to help solve some of the clues.

Dong claims the makeup of what the team is witnessing remains “shrouded in mystery” because all known theories of energy meet challenges when put against ASASSN-1l5h’s might.

Dong said ASASSN-15lh “may lead to new thinking and new observations of the whole class of super luminous supernova”.

Gordon Hunt was a journalist with Silicon Republic