What is 10 miles across, but powers an explosion brighter than the Milky Way?

This is an artist’s impression of the record-breakingly powerful, superluminous supernova ASASSN-15lh as it would appear from an exoplanet located about 10,000 light years away in the host galaxy of the supernova. Credit: Beijing Planetarium / Jin Ma

Astronomers studying what may be the most powerful supernova ever seen, with energy of hundreds of billions of suns. At its heart is an object a little larger than 10 miles across that could be a very rare type of star called a magneta – but one so powerful that it pushes the energy limits allowed by physics. An international team of professional and amateur astronomers spotted the possible supernova, now called ASASSN-15lh, when it first flared to life in June 2015.

Krzysztof Stanek, turned to the movie This is Spinal Tap to find a way to describe it. “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. (“on a scale of 1 to 10.”) The gas ball surrounding the object can’t be seen with the naked eye, because it’s 3.8B light years away. But it was spotted by the All Sky Automated Survey for Supernovae (ASAS-SN, pronounced “assassin”) collaboration. Led by Ohio State, the project uses a cadre of small telescopes around the world to detect bright objects in our local universe.

Though ASAS-SN has discovered some 250 supernovae since the collaboration began in 2014, the explosion that powered ASASSN-15lh stands out for its sheer magnitude. It is 200X more powerful than the average supernova, 570 billion times brighter than our sun, and 20X brighter than all the stars in our Milky Way Galaxy combined.”…we do not know what could be the power source for ASASSN-15lh,” said Prof. Subo Dong. The discovery “may lead to new thinking and new observations of the whole class of superluminous supernova.”

Prof Todd Thompson at Ohio State said the supernova could have spawned an extremely rare type of star called a millisecond magnetar, a rapidly spinning and very dense star with a very strong magnetic field. To shine so bright, this particular magnetar would also have to spin at least 1,000 times/s, and convert all that rotational energy to light with nearly 100% efficiency.

The Hubble Space Telescope will help settle the question later this year, in part because it will allow astronomers to see the host galaxy surrounding the object. If the team finds that the object lies in the very center of a large galaxy, then perhaps it’s not a magnetar at all, and the gas around it is not evidence of a supernova, but instead some unusual nuclear activity around a supermassive black hole.

If so, then its bright light could herald a completely new kind of event, said study co-author Christopher Kochanek, professor of astronomy at Ohio State and the Ohio Eminent Scholar in Observational Cosmology. It would be something never before seen in the center of a galaxy. https://news.osu.edu/news/2016/01/14/brightlight/