ASASSN-15lh powerful supernova (3)
Astronomers find the brightest and most powerful supernova explosion ever, located 3.8bn light-years away, which is more luminous than entire Milky Way!

For most of 2016, astronomers have been viewing a ball of hot gas billions of light years away that is radiating the energy of hundreds of billions of suns. At its heart is an object a little larger than 10 miles across. And astronomers are not entirely sure what it is. If, as they suspect, the gas ball is the result of a supernova, then it’s the most powerful supernova ever seen.
Most astronomers today believe that one of the plausible reasons we have yet to detect intelligent life in the universe is due to the deadly effects of local supernova explosions within 100 light years that wipe out all life in a given region of a galaxy. While there is, on average, only one powerful supernova per galaxy per century, there is something on the order of 100 billion galaxies in the observable Universe. Taking 10 billion years for the age of the Universe (it’s actually 13.7 billion, but stars didn’t form for the first few hundred million), Dr. Richard Mushotzky of the NASA Goddard Space Flight Center, derived a figure of 1 billion supernovae per year, or 30 supernovae per second in the observable Universe!
ASASSN-15lh most powerful supernova
An artist’s impression of the superluminous, record-breakingly powerful 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)

The Discovery

In June of 2015, this flaring spot of light was found by the All Sky Automated Survey for Supernovae (ASASSN) run by Ohio State astronomers and labelled ASASSN-15lh. Located about three billion light years distant, the source appears tremendously bright for anything so far away: roughly 200 times brighter than an average supernova, and temporarily 20 times brighter than all of the stars in our Milky Way Galaxy combined. The above-featured artist’s illustration depicts a hypothetical night sky of a planet located across the host galaxy from the outburst.

See Also: Photos: 6 Amazing Views of the Famous Crab Nebula

“If you walked outside and saw a person who was six feet tall, and then someone who was six thousand feet tall, you would notice,” says team member Todd Thompson of Ohio State University. “You begin to question whether this is even a person.”

The Ohio State team report in the January 14 2016 issue of the journal Science that the object at the center could be a very rare type of star called a magnetar. One so powerful that it pushes the energy limits allowed by physics.

ASASSN-15lh most powerful supernova (1)
A galaxy 3 billion light years away (left, seen in 2014) blazes with the light (right, seen in 2015) from the brightest known most powerful supernova, dubbed ASASSN-15lh.
Magnitude As Never Seen Before

The gas ball surrounding the object cannot be seen with the naked eye because it’s 3.8 billion light years away. Led by Ohio State, the ASASSN project uses a cadre of small telescopes around the world to detect bright objects in our local universe.

Though ASASSN 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 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.

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“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.”

Subo Dong, lead author of the Science paper and a Youth Qianren Research Professor of astronomy at the Kavli Institute for Astronomy and Astrophysics at Peking University, said that “The honest answer is at this point that we do not know what could be the power source for ASASSN-15lh.”

ASASSN-15lh most powerful supernova (2)

Is It Even Possible?

Todd Thompson, professor of astronomy at Ohio State, offered one possible explanation. The most powerful 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 a second, and convert all that rotational energy to light with nearly 100 percent efficiency, Thompson explained. It would be the most extreme example of a magnetar that scientists believe to be physically possible.

“Given those constraints,” he said, “will we ever see anything more luminous than this? If it truly is a magnetar, then the answer is basically no.”

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 powerful 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. 

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