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Astronomer Have Spotted A Mysterious Object, Which Is 570 Billion Times Brighter than the Sun

A network of small, ground-based telescopes stalking the night-time skies for transient supernovas fished out a whopper -- a one-of-a-kind cosmic explosion that at its peak blasted out more light than 50 times all the stars in the Milky Way galaxy.

The object, which takes its name, ASASSN-15lh from the All-Sky Automated Survey for SuperNovae, was first discovered on June 14, 2015. A week later, astrophysicist Subo Dong, with the Kavli Institute for Astronomy and Astrophysics at Peking University, was looking at the object’s spectra, a chemical breakdown of its light, and realized something strange was going on.

The measurements were so diverse, the survey's automated software didn't even distinguish it as a supernova, Dong wrote in an email to Discovery News.

“We believed about various non-supernova, exotic situations, but none appeared to work,” Dong said.

Working with associates at observatories worldwide, Dong started thinking the object may belong to a uncommon class of so-called superluminous supernovae, a suspicion bolstered by follow-up measurements taken by the 10-meter South African Large Telescope .

“Seeing the SALT spectrum was the moment we knew for sure that we were on to something big,” Dong said.

ASASSN-15lh is situated about 3.8 billion light-years away, but is so bright that if were as near as Sirius, a bright star 8.6 light-years away from Earth, the supernova would seem to be almost as bright as the sun. It is 200 times more powerful than the average supernova and more than double as bright as any supernova formerly discovered.

Researchers are virtually in the dark about what generated the blast. One theory is that a dense, swiftly spinning neutron star, known as a magenetar, is driving the supernova. The star would have to be spinning at least 1,000 times a second, a speed that challenges the laws of physics. It also would have to be approximately 100 percent proficient at converting its spin energy into light, another theoretical limit.

Another option is that ASASSN-15lh is driven by some nuclear reactions related to a supermassive black hole at the center of its host galaxy, but researchers don’t know of any such phenomenon, nor have they pinpointed the object’s precise position in its galaxy. Additional information is expected this year from Hubble Space Telescope observations.

“The Hubble observations are meant to show whether or not the event occurred right at the nucleus of the host galaxy, or whether it is offset from the center. If it is offset, this would rule out the explanation of this event as somehow related to the host galaxy's central supermassive black hole -- assuming it has one, as most massive galaxies do,” Ohio State astrophysicist Todd Thompson wrote in an email to Discovery News.

“What kind of event from a supermassive black hole could yield such an event? We don't know since we've never perceived something like it, but it has been proposed that it might be a so-called ‘tidal disruption event’ -- a bright explosion rising when a star gets torn apart and then consumed by a supermassive black hole. The problem is that we've grasped these events before, and they don't look like ASASSN-15lh. In particular, most stars are composed of generally hydrogen and helium, and yet the spectra of ASASSN-15lh show no signs of either,” Thompson said.

The supernova’s host galaxy itself presents another puzzle. Most superluminous supernovae are found in small, dwarf galaxy where lots of stars are forming. ASASSN-15lh, in contrast, seems to be in a large, but comparatively quiescent galaxy about three times more massive than the Milky Way.

Researchers have rejected the likelihood that the supernova appears brighter than it actually is due to any magnifying effects of intervening galaxies, a phenomena known as gravitational lensing.

“The good news is that ASASSN-15lh is bright, so it is comparatively easy to get high-quality observations. Many groups of astrophysicists are using some of the most advanced telescopes, ground- and space-based, to study ASASSN-15lh. I am sure that in the near future, we will understand it much better,” Dong said.

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