72 Incredibly Bright Mysterious Explosions Detected—And Astronomers Don't Know Where They Came From

An international team of astronomers have detected 72 extremely bright events in the sky, but no one has been able to convincingly explain their origins, according to findings presented at the European Week of Astronomy and Space Science by astronomer Miika Pursiainen on Tuesday.

The events were detected in data collected by the Dark Energy Survey Supernova Program (DES-SN)—a global initiative that is trying to understand dark energy, an unexplained force that scientists think is accelerating the expansion of the universe.

Using the Cerro Tololo Inter-American Observatory in the Chilean Andes, DES-SN has been searching for supernovas—titanic explosions that occur at the end of a massive star's life, some of which produce so much light that they can be briefly appear as bright as entire galaxies.

But what exactly were the 72 recently detected phenomena?

"We don't really know all that much [about them]," Pursiainen told Newsweek. "They are as bright as supernovae but last for significantly shorter periods of time. Next to that, they seemed to be both hot and large and appeared to expand in time. But we can't say too much about their origin yet."

The celestial events measured anywhere between 10,000 and 30,000 degrees Celsius (around 18,000 to 54,000 degrees Fahrenheit) in temperature and ranged in size from several times the Earth-sun distance (roughly 93 million miles) to a hundred times this distance.

Images of one of the transient events, from eight days before the maximum brightness to 18 days afterward. This outburst took place at a distance of 4 billion light-years. M. Pursiainen/University of Southampton and DES collaboration

According to the astronomers, the phenomena also appeared to expand and cool over time, suggesting that they were some kind of explosion, like a supernova. However, the events lasted for only about a week to a month, whereas supernovas tend to last for several months at least.

What then could explain these observational differences? The astronomers have put forward one possible explanation.

"These events appear to originate in star-forming galaxies, which is why we have been mostly considering core-collapse supernova scenarios," Pursiainen said. "However, it is far too early to say anything for certain "

In this scenario, a star sheds a vast quantity of material before exploding as a supernova and becoming enshrouded in a cloud of matter. When the supernova does occur, it heats the surrounding cloud of material, which astronomers are then able to detect, rather than the exploding star itself.

However, Pursiainen said more data will be needed before this hypothesis can be confirmed.

"The DES-SN survey is there to help us understand dark energy, itself entirely unexplained," Pursiainen said in a statement. "That survey then also reveals many more unexplained transients than seen before. If nothing else, our work confirms that astrophysics and cosmology are still sciences with a lot of unanswered questions!"