Astronomers have discovered a mysterious exploding star, located in the constellation Eridanus, that cannot be classified as either a nova or a supernova – the star was around 100 times brighter to be the former and faded too quickly to qualify as the latter.
“The combination of properties is puzzling,” said Mario Livio, an Astrophysicist at the Space Telescope Science Institute in Baltimore, Maryland. “I thought about a number of possibilities, but each of them fails.”
This cosmic anomaly was detected in January and August of 2014 by a team of astronomers led by Steven Rodney from the Johns Hopkins University, and presented on April 21 of this year at a symposium in Baltimore to celebrate Hubble’s 25th anniversary.
Rodney’s team came across the event while participating in a Hubble project that uses galaxy clusters as “gravitational lenses” – sort of cosmic magnifying glass – to collect images of far-away galaxies that lie beyond them. This technique was also behind last year’s supernova “kaleidoscope”.
The light that Hubble recorded from the newly-found outburst left its home galaxy 7.8 billion years ago. Based on preliminary analysis, the scientists are now considering the possibility that the images show two separate events.
Another reasonable explanation would be that the outburst was caused by two colliding neutron stars, which is an incident astronomers call a kilonova. But since kilonovas are extremely rare, observing two of them in a single year would be hard to explain.
“We’d be lucky to see one such event,” noted Rodney.
A further complication for this line of reasoning would be the fact that neither NASA’s Swift satellite, nor the space agency’s Chandra X-ray Observatory detected any X- or γ-rays that typically accompany a kilonova.
“This is a peculiar [outburst], that though the analysis is preliminary, challenges our models,” said Rodney. He claims that if the outburst turns out to be an entirely new class of phenomena that is common to our Universe, future wide-field surveys conducted with the Large Synoptic Survey Telescope and the proposed Wide Field Infrared Space Telescope should be able to detect it again, thereby establishing the existence of this new phenomenon for good.