Almost three years ago, astronomers using the Hubble Space Telescope were perusing a cluster of galaxies about eight billion light-years from Earth when they came upon a flash of light unlike anything they had seen before.
Over the next 100 days, the object gradually brightened. Then it spent another 100 days growing dimmer, until it finally vanished from view.
Astronomers speaking last week at the American Astronomical Society meeting in Long Beach, Calif., still have no idea what it was — or is.
Chemical analysis of the light proved just as puzzling as its visual effects, said Kyle Barbary of the Lawrence Berkeley National Laboratory in Berkeley, Calif.
"We have never seen anything like it," Barbary told reporters. "No one has been able to come up with a good explanation for this object."
The target was given the designation SCP 06F6 — a nod to the Supernova Cosmology Project survey that was underway when the object was discovered on Feb. 21, 2006. It does not match any known supernova or other cosmological event.
Astronomers also do not know if SCP 06F6 was relatively near, possibly even in our Milky Way galaxy, or quite far.
A paper submitted to the journal Astrophysical Journal Letters in September reported that a chemical analysis of the object seemed to match emissions from a distant, cool and carbon-rich atmosphere. Lead author Boris Gaensicke, an associate professor of physics with the United Kingdom's University of Warwick, and colleagues theorized that the object is a new class of supernova or perhaps a disruption of a carbon-rich star.
Gaensicke's team also discovered a strong X-ray source — two orders of magnitude higher than any observed supernova — that appeared to be associated with SCP 06F6's declining phase.
"In my view, the crucial next step is to probe for an underlying host galaxy around SCP 06F6," Gaensicke wrote in an e-mail to Discovery News. "The detection of a host galaxy would (a) confirm the extragalctic nature ... and (b) permit some insight into the nature of the progenitor of SCP 06F6."
Last month, a team of Israeli scientists came up with some additional theories, including the destruction of a carbon-rich white dwarf star by a medium-sized black hole; a supernova explosion inside a carbon star; a collision between an asteroid and a white dwarf star; and a collapse of a supernova core.
"Perhaps it is a new type of supernova," Stefan Immler, a NASA astrophysicist with the Goddard Space Flight Center in Greenbelt, Md., told Discovery News. "We really haven't learned anything else new about it."