Messages from a long-lost universe (Image: Tim Gravestock)

At first, there didn’t seem anything earth-shattering about the tiny point of light that pricked the southern Californian sky on a mild night in early April 2007. Only the robotic eyes of the Nearby Supernova Factory, a project designed to spy out distant stellar explosions, spotted it from the Palomar Observatory, high in the hills between Los Angeles and San Diego.

The project’s computers automatically forwarded the images to a data server to await analysis. The same routine kicks in scores of times each year when a far-off star in its death throes explodes onto the night sky, before fading back to obscurity once more.

But this one did not fade away. It got brighter. And brighter. That’s when human eyes became alert.

The supernova finally reached its peak brightness after 77 days. After 200 days – long after most supernovae have dwindled back into obscurity – it was still burning brightly. Only in October 2008, an unprecedented 555 days after it was first spotted, had it faded enough for the supernova hunters to call off their observations.

Digesting what they had seen took longer still. SN 2007bi, as dry protocol labelled the event, was one of the most extreme explosions ever recorded, of that there was no doubt. It was so intense that it didn’t fit any model of how normal stars die. But then, it was rapidly becoming clear that, in life as in death, this had been no normal star.

If the interpretation of what popped up that April night is correct, this was a star that should not have existed, …