Runaway Dead Stars Are Clues for a Cosmic Mystery

Astronomers call a special kind of supernova a “cosmic yardstick” for good reason: The so-called Type Ia supernova gives off a predictable amount of light, making it a handy tool for measuring distances in space.

These particular supernovas are useful but still puzzling, with scientists still unsure of what triggers their blasts. NASA estimates they happen only twice per millennium in the Milky Way.

A leading idea has been that in an orbiting pair of white dwarfs — the remains of dead sun-size stars — one bursts apart almost immediately, while the other survives, perhaps hurtling away at breakneck speed because it’s no longer tethered by gravity to its companion.

But that can’t explain all Type Ia supernovas, according to researchers led by Technion — Israel Institute of Technology. By studying what could cause a dead-star remnant to suddenly go rogue — flying so fast it could escape the galaxy — the international team discovered a new scenario for a white dwarf explosion. Based on how often Type Ia supernovas occur, scientists can infer how many runaway white dwarfs they should see overall, said Hagai Perets, who co-led new research published in Nature Astronomy.

Hagai Perets is a faculty member in Technion’s Department of Physics.