A zombie star’s spiky filaments shed light on a 12th century supernova

Some 6,500 light-years from Earth lurks a zombie star cloaked in long tendrils of hot sulfur.

Nobody knows how those tendrils formed. But astronomers now know where they’re going. New observations, reported in the Nov. 1 Astrophysical Journal Letters, capture the 3-D structure and motion of debris left in the wake of a supernova that was seen to detonate almost 900 years ago.

“It’s a piece of the puzzle towards understanding this very bizarre [supernova] remnant,” says astronomer Tim Cunningham of the Harvard & Smithsonian Center for Astrophysics in Cambridge, Mass.

The supernova was first recorded in 1181 as a “guest star” by astronomers in ancient China and Japan (SN: 4/17/02). Astronomers didn’t find the remains of that explosion, now called the Pa 30 nebula, until 2013.

And when they did find the remnant, it looked weird. The supernova appeared to be a kind called type 1a, wherein a white dwarf star detonates, destroying itself in the process (SN: 3/23/16). But in this case, part of the star survived.

Stranger still, the star was surrounded by spiky filaments stretching about three light-years in all directions. “This is really unique,” Cunningham says. “There’s no other supernova nebula that shows filaments like this.”

He and colleagues used a telescope at the W.M. Keck Observatory in Hawaii to record how fast the filaments are moving relative to Earth. Then they built a 3-D reconstruction of the filaments and their motions through space.

The team found that the system is structured “kind of like a three-layered onion,” Cunningham says. The inner layer is the star. Then there’s a gap of one or two light-years, which ends in a spherical shell of dust. The final layer is the filaments, which emerge from the dust shell.

Researchers still aren’t sure how the filaments formed, or how they’ve maintained their straight-line shapes for centuries. One possibility is that a shock wave from the explosion ricocheted off the diffuse material between stars and bounced back toward the white dwarf. That wave could have sculpted the material into the spikes astronomers see. Future theoretical studies using the new observations might help solve the puzzle.

The study did show that this remnant is almost definitely from the guest star of 1181. Taking the speeds and positions of the filaments and tracing them backward show they all emanated from the same point around the year 1152, give or take 75 years.