The spiky filaments of a zombie star shed light on a 12th-century supernova

About 7,500 light years from Earth lurks a zombie star cloaked in long tentacles of hot sulfur.

No one knows how those tents were formed. But astronomers now know where they are going. New observations, reported on November 1 Astrophysical Journal Letterscaptures the 3-D structure and motion of the debris left behind by a supernova that was seen to explode almost 900 years ago.

“It’s a piece of the puzzle to understand this very strange [supernova] debris,” 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: 17.4.02). Astronomers didn’t find the remnants of that explosion, now called the Pa 30 nebula, until 2013.

And when they found the remains, it seemed strange. The supernova appeared to be a type called type 1a, where a white dwarf star explodes, destroying itself in the process. (SN: 3/23/16). But in this case, part of the star survived.

Even more strangely, the star was surrounded by spiny filaments that extended about three light years from the star in all directions. “This is really unique,” says Cunningham. “There is no other supernova nebula that shows filaments like this.”

He and colleagues used a telescope at the WM Keck Observatory in Hawaii to record how fast the filaments move relative to Earth. Then they built a 3-D reconstruction of the filaments and their movements through space.

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

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

The study showed that this remnant is almost certainly from the guest star of 1181. Taking the speeds and positions of the filaments and tracing them back shows that they all exited from the same point around 1152, give or take 75 years.