Astronomers May Have Finally Solved 843-Year-Old Mystery Of A Zombie Star

An international group of astronomers may have solved an 843-year-old mystery surrounding the origins of a zombie star. The researchers connected ancient records from China and Japan, which spoke about a supernova event near the constellation Cassiopeia in the year 1181, to a zombie star seen today, called guest star SN 1181.

Astronomers and scientists around the world are currently waiting on a once-in-a-lifetime event, when a binary system in the Northern Crown will eventually trigger a thermonuclear explosion, or a nova, big enough to be seen from Earth. A similar event occurred a little over 840 years ago, when a supernova explosion was spotted in the skies of China and Japan. That ancient event, along with studies of guest star SN 1181, has led a group of astronomers to believe the two are connected.

While amateur astronomer Dana Patchick discovered the zombie star in 2013, it was not until 2021 that Albert Zijstra, a professor of astrophysics at the University of Manchester in England, made the connection to SN 1181.

Zijlstra, who was not part of the new study, remarked, “During (the height of) Covid, I had a quiet afternoon and was sitting at home. I matched the supernova to the nebula using records from ancient Chinese catalogs.” The professor added, “I think that has been now generally accepted — a lot of people have looked at it and they have agreed and that it seems to correct. This is the remnant of that supernova.”

The researchers remarked in their study the analysis strongly suggests SN 1181 belongs to a rare class of supernova, called Type Iax. With this type of supernova, the resulting thermonuclear flare-up may be the result of not one but two white dwarfs which have violently collided, but have not yet detonated completely, leaving behind a “zombie star.”

“There are 20 or 30 candidates for Type Iax supernovas,” explained Takatoshi Ko, lead author of the study published July 5 in The Astrophysical Journal. “But this is the only one that we know of in our own galaxy.”

Using a computer model to track the remnant’s evolution, the group confirmed SN 1181 was consistent with a Type Iax supernova. The study also revealed the remnant consisted of two distinct shock regions, one of which formed when SN 1181 ejected material outward into space. The second lies toward the middle of the remnant, indicating the zombie star somehow reignited, even though the star has grown dimmer over the last 100 years.

“We do not fully understand why the star reignited and the stellar wind started so recently,” explained Ko. “We theorize that the star reignited because SN 1181 was a Type Iax supernova, which is an incomplete explosion. As a result, the material ejected by the explosion did not escape completely and remained within the gravitational influence of the central white dwarf.” Ko concluded, “This material could eventually have accreted onto the white dwarf due to its gravity, causing it to reignite.”

While the study of the zombie star may have answered a few questions, it raised a few more. Ko and the rest of the team hope to investigate SN 1181 further using the Subaru Telescope and the Very Large Array telescope.