Ellen Phiddian
Cosmos science journalist
A supernova seen by astronomers more than 800 years ago has had its remnants thoroughly examined – and they’re weird.
Researchers have found a “zombie star” remaining at the centre of the supernova explosion, with dandelion-like filaments peeling away from it.
They’ve published their description in the Astrophysical Journal Letters.
The supernova was spotted by Chinese and Japanese astronomers in 1181, when it was visible gleaming from the Cassiopeia constellation for 6 months. They dubbed it the “guest star”. It’s one of just 5 confirmed galactic supernovae seen during human history.
The remaining nebula went unspotted until 2013, and was only formally identified as the 1181 supernova’s source in 2021.
This team used the Keck Cosmic Web Imager, a spectrograph on the Mauna Kea volcano in Hawai‘i, to investigate the dust cloud more closely.
Using the data from this instrument, the team could construct a 3D map of the ex-supernova and estimate how quickly dust particles were flying away from it.
They calculated that the filaments were zooming away from the site at about 1,000km per second.
“This means that the ejected material has not slowed down, or sped up, since the explosion,” says lead author Tim Cunningham, a NASA Hubble Fellow at the Center for Astrophysics, Harvard & Smithsonian, USA.
This allowed the team to confirm the nebula as the 1181 supernova’s source.
“From the measured velocities, looking back in time allowed us to pinpoint the explosion to almost exactly the year 1181,” says Cunningham.
The study also found surviving remains of the white dwarf that triggered the supernova explosion.
Usually, the thermonuclear explosion that resulted in supernova would destroy the star at its centre, but some of this white dwarf has remained behind as a sort of “zombie star”.
“Our first detailed 3D characterisation of the velocity and spatial structure of a supernova remnant tells us a lot about a unique cosmic event that our ancestors observed centuries ago,” says co-author Assistant Professor Ilaria Caiazzo, an astronomer at the Institute for Science and Technology Austria.
“But it also raises new questions and sets new challenges for astronomers to tackle next.”
