Astronomers in China and Japan observed the appearance of a “guest star” in 1181 CE. It was a supernova and for the following 840 years it was lost. In 2021, a peculiar nebula was spotted by citizen scientist Dana Patchick and it was linked back to the witnessed event. Called Pa 30, it became a fascinating mystery because it doesn’t look like any other supernova remnant. It looks like a dandelion.
Astronomers do not know why it looks that way. Its uniqueness required more indepth observations. Using the Keck Cosmic Web Imager (KCWI) at the W. M. Keck Observatory on Maunakea, Hawai’i Island, researchers were able to measure how the peculiar tendrils move and figure out its three-dimensional structure.
“We find the material in the filaments is expanding ballistically,” co-lead author Tim Cunningham, a NASA Hubble Fellow at the Center for Astrophysics, Harvard & Smithsonian, said in a statement. “This means that the material has not been slowed down nor sped up since the explosion. From the measured velocities, looking back in time, you can pinpoint the explosion to almost exactly the year 1181.”
Thanks to the observations, the team was able to work out that there is a spherical structure within the fireworks streaks of the supernova remnant – and the explosion is likely to have been asymmetrical. The source of the filaments though, remains uncertain.
“A reverse shock wave may be condensing surrounding dust into filaments, but we don’t know yet,” added Cunningham. “The morphology of this object is very strange and fascinating.”
Observations of Pa 30. It does look like a dandelion!
Image Credit: Robert Fesen
Scientists believe this was a Type Iax supernova, a subclass of the Type Ia. In these supernovae, a white dwarf could merge with another white dwarf or it might steal material from a companion until it reaches a critical level and explodes. In the specific Iax subclass, the white dwarf is not completely annihilated by the process leaving behind a remnant white dwarf, which is called a zombie star.
“Because this was a failed explosion, it was fainter than normal supernovae, which has been shown to be consistent with the historical records,” added co-lead author Ilaria Caiazzo, assistant professor at the Institute of Science and Technology Austria.
While weaker than other events, the explosion was still formidable. The filaments are moving away from the site of the supernova at about 1,000 kilometers (610 miles) per second.
A paper discussing the results is published in The Astrophysical Journal Letters.
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