A Star Exploded 850 Years Ago and Is Still Alive

Keypoints:

• New Gemini North telescope images reveal about 10 times more filaments in the supernova remnant Pa 30
• The filaments are chains of gas knots of similar size
• Pa 30 is linked to a supernova recorded in 1181 in Japanese, Chinese and Arabic sources
• It is the only known Type Iax supernova remnant in the Milky Way
• The surviving "zombie star" at its center burns at about 200,000 degrees Celsius

Astronomers have captured the most detailed view yet of Pa 30. It is a firework-shaped cloud left by a supernova that people saw nearly 850 years ago. The Gemini North telescope on Maunakea in Hawaii took the images. The team was co-led by Timothy Cunningham of the Center for Astrophysics, Harvard & Smithsonian and Ilaria Caiazzo of the Institute of Science and Technology Austria. The work appears in The Astrophysical Journal.

The history is unusual. Observers in Japan, China and the Arab world recorded a "guest star" in 1181 that stayed visible for 185 days. Yet Pa 30 itself was not found until 2013, when a citizen scientist identified it. Astronomers later linked it to the historical event.

The new images used a sulfur emission filter. They resolved about ten times as many filamentary features as earlier pictures. The filaments turn out to be tight chains of gas knots with remarkably similar sizes. Caiazzo said each knot is wide enough to fit the region of the solar system out to Neptune about ten times over.

The explosion was unusual too. Pa 30 is thought to come from a Type Iax supernova. That is a lower-energy, incomplete explosion that leaves a surviving star. Standard Type Ia supernovae destroy their stars. Pa 30 is the only known Type Iax remnant in the Milky Way. A few similar objects are known in other galaxies, but only here can telescopes see the survivor at the core.

That survivor is nicknamed a zombie star. Its temperature is about 200,000 degrees Celsius. It sits almost exactly at the center of the nebula. Surviving stars are usually kicked sideways by an explosion, so a small kick suggests an unusually symmetrical blast.

The researchers say Pa 30 could guide the search for other explosions that left survivors. If more exist, how many stellar deaths have been incomplete?