[Reading Science] Rare 'Fireworks-type' Supernova Discovered

Research Team at Dartmouth College, USA

[Asia Economy Reporter Kim Bongsu] Astronomers at a university in the United States have attracted attention by discovering a supernova exploding in all directions like fireworks. Usually, supernovae appear irregular like sea anemones due to entangled gas and dust generated during the explosion, but this is the first time a supernova resembling fireworks has been observed.

Pa 30, a rare supernova emitting thin rays in all directions like fireworks. Photo by Dartmouth College, USA.

Astronomers at Dartmouth College in the eastern United States announced these observational results at the 241st meeting of the American Astronomical Society held on the 12th. The photos they presented were of the 'Pa 30' supernova, discovered in 2013 by an amateur astronomer using observation data from NASA's Wide-field Infrared Survey Explorer (WISE). However, the more this supernova was observed, the more it surprised astronomers. In 2019, a research team from Lomonosov Moscow State University found that the surface temperature of the star at the center of Pa 30 was as high as 200,000 Kelvin (199,700 degrees Celsius), and the stellar wind was blowing outward at about 5% of the speed of light, approximately 16,000 km/s. These values were much higher than typical temperatures and stellar wind speeds. In 2021, a research team from the University of Hong Kong proposed the theory that this supernova is the remnant of a supernova explosion witnessed 850 years ago in 1181, drawing interest.

The research team that observed this rare phenomenon of a 'fireworks-type' supernova explosion focused on wavelengths related to the sulfur element in the spectrum emitted by the remnants to recreate images. Using the 2.4-meter Hiltner Telescope at the Michigan-Dartmouth-MIT Observatory located at Kitt Peak, Arizona, they imaged the remnants with optical filters sensitive to sulfur.

Through this observation, the team helped confirm that the 'Pa 30' supernova is indeed the remnant of the supernova explosion observed in 1181. Moreover, they observed a phenomenon never before seen in any other supernova: hundreds of small, thin rays being ejected outward. This was a completely different image from the expected rounded, sea anemone-like shape of the Crab Nebula supernova or the chaotic ball-like image of the Tycho supernova.

The cause of this fireworks-type remnant ejection phenomenon in the supernova is still unknown. For now, the University of Hong Kong research team has proposed classifying this type of supernova as lax. Typical la-type supernovae occur when a white dwarf absorbs a companion star, grows larger, and finally explodes, scattering remnants. However, in the case of the newly discovered lax-type supernova, the star survives in some way, earning it the nickname 'zombie star.'

The University of Hong Kong team believes that a collision between two white dwarfs could cause a fireworks-type explosion like Pa 30. This would explain why a large amount of sulfur was observed in the infrared spectral analysis while lighter elements were not detected. However, this contradicts the existing theory that supernovae occur when a white dwarf absorbs a companion star, grows beyond its weight limit, and explodes, posing a challenge.

The research team plans to resolve these questions through additional precise observations of the 'Pa 30' supernova using the Hubble Space Telescope and the James Webb Space Telescope (JWST). Fortunately, this supernova is only 2.3 kiloparsecs (1 kiloparsec = 3,260 light-years) away from Earth, making it relatively easy to observe.