Images of a 850 Year Old Stellar Collision
A Dartmouth professor's images of the explosive aftermath from the collision of two dying stars could help scientists better understand this rare type of astronomical event - and may finally confirm the identity of a brilliant but short-lived star observed nearly 850 years ago.
Pa 30 is a dense region of illuminated gas, dust and other matter known as a nebula. Fesen and his co-authors report that Pa 30 appears to contain little to no hydrogen and helium but is instead rich in the elements of sulfur and argon
The nebula's unusual structure and characteristics match the predicted result of a collision between end-stage stars known as white dwarfs, Fesen said. White dwarfs are faint, extremely dense stars about the size of Earth that contain the mass of the Sun. The merger of two white dwarfs is one proposed explanation for a subclass of supernovae - or star explosions - called Iax events, in which the star is not completely destroyed, Fesen said.
"I have never seen any object - and certainly no supernova remnant in the Milky Way galaxy - that looks quite like this, and neither have any of my colleagues," Fesen said. "This remnant will allow astronomers to study a particularly interesting type of supernova that up to now they could only investigate from theoretical models and examples in distant galaxies."
The size of Pa 30 and the speed at which it is expanding - about 2.4 million miles per hour - suggest the explosive collision occurred around the year 1181, the researchers report. That coincides with observations by Chinese and Japanese astronomers at the time of a very bright star that suddenly appeared in the constellation Cassiopeia and was visible for about six months as it slowly faded. These fleeting stars are known as "guest stars."
The images Fesen captured of the nebula's structure and luminosity not only provide the most accurate estimate yet of its age, but also could allow astronomers to refine existing models of white dwarf mergers. Pa 30 was discovered in 2013 by co-author and amateur astronomer Dana Patchick, but up until now, images of the nebula had shown only an extremely faint and diffuse object, Fesen said.
Fesen took the images of Pa 30 in late 2022 using the 2.4-meter Hiltner Telescope at the MDM Observatory - which Dartmouth owns and operates with four other universities - adjacent to Kitt Peak National Observatory in Arizona. Fesen equipped the telescope with an optical filter sensitive to a particular emission line of sulfur. He captured Pa 30 in three 2,000-second exposures under very clear skies and took additional data on the nebula's structure, size and velocity.