The recent deaths of two white dwarf stars challenge our understanding of novae and the powerful physics behind star deaths. According to astronomer John Monnier, the initial analysis of these often dramatic novae offers an “extraordinary leap forward” for the field.
“The fact that we can now watch stars explode and immediately see the structure of matter thrown into space is remarkable,” said the University of Michigan astronomer and co-author of a study published Dec. 5 in the journal Natural astronomy. “It opens a new window into some of the most dramatic events in the universe.”
It takes two to nova. These spectacular moments occur after a dying white dwarf siphons off enough material from a nearby companion star. However, experts have long assumed that novae ignite as a single explosive event and two examples contradict this hypothesis.
In 2021, researchers at the Center for High Angular Resolution Astronomy (CHARA) Array in California captured images of the flares of Nova V1674 Herculis and Nova V1405 Cassiopeiae. Herculis brightened and faded in just a few days, making it one of the fastest novas ever recorded, but it also produced two perpendicular gas outflows. These jets imply that multiple intermingled ejections propelled the nova.
These same streams from Nova V1674 Herculis and Nova V1405 Cassiopeiae were also observed by NASA’s Fermi Gamma-ray space telescope. However, Cassiopeia went nova much more gradually in these observations. The star retained its outermost layers for more than 50 days before finally ejecting them, providing astronomers with the first direct evidence of a delayed nova expulsion. As in the case of Herculis, gamma rays from Cassiopeia were also recorded by the Fermi telescope.
“These observations allow us to observe a stellar explosion in real time, which is very complicated and has long been considered extremely difficult,” explained Elias Aydi, an astrophysicist and co-author of the study at Texas Tech University. “Instead of seeing a single flash of light, we are now seeing the true complexity of how these explosions unfold. It’s like going from a grainy black-and-white photo to a high-definition video.”
The major advances are due to a technique called interferometry. This powerful technique allows astronomers to compile light from multiple telescopes to fine-tune the image resolution enough to document dynamic and rapidly evolving events like novae. In addition to recent observations of novae, interferometry is best known for allowing researchers to finally image the central black hole of the Milky Way.
Although these new data will likely upend some long-held theories about novae behavior, experts say their findings will soon help expand our understanding of cosmic interactions.
“Novae are more than fireworks in our galaxy: they are laboratories for extreme physics,” added study co-author and Michigan State University astronomer Laura Chomiuk. “By observing how and when material is ejected, we can finally make the connection between nuclear reactions on the star’s surface, the geometry of the ejected material, and the high-energy radiation we detect from space.”
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