The recent deaths of two white dwarfs are challenging our understanding of the powerful physics behind novae and stellar death. Astronomer John Monnier said the initial analysis of these often striking new stars provides an “extraordinary leap forward” for the field.
“The fact that we can now see stars exploding and immediately see the structure of the material being blasted into space is pretty remarkable,” said a 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 make a new star. These spectacular moments occur after the dying white dwarf star has sucked enough material from its nearby companion star. However, experts have long believed that nova ignition was a single explosive event, and two examples contradict this assumption.
In 2021, researchers at the Center for High Angular Resolution Astronomy (CHARA) array in California captured images of eruptions from nova V1674 Hercules and nova V1405 Cassiopeia. Hercules brightens and fades in just a few days, making it one of the fastest novae on record, but it also produces two vertical outflows of gas. These jets mean multiple mixed jets power the nova.
NASA’s Fermi Gamma-ray Space Telescope also observed the same stream from Nova V1674 Herculis and Nova V1405 Cassiopeiae. In these observations, however, Cassiopeia’s novae exploded much more slowly. The star’s outermost layers were retained for more than 50 days before they were eventually ejected, providing astronomers with the first direct evidence of delayed nova ejection. As was the case with Hercules, gamma rays from Cassiopeia were recorded by the Fermi telescope.
“These observations allow us to watch stellar explosions in real time, a very complex phenomenon that has long been considered extremely challenging,” explains Elias Eddy, an astrophysicist at Texas Tech University and study co-author. “What we are now seeing is more than a simple flash of light, but reveals 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 main breakthrough was attributed to a technique called interferometry. This powerful technique allows astronomers to pool light from multiple telescopes to improve image resolution, enough to record rapidly evolving dynamic events such as novae. In addition to recent observations of novae, interferometry is best known for allowing researchers to finally image the black hole at the center of the Milky Way.
While the new data may upend some long-standing theories of nova behavior, experts say their findings could soon help expand our understanding of cosmic interactions.
“Nova stars are more than just fireworks in our galaxy, they are laboratories of extreme physics,” added study co-author Laura Chomick, an astronomer at Michigan State University. “By observing how and when material is ejected, we can ultimately connect the dots between nuclear reactions at the star’s surface, the geometry of the ejected material, and the high-energy radiation we detect from space.”
