For the first time, scientists have closely examined the fascinating eruptions on two white dwarfs. These blast-like events, called nova eruptions, show that they’re more complicated than we thought.
The research comes from the CHARA array in California, an advanced optical instrument that combines light from six telescopes. It focused on two nova events: V1674 Herculis and V1405 Cassiopeia. Astronomers have discovered that a nova doesn’t destroy a white dwarf star like a supernova would. Instead, it happens when the white dwarf pulls too much material from a nearby red giant star. This builds up until a massive explosion occurs, lighting up the star but leaving its core intact.
When viewed from Earth, a nova looks like a brilliant flash, making it visible to the naked eye. The term “nova,” meaning “new star” in Latin, was coined by the 16th-century astronomer Tycho Brahe. Traditionally, astronomers thought nova eruptions were just single events of material ejecting from a point on the white dwarf. However, high-energy signals detected by the Fermi Space Telescope hinted at a more intricate picture.
In 2021, the CHARA array was able to observe the two nova eruptions shortly after they occurred. Gail Schaefer, the Director of CHARA, described how the images provided insight into how material blasts away from the star during these explosions. The two nova events behaved very differently. V1674 Herculis had one of the fastest eruptions ever recorded, brightening rapidly and fading within days. In this case, CHARA detected two perpendicular outflows rather than a single explosion, and the Fermi Telescope recorded gamma rays from violent collisions within those outflows.
On the other hand, V1405 Cassiopeia erupted more slowly. It took fifty days for substantial material to be ejected after the initial brightening. The ejected matter created new impacts and also produced gamma rays, eventually shining bright enough to be seen without a telescope from dark locations.
Additional data from the Gemini North Telescope in Hawaii tracked the ejected matter, revealing its chemical makeup. This included ionized iron, helping scientists to connect the dots between nuclear reactions on the white dwarfs and the types of radiation observed from Earth.
Understanding these explosions is crucial. Laura Chomiuk from Michigan State University noted that these observations help us link the chemistry, the explosion’s geometry, and the radiation detected from space. This research sheds light on a poorly understood aspect of stellar evolution and offers new insights into the dynamics of such explosive celestial events.
These findings were published in Nature Astronomy on December 5. The study not only opens new avenues in astronomy but also fuels our understanding of the life cycles of stars.
