April 13 (UPI) -- High-resolution observations of a nova explosion, including images captured by a pair of NASA missions, suggest shock waves are responsible for producing most of the light generated during an outburst.
Nova explosions happen when a stream of hydrogen flows from a companion star onto the surface of a white dwarf -- stars that were once like our sun, but have since shed their layers and contracted.
In 2018, NASA's Fermi and NuSTAR space telescopes, as well as the Canadian BRITE-Toronto satellite, recorded a nova explosion from V906 Carinae, a star situated 13,000 light-years away in the constellation Carina.
"Thanks to an especially bright nova and a lucky break, we were able to gather the best-ever visible and gamma-ray observations of a nova to date," researcher Elias Aydi, an astronomer at Michigan State University, said in a news release. "The exceptional quality of our data allowed us to distinguish simultaneous flares in both optical and gamma-ray light, which provides smoking-gun evidence that shock waves play a major role in powering some stellar explosions."
After accumulating hydrogen from its companion, perhaps for thousands of years, the hydrogen layer of V906 Carinae reached a critical temperature and mass and exploded. The outburst released 10,000 to 100,000 times the energy our sun puts out in a year.
Previous X-ray and radio wave analysis of nova explosions has revealed the presence of shock waves, but until now, scientists had yet to observe gamma rays, the highest-energy form of light, emanating from a nova outburst. Shock waves are capable of accelerating matter to speeds capable of producing gamma rays.
The new analysis showed visible light and gamma ray emissions coming from the V906 Carinae explosion peaked at the same time, suggesting nova shock waves are a significant source of visible light.
Scientists wouldn't have been able to make the link between gamma rays and visible light without the high-resolution observations made by Fermi, NuSTAR and BRITE. Researchers shared their analysis of the telescope data in the journal Nature Astronomy on Monday.
"When we compare the Fermi and BRITE data, we see flares in both at about the same time, so they must share the same source -- shock waves in the fast-moving debris," said study co-author Koji Mukai, an astrophysicist at the University of Maryland Baltimore County and NASA's Goddard Space Flight Center. "When we look more closely, there is an indication that the flares in gamma rays may lead the flares in the visible. The natural interpretation is that the gamma-ray flares drove the optical changes."
The new analysis suggests the shock waves of debris likely absorb much of the high-energy light produced by the nova. The light gets emitted by the debris at lower energies, yielding large of amounts of visible light.
During the nova explosion of V906 Carinae, a few rounds of shock waves were produced over several days. Newer faster shock waves crashed into earlier, now-slower donut-shaped waves of expelled debris. The series of colliding shock waves produced a pattern of flares featuring both gamma rays and visible light.
According to the new study, this succession of shock waves can explain how a relatively small explosion is able to produce the kind of high-energy emissions normally associated with bigger cosmic phenomena, such as supernovae and tidal disruption events involving black holes.