NASA missions reveals the power of shock waves in nova explosions

An uncommon nova outburst captured by three satellites in 2018 has given direct proof that most of visible light from the explosion is caused by shock waves.

Shock waves are sudden changes of both tempertaure and pressure in the debris of the nova explosion, NASA reported earlier this week.

“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,” Elias Aydi, an astronomer at Michigan State University in East Lansing, said in the NASA report.  "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."

The 2018 nova outburst came from the star V906 Carinae, which is about 13,000 light-years away in the Carina constellation and is visible in Earth's southern skies.

The V906 Carinae observations were published in the paper "Direct evidence for shock-powered optical emission in a nova" on April 13 in Nature Astronomy.

NASA's Fermi and NuSTAR space telescopes, along with the BRITE-Toronto satellite, provided insights into the 2018 nova outburst by studying the structure and evolution of the star, according to the NASA report. 

“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,” Koji Mukai, an astrophysicist at the University of Maryland Baltimore County and NASA’s Goddard Space Flight Center in Greenbelt, said in the NASA report. 

Kirill Sokolovsky, with Michigan State, said flares of light were seen on the BRITE-Toronto when the nova peaked. 

“BRITE-Toronto revealed eight brief flares that fired up around the time the nova reached its peak, each one nearly doubling the nova’s brightness. We’ve seen hints of this behavior in ground-based measurements, but never so clearly. Usually we monitor novae from the ground with many fewer observations and often with large gaps, which has the effect of hiding short-term changes," Sokolovsky said in the NASA report.

Astronomers said the shock waves explain short-lived events, according to the report. The BRITE, Fermi and NuSTAR have recorded observations of the larger blasts such as stellar mergers, tidal disruption events and supernovae. 

"Further studies of nearby novae will serve as laboratories for better understanding the roles shock waves play in other more powerful and more distant events," the report said.