Unprecedented observations of a nova outburst in 2018 by a trio of satellites, including NASA’s Fermi and NuSTAR space telescopes, have captured the first direct evidence that most of the explosion’s visible light arose from shock waves — abrupt changes of pressure and temperature formed in the explosion debris.
A nova is a sudden, short-lived brightening of an otherwise inconspicuous star. It occurs when a stream of hydrogen from a companion star flows onto the surface of a white dwarf, a compact stellar cinder not much larger than Earth.
The 2018 outburst originated from a star system later dubbed V906 Carinae, which lies about 13,000 light-years away in the constellation Carina. Over time — perhaps tens of thousands of years for a so-called classical nova like V906 Carinae — the white dwarf’s deepening hydrogen layer reaches critical temperatures and pressures. It then erupts in a runaway reaction that blows off all of the accumulated material.
Fermi detected its first nova in 2010 and has observed 14 to date. Gamma rays the highest-energy form of light require processes that accelerate subatomic particles to extreme energies, which happens in shock waves. When these particles interact with each ...