Exploding Stellar Fireball from a White Dwarf Captured for the First Time

Astronomers have managed to image an exploding fireball from a nova that erupted last year. The new images reveal a bit more about this type of interaction and shows how the structure of the ejected material evolves as the gas expands and then cools.

A nova occurs when a thin layer of hydrogen on the surface of a white dwarf star builds up. A white dwarf star itself is a highly evolved star with a diameter about the size of Earth and a mass roughly equivalent to that of our sun. The hydrogen that builds up is usually provided by a close companion star. This hydrogen "ocean" is acted upon by the enormous gravity of the white dwarf. This triggers a thermonuclear fusion-essentially a stellar H-bomb.

In this case, the scientists pointed the telescopes of the CHARA Array toward the nova, called Nova Del 2013, in order to image it. Over the course of two months, the scientists took the first measurements to find out the size of the nova event.

Using this data, the researchers determined that Nova Del 2013 is about 14,800 light-years from the sun. This means that while the explosion was witnessed here on Earth last August, it actually took place nearly 15,000 years ago.

The observations also showed that the outer layers of the fireball became more diffuse and transparent as the fireball expanded. After about 30 days, the researchers saw evidence for a brightening in the cooler, outer layers; this was potentially caused by the formation of dust grains that emit light at infrared wavelengths.

The findings reveal a bit more about novae and show more about the earliest stages of explosions. This, in turn, will inform future research and may validate theoretical models of novae eruptions.

The findings are published in the journal Nature.