We hear about supernovae, spectacular in their brightness. Supernovae are on the first string of the violent event team in our universe. Novae, on the other hand, seem to be relegated to obscurity. No respect.
The difference between novae and supernovae starts with mass accumulation. Interestingly, they both usually involve a white dwarf with a companion star. There the similarity ends.
A white dwarf with a more distant companion star gets fed less plasma from its companion than the white dwarf with a closer star.
The companion star’s makeup is a factor too. If it’s more compact, like a main sequence star, its gravity controls more of its plasma. If it’s a red giant companion – the bloated evolutionary phase of a Sun-like star in its late stages, its plasma is more loosely held by gravity and easier for the intense gravity of a white dwarf to collect.
A close red giant companion gives up plasma readily and the white dwarf gains mass, so much and so fast it explodes as a supernova, destroying its companion in the process. Depending on the amount of mass it gained before exploding, the white dwarf can become a neutron star, black hole, or simply be blown apart. This action seeds our universe with many heavy elements.
A main sequence or a distant red giant companion star gives up its plasma more slowly. The resulting mass increase for the white dwarf initiates a more complex set of events. First, the surface of the white dwarf gets layered with plasma that is compressed by the white dwarf’s intense gravity. Once pressure gets high enough in the plasma and temperatures reach 20 million Kelvin, fusion begins. As more material is deposited the chain reaction gets out of control and BAM! A nova is born. If this explosion isn’t too violent, the white dwarf and companion are only bruised a bit. The process of plasma accretion sometimes begins again, becoming a cycle that repeats every 10,000 to 100,000 years.
The circumstances of a nova produce unique results. Rather than heavier elements, as coming from a supernova, novae produce light elements such as lithium. Hmmm, lithium seems to be a rather important element these days. It is estimated that as much as 70% of the lithium we have on Earth came from novae.
While around 30 novae occur each year in our Galaxy, the Milky Way, bright novae have seemingly disappeared. In the first half of the 20th century, we could rely on one naked eye bright nova per decade. No bright novae have been spotted in 80 years! Keep your fingers crossed and keep looking up!
What’s in the Sky?
Tonight, March 25th; Astronomy Night at Tye Preston Memorial Library in Canyon Lake: We start inside with an orientation, then on to the observatory if the sky is clear.
March 27; 8pm CDT; west: Starting at the horizon…Mercury, Jupiter, Venus, Uranus, the Moon, and Mars line up. You will need binoculars for Uranus and possibly Me