How was your Orionid experience? I hope the loss of sleep was rewarded by at least a few shooting stars. According to the International Meteor Organization’s quicklook data, the shower peaked overnight into this morning with a maximum of 29 meteors per hour. That preliminary number may change as more observers contribute reports. I wasn’t in a position to watch the shower outdoors, but did spend a half-hour peering at the sky from under a window shade from 4-4:30 a.m. before fog slowly blotted out the stars. My tally: one Orionid and one sporadic.
The European Southern Observatory (ESO) shared news and a photo earlier this week of an extraordinary celestial spiral unwinding around the red giant star R Sculptoris in the southern constellation of Sculptor. The photo was made using data gathered by the ALMA radio telescope array that studies light emitted by stars in the short wavelength (millimeter-long) radio wave spectrum just beyond infrared.
R Sculptoris may once have resembled the sun in size and brightness, but as it aged, the star used up the hydrogen fuel in its core. The fusion of hydrogen atoms under the ferocious heat and pressure in a star’s core converts it into helium, the same gas that pumped into balloons that float away when you let them go. A tiny amount of matter in the reaction – just 0.7% – is transformed into pure energy a la Einstein’s famous E=mc² equation, and this is what makes stars shine.
The core next contracts and compacts, heating the helium to the burning point. Helium provides the energy that powers the star while transforming itself via nuclear alchemy into carbon and oxygen “ash”. These collect in the core, which is now surrounded by a thin shell of helium. Once again, pressure and heat inside the star are extreme enough to ignite the shell in a sudden “shell helium flash”. Old-age stars in the sun-size range experience these internal flashes, also called thermal pulses, every 10,000 to 50,000 years. Each flare-up lasts only 200-300 years.
The blast from the pulse made R Sculptoris expel a circumstellar shell of gas and dust into space. Astronomers estimate the most recent pulse happened about 1,800 years ago and lasted for about 200 years. Meanwhile, a companion star, not visible in the photo, shaped the outgoing wind into a spiral structure through a combination of its gravity and orbital motion around the red giant.
A few billion years from now the sun will become a red giant star like R, shedding its outer atmosphere as a gigantic shell while pulses of helium ignition rock its interior. Since the sun’s a third or fourth generation star, having formed from the matter shed in part by previous red giants, it’s satisfying to know it will give back a little of what it borrowed in its youth to seed the next generation of stars.