Orionid Update; R Sculptoris Sculpts A Spacey Spiral

Orionid meteor from near Tucson, Arizona this morning Oct. 21, 2012. Credit: Bill Vaughn

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 Atacama Large Millimeter/submillimeter Array radio telescopes have revealed an unexpected spiral structure in the material around the old star R Sculptoris probably caused by a hidden companion star orbiting the star. A bright shell surrounds the spiral. Credit: ALMA (ESO/NAOJ/NRAO)

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.

Artist’s impression of the structure of a sun-like star and a red giant. The two images are not to scale – the scale is in the lower right corner. Helium burning in the shell around the red giant’s core produces the flashes that create the star’s dust shell. Credit: ESO

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 Hubble Space Telescope captured this picture of another red giant surrounded by multiple dust shells created by a companion star that orbits the giant every 800 years. Each shell formed 800 years after the other in sync with the companion’s period. Credit: ESA/NASA & R. Sahai

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.

4 Responses

  1. Robert

    Hi Bob. Went out early this morning about 3 am. I didn’t see any meteors but the sky was so clear and dark without a moon I was amazed at how majestic Orion stood in front of me. Jupiter was bright and was in perfect line in a star triangle almost straight up. Sirius was bright too and doing it’s normal flashes of red, blue, and white but the colors seemed more distinct. Just a good night of star gazing. The sky was brilliant at that time of day.

    1. astrobob

      Thanks for writing Robert and sharing your impressions of the morning. Wished you’d seen a few meteors, too! That’s how astronomy is – you go out for one thing and often find another.

  2. katesisco

    What controls the ‘thermal pulses’ so that this energy isn’t committed to a catastrophic explosion? Shedding this energy every 10,000 y and now 1,800 ?
    It sounds like O Manuel’s theory of the Iron Sun. He says the sun underwent a controlled collapse (exactly what is proposed here) that ordered the elements. And of course, our sun had a northern hemisphere collapse in January 2012, and Earth’s north magnetic pole underwent ‘wander.’
    It seems strange that we do not know about this type of event. Since we have not called the collapse of the n hemisphere of the sun a gravity wave, we can hardly do so here.

    1. astrobob

      These thermal pulses have been observed in many stars late in their evolution prior to losing their atmospheres altogether and evolving into white dwarfs. The pulses are controlled by the available helium in the shell. As its depleted, hydrogen in another shell next to the helium-burning one, is burning to create more helium. When enough is made for helium fusion to occur, another flash or pulse happens. The sun is much too young still for this to happen. It has yet to even begin burning helium – it still has plenty of hydrogen fuel on hand for a long, long time.

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