Friday, November 10, 2006

Giant Stellar Flares

Image above: This movie shows a massive solar flare from October 2003, captured by the SOHO satellite. Note the burst of high-speed particles after the flare creating a snowstorm effect. The stellar flare that Swift detected from a star system called II Pegasi was millions of times more powerful. Credit: NASA-ESA/SOHO/EIT

The flaring star in II Pegasi is 0.8 times the mass of the sun; its companion is 0.4 solar masses.
The stars are close, only a few stellar radii apart. As a result, tidal forces cause both stars to spin quickly, rotating in step once in 7 days compared to the sun's 28-day rotation period. Fast rotation is conducive to strong stellar flares.

Young stars spin fast and flare more actively, and the early sun likely generated solar flares on par with II Pegasi. Yet II Pegasi could be at least a billion years older than our middle-aged 5-billion-year-old sun. "The tight binary orbit in II Pegasi acts as a fountain of youth, enabling older stars to spin and flare as strongly as young stars," said Steve Drake of NASA Goddard, a co-author with Osten on an upcoming Astrophysical Journal paper.

The key finding in the II Pegasi flare was the detection of higher-energy X-rays. Swift's Burst Alert Telescope usually detects gamma-ray bursts, the most powerful explosions known, which arise from star explosions and star mergers. The II Pegasi flare was energetic enough create a false alarm for a burst detection. Scientists quickly knew this was a different kind of event, however, when the flare overwhelmed Swift's X-ray Telescope, a second instrument.

Higher-energy "hard" X-ray detection in this case is the telltale signal of electron particle acceleration, creating what is called non-thermal X-rays. NASA's RHESSI mission sees this in the sun's solar flares. While lower-energy "soft" X-rays from thermal emission have been seen on other stars, scientists have never seen hard X-rays on any flaring star other than the sun. Because the hard X-rays occur earlier in the flare and are responsible for heating the coronal gas, they reveal unique information about the flare's initial stages.

Had the sun flared like II Pegasi, these hard X-rays would have overwhelmed the Earth's protective atmosphere, leading to significant climate change and mass extinction. Ironically, one theory posits that stellar particle outbursts are needed to condition dust to form into planets and perhaps life.

The Swift observation demonstrates that such outbursts do occur."Swift was built to catch gamma-ray bursts, but we can use its speed to catch supernovae and now stellar flares," said Swift Project Scientist Neil Gehrels of NASA Goddard. "We can't predict when a flare will happen, but Swift can react quickly once it senses an event.

Swift catches Stellar bursts & giant flares from NASA 06 Nov 2006

Science Daily release:
A Leading Edge
Camera For Molecules

Researchers at the Max Planck Institute for Nuclear Physics in Heidelberg have visualised vibration and rotation in the nuclei of a hydrogen molecule as a quantum mechanical wave packet.

What is more, this has been achieved on an extremely short spatio-temporal scale. They "photographed" the molecule using intensive, ultrashort laser pulses at different points in time and compiled a film from the separate images. This allowed them to visualise the quantum mechanical wave pattern of the vibrating and rotating molecule (Physical Review Letters, Online-Edition, November 6, 2006).

Cameras and light microscopes are not viable options when photographing molecules: a hydrogen molecule is around 5,000 times smaller than the wavelength of visible light and it is therefore not possible to create an optical image of these molecules. Instead, for some time Max Planck researchers have been using pump-probe technology to make high-resolution and ultrahigh-speed images. The molecules are first "bumped" with a "pump" laser pulse and then after a specific time measured with a "probe" laser pulse.
Molecular Photography by JoAnne Hewett @ Cosmic Variance
Double-eyed vortex at Venus' South Pole from ESA 09 Nov 2006
Lisa Randall on Xtra dimensions by Sabine Hossenfelder 09 Nov 2006

Labels: ,