Research teams in the U.S. and Germany have independently discovered a new form of solar ejection that they believe could be responsible for accelerated particle emissions from the Sun. These unusual emissions had been spotted before, but until now, their origins remained unclear.
The American team is led by Nariaki Nitta from the Lockheed Martin Advanced Technology Center, while the German one is led by Radoslav Bučík from the Max Planck Institute for Solar System Research (MPS). The German team has published their results in The Astrophysical Journal.
The Sun has an active surface with an intensity that varies on an 11-year cycle. A particularly spectacular phenomenon is the coronal mass ejection, a disruptive magnetic interaction that propels plasma into interplanetary space, often seen in conjunction with solar flares – sudden flashes of brightness observed near sunspots. The newly discovered type of ejection, called blast waves, seem to be independent of these well-known events.
"The new phenomenon is like a kind of explosion," said Dr. Bučík, who headed the team of researchers at the MPS, in a statement. It was seen in data from January 26 through February 2, 2010. It was discovered and tracked by looking at the Sun’s atmosphere in extreme ultraviolet light. The scientists observed a weak X-ray flash followed by a large wave that extended for at least 500,000 kilometers (310,000 miles) and moved with a speed of 300 kilometers (190 miles) per second. These waves are believed to be the underlying cause of an observed emission of helium-3 particles, a special isotope of helium, from the blast wave location.
Due to the Sun's rotation on its axis, particles get thrown into space on a curved trajectory. To find a connection between blast waves and helium-3, the scientists needed a 360-degree observation of our star.
STEREO A UV observation of the Sun when the blast wave happened. Credit: NASA/STEREO A/MPS/AAS
This result was possible by using two spacecraft – STEREO A and ACE – simultaneously. The Advanced Composition Explorer, or ACE, studies the solar wind, while STEREO A (Solar Terrestrial Relations Observatory) is one of the two twin probes launched to provide stereoscopic imaging of the Sun and solar phenomena. We lost communication with STEREO-B last year. STEREO A travels independently around the Sun, slightly faster than Earth (347 days), while ACE orbits near the Earth. In 2010, they were at the right position around our star to detect the flow of particles as well as its cause. It will take 10 years before the probes will have the same favorable position again.