'Blast waves' observed in Sun's atmosphere

A unique observing opportunity has allowed two teams of researchers to discover blast waves occuring within the solar atmosphere.

An ultraviolet view of the Sun's right limb, showing a blast wave traveling through the solar atmosphere.

A new solar phenomenon in the form of massive waves accompanied by energetic particle emissions has been uncovered by two teams of researchers.

The Sun is highly energetic and continuously emits energetic particles and radiation into space in the form of short X-ray flares and also coronal mass ejections (CMEs), in which a plasma of electrons, protons and atoms is hurled into space. These phenomena happen in tandem with solar eruptions.

A different type of solar ejection has now been observed: large waves in the Sun's atmosphere accompanied by particle flows rich in helium-3, a light variety of helium.

The waves were detected in data from 26 January and 2 February 2010 using NASA's STEREO A and ACE spacecrafts, which enabled the teams to simultaneously observe the Sun from two different directions.

The waves extended over half a million kilometres and reached a speed of about 300 kilometres per second, occurring just after a weak X-ray flash. The team noted that no coronal mass ejections were observed that could have triggered the waves.

"The new phenomenon is like a kind of explosion," says Radoslav Bucík from the Max Planck Institute for Solar System Research (MPS) in Germany, one of the teams that discovered the phenomena. The other was led by Nariaki Nitta from the Lockheed Martin Advanced Technology Center in the USA.

At the same time these waves are occurring, the Sun is hurling a particle stream rich in helium-3 into space. Such emissions have been known for years, but could never be properly accounted for. “We believe that the blast waves accelerate the helium-3,” says Davina Innes, from MPS.

"Our analysis shows that typical characteristics of the waves, such as their energy, influence the properties of the particles”, adds Lijia Guo, also from MPS.

In order to discover the phenomena, the teams had to observe the Sun from two directions. Because the Sun rotates, its ejected particles travel on a curved trajectory. The particles reaching us originated on the right side of the Sun, which is not clearly visible from Earth.

It is thought that these phenomena are by no means rare, but could not be observed until this unique opportunity arose. The astronomers behind the study have noted that such an opportunity will not arise again in the foreseeable future.

Front image: NASA's Solar Dynamics Observatory captures a solar flare on 12 November 2012.
Credit: NASA/SDO
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