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Sun's major heat source discovered

23 January 2013

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Sharpest-ever images of corona catch a glimpse of magnetic braids that may heat the solar atmosphere

The University of Central Lancashire (UCLan) in collaboration with NASA, the Harvard-Smithsonian Center for Astrophysics and other partners* have captured the highest resolution images ever achieved of the Sun’s outer atmosphere (corona), the results of which are outlined this week in the journal Nature.

NASA's High Resolution Coronal Imager, or Hi-C, was launched to the edge of space on July 11 2012, from White Sands Missile Range in New Mexico, USA. The resulting images provide intriguing hints of a mechanism that likely contributes significantly to the heating of the solar corona.



For several decades scientists have sought to understand why the outer parts of the solar atmosphere are on average about two million degrees Kelvin, about 400 times hotter than the surface of the Sun.

For the first time, Hi-C's image sequences show the twisting up or braiding of the magnetic field that is threaded through the corona. This distinctive braiding of the magnetic field is a clear signal that energy is being added into the corona which may then be released violently, heating the electrified gases to well over 2 million degrees.

“To view this magnetic braiding directly is a game changer. For the first time we can see the reconnection and unraveling of the braids within the Sun’s outer atmosphere”

The Hi-C team captured dynamic images of the solar atmosphere at a resolution five times higher than previously obtained, acquiring data at a rate of approximately one image every five seconds.

The telescope focused on a large, magnetically-active region on the Sun, and some of its images reveal the intricate structure of the solar atmosphere in the finest ever detail.

The images were taken in the extreme ultraviolet part of the electromagnetic spectrum.


This higher-energy wavelength of light is optimal for viewing the hot solar corona. The corona is widely believed to be the origin of energetic events called flares. The clarity of these new images will help scientists better understand the driving force for these eruptions and help predict with greater accuracy when violent solar eruptions might take place which could threaten Earth’s own space environment.

“As a University we are extremely proud that our physicists and engineers have played an integral part in developing the Hi-C camera”


“Scientists have tried for decades to understand how the solar corona is heated to millions of degrees,” said Marshall heliophysicist Dr Jonathan Cirtain, principal investigator for the Hi-C mission. “Our team developed an exceptional instrument capable of revolutionary image resolution of the solar atmosphere. Due to the level of activity, we were able to clearly focus on an active sunspot, thereby obtaining some remarkable images.”

Solar physicist Dr Robert Walsh, UCLan’s University Director of Research, added: “To view this magnetic braiding directly is a game changer.  For the first time we can see the reconnection and unraveling of the braids within the Sun’s outer atmosphere and confirms our theory that this is one of the key processes responsible for the heating of the Sun.

“It is similar to looking at a rope that is mooring a boat at a harbour. From a distance, the rope looks like a single object, which moves back and forth as the boat bobs up and down by the quayside. However, when you go up to the boat itself, you see the rope is made up of several individual strands, braided around one another. Up to now we have been viewing these magnetic “ropes” from afar – with Hi-C we now have the vision sharp enough to see the constituent braids.”

Dr Walsh added: “As a University we are extremely proud that our physicists and engineers have played an integral part in developing the Hi-C camera.”

The high-resolution images were made possible by a set of innovations on Hi-C's optics array.

The telescope includes mirrors made at the Marshall Space Flight Center, in Huntsville, Alabama, some of the finest mirrors ever made for space-based instrumentation.

The Harvard-Smithsonian Center for Astrophysics developed an innovative approach to mounting these mirrors to preserve the mirror resolution capability.


“This flight represents the culmination of 30 years of effort to develop these exceptionally high quality optics," said Dr Leon Golub, Co-investigator at the Smithsonian Astrophysical Observatory, which is part of the Harvard-Smithsonian Center for Astrophysics.

“The Hi-C observations zoom in on what happens within the global view of the Sun that is seen with NASA’s Solar Dynamics Observatory. The combination of the big-picture view with the unprecedented Hi-C images shows us processes in action that we could only theorise about until now, processes that are fundamental to the workings of the solar atmosphere and all of space weather, and that apply at any other sun-like star where we would never be able to see them in action,” said Dr Karel Schrijver, SDO principal investigator and solar physicist at Lockheed Martin Solar and Astrophysics Laboratory. “The Hi-C images demonstrate that we now have the technology to make the next leap in understanding the Sun’s violent magnetism.”

*Partners associated with the development of the Hi-C telescope include the Smithsonian Astrophysical Observatory in Cambridge, Mass.; L-3Com/Tinsley Laboratories in Richmond, California.; Lockheed Martin's Solar Astrophysical Laboratory in Palo Alto, California.; the University of Central Lancashire in Lancashire, England; and the Lebedev Physical Institute of the Russian Academy of Sciences in Moscow.

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