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2 January 2015 Mystery at the Sun's south pole: NASA reveals huge 'coronal hole' (Sorurce: DailyMail):
The Sun has started 2015 with a mysterious event - a huge hole has appeared. Known as a coronal hole, the phenomenon occurred near the south pole - and is seen as a dark area covered all of its base The incredible image was captured on Jan. 1, 2015 by the Atmospheric Imaging Assembly (AIA) instrument on NASA's Solar Dynamics Observatory, shows the coronal hole as a dark region in the south. Coronal holes are regions of the corona where the magnetic field reaches out into space rather than looping back down onto the surface.Particles moving along those magnetic fields can leave the sun rather than being trapped near the surface. Those trapped particles can heat up and glow, In the parts of the corona where the particles leave the sun, the glow is much dimmer and the coronal hole looks dark. Coronal holes were first seen in images taken by astronauts on board NASA's Skylab space station in 1973 and 1974.They can be seen for a long time, although the exact shape changes all the time. The polar coronal hole can remain visible for five years or longer. Each time a coronal hole rotates by the Earth we can measure the particles flowing out of the hole as a high-speed stream, another source of space weather. Charged particles in the Earth's radiation belts are accelerated when the high-speed stream runs into the Earth's magnetosphere. The acceleration of particles in the magnetosphere is studied by NASA's Van Allen Probes mission. As Solar Cycle 24 fades, the number of flares each day will get smaller, but the coronal holes provide another source of space weather that needs to be understood and predicted. While the sun is too bright for other telescopes such as NASA's Chandra X-ray Observatory, NuSTAR can safely look at it without the risk of damaging its detectors. The sun is not as bright in the higher-energy X-rays detected by NuSTAR, a factor that depends on the temperature of the sun's atmosphere. The first solar image from NuSTAR demonstrates that the telescope can in fact gather data about Sun. And it gives insight into questions about the remarkably high temperatures that are found above sunspots -- cool, dark patches on the sun. Future images will provide even better data as the sun winds down in its solar cycle. The sun gets quiet, its activity will dwindle over the next few years. With NuSTAR's high-energy views, it has the potential to capture hypothesized nanoflares -- smaller versions of the sun's giant flares that erupt with charged particles and high-energy radiation. Nanoflares, should they exist, may explain why the sun's outer atmosphere, called the corona, is sizzling hot, a mystery called the 'coronal heating problem.' The corona is, on average, 1.8 million degrees Fahrenheit (1 million degrees Celsius), while the surface of the sun is relatively cooler at 10,800 Fahrenheit (6,000 degrees Celsius). It is like a flame coming out of an ice cube. Nanoflares, in combination with flares, may be sources of the intense heat. The X-ray observatory can search for hypothesized dark matter particles called axions. Dark matter is five times more abundant than regular matter in the universe. Everyday matter familiar to us, for example in tables and chairs, planets and stars, is only a sliver of what's out there. While dark matter has been indirectly detected through its gravitational pull, its composition remains unknown. The axions would appear as a spot of X-rays in the center of the sun. Meanwhile, as the sun awaits future NuSTAR observations, the telescope is continuing with its galactic pursuits, probing black holes, supernova remnants and other extreme objects beyond our solar system.http://tinyurl.com/ofx7y5z
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