09Feb2013

 Close To Unlocking The Mystery Of A Star.

 In their quest to unlock the secrets of the Sun, aleady  scientists from the University of Sheffield and Queen’s University Belfast observed Magnetohydrodynamic waves (MHD waves).

They see them and measure them in gigantic magnetic holes. They’re in search of answers. Why is the outer edge of the Sun much hotter than its surface? Now, a team of scientists from Sheffield and Belfast led by Dr Richard Morton, Northumbria University are close to solve the puzzle.

They have examined the MHD waves using a UK-built solar imager ROSA – Rapid Oscillations of the Solar Atmosphere –, to observe the chromosphere with a high degree of clarity.

Magnetic loop structures in the corona of the Sun. The loops highlight the Sun’s magnetic field and are visible because they support the dense, million degree gas typical of the corona. The image is courtesy of the Science Team for NASA’s Solar Dynamic Observatory.

They have used cutting-edge solar-imaging technology to observe the Sun’s chromosphere – a region of the Sun’s atmosphere sandwiched between its surface (photosphere) and outer layer (corona) – to an unprecedented level of detail.

For years astronomers have looked for the elusive mechanism that causes some stars to have a corona that is almost 200 times hotter than their photosphere, despite being further away from the heat source at the star’s core.

It is believed that the cause of the increased temperature is due to magnetohydrodynamic (MHD) waves that distribute the energy generated below the star’s surface to the outer layers of the Sun’s atmosphere

The powerful ROSA tool enabled some of the highest resolution images of the chromosphere to be obtained, allowing the scientists to study the speed and power of the waves and then estimate the amount of energy that they transport.

Their calculations confirm that the MHD waves could be responsible for transporting energy from below the solar surface, out through the chromosphere, into the corona and leading to heating of the outer layers in excess of a million degrees.

Chromosphere of the solar atmosphere
Bright patches correspond to concentrated magnetic flux. Credit: SOHO

“The Sun is our closest star and provides a unique opportunity to study the properties of stars in detail. Stars generate heat through thermonuclear reactions in their core and the temperature decreases towards the star’s surface.

However, a significant number of stars have higher temperatures at the outer edges of their atmospheres than they do on their surface,” Dr Morton said.“Our observations have permitted us to estimate the amount of energy transported by the magnetic waves, and these estimates reveal that the waves’ energy meets the energy requirement for the unexplained temperature increase in the corona.” Source: Message to Eagle

 

See The Sun Like Never Before!

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One way we can learn about the Sun is by looking at it through many different wavelengths simultaneously with each wavelength telling us something different about it’s properties and processes.  This collage contains images captured using 48 different wavelengths.  Pretty cool! 

Taking a photo of the sun with a standard camera will provide a familiar image: a yellowish, featureless disk, perhaps colored a bit more red when near the horizon since the light must travel through more of Earth’s atmosphere and consequently loses blue wavelengths before getting to the camera’s lens. The sun, in fact, emits light in all colors, but since yellow is the brightest wavelength from the sun, that is the color we see with our naked eye — which the camera represents, since one should never look directly at the sun. When all the visible colors are summed together, scientists call this “white light.”

Specialized instruments, either in ground-based or space-based telescopes, however, can observe light far beyond the ranges visible to the naked eye. Different wavelengths convey information about different components of the sun’s surface and atmosphere, so scientists use them to paint a full picture of our constantly changing and varying star.

An illustration of the structure of the Sun: 1...

An illustration of the structure of the Sun: 1. Core 2. Radiative zone 3. Convective zone 4. Photosphere 5. Chromosphere 6. Corona 7. Sunspot 8. Granules 9. Prominence (Photo credit: Wikipedia)

Yellow-green light of 5500 Angstroms, for example, generally emanates from material of about 10,000 degrees F (5700 degrees C), which represents the surface of the sun. Extreme ultraviolet light of 94 Angstroms, on the other hand, comes from atoms that are about 11 million degrees F (6,300,000 degrees C) and is a good wavelength for looking at solar flares, which can reach such high temperatures.
By examining pictures of the sun in a variety of wavelengths – as is done through such telescopes as NASA’s Solar Dynamics Observatory (SDO), NASA’s Solar Terrestrial Relations Observatory (STEREO) and the ESA/NASA Solar and Heliospheric Observatory (SOHO) — scientists can track how particles and heat move through the sun’s atmosphere.

We see the visible spectrum of light simply because the sun is made up of a hot gas – heat produces light just as it does in an incandescent light bulb. But when it comes to the shorter wavelengths, the sun sends out extreme ultraviolet light and x-rays because it is filled with many kinds of atoms, each of which give off light of a certain wavelength when they reach a certain temperature.

 Not only does the sun contain many different atoms – helium, hydrogen, iron, for example — but also different kinds of each atom with different electrical charges, known as ions. Each ion can emit light at specific wavelengths when it reaches a particular temperature. Scientists have cataloged which atoms produce which wavelengths since the early 1900s, and the associations are well documented in lists that can take up hundreds of pages.

Solar telescopes make use of this wavelength information in two ways. For one, certain instruments, known as spectrometers, observe many wavelengths of light simultaneously and can measure how much of each wavelength of light is present. This helps create a composite understanding of what temperature ranges are exhibited in the material around the sun. Spectrographs don’t look like a typical picture, but instead are graphs that categorize the amount of each kind of light.

On the other hand, instruments that produce conventional images of the sun focus exclusively on light around one particular wavelength, sometimes not one that is visible to the naked eye. SDO scientists, for example, chose 10 different wavelengths to observe for its Atmospheric Imaging Assembly (AIA) instrument. Each wavelength is largely based on a single, or perhaps two types of ions – though slightly longer and shorter wavelengths produced by other ions are also invariably part of the picture. Each wavelength was chosen to highlight a particular part of the sun’s atmosphere. Source: WDRB.Com