LONDON : A new view of the dark, contorted centre of a sunspot that is nearly twice the diameter of the Earth, along with other invisible details of our Sun, has been unveiled by scientists.
The results are an important expansion of the range of observations that can be used to probe the physics of our nearest star.
The Atacama Large Millimetre/submillimetre Array (ALMA) antennas had been carefully designed so they could image the Sun without being damaged by the intense heat of the focused light.
Astronomers have harnessed ALMA’s capabilities to image the millimetre-wavelength light emitted by the Sun’s chromosphere – the region that lies just above the photosphere, which forms the visible surface of the Sun.
Researchers including those from European Southern Observatory (ESO), produced the images as a demonstration of ALMA’s ability to study solar activity at longer wavelengths of light than are typically available to solar observatories on Earth.
Astronomers have studied the Sun and probed its dynamic surface and energetic atmosphere in many ways through the centuries.
However, to achieve a fuller understanding, astronomers need to study it across the entire electromagnetic spectrum, including the millimetre and submillimetre portion that ALMA can observe.
Since the Sun is many billions of times brighter than the faint objects ALMA typically observes, the ALMA antennas were specially designed to allow them to image the Sun in exquisite detail using the technique of radio interferometry – and avoid damage from the intense heat of the focused sunlight.
The result of this work is a series of images that demonstrate ALMA’s unique vision and ability to study our Sun.
The data from the solar observing campaign are being released this week to the worldwide astronomical community for further study and analysis.
The team observed an enormous sunspot at wavelengths of 1.25 millimetres and three millimetres using two of ALMA’s receiver bands. The images reveal differences in temperature between parts of the Sun’s chromosphere.
Understanding the heating and dynamics of the chromosphere are key areas of research that will be addressed in the future using ALMA.
Sunspots are transient features that occur in regions where the Sun’s magnetic field is extremely concentrated and powerful.
They are lower in temperature than the surrounding regions, which is why they appear relatively dark.
The difference in appearance between the two images is due to the different wavelengths of emitted light being observed.
Observations at shorter wavelengths are able to probe deeper into the Sun, meaning the 1.25 millimetre images show a layer of the chromosphere that is deeper, and therefore closer to the photosphere, than those made at a wavelength of three millimetres.
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