A sunspot with centre twice the size of Earth

• Atacama Large Millimeter/submillimeter Array (ALMA) have revealed otherwise invisible details of Sun, including a new view of the dark, contorted centre of a sunspot that is nearly twice the diameter of the Earth.
• Astronomers have studied the Sun and probed its dynamic surface and energetic atmosphere in many ways through the centuries. But, 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.
• A map of the whole disc of the Sun was also made with a single ALMA antenna, using a technique called fast-scanning, at a wavelength of 1.25 millimetres. The accuracy and speed of observing with a single ALMA antenna make it possible to produce a map of the entire solar disc in just a few minutes. These maps show the distribution of temperatures in the chromosphere over the whole disc at low spatial resolution and therefore complement the detailed interferometric images of individual regions of interest.
• 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 focussed sunlight. The result of this work is a series of images that demonstrate ALMA’s unique vision and ability to study our Sun.
• The astronomers observed an enormous sunspot at wavelengths of 1.25 millimetres and 3 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.

What are sunspots?

• Sunspots are darker, cooler areas on the surface of the sun in a region called the photosphere.
• The photosphere has a temperature of 5,800 degrees Kelvin. Sunspots have temperatures of about 3,800 degrees K. They look dark only in comparison with the brighter and hotter regions of the photosphere around them.
• Sunspots can be very large, up to 50,000 kilometers in diameter. They are caused by interactions with the Sun's magnetic field which are not fully understood. But a sunspot is somewhat like the cap on a soda bottle: shake it up, and you can generate a big eruption. Sunspots occur over regions of intense magnetic activity, and when that energy is released, solar flares and big storms called coronal mass ejections erupt from sunspots.

About ALMA telescope:

• The Atacama Large Millimeter/submillimeter Array (ALMA) is a revolutionary instrument in its scientific concept, its engineering design, and its organization as a global scientific endeavor.
• It is situated in the thin, dry air of northern Chile's Atacama desert at an altitude of 5,000 meters above sea level.
• ALMA will open an entirely new "window" on the Universe, allowing scientists to unravel longstanding and important astronomical mysteries, in search of our Cosmic Origins.
   

By: Vishal