New look at our sun

ALMA telescopes show our home star for the first time in millimeter light

This ALMA image of a huge sunspot was taken at a wavelength of 1.25 millimeters. In the center of such patches, there is a lower temperature than in the surrounding regions, so that they appear relatively dark. © ALMA (ESO / NAOJ / NRAO)
Read out

Deep insight: astronomers can now look deeper into the seething surface of the sun than ever before. This is made possible by the ALMA telescopes in Chile. They have been specially adapted so that the direct view of the sun can not damage the sensitive detectors. First images show the chromosphere under a huge sunspot - and thus processes that are just below the visible surface of the sun.

Normally, the Atacama Large Millimeter / Subillimeter Array (ALMA) in Chile tends to direct its telescope eyes into the depths of space. With him astronomers have already observed the birth of a triple star, tracked down a dark galaxy and solved the mystery of the mysterious Lyman Alpha lumps.

Conversion of the sensitive optics

Now, however, the ALMA telescopes have a new, much closer goal: our sun. For the sensitive telescope optics, this is not dangerous because of the close proximity of our star: At the Swedish ESO Submillimeter Telescope (SEST) even a fire broke out at the secondary mirror, after the telescope was accidentally pointed at the sun.

To protect the ALMA antennas from such damage, their receivers had to be reconfigured in 30 months of work. Only in this way can they reproduce the sun in extraordinary detail with the radio-interferometry technique, without being damaged by the enormous heat of the bundled sunlight.

View into the chromosphere

ALMA makes it possible for the first time to look into the sun's chromosphere - and thus the region that lies just above the visible surface of the sun. Thus, the possibilities for observing and exploring the physics of our next star have been augmented by an important component. The telescope can look into the sun so deeply because it picks up the star in the relatively long-wave millimeter and submillimeter wave range of the light. display

The sun in ultraviolet light taken by NASA's Solar Dynamics Observatory (left) and millimeter wavelength imaging by ALMA. NASA / SDO, ALMA

"We are accustomed to the sight of our Sun in visible light, but this can not tell us anything about the dynamic surface and atmosphere of our star, " explains Tim Bastian of the US National Radio Astronomy Observatory Charlottesville. "To fully understand the Sun, we need to examine it throughout the electromagnetic spectrum including millimeter and submillimeter coverage covered by ALMA."

Heart of a sunspot

Among the first images of the sun in the millimeter light is a look into the dark, curved heart of a sunspot. Alone its center is almost twice as big as our earth. The brightness differences of the image reflect the temperature differences in the solar chromosphere at this point: zones of particularly strong magnetic forces are coolers and therefore darker.

The ALMA telescopes observe the sun in two different wavelengths, 1.25 and 3 millimeters. This makes it possible to look at the same place at different depths into the chromosphere. For the sunspot, this implies that the temperature variations in different layers of the chromosphere are also distributed differently.

(ESO, 18.01.2017 - NPO)