Ahrgebirge · Astronomers actually use the Effelsberg radio telescope to explore celestial bodies outside the solar system. Nevertheless, Nasa benefits from the facility in the Eifel for its current Mars mission - and not for the first time.
In the control room, it looked like it did during a space mission at the Kennedy Space Center: Even though not quite as many people were sitting there with not quite as many and as huge monitors, they too were cheering because of a successful mission. Only they were not in Florida but in the Eifel and were not looking at the moon but at Mars. Last week, during what Nasa calls the "critical seven minutes" when the Perseverance rover was landing on Mars, Effelsberg had better contact with the Red Planet than anywhere else on Earth: Better even than Green Bank in West Virginia, where the other of the world's two largest fully mobile radio telescopes, which was also involved in the Mars mission, is located.
The funnel-shaped parabolic antenna of the Effelsberg radio telescope, with its 100-meter diameter, is otherwise used to receive radio signals of natural origin from the universe. For the Mars mission, however, it was directed at the artificial signals transmitted by the Mars rover. Because Nasa does not operate its own receiving antennas for wavelengths of 74 centimeters, it asked for "neighborly help," explains Norbert Junkes of the Max Planck Institute for Radio Astronomy (MPIfR) in Bonn, which is responsible for the Effelsberg radio telescope.
The actual targets of the Effelsberg radio telescope are much farther away than Mars
Mars, he said, was about eleven light minutes, or nearly 200 million kilometers, away from Earth at the crucial time. "That's just the cosmic front yard for us," Junkes says. That's because radio astronomers are actually using radio waves captured by the telescope from celestial bodies far beyond our solar system to research questions such as: What is the stuff of stars? Where do condensations form that give rise to new stars? What do cosmic magnetic fields look like in galaxies?
The radio telescope looks into galaxies billions of light-years away and detects radio sources such as supernova remnants or pulsars. The radio telescope is something like an eye into space. "Although we talk radio waves, it's not an ear into space. That's because radio programs can be heard, but only through a speaker. Radio waves received by the telescope are electromagnetic waves just like the light we see. The only difference is that our eyes are not sensitive to them, but the parabolic mirror is," says Junkes.
It can measure extremely weak radio signals and has made headlines before. For example, in 2008. "At that time, one of our doctoral students set a world record with Effelsberg by finding the most distant signature of water in the universe," Junkes reports. "The signal from the galaxy was more than 11 billion years away. So it came from a time when neither the sun nor the solar system even existed." The radio telescope has also been used to create radio maps of the entire sky at, say, 73-centimeter wavelengths, depicting the 408-megahertz world in dazzlingly bright colors, or a map of the sky in the light of the hydrogen line, the most abundant element in the universe.
50 years ago, the Effelsberg radio telescope was inaugurated on May 12, 1971, after 3.5 years of construction. The initiator of the Max Planck Society's project, which cost 34 million German marks at the time, was astrophysicist Otto Hachenberg, a professor at Bonn University who also became director of the MPIfR, which was founded in 1967 to realize and operate the radio telescope. As Junkes further explains, the choice fell on the Eifel valley immediately on the border of the district of Euskirchen within the district of Ahrweiler because the telescope was still to be located in North Rhine-Westphalia due to the institute's headquarters in Bonn.
The surrounding hills protect the telescope from wind
It was also important that the sensitive facility be protected from unwanted interference, which is why even today every visitor should at least switch his or her cell phone to airplane mode. In addition, the surrounding hills offered protection from wind in view of an antenna surface of more than 900 square meters, which must be brought into a safe position in gusts of more than 15 meters per second. The telescope's steel structure weighs more than 3,000 metric tons, and Junkes reports that Krupp and MAN, two rival companies, joined forces to build it. The colossus can be positioned with an accuracy of 0.3 millimeters via slewing rings and gear wheels and on a rail circle with a diameter of 64 meters. It takes just under fifteen minutes to rotate the telescope's parabolic mirror through 360 degrees, and five minutes to tilt it through almost 90 degrees.
A total of about 40 employees work on site, mainly around-the-clock operators. And it's not just Max Planck Institute staff who work there. Scientists from all over the world can apply for periods of time to conduct research with the radio telescope. A panel of experts decides who gets the contract.
Although the Effelsberg radio telescope is no longer the world's largest moving radio telescope since the Green Oak telescope, which is two meters larger in diameter, went into operation in 2000, it continues to play in the "Champions League," Junkes said. That also has to do with continuous development and maintenance, he said: Every summer, painters come in for about eight weeks. Such work takes place during the day, while astronomical measurements are carried out mainly at weekends and especially at night, because that is when the sun, which is also a powerful radio source, is below the horizon.
Effelsberg was already involved in the Mars "InSight" mission
Already in November 2018 during the Mars mission "InSight" the radio telescope Effelsberg has participated after Nasa request. But even after the landing of "Perserverance" it turns away from Mars again and to its real métier. Specifically, among other things, pulsars, that is, the final stages of stellar evolution. "Their cores are as heavy as the sun but only as big as Cologne," Junkes says. Pulsars are not only extremely dense, but also fast, rotating on their own axis up to 700 times or more per second.
Translation: Mareike Graepel