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Annual review 2020

This year physicists got to the bottom of puzzles big and small in our universe - from the surprising darkening of a red supergiant to processes inside our sun and the center of our galaxy. But even tiny structures such as those of the new type of coronavirus were carefully examined. Here we look back on these and other crucial discoveries made in 2020.

The year began with a sensational observation of the sky: Betelgeuse, the left shoulder star of the constellation Orion, has lost more and more of its luminosity since October 2019. In February, the star, which is about 600 light-years away, darkened to just 40 percent of its average brightness - and shone as faintly as never before seen. Many amateur astronomers already speculated at the beginning of the year about the possible causes of the surprising darkening. Some saw it as an indication of an imminent explosion of the star - a so-called supernova.

Size comparison between Betelgeuse and our solar system

“As a red super giant, Betelgeuse is definitely a possible candidate for a supernova,” commented astrophysicist Hans-Thomas Janka from the Max Planck Institute for Astrophysics in Garching on the debate in an interview with Welt der Physik. However, the darkening of the star does not indicate an imminent explosion, Janka made clear. Rather, the observation could be explained by another phenomenon, because Betelgeuse regularly expels gas from its shell into space. This gas cloud then cools down and shields the star's radiation in such a way that it appears darker from Earth. Photos from the Hubble space telescope finally provided the final proof in August: They showed a particularly large gas cloud surrounding the red supergiant. And now Betelgeuse can be seen again in its full luminosity in the night sky.

On the trail of the mystery of antimatter

Scientists at the CERN research center got to the bottom of a much more fundamental problem - the hitherto unsolved mystery of antimatter: shortly after the Big Bang, matter and antimatter were supposed to have arisen in equal parts. Today the universe obviously only contains matter from which stars, planets and ourselves are made. Physicists do not yet know the reason for this imbalance.

In the ALPHA experiment, researchers are therefore looking for differences between matter and antimatter that could possibly explain the imbalance. To do this, they investigated anti-hydrogen, which is composed of the antiparticles of an electron and a proton. But in February the researchers confirmed the previous results again: There is no difference between hydrogen and anti-hydrogen.

Contributions to combating the corona pandemic

Coronavirus SARS-CoV-2

Just a few days later, it wasn't just our everyday life that began to change dramatically. Regular operations at scientific institutions such as the CERN research center were also shut down in the weeks that followed - in response to the global COVID-19 pandemic. But that did not apply to all research facilities. Because in the search for a suitable active ingredient, scientists around the world tried, among other things, to examine the new coronavirus SARS-CoV-2 with various methods. “Each of these processes has its own advantages and disadvantages. The good thing, however, is that we can combine these processes with one another and thus get a more detailed picture, ”reports Dieter Willibold from the University of Düsseldorf and the Jülich Research Center in an interview.

For example, very intensive X-ray lasers make the structure of the individual virus components visible with almost atomic accuracy. "That makes the search for suitable active ingredients a lot easier," said Manfred Weiss from the Helmholtz Zentrum Berlin in an interview. In addition to X-rays, neutron beams are also used. "With the coronavirus, the contact point on its surface is of particular interest, with which the virus couples to the receptor of a human cell," reported Wibke Lohstroh from the Technical University of Munich.

Since it has been important since then to stay at home as much as possible, the editors of Welt der Physik published a new section in April. In Physics for the Home, we present a wide range of digital offers - from virtual tours through research institutions and museums to experiments for at home and online astronomy projects that you can participate in. In the Radio Galaxy Zoo project, for example, everyone can become an astronomer and sort real observation data from the LOFAR telescope system - and maybe even discover something new in the process.

The center of the Milky Way

An extensive data analysis was also necessary for the discovery of Reinhard Genzel from the Max Planck Institute for Extraterrestrial Physics in Garching and the University of California in Berkeley and Andrea Ghez from the University of California in Los Angeles. The two researchers and their colleagues have been observing the positions of the brightest stars near the galactic center since the early 1990s. Apparently the stars move at a high speed on stable, but extremely elliptical orbits around the center of the Milky Way. From this, the astronomers concluded that their observations could only be explained by an extremely massive, invisible object - a supermassive black hole.

Rosette orbit of the star S2

As a result, scientists have been studying the central black hole called Sagittarius A * more and more closely in recent years. In particular, the elliptical orbit of a star - labeled S2 - was particularly interesting as it approaches the black hole closer to its orbit than any other star. In April of this year, the GRAVITY instrument of the Very Large Telescope in Chile finally succeeded in making the star's twisted elliptical orbit visible. "The exact course of these orbits can be calculated with Albert Einstein's general theory of relativity, but the resolution of the previous recordings was not sufficient to test these predictions experimentally," said Christan Straubmeier, commenting on the discovery in an interview. “Now we have finally obtained certainty” - and Einstein's theory has been confirmed again.

For their pioneering work, which provided the most convincing evidence to date of a black hole in the center of the Milky Way, Genzel and Ghez were honored with half of this year's Nobel Prize in Physics. The other half of the Nobel Prize went to Roger Penrose, who developed the mathematical tools with which, among other things, black holes as a result of general relativity can be explored.

Another phenomenon that Albert Einstein predicted over a hundred years ago are gravitational waves. The stretching and compressing of space and time can arise, for example, when two black holes approach each other and finally merge into an even more massive object. After gravitational waves were observed for the first time in 2015, this September astronomers reported a signal that set new records in two ways: At seven billion light years, the source is not only as far away as it has been before. With 142 solar masses, it is also the most massive source of gravitational waves to date, which was created when two black holes merged.