All ranges of electromagnetic spectrum are used for this – from radio waves to high-energy gamma rays. The truth is that every spectral range opens up its own window onto space. Supercomputers analyse the immense volumes of data. This means that all kinds of cosmic phenomena can be analysed to a previously unknown level of precision. In 2015 an additional, completely new method was added to the range of analysis techniques: scientists can now measure gravitational waves even on the Earth– and this enables them to explore astronomical events for which there never used to be a method of measurement.

Virtual space
For what is so far the largest and most detailed simulation of the processes that occurred at the origins of the Universe, IllustrisTNG, researchers “feed” the high-performance computer Hazel Hen in Stuttgart with data from the earliest beginnings of the cosmos. The supercomputer then calculates the development of the Universe over more than 13 billion years. To do this it needs 16,000 processor cores working round the clock for over a year – on a single modern PC this would be equivalent to a processing time of 15,000 years. The simulation shows researchers the large-scale structures of the Universe in an unprecedented form and accuracy, but also details such as gas flows in galaxies.

Dark matter and dark energy
Only a very small proportion of the Universe consists of stars, planets and other celestial bodies that we can observe. The rest – a sizeable 95 per cent – is dark matter and dark energy.

Dark matter is not visible, but it can be detected thanks to its gravitational effects. If dark matter didn’t exist, then the visible material in the cosmos would behave differently. For example galaxies like our Milky Way would break apart. Dark energy is the term for an effect astronomers use to describe the accelerated expansion of the Universe. Because of the mutual attraction between masses, the expansion of the Universe should be slowing down. But the opposite has been measured: the Universe is expanding faster and faster! This can only be explained if the Universe consists of around 70 per cent dark energy.

The search for the ghost particle
Dark matter, which is five times more common in space than “normal” matter, is something we can neither see nor measure directly. Researchers suspect that it is made up of elementary particles that we don’t yet know anything about, which interact only very minimally with the visible “normal” matter. They are searching for this particle in the CRESST experiment: under the Gran Sasso, a mountain range in Italy, there is an underground lab with highly sensitive detectors – shielded all around by more than 1400 metres of rock. All “normal” particles that reach the Earth from space are absorbed by the matter making up the mountain. The “dark” elementary particles by contrast should pass through the rock almost unimpeded. The actual measuring instruments are ultra-pure calcium tungstate crystals cooled to almost –273 degrees Celsius. When a dark matter particle collides with one of these crystals, the temperature rises by around one-millionth of a degree. This minimal difference can be measured by highly sensitive thermometers.
  Two researchers assemble the detector of the CRESST experiment in the Gran Sasso underground lab. | © Astrid Eckert
Big Bang
One of the greatest puzzles of science is the question of the origin of the Universe. We know today that the Universe is expanding. We also know the way in which this is happening. Viewed in reverse, matter and energy become infinitely denser. And that’s exactly where the start of our Universe today has to be found – purely in mathematical terms that’s 13.8 billion years ago. But this Big Bang doesn’t describe an explosion in a space. According to today’s prevalent theory, it’s the beginning of space, time and matter.

© But how is the immense quantity of matter and energy that the Universe contains supposed to be compressed into such a tiny dot? For the Big Bang – as it’s referred to today – to function, there must have been a very brief, extremely rapid expansion right at the start: faster-than-light inflation. It isn’t possible to analyse this area with measurement methods based on electromagnetic radiation – but it can be done using gravitational waves.

Big Bang or Big Collision?
In the Big Bang, space, time and matter emerged from nothing – according to the current theory. With the knowledge we have today, all processes from around a billionth of a second after the Big Bang can be calculated. The very short interval – which is however crucial to our understanding – directly after the “Bang” is still in the dark. This is the research focus of Anna Ijjas, a young scientist at the Max Planck Institute of Gravitational Physics. The cyclical model she’s working on proposes that a previous universe slowly contracted to around 10-25 cm and then expanded again. According to that theory the Big Bang was more of a gentle collision. A necessary component of the Big Bang theory that science has been as yet unable to explain is inflation – the extremely fast expansion immediately after the “Bang”. The Big Bang model works without this assumption.
  What came before the Big Bang? Maybe an earlier universe? | © Anna Ijjas

Gravitational waves
Albert Einstein was right again: on 14th September 2015 gravitational waves were measured for the first time, 100 years after he described them in his Theory of Relativity. But what are gravitational waves? According to Einstein, any mass leaves ripples in four-dimensional space-time. If these masses move, they create waves. These waves spread out through the cosmos at the speed of light, distorting space in the process.

Gravitational waves are being produced all the time in space. But they can only be measured on Earth if very large masses are moving very fast – for instance when two black holes merge. That’s precisely what was measured in September 2015. Highly sensitive measuring instruments were needed for this: the two huge interferometers that capture the signal are in the USA. But a large proportion of the high-precision technology used in this measuring equipment, and also many of the analysis programs, come from Germany – from the Max Planck Institute for Gravitational Physics in Potsdam and Hanover.
  Galaxies
Galaxies are “islands of worlds” in the infinite sea that is the cosmos. Stars, planet systems, dust clouds, gas nebulas and dark matter are collected together here. They are all held together by gravity. Galaxies have different structures – from simple ellipses to highly complex spiral galaxies with defined “arms” like our Milky Way. Several galaxies can finish up merging in groups and clusters of varying sizes. The largest of these galaxy clusters contain several thousand galaxies.

The Andromeda nebula is our nearest neighbour, it is around the same size of the Milky Way. It is the most distant astronomical object that we can see from Earth with the naked eye.

  © ESO/S. Brunier
Supernova
Some stars die a spectacular death: the bright explosion of a high-density star at the end of its development is called a supernova. The term (nova = new in Latin) goes back to Tycho Brahe. The Danish astronomer observed the sudden emergence of a very, very bright star in in 1572, where previously absolutely nothing was visible.

With a supernova explosion, a large part of the star is converted into energy and emitted all at once. What remains is a neutron star or a black hole. A supernova is particularly impressive when a high-density giant star, such as a red giant, has consumed all its fuel. It collapses inwards due to its own gravity and releases huge amounts of energy. For a while, the supernova can shine more brightly than the entire galaxy in which it is located.