Astronomy and Astrophysics
Astronomy
The focus of the Chair for Astronomy is extragalactic astronomy.
We study galaxies with the aim to understand structure formation as a constant compression of matter since the Big Bang due to the influence of the so-called “dark matter”. The release of energy from active galactic nuclei and stars through radiation, stellar winds and supernova explosions plays as important a role as the interaction of outflowing gas with fresh incoming gas from intergalactic space.
These processes influence the distribution, composition and kinematics of the interstellar gas and therefore have an impact on following stellar generations as well as the general appearance of galaxies. For our research we use observations made with radio telescopes like the Very Large Array (VLA) in New Mexico (USA) or the new Low Frequency Array (LOFAR) in Europe but also measurements from research satellites (e.g. the Hubble telescope or ESA’s XMM/Newton telescopes) or the European large telescopes from ESO in Chile. Within the context of a German consortium we also collaborate on the camera for the biggest optical telescope in the world, the Large Binocular Telescope (LBT) on Mt. Graham, Arizona. Our investigations considering the distribution of cosmic magnetic fields are an important link to high-energy astrophysics.
Astrophysics
Time on a telescope is valuable and available to the astronomer only for a couple of hours per year at the world’s big observatories – if (s)he’s lucky. Detailed long-term observations of variable objects are virtually impossible, let alone spontaneous measurements. That is why the Chair for Astrophysics built its own observatory in the Chilean Atacama Desert in a height of 2,800 metres where projects can be carried out 350 nights per year on one of the best sites in the world. There are three research fields in the centre of our attention:
the formation of stars
the search for extrasolar planets
the structure of active galactic nuclei
All these areas are concerned with variable phenomena that can only be studied and understood through months of observations. Their physical structure is also similar – although on different length scales. Young stars as well as black holes in the centres of galaxies grow by collecting matter from their environment. In such a process, matter does not flow directly onto the object but through a disc of gas and dust. In such discs around young stars planets are practically always formed. RUB students and partners from different countries carry out projects in visible and infrared light on five telescopes that can be controlled via internet.
Observational Cosmology
One of the biggest questions in modern cosmology is what drives the accelerated expansion of the Universe? Is this surprising property of the cosmos a hint for a cosmological constant? Is it caused by a new type of energy, the so-called Dark Energy, or by a new, so far unobserved particle/field? Or is our theory of gravitation, Einstein’s Theory of General Relativity, not sufficient? Today’s cosmologists try to answer these questions using a range of different observational techniques.
Research projects in the group for Observational Cosmology focus on exploiting weak gravitational lensing which is potentially the most precise observational method to explore the accelerated expansion. Masses in the Universe, for example galaxies and galaxy clusters, influence the propagation of light, acting similar to optical lenses. This leads to tiny distortions in images of background galaxies which we observe with large telescopes. Combining measurements of these distortions with distance measurements (redshift) of the background galaxies allows us to measure masses in the Universe, i.e. to weigh cosmical objects.
Such measurements are taken with large-format cameras installed at special wide-field telescopes. Since this is a very small effect, we need to depict huge areas on the sky to have enough galaxies (many millions) available for significant measurements. The group currently mainly uses data of the European projects KiDS (Kilo-Degree Survey; http://kids.strw.leidenuniv.nl/) and VIKING (VISTA Kilo-Degree Infrared Galaxy Survey). In the future, we will use data from the LSST (Large Synoptic Survey Telescope) as well as the ESA/NASA Euclid satellite mission.
Plasma-Astroparticle Physics
In high-energy particle astrophysics we are engaged in searching the sources of cosmic radiation. Although it has been known for 100 years that a constant stream of charged particles continuously hits the earth, its origin remains unknown. Problems are caused by magnetic fields that permeate the Universe: They divert the charged particles from their original path so that they arrive on earth from every direction with no trace of where they came from.
In Bochum, we are specifically concerned with the theoretical description of the interaction and propagation of cosmic radiation. When energetic particles interact with matter or photon fields, neutral particles – neutrons and photons – are created. Because they are neutral, they have a straight trajectory through the Universe. Thus, they can help to identify the origin of cosmic radiation.
Cosmic radiation itself can be studied comparing simulated propagations through the cosmic magnetic fields and the observed particle distribution. These theoretical results are then compared to the latest measurements from large instruments of astroparticle physics. The group is involved in some of the leading experiments in the field: the IceCube Telescope at the geographical south pole and the H.E.S.S. experiment in Namibia.
Multi-wavelength Astrophysics
In the multi-wavelength astronomy group we observe the Universe in light at different wavelengths ranging from radio to gamma-ray energies. Furthermore we open a new window onto the Universe by doing astronomy with messengers different from light, namely high-energy particles. Of special interest are neutrinos, which are weakly interacting particles, without charge and with only a tiny mass. Neutrino can trace the most energetic sources in the Universe, which are able to accelerate protons to energies 100 million times larger than what we can archive at LHC at CERN.
To get a better understanding of those sources, we combine observations of the IceCube neutrino observatory located at the South Pole with optical data collected by the Zwicky Transient Facility in California, the Fermi gamma-ray space telescope and in the future the Cherenkov Telescope Array on La Palma. In addition we build an optical telescopes consisting of about 30 small telescopes to scan the sky in polarized light. We describe the collected data with theoretical models to get a better understanding of the underlying physical processes in the source.
First source candidates under investigations include super-massive black holes, that shred entire stars in so-called tidal disruption events or sent relativistic jets in our direction (so-called blazars).