Andreas Müller

Astrophysicist

Prologue

Author and reader have a common interest just as artist and audience: interest in something beautiful. The beautiful thing that I present on my website is Nature - especially nature above us at the sky. It is not only an external, purely contemplative beauty that is characterized by nice coloring and shape but also some inner beauty that manifests in fascinating order and arrangement. Knowledge in inner beauty enhances external beauty and gives awe and humility of nature. So, we participate in sensing the beauty. We observe, model, understand and find ourselves in a sophisticated and complex world: our Universe.

We should not take for granted the way things are. I would like to give an insight in astronomy and astrophysics - the oldest discipline of natural sciences that awoke human's curiosity. Astronomy is one of the facets of modern science that proves the beauty of nature.

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Why launching this website?

This website provides information about astrophysics. However there is more! It was anticipated in the prologue that there is something behind pure information, some kind of superstruction. Information building blocks are linked together to something global. Therefore, I decided to write down some of my interests - especially aspects from astrophysics. This knowledge implies aspects to arts.
But there is also another motivation: I wanted anybody to have an easy access to astrophysical knowledge. Hence, I developed a German dictionary for astrophysics. Now, it contains 550 entries with a compact explanation. Additionally, I present selected research topics, e.g. black holes. As intended the dictionary provides fast access to pure and compact information whereas the web essays link together these building blocks to something global: deep insights into nature.
Dear English-speaking people: I must apologize that these resources are only in German available. However, you may want to explore my popular and scientic talks that are partly in English.

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Career

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Research

I am particularly concerned with relativistic astrophysics, e.g.

• black holes,
• active centers of galaxies, the Active Galactic Nuclei (AGN),
• accretion physics,
• relativistic spectra, in particular emission lines,
• formation of jets,
• X-ray binaries,
• compact relics of stellar evolution, i.e. compact objects,
• and of course Einstein's General Relativity.

My research interest is also directed to neighbouring branches such as cosmology, modern gravity theories, and astroparticle physics.

Diploma thesis

In my diploma thesis (2000), I treated the problem of light propagation in the vicinity of rotating black holes. Astronomers are interested in this aspect because of they found a number of candidates in the cosmos that fit nicely the features of black holes. These black hole candidates emit also radiation from their surroundings. This radiation carries information about the black hole and its neighbourhood - especially about the matter stream flowing into the hole, the so-called accretion flow. The flow may flatten and take the form of an accretion disk.
An interpretation of observational data requires theoretical understanding of the source. Mathematical and numerical techniques of theoretical physics provide a suitable approach to simulate on a computer what's happening. In my diploma thesis I applied a certain method called relativistic ray tracing. This technique allows to visualize images of accretion disks on a computer - relativistically correct! The black hole strongly distorts the usual images due to the fact that it acts like a gravitational lense. Light and any kind of radiation is bent by the curved space-time.
A special observational feature in X-ray astronomy is the relativistically broadened emission line - mainly emitted by ionized iron that constitutes the accretion disk. These relativistic iron K lines can also be simulated via ray tracing. Finally, observed and simulated lines can be compared. Then, astronomers get a physical understanding of the source and are able to derive parameters of black hole and accretion flow.
Typically, this model can be applied to AGN and X-ray binaries. A new aspect of my work in 2000 was the consideration of a more complex plasma kinematics beyond pure rotation. Hence, it became possible to investigate the influence of an overlayed radial plasma motion in computer simulations. Main result was that radial drift motion enhances gravitational redshift effects and lowers the line flux especially at the red wing. For details, please have a look into the following resources:

• German web article: Gefangenes Licht - Relativistisches Ray Tracing
• German web article: Röntgenlinien - Sendboten von Loch und Scheibe
• my diploma thesis: Emissionslinienprofile relativistischer Scheiben um rotierende Schwarze Löcher (in German), DOWNLOAD (pdf, 3.9 MB)
• a scientific publication: Relativistic emission lines from accreting black holes - The effect of disk truncation on line profiles, Müller & Camenzind, A&A 413, 861, 2004; as preprint at astro-ph/0309832

PhD thesis

I continued to wor on black holes in my PhD thesis. The challenge was to understand the kinematics of matter near the hole. Main question was: How does a magnetized fluid fall into a rotating black hole?
Therefore, I worked on magnetohydrodynamics (MHD) in curved spacetime (General Relativistic Magnetohydrodynamics, GRMHD). My dissertation presents black holes in Relativity and astrophysics, introduces into accretion physics and non-radiative GRMHD and reports on GRMHD codes. Concerning Kerr ray tracing, a new model is presented which includes also radial plasma motion towards the hole.
In particular, the PhD thesis ius dedicated to the formation of relativistic Jets by rotating black holes (see Frame-Dragging and Poynting fluxes in the German online dictionary). This theoretical research is connected to an understanding of the centres of galaxies and give insight in the centre of our own galaxy, the Milky Way, too.

• DOWNLOAD my PhD thesis Black Hole Astrophysics: Magnetohydrodynamics on the Kerr geometry, pdf (9.9 MB) or zipped ps (14.4 MB)

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Publikations

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Teaching

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Public relations

I have fun and success in doing popular science:

I am happy to have these possibilities and to give people insights into these fascinating science topics. No other discipline than astronomy is so much fundamental research, no other discipline than astronomy has so much impact on human culture - until today.

Übersicht

Looking inside

Astrophysics is really important to me but I also have some further interests such as interdisciplinarity, philosophy, languages, and rhetorics. Working in astronomy and particularly in cosmology stimulates questions where natural sciences and the arts overlap. Therefore, I have written some essays (only in German) which treat such topics.

I am interested in rhetorics, languages, speech, evolution of language, linguistics, semantics and etymology. The origin of expressions and idioms, their adequate use is exciting and challenging. On one hand, there is an psychological aspect: the spoken language unreveals many features of the speaker; on the other hand, the word is an image of human evolution, formed, merged and transformed in centuries.
History of language (with regard to dialects, language reforming, artificiel languages, even programming languages) shows always evolutionary steps of man.

Knowledge and information are very important for me. I love it to dive into an interesting context. Apart from the classical source for information, the book, the modern IT medium internet intervenes and has become an unexploitable source of knowledge that I don't want to miss neither professionally, nor in private life. I hope that my website contributes to that idea so that you can find some useful information.

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Hobbies

My favorite relaxing hobbies are mountain biking, playing guitar, music and billard.

Family

My biggest treasure is my family: my wife Anja and my sons Pascal und Dominic.

Epilogue

We return to aspects that were discussed in the prologue: Our interest in something beautiful gives us insights into the context of the whole thing. This knowledge brings us back to ourselves. We realize that we are human beings in the universe, something small in something large and something complex in something simple.

Don't take anything for granted! Observe, read, understand and be astonished about the miracles of the universe!

Yours Andreas Müller

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© Andreas Müller, August 2007