insightLMU RESEARCH
Issue 02 · 2010
INTERDISCIPLINARY INSIGHTS
THORSTEN NAESER
THE
MULTIFACETED
UNIVERSE
The cluster of excellence devoted to the study of “The Origin and Structure of the
Universe” draws on the talents of astrophysicists, particle physicists and nuclear
physicists from several research centers in Munich, including LMU. The collaboration
employs a broad range of approaches to explore the fabric and the evolution of the
cosmos. The hot topics range from black holes and supersymmetry to the search for
the elusive Higgs boson.
In 1600 astronomy was a sparsely populated discipline, and the few experts were much
sought after as astrologers. Johannes Kepler came to the Imperial Court in Prague that year
to work with Tycho Brahe, whom he would succeed as Court Astronomer. Brahe’s observations represented the most accurate set of astronomical data then available. Kepler had
just developed a version of the Copernican heliocentric system of the heavens, and Brahe’s
observations were what he needed to test it. Kepler was a fine mathematician, Brahe was
a gifted observer, and Kepler’s analysis of Brahe’s results ultimately led him to his three
laws of planetary motion. Newton later used Kepler’s laws to derive his own universal law
of gravity.
Today, some 400 years later, the heavens have lost none of their fascination, but the research
teams who study them have grown in size. Since its establishment in 2005, some 250 scientists from 45 different groups have contributed to the work of the Munich cluster of
excellence on “The Origin and Structure of the Universe”. The management of the 5-year
interdisciplinary project is in the hands of the Technische Universität München (TUM).
Participants from the Faculties of Physics at TUM and LMU, several Max Planck Institutes
and the European Southern Observatory (ESO) form the backbone of the project.
The questions astronomers pose today are framed in very different terms from those asked
by their predecessors 400 years ago. How did the Universe begin? What is it made of? How
do galaxies, stars and planets form? How will our 13.7 billion-year-old Universe evolve in
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the future? One of the trickiest problems concerns the so-called Standard Model of Physics.
The Standard Model assumes that the laws of physics as we know them on Earth hold for
the whole cosmos. The model is based on quantum field theory and accounts for the known
elementary particles of matter (fermions) and the forces (carried by a class of particles
called bosons) that mediate their interactions. But the model is incomplete, and cannot
adequately explain many aspects of particle physics, astrophysics and cosmology.
Theoretical extensions of the Standard Model, such as supersymmetry (SUSY) and string
theory can, in principle, describe the ultrahigh-energy processes that occurred during the
earliest stages of the history of the Universe. SUSY postulates an underlying symmetry
between fermions and bosons, while string theory predicts the existence of extra dimensions. “One of the biggest problems in theoretical physics is the unification of quantum
theory with Einstein’s General Theory of Relativity and its treatment of gravity”, explains
Professor Ilka Brunner. Professor Brunner is a theoretical physicist and heads a Junior
Research Group on String Theory at LMU, which is part of the “Universe Cluster”. “String
theory offers one of the most promising approaches to solving this problem”, she says. In
string theory elementary particles are not seen as point particles, but as extended onedimensional objects or strings. In string theory, the various classes of elementary particles,
such as the quarks that make up the protons and neutrons of atomic nuclei, leptons (which
include electrons) and photons (the carriers of the electromagnetic force) can be described
as strings that vibrate at different frequencies. The trouble is − there is, as yet, no experimental evidence for the existence of strings.
H OW STA R S W I T H P LA N E TA RY SY ST E M S O R I G I N AT E
Other areas, such as the origin of the elements, rest on more secure foundations. The lightest elements − hydrogen, helium and lithium − are known to have been formed very early in
the history of the Universe, and provided the material for the first stars, galaxies and black
holes. The rest of the natural elements, from beryllium to uranium, are formed at the center
of massive stars. Stellar energy is initially derived from the fusion of hydrogen to give helium. As these are used up, stars contract, fusing ever larger nuclei together. Stars larger
than about 8 times the mass of the Sun eventually explode cataclysmically as supernovae,
spewing the heavy elements into space, and leaving behind a collapsed, dense core as a
neutron star or a black hole. All these components form part of the cosmic cocktail.
In the 1990s the first exoplanets − planetary bodies that orbit stars beyond our own
solar system – were discovered. They cannot be visualized directly, but their presence
and properties can be inferred by measuring the dimming of starlight as they pass in front
of their parent star. How stars with planetary systems originate is what interests Professor
Andreas Burkert, who holds the Chair for Computational and Theoretical Astrophysics at
LMU, and his team. Professor Burkert is also one of the spokespersons for the cluster of excellence. The basic data for his studies are the spectacular images made by telescopes such as
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the Hubble Space Telescope. These show
distant stars, nebulae, remote galaxies
and enormous clouds of cosmic dust. One
does not need to be an expert on astrophysics to find these pictures fascinating,
and they are often featured on the front
pages of our newspapers. Andreas Burkert explains the physical processes going
on within one of the best known nebulae,
the Horsehead Nebula. “The Horsehead
Nebula is 1600 light years away and is
part of a gigantic, dark and dense cloud
of gas and dust in the constellation Orion.
New stars and probably new planets are
The Horsehead Nebula is 1600 light years away and is part of a gigan-
continuously being born in this region.“
tic, dark and dense cloud of gas and dust in the constellation Orion.
Based on the data contained in one of
New stars and probably new planets are continuously being born in
this region.
Source: ESA
the images returned by the Hubble Telescope, Burkert’s team has developed a
model for how this structure, which indeed resembles a horse’s head, was shaped. Burkert
demonstrates a simulation of the process on his computer. “A stream of ionizing radiation is
coming from the right and impinges directly on the cloud. Under the influence of this ionizing wind, the inhomogeneous cloud is compressed, heated and eventually torn apart”, he
says. “In some areas, however, mainly on the side of the cloud closest to the source of the
wind, the material clumps together”, he points out, as the simulation continues to unfold
on the monitor. “These clumps are the sites where new stars form.“ To conduct simulations
like this needs huge amounts of computing power.
The astrophysicists make use of the resources available at the Leibniz Computer Center, but
they also have a dedicated supercomputer at the Stellar Observatory in Bogenhausen near
Munich. “The laws of physics are valid throughout the Universe”, says Andreas Burkert.
So one can use them to model astronomical phenomena such as black holes, simulate how
these evolve, and compare the results with real observations. − Black holes have undergone
extreme gravitational collapse and are so dense that no light can escape from them. Their
presence must be inferred from their effects on their surroundings. “There appears to be a
black hole at the center of every galaxy, and its mass corresponds to about one-thousandth
of the total mass of its host galaxy” says Burkert. The significance of this relationship remains a mystery. Does the black hole influence the evolution of the galaxy or vice versa? To
tackle questions like this, one needs to consider a whole list of factors. How much matter is
involved, how does gravity affect the system, what influence do external forces such as interactions with surrounding galaxies and clusters of galaxies have on the galaxy and black
hole of interest? “Usually, we try to work back from complex questions to simpler solutions.”
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What motivates Andreas Burkert to dedicate himself to a branch of science that, at first
sight, is concerned with such − literally − remote problems? “The goal is to refine our
understanding of the cosmos of which we are a part”, says Burkert. “We humans are made
of stardust − carbon and water. My aim is to understand where we come from and how we
relate to the vast entity we call our Universe”, he explains. Many of the most perplexing
mysteries of the Universe can be approached only via mathematical models. Nevertheless, astronomy is fundamentally an observational science, and telescopes remain at the
heart of the discipline, as they have since the first ones were trained on the heavens in the
17th century. A rather more modern telescope sits at the top of the Wendelstein, a peak
in the Bavarian Alps, where the LMU’s Observatory is located. At present, preparations are
underway for the installation of a new and more powerful instrument, which will come into
operation in early 2011. The new telescope will have a mirror with a diameter of 2 meters
and is designed to enable long-term observations of the sky. Professor Ralf Bender is the
Director of the Observatory and a member of the cluster of excellence. He is excited about
the new opportunities that the instrument will open up for the observers on the mountain.
“On Wendelstein we will then have everything we need to carry out long-term monitoring
programs, which are not possible on the largest telescopes because of the intense competition for observing time“, says Bender. “For example, we can observe individual stars for
periods long enough to be able to detect minor changes in stellar velocity that betray the
presence of exoplanets.“ In addition, smaller telescopes can react rapidly to the appearance
of supernovae and other short-lived phenomena. And of course, a 2-m telescope is just the
right size for preparatory or follow-up observations on systems that large telescopes choose
to look at in more detail, according to Ralf Bender.
P I C T U R E S O F P R O C E S S E S I N D I S T A N T R E G I O N S O F S PA C E
These tasks will soon be shared with two other instruments that have been built with the
financial support of the cluster of excellence. Both of these will analyze radiation that reaches us from the far reaches of the cosmos. Astronomical objects are visible to us only because they are sources of electromagnetic radiation, which may originate from single stars
or distant galaxies, as well as from dust and gas in the spaces between them. In addition
to visible light of all colours, astronomical objects can emit radio signals with very long
wavelengths as well as highly energetic X-rays with ultrashort wavelengths. “These signals
allow us to make inferences about the structure of the objects that produce them“, explains
Ralf Bender. Electromagnetic radiation thus enables astronomers to study galaxies that are
billions of light years away from us.
One of the new cameras with which the Wendelstein telescope will be equipped is sensitive
to radiation at red/infrared and ultraviolet wavelengths, which bracket the visible spectrum.
“This combination en-ables us to obtain a highly detailed picture of processes in distant
regions of space”, explains Ralf Bender. The instrument will be used to obtain insights
into what happens when massive stars explode to form supernovae. “The camera will also
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be used to study the optical/infrared “echoes” or afterglows associated with so-called gamma-ray
bursts. ”Gamma-ray bursts are
the product of the most powerful
explosions in the Universe, releasing more energy in a few seconds
than our Sun has produced since it
formed 4.6 billion years ago. The
The picture shows LMU Munich‘s Oberservatory located at the top
of the Wendelstein, a peak in the Bavarian Alps. At present, preparations are underway for the installation of a new and more powerful
instrument,
which
will
Source: LMU Munich
come
into
operation
in
early
2011.
underlying mechanism responsible for gamma-ray bursts is not
yet fully understood. One theory
postulates that they are produced
when stars with masses greater
than 20 times that of the Sun explode as hypernovae. The other new camera, the Wide
Field Imager, is designed for observations in the visible spectrum. “Its field of view (0.5x0.5
degrees of arc) roughly corresponds to the diameter of the full moon”, says Ralf Bender.
With this camera, it will be possible to measure with high precision very weak fluctuations
in starlight, such as those caused by nearby dark matter. So the instrument promises to give
us basic information about dark matter and dark energy.”
Dark matter and dark energy form the focus of research in Ralf Bender’s group. Only about
5% of the Universe is made up of ordinary atomic matter − stars, planets, dust and gas. Unseen dark matter makes up 23% and a mysterious dark energy accounts for the other 72%.
The dark components make their presence felt because they contribute significantly to the
speed with which the Universe is expanding, and influence the evolution of galaxies and
galactic clusters. Although dark matter cannot be seen directly, its effects were recognized
in the 1930s. “Galaxies are heavier than the combined weights of their stars and gas”, explains Ralf Bender. “The excess mass consists of dark matter.“ The presence of dark matter
can be inferred from measurements of the rotation velocities of galaxies and of gravitational
lensing. As predicted by Einstein, light-rays are bent by the gravitational attraction of large
concentrations of mass. This can focus and distort the image of a background galaxy seen
from Earth. Measurements of the degree of distortion allow us to determine the size of
the intervening mass.
The distribution of dark matter, unlike dark energy, is fairly well understood. Dark energy
must be postulated to account for some of the observed characteristics of the Universe,
and its precise nature is unknown. It is, for example, required to explain the fact that the
Universe has flat spatial geometry and is expanding at increasing speed. “So far, the nature
and distribution of dark matter and dark energy can only be inferred from observations of
the large-scale structure of the Universe”, says Ralf Bender. But deeper understanding may
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come from observations at very much smaller scales. “Perhaps the LHC, the new particle
accelerator that has just begun to operate at CERN, will give us some new clues.”
Particle physicist Professor Dorothee Schaile spends much of her time at the Large Hadron
Collider (LHC) in Geneva. Together with her research team, she hopes to throw new light
on what was happening fractions of a second after the Big Bang. “Our goal is to understand how particles were behaving one thousandth of a billionth of a second after the Big
Bang”, she says. Particle physicists and astronomers have a very precise grasp of what
happened after this point, but events prior to that are a terra incognita. In the LHC, beams
of protons and antiprotons are accelerated to extremely high energies and allowed to collide. The energy released in the collision goes into the creation of new particles. These
are then detected by a kind of giant microscope, which the Munich researchers helped to
design. The cylindrical detector used for the ATLAS experiments is 20 meters in diameter,
40 meters long and weighs 7000 tons. ATLAS should provide insights into the nature of the
particles that formed the unimaginably hot plasma that emerged from the Big Bang. The
proton-antiproton collisions may also give particle physicists their first glimpse of the socalled Higgs boson. This is the particle associated with a quantum field required to confer
mass on elementary particles. “The Higgs boson is the missing link needed to complete the
Standard Model of particle physics”, explains Dorothee Schaile. “But the Higgs system is
sure to raise new problems that the Standard Model cannot solve, and the LHC should help
us to answer these questions too.“ – For example, SUSY in its simplest form requires not
one, but five Higgs bosons.
With its diverse membership, the cluster of excellence provides an ideal framework for
fruitful discussions between specialists in different fields, and interdisciplinary interactions
promise to lead to new insights. The network brings nuclear physicists into close contact
with astrophysicists and particle physicists. “That helps us to view problems from a variety of angles”, Andreas Burkert points out. Junior researchers also profit from such interactions. “Students who do their graduate research with us get a chance to look beyond
the boundaries of their own fields and can learn more than many of their contemporaries
elsewhere.” Not only students benefit from interdisciplinary training. The members of the
Cluster also offer a program for schools, which allows local pupils to become acquainted
with the physicists’ work. In addition, a special exhibition on the Evolution of the Universe
has been organized at the Deutsches Museum in Munich with the cooperation of the Universe Cluster. Here visitors can see for themselves what physicists have discovered about
the origin of the Universe, the formation of planets and the role of dark matter.
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Prof. Dr. Andreas Burkert became Professor of Astronomy and Astrophysics at LMU Munich in 2003. He also acts
as one of the spokespersons for the cluster of excellence ”Origin and Structure of the Universe“, set up in 2006.
www.usm.uni-muenchen.de/people/burkert/
[email protected]
Prof. Dr. Ralf Bender has been Professor of Astronomy at LMU Munich since 1994. In 1998, he was named Head
of the LMU’s University Observatory, and in 2002 he became a Director of the Max Planck Institute for Extraterrestrial Physics.
www.physik.lmu.de/personen/professoren/bender
[email protected]
Prof. Dr. Ilka Brunner holds a Professorship at the Institute of Theoretical Physics and Mathematical Physics at
LMU Munich.
http://homepages.physik.uni-muenchen.de/~ilka.brunner
[email protected]
Prof. Dr. Dorothee Schaile holds the chair of Elementary Particle Physics at LMU Munich.
www.etp.physik.uni-muenchen.de
[email protected]
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