Frank Löffler's Research Interests
My strong background in software design and development stems from
years of immersion in cutting-edge, international software development
teams. This primarily includes scientific software development, often
assessing and using the latest available technology. Thus, I contribute
to activitis that highlight software development and its role
especially in science, e.g., WSSSPE, Force11, and I
am one of the main founders of the German chapter of the RSE community:
de-RSE.
One of my scientific interests has for a long time been the behavior of
matter in strongly curved environments, where both the dynamics
of nuclear matter as well as general relativity are important.
Most of my current research involves simulations of neutron stars, either as
single neutron stars that may undergo instabilities, or together with a
companion that is either a black hole or another neutron star.
Research in this direction is
particularly timely and urgent, as gravitational waves from neutron star
binaries are expected to be observed in the near future,
potentially making a direct connection between such systems
and short gamma-ray bursts.
I led research projects in numerical relativity, relativistic astrophysics
and community software engineering. I also consulted LSU faculty and staff in
questions of technology and software development. This included efficient
use of current IT infrastructure, as well as strategic planning with future
trends in mind. To follow and understand the ever-increasing influence of
digital technologies on society, future job markets and teaching methods is
going to be even more than in the past essential for success. Communicating
this to the next generation is one of my motivations to offer lectures at
elementary schools, to train and mentor robotics teams at local schools, and
to teach regular courses at LSU.
Binary Neutron Star Mergers
Binary neutron star mergers are interesting for several reasons.
One of them is the possible connection with some of
the most energetic events in the universe, gamma-ray bursts.
Currently, the leading hypothesis for the origin of
the "short" kind of these gamma-ray bursts is the merger of
a neutron star with either a black hole or another neutron star.
This hypothesis could be confirmed soon through a concurrent detection of gravitational
and electromagnetic waves from such a system.
Another reason is that the gravitational wave signal from binary neutron stars contains more information than
the recently detected signal from binary black holes.
In particular, the merger and post-merger signal
carries information about the equation of state of matter in the extreme
environment of a neutron star.
It is both amazing and intriguing at the
same time, how little we still know about these systems.
The list of still open questions includes:
- Can simulations rule out some of the many proposed approximations for the
equation of state of neutron star matter, even without observations?
- To what extent can gravitational waves be observed by current or planned detectors,
and how might these observations constrain the equation of state?
- How strong is the typical magnetic field of a neutron star, both before a merger,
but especially during and possibly after the merger?
- What exactly happens to a merger remnant that does not immediately collapse to a
black hole? For how long can it "resist" gravitational collapse and which
signals would such a system emit?
- Could a merger produce a spinning disk around a remnant? How massive can such
a disk become, and for how long can it exist?
Single Neutron Stars
While neutron star binary mergers are currently studied by
many groups, research on single neutron stars is still far from being
complete. Single and binary neutron star systems are related in two ways: first, a single,
hot neutron star can be the intermediate remnant of a binary neutron star
merger; and second, both can often be modeled using the same numerical techniques.
However, single neutron stars exhibit interesting behavior also on much
longer timescales than binary mergers. Approximations not applicable to a merger
are beneficial to study, e.g., instabilities that only occur
after a remnant has cooled sufficiently. It is thus vital to find ways to
overlap these two regimes, in order to model the same physical system for a much
longer time. Preliminary results show that the necessary "relaxation time" depends
strongly on the assumed equation of state, and might be longer than previously
thought due to neutron star instabilities. These instabilities, if confirmed,
would also emit gravitational waves, but whether they could be observed is
still an open question.
Software Infrastructure Development
The currently best way to study neutron star dynamics in detail is through
computer simulations. These often couple models for different physical
processes, e.g., for a general relativistic spacetime, relativistic
hydrodynamics, an approximation of the equation of state of nuclear matter, magnetic
fields, and potentially neutrino and electromagnetic wave radiation. Combining
these to an accurate mathematical description of the physical system that is
both numerically stable and reasonably fast requires the development of both
new analytic and numerical methods.
The need for dedicated software development in this area has been acknowledged
by the USA National Science Foundation, e.g., in a series of my research
grants to the software framework "Einstein Toolkit". The same software also has
a substantial presence in Europe.
One evidence for this is the representation of 9 European countries by researchers
attending the Einstein Toolkit workshop in Trento, Italy, in 2016.
Collaborations
The required computational research component makes it necessary to invest in
skills that on first glance don't appear to belong into physics, e.g., good
software engineering practices and parallel programming. However, they are not
only necessary for competitive progress in this area, they also provide a
natural basis for collaborations between otherwise isolated fields. In
my experience, such collaborations are often very valuable, and I will continue
to engage them with interest.
Another crucial component of this type of research is the availability of
supercomputer time allocations. Besides my large computing time awards
at LSU in the US, I am familiar with allocations from the highly competitive
call by PRACE (Partnership for Advanced Computing in Europe), often in
collaboration with the gravity group at Parma University in Italy. A gallery
with pictures of that work can be found here.
In contrast to the majority of the
research in this field, we not only publish a general outline of used algorithms,
methods and work-flows alongside scientific results. Instead, we ensure all of the
used research software is open source, all of our input data is made public in
a directly usable form, and all post-processing and analysis steps are also released
as free software, making our research as much
Open Science as possible.
