Ferreting out gravitational waves from data

Dr. Berit Behnke to receive the Otto Hahn Medal

For her excellent doctoral dissertation, Dr. Berit Behnke, junior scientist at the Max Planck Institute for Gravitational Physics (Albert Einstein Institute), has been honoured with the Otto Hahn Medal. The prize for her dissertation about ferreting out gravitational waves which are being sent out from neutron stars in the Galactic Center carries an award sum of 7500 Euros. The medal will be conferred on 4 June within the framework of the Annual Meeting of the Max Planck Society in Munich.

When Albert Einstein predicted the existence of gravitational waves in 1916, he was convinced that the waves would never be able to be directly measured. The interaction of gravitational waves with matter is too slight, and the effects would not be able to be measured. To date, a direct measurement has in fact not been achieved; however, in the meantime, the detectors are so sensitive that a discovery is anticipated in the next few years.

For direct detection of gravitational waves, not only must the measuring devices be sensitive enough, the collected signals must be filtered out of the data. This is a difficult and very computationally intensive task, as the signals are extremely weak and can easily be drowned out in extraneous noise. For gravitational wave signals from neutron stars in the centre of our galaxy, Berit Behnke has now developed new methods in order to more easily identify promising data-based candidates for actual gravitational wave signals.

“Blind” search for billions of differing signals

Behnke’s dissertation, for which she was awarded her doctorate with honours, presents the first search thus far for continuous gravitational waves from unknown neutron stars in the heart of our galaxy, where there are presumably a large number of neutron stars, making it a very promising location for tracking down gravitational waves. The problem: we have not yet identified these neutron stars and thus also do not know the parameters of the gravitational waves emitted from them. Therefore, a so-called “blind” search is being carried out in which the search for a vast number of different signals (several billion) is underway.

In her dissertation, Berit Behnke evaluated data from the two US LIGO detectors in Hanford and Livingston recorded over a period of around two years. As part of the investigation, every possible form of signal is assigned a value that indicates with which probability this signal form is found in the data. However, this still leaves the question as to whether a signal is real or has been caused by a local disturbance. This requires computing capacities which even the latest supercomputers cannot provide. Berit Behnke has made an important contribution to solving this problem: the methods she developed are useful in ascertaining whether it is actually a signal or not. As these new methods are very effective, a much larger proportion of the analysis results can now be sifted through in the search for signals. This enables the detection of even extremely weak signals.

Even though no signal has been able to be discovered using the new search method, important results have been attained thanks to this work: The absence of signals of a certain strength enables the narrowing down of the possible maximum signal strength of the investigated signal forms. In this way, conclusions can be drawn about the characteristics of the astrophysical objects.

Dr. Berit Behnke (b. 1983) studied physics at Universität Hamburg and completed her doctoral work at the Max Planck Institute for Gravitational Physics in Potsdam in the “Astrophysical Relativity” Department of Prof. Dr. Bernard F. Schutz under the supervision of Dr. Maria Alessandra Papa. Since June 2013, when she received her doctorate, Berit Behnke has worked as an academic staff member at the AEI Hannover and will take up a post as academic staff member at the Physikalisch-Technischen Bundesanstalt (PTB) in Braunschweig on 1 June 2014.

Recognition for excellent junior scientists

Since 1978, the Max Planck Society has been annually honouring young scientists with the Otto Hahn Medal for outstanding scientific achievements, which they have achieved mostly within the framework of their doctoral dissertation. This carries a recognition prize of 7500 Euros.  Dr. Berit Behnke is to receive this distinction for her dissertation “A directed search for continuous Gravitational Waves from unknown isolated Neutron Stars at the Galactic Center”.