As publicized on this blog, last Friday I attended the 3rd Dutch Gravitational Wave Meeting. I followed the event on my Twitter account and this post is a summary about the most exciting news discussed during the day. Below you will find only my personal selection of some of the talks presented during the day. You can find some further notes about the other speakers on my Twitter page.
Several updates were presented about the current status of the international effort towards the first gravitational wave detection. Important news were discussed about three different instruments: the ground-based detector Advanced Virgo, the ESA space mission eLISA and the Pulsar Timing Array network.
Jo van den Brand – Many components of the Advanced Virgo detector are currently being mounted, the instrument upgrade seems to be on schedule and the goal is to go online together with Advanced LIGO and the other detectors. The instrument has the interesting feature of being “tunable” to specific sources, meaning that its sensitivity curve can be changed and optimized according to the targeted object.
Gijs Nelemans – eLISA is the approved L3 ESA mission that will fly in 2034. In 2015 the LISA pathfinder (that will test the eLISA technologies) will be launched. The technology that will be used for eLISA needs to be investigated and selected by 2019. The Netherlands is now forming the eLISA-NL consortium, deciding the pay-load contributors and consolidating the science community.
Joris Verbiest – There are currently three Pulsar Timing Array projects, one US based (NANOGrav) an European (EPTA) and an Australian one (PPTA). Each of these projects is becoming more and more sensitive and is providing better and better constraints on the gravitational wave strain amplitudes. So far the best upper limits on the dimensionless gravitational wave strain amplitude are given by the PPTA (<2.4e-15) but the EPTA and NANOGrav results are improving and will shortly provide better constraints. The sensitivity (that depends on the number of millisecond pulsars used and the quality and quantity of data) that we have today is very close to that necessary to detect the signals expected from merging binary super-massive black holes. An international effort of combining all three projects in a World-wide pulsar timing array is taking shape and is happening right now. The results will come very soon.
Cees Bassa – Within the EPTA project there is LEAP (Large European Array for Pulsars) which combines the sensitivity of five of the largest 100-m class European radio telescopes (Effelsberg, Westerbork, Sardinia, Nançay and Lovell) and new techniques to improve the signal-to-noise of collected data and bring the sensitivity up to the level required for the first gravitational wave detection. The project is currently running and first results show a dramatic improvement of the sensitivity when the data of millisecond pulsars are combined together.
Anne Archibald – One of the most exciting news was about the triple pulsar system PSR J0337+1715. In this system the inner companion (a white dwarf) and the millisecond pulsar are falling in the outer companion’s gravity (another white dwarf). Since the gravitational force exerted by the outer white dwarf on the inner binary is very strong, it is possible to perform stringent tests of the Strong Equivalence Principle (SEP) with unprecedented precision (the best current SEP test done so far has the Earth and the Moon falling in the Sun’s gravity, which is orders of magnitude weaker than the pulsar triple system !!). This is nonetheless a difficult task because of a number of microsecond-level pulsar timing effects that need to be accurately removed from the data. An interesting final question was: how do we model gravitational wave emission in triple systems ? No literature seems to discuss this…
Tim Pennucci – NANOGrav is the North American pulsar timing array, utilizing the Greenbank and Arecibo telescopes to observe about 30 millisecond radio pulsars. New algorithms are being used to analyze the data and the first results show that indeed the detrimental effect of the interstellar medium effect is mitigated and the timing precision improves substantially.
Jason Hessels – LOFAR (Low-Frequency Array for radio astronomy) can take 1-s images of the sky at the lowest frequencies that can be received from Earth. We need to understand what kind of transients are out there before we detect the first gravitational waves. Indeed many of the most exotic phenomena producing gravitational waves might well be transients in the LOFAR waveband. So far LOFAR has 10.000+ sources detected, 2000+ images analyzed and 800+ transients candidates. The difficulty is to distinguish transients and fake signals. DRAGNET is the World’s fastest wide-angle camera for radio astronomy: under construction, will find prompt emission from extreme transients.
Chris van der Broek – Gravitational waves can solve the neutron stars equation of state problem. Binary neutron stars that coalesce will be the most likely gravitational wave sources (expected first detection in 2017). Binary neutron stars have tidal deformation and the strength of this effect depends on the equation of state of ultra-dense matter. The effect of tidal deformation on the signal is weak [deformation ~ (v/c)^10]. Can we distinguish at least whether a neutron star has an hard/soft type of equation of state ? Yes, but only statistically: we need to study many sources (of the order of few tens). Simulations show that this can be done.
Paul Groot – BlackGEM is an array of optical telescopes in La Silla, Chile, which has the aim of detecting the electromagnetic counterparts of gravitational wave sources. The biggest challenge is that the optical counterparts are fast & faint whereas the search area provided by the gravitational wave detectors will be huge (of the order of 100 square degrees). With BlackGEM you see a large area of sky and once the counterpart is found you can then zoom in and identify the object. BlackGEM will be remotely-controlled and triggered by Virgo/LIGO events. It consists of 20x 65 cm telescopes. BlackGEM is expected to work in 2016 and run in trigger mode in 2017.