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Gravitational Waves Saw Its Initial Quired to Grasp Them and the for the Whole Spatium Series Flimsy Dawn

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Gravitational Waves Saw Its Initial Quired to Grasp Them and the for the Whole Spatium Series Flimsy Dawn INTERNATIONAL SPACE SCIENCE INSTITUTE SPATIUM Published by the Association Pro ISSI No. 39, May 2017 171925_Spatium_39_2017_(001_016).indd 1 11.05.17 10:35 Editorial Today, dear reader, we invite you second performance enthused the to an experience you have never audience as an unexpected bonus Impressum had before. Let us visit a concert suggesting that the artists might of- hall whose stage is not just a few fer such presentations frequently planks, but rather the entire Uni- and accessibly to all those prepared verse and the audience, to whom to listen. ISSN 2297–5888 (Print) we humans have just belonged ISSN 2297–590X (Online) since autumn 2015, is a multitude To take full advantage of the new of unknown beings scattered right opportunity, a connoisseur is throughout the Universe (if there needed who helps interpret the SPATIUM are any others …). The principle melodies. Fortunately, we have a Published by the performers are such prominent art- renowned expert amongst us: Pro- Association Pro ISSI ists as neutron stars, black holes, fessor Karsten Danzmann of the etc. Similar, however, to earthly Max Planck Institute for Gravita- entertainers, their programme is tion Physics and the Institute for devoted to the saga of birth and Gravitation Physics of the Leibniz death, the two very vital themes so Universität, Hannover. In his en- Association Pro ISSI mercilessly ruling our lives and thralling Pro ISSI talk on 12 Oc- Hallerstrasse 6, CH-3012 Bern that of the cosmic artists too. tober 2016, he portrayed gravita- Phone +41 (0)31 631 48 96 tional waves, their cosmic sources, see One hundred years ago, the idea of the marvellous technologies re- www.issibern.ch/pro-issi.html gravitational waves saw its initial quired to grasp them and the for the whole Spatium series flimsy dawn. Discarded again by messages they convey. One thing the most prominent luminaries at became very clear in his talk: tre- President the time, it returned with clearer mendous progress in a variety of Prof. Adrian Jäggi, contours briefly, just to fall into technological and scientific fields University of Bern oblivion again. Some decades later, has been required to enable hu- its elusive shadow reappeared sud- mankind to attend the universal Layout and Publisher denly when astronomers observed concertos. In fact: a new concert Dr. Hansjörg Schlaepfer a pair of stars, which obviously season has begun. CH-6614 Brissago were emitting energy in the form of gravitational waves. That earned We are thankful to Prof. Danz- Printing the lucky discoverers the Nobel mann for his most valuable support Stämpf li AG Prize. Again, however, a lot of in publishing the current issue of CH-3001 Bern time passed without an iota of a Spatium and wish our readers trace on the scene where in the some memorable moments in the meantime an armada of engineers company of the cosmic philhar- and scientists had gathered to get monic orchestra. hold of gravitational waves. They made it finally on 14 September Hansjörg Schlaepfer 2015 when signals allowed them to Brissago, May 2017 listen to the first sounds of the dark Universe. The piece was a thren- ody of two merging black holes, not quite on front stage, no, rather, an exciting 1.3 billion light years away. Only a few months later, a SPATIUM 39 2 171925_Spatium_39_2017_(001_016).indd 2 11.05.17 10:35 Gravitational Waves: the Sound of the Dark Universe1 by Prof. Karsten Danzmann, Max Planck Institute for Gravitation Physics and Institute for Gravitation Physics of the Leibniz Universität, Hannover nal? Marco’s interest is aroused. He drew gets excited at once. They Prologue decides to inspect the waveform on decide to alarm their colleagues at the screen (Fig.) 2 in more detail. the detector operations centre in No doubt, it is a marvellous signal, the United States from where the Albert Einstein Institute, Hannover too exciting to be artificial. Hence, signal came from. Yet, it is the 14 September 2015 he calls his colleague Andrew middle of the night there with only Lundgren from across the hall. An- the night watch on duty, who, of Physicist Marco Drago sits calmly in front of his computer screen: he cannot know that this day will Fig. 1: Albert Einstein on the summit of his career, 1921. In the frame of his change his and all his colleagues’ theory of general relativity, he had predicted the existence of gravitational waves five years before. The science community then had to wait a hundred years to see lives. Just before leaving for lunch, Einstein’s prediction verified experimentally in 2016. (Image credit: Ferdinand at 11:50, Marco notices an alert on Schmutzer). his screen. This is not very excit- ing though: such alerts appear rou- tinely at irregular intervals. On the other hand, Marco also knows that an alarm might indicate a dramatic event billions of light years away. This is the stuff he and hundreds of colleagues all over the world have been chasing after for many years. In order to facilitate the physicists’ job, a variety of software packages monitors the incoming signals. Each of these programmes can generate an alarm urging the scientist on duty to have a closer look at the event. One of those packages aims at recognizing pat- terns possibly coming from two merging black holes. Another sys- tem screens the signal in search of orbiting neutron stars and still an- other systems aims at characteriz- ing the statistic properties of the detector noise. No wonder, therefore, that Marco at first interprets the alarm as a sys- tem-generated check alert as he had seen so many before. Yet, what if this very alert indicated a real sig- 1 The text reports on a talk by Prof. Karsten Danzmann for the Pro ISSI audience on 12 October 2016. It was prepared by Dr. Hansjörg Schlaepfer and reviewed by Prof. Danzmann. SPATIUM 39 3 171925_Spatium_39_2017_(001_016).indd 3 11.05.17 10:35 course, wonders about the excited velope opened stating that the en- and final outcry of a pair of orbit- nocturnal call. Upon returning to igmatic Big Dog signal was an ing black holes when they yelled their office, all the scientists plunge artificial injection. The huge com- just before merging into one sin- into an examination of the myste- mon disappointment now prevents gle very massive black hole. Scien- rious signal concluding that it hundreds of people from talking to tists rated their individual masses could indicate a real event indeed. the media thereby granting a hand- at 29 and 36 times the mass of the At that moment, however, every- ful of senior specialists the time to Sun, while the resulting black hole one remembers the Big Dog event analyse the event so rigorously as holds 62 solar masses. Within a when a similar signal caused so to exclude any false inter preta tion. fraction of a second, the remaining much turmoil. That waveform Half a year later and exactly one three solar mass equivalents were looked exactly as if it were coming hundred years after Albert Ein- converted into energy2. With the from a pair of coalescing black stein’s publication of the general speed of light, gravitational waves holes in the constellation of the Big theory of relativity, the historic then carried the energy through Dog: the seminal victory seemed first direct detection of a gravita- the Universe, where, 1.3 billion within their grasp. In no time, an tional wave is presented at a press years later on Earth, they squeezed urgent Physical Review Letters pa- conference at Washington DC on the detectors’ 4-km long arms by per is written and then a secret en- 11 February 2016. It was the last a few 1/10,000 of the width of a proton. So dwarfish might be the vestiges of a great event! Fig. 2: The epoch making first signal of a gravitational wave as observed by the Livingstone detector of the US Laser Interferometer Gravitational Observatory Marco Drago’s and his colleagues’ (LIGO) on 14 September 2015. The horizontal axis represents time, while the ver- observation marks a turning point tical axis shows the strain on the detector exerted by the gravitational wave in ar- in science history comparable only bitrary units. The source of the waves is a pair of in-spiralling and then merging black holes. Before merging at t=0.22 s, their orbit rate steadily increases produc- with the moment when Galileo ing a detector signal with steadily increasing frequency and amplitude. Upon merg- Galilei directed the first telescope ing, both, the frequency and the amplitude decay rapidly reflecting the remaining to the sky in 1610. While Galilei oscillations of the unified black hole. (Credit: Max-Planck-Institut für used electromagnetic waves to ob- Gravitationsphysik) serve the stars, the new carriers are gravitational waves that possess so radically different properties that their detection inaugurates a new epoch in astronomy. The current issue of Spatium is de- voted to gravitational waves, their sources and the marvellous tech- nologies required for observing them. Over and above, this issue renders homage to Albert Einstein3 and the scientists of his time, who laid the cornerstone for our under- standing of gravitational waves. 2 According to Einstein’s most famous equation E = mc² stating that energy E equals mass m times the speed of light c to the square. 3 Albert Einstein, 1879, Ulm, Germany – 1955, Princeton, USA, theoretical physicist, Nobel Prize Laureate in physics, 1922. SPATIUM 39 4 171925_Spatium_39_2017_(001_016).indd 4 11.05.17 10:35 The History of when he derived a new formula for Richard Feynman8, a broad con- the emission of gravitational waves sensus emerged that gravitational Gravitational that, apart from a factor of two, is waves were a physical reality.
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