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S C HW E R P U N K T 39 04 | LICHT GEDANKEN Contact Dr Markus Mugrauer Institute of Astrophysics and University Observatory Schillergässchen 2-3, D-07743 Jena, Germany Phone: +49 36 41 9-47 514 Email: markus@astro.uni-jena.de www.astro.uni-jena.de The University Observatory online : www.astro.uni-jena.de/index.php/gsh-home Way. A gigantic accretion disc—an orbiting disc, which transports huge amounts of matter around its central body—surrounds this colossus. And, as if that weren’t spectacular enough, this huge black hole is orbited by a sec- ond black hole. This second black hole is also enormous, measuring around 150 million solar masses. »The fasci- nating thing about this constellation is that it allows us to pretty much test the validity of Albert Einstein’s general theory of relativity.« Markus Mugrauer is in his element. »GTR« he says, refer- ring to the general theory of relativity. »Whenever the smaller of the two black holes passes through the accretion disc of the larger, it causes enormous out- bursts of luminosity, which can be ob- served from earth and which precisely correspond to the predictions calculat- ed using GTR.« Light from the quasar would also be visible from the »end of the universe« Even without Einstein and his gener- al theory of relativity, I am impressed: OJ287 is located around 3.5 billion light years away from us. The light of this minute light spot, which I can see on the small monitor, has been travelling here for 3.5 billion years. These di- mensions of time and distance are un- fathomable. As are the mighty forces, which control it all. »The object is so bright that you could place it at the end of the universe, and we would still be able to see it here with our telescope«, Mugrauer is convinced. But enough philosophizing; now it is time to measure. We take more bright- ness measurements for OJ287. These will later be used, together with the data from other international partners, to produce light curves. »This allows us to practically keep OJ287 in view at all times.« The last great outburst of luminosity took place in 2015. The next observable outburst is expected in 2022. If this happens—and Markus Mugrauer has no doubt it will—he and his colleagues will be able to watch it live from Großschwabhausen; if you ignore the 3.5-billion-year time delay, of course. The two black holes will also soon collide, precisely as the predic- tions from GTR suggest. »In just an- other 10,000 years, we will be able to measure a gigantic gravitational wave signal«, promises Mugrauer. Seriously. Until then, the researchers at Jena will continue to fill the astronomical data- bases with their observations. Despite the repetitive routines, the night-time observations lose none of their fascina- tion for Markus Mugrauer. »Each indi- vidual star that we look at could be the host star of a planetary system, similar to ours.« He is still and will always be fascinated by looking at and discover- ing new objects. These words are revolving around my head as I drive back towards Jena, one hour before midnight. Maybe on one of these planets out there, there is even a life form which is using refined in- struments to capture the light of the stars to create an image of the world. Observing our sun from afar; a medi- um-sized star in an advanced age, and, in doing so, discovering that this star is surrounded by a planetary system. Seeing the clusters of stars and double stars and analysing the black holes. In that moment, after looking into space, it doesn’t seem that unlikely at all. Dr Susanne Hoffmann and Dr Markus Mu- grauer control the instruments, the telescope and the dome of the Observatory from the control room. Astrophysicists from the Uni- versity of Jena observe the night sky some 120 nights a year.