Lichtgedanken 04

S C HW E R P U N K T 38 ing about a double star? »It is actually at least two stars, which are circling around each other«, confirms Mugrau- er, »but they are so close together that, from the Earth, it just looks like one star.« The objective of the current ob- servation is to precisely measure the orbital parameters of the two celestial bodies. How quickly, how eccentrical- ly, how frequently they revolve around one another—all of this can be calcu- lated from the spectral data. Over the course of the night, Susanne Hoffmann and Markus Mugrauer will focus on around a dozen other objects of this kind. Observers work together in pairs for themselves and for their colleagues The observers follow a precise proce- dure: all of the latest research projects are summarised in the observation handbook—a thick document file. »We work in service mode«, says Susanne Hoffmann. This means that each ob- servation night, the team on site re- cords images and spectra for all of the on-going projects. »As the observers take turns, everyone plays their part in recording data for themselves and their colleagues.« There are currently around ten members of staff and stu- dents working as observers, and there are always two people in the Observa- tory each night. YETI is one of the most extensive pro- jects currently running. It is being conducted by the Jena astrophysicists in collaboration with partners from around the world. YETI stands for »Young Exoplanet Transit Initiative« and focuses on the search for young planets in young, open star clusters. The stars that come into consideration are continuously observed for a period of several weeks and their brightness is measured precisely. If a planet is or- biting a star, it can eclipse it from our perspective on the Earth, which in turn reduces the brightness level of the star. Thousands of planets have been found using this transit method, although predominantly with old stars. How- ever, the Jena astrophysicists together with their partner in YETI are looking for young planets. In this case, young means less than 10 million years old. They make it possible to check the va- lidity of the current models of planet formation and evolution. As we talk, several double stars are spectroscoped. Then—a good two hours after we started—the conditions have been met to set the telescope up on a totally different object. OJ287 is located in the sky above Großschwab- hausen. Markus Mugrauer takes an overview image. It features a dozen light spots of various brightness and size. Our object is one of the hardest to see. OJ287—a quasar—a quasi-stellar object—is not a star. »It is the brightly shining nucleus of a galaxy with one of the largest black holes that we have come across.« With 18 billion solar masses, it is over 4,000 times as massive as the enormous black hole in the centre of our Milky Final movements before the observation begins. Dr Markus Mugrauer checks the small Cassegrain telescope, which is located next to the large 90-centi- metre reflector. The refracting telescope can be seen in the bottom right.