Astroparticle Physics

16 Glossary 303The Big Rip is a cosmological hypothesis about the ultimate fateof the universe. The universe has a large amount of dark energycorresponding to a repulsive gravity, and in the long run it will winover the classical attractive gravity anyhow. Therefore, all matterwill be finally pulled apart. Galaxies in galactic clusters will beseparated, the gravity in galaxies will become too weak to hold thestars together, and also the solar system will become gravitationallyunbound. Eventually also the Earth and the atoms themselves willbe destroyed with the consequence that the Big Rip will shred thewhole physical structure of the universe.Binary stars are two stars that orbit around their common center ofmass. An X-ray binary is the special case where one of the starsis a collapsed object such as a neutron star or black hole. Matteris stripped from the normal star and falls onto the collapsed starproducing X rays or also gamma rays.The energy that has to be invested to desintegrate a nucleus into itssingle constituents (protons and neutrons, nuclear binding energy).Scientific branch of astronomy that deals with the question of theorigin of life, e.g., whether organic material has been delivered toEarth from exraterrestrial sources. The techniques are to look forbiomolecules with spectroscopic methods used in astronomy.A hypothetical body that absorbs all the radiation falling on it. Theemissivity of a blackbody depends only on its temperature.The radiation produced by a blackbody. The blackbody is a perfectradiator and absorber of heat or radiation, see also Planck distribution.A massive star that has used up all its hydrogen can collapse underits own gravity to a mathematical singularity. The size of a blackhole is characterized by the event horizon. The event horizon is theradius of that region, in which gravity is so strong that even lightcannot escape (see also Schwarzschild radius).Short for variable active galactic nuclei, which are similar to BL-Lacertae objects and quasars except that the optical spectrum isalmost featureless.Reduction of the wavelength of electromagnetic radiation by theDoppler effect as observed, e.g., during the contraction of the universe.Variable extragalactic objects in the nuclei of some galaxies, whichoutshine the whole galaxy. BL stands for radio loud emission in theBband(≈ 100 MHz); lacerta = lizard.Big Ripbinary starsbinding energybioastronomyblackbodyblackbody radiationblack holeblazarsblueshiftBL-Lacertae objects