Astroparticle Physics

1.3 Start of the Satellite Era 151974, by observing a binary star system that consisted ofa pulsar and a neutron star (Nobel Prize 1993). They wereable to precisely test the predictions of general relativity usingthis binary star system. The rotation of the orbital ellipse(periastron rotation) of this system is ten thousand timeslarger than the perihelion rotation of the planet Mercury. Thedecreasing orbital period of the binary is directly related tothe energy loss by the emission of gravitational radiation.The observed speeding-up rate of the orbital velocities ofthe partners of the binary system and the slowing-down rateof the orbital period agree with the prediction based on thetheory of general relativity to better than 1‰.It is to be expected that there are processes occurring inthe universe, which lack an immediate explanation. This wasunderlined by the discovery of gamma-ray bursters (GRB)in 1967. It came as a surprise when gamma-ray detectorson board military reconnaissance satellites, which were inorbit to check possible violations of the test-ban treaty onthermonuclear explosions, observed γ bursts. This discoverywas withheld for a while due to military secrecy. However,when it became clear that the γ bursts did not originatefrom Earth but rather from outer space, the results were published.Gamma-ray bursters light up only once and are veryshort-lived, with burst durations lasting from 10 ms to a fewseconds. It is conceivable that γ bursts are caused by supernovaexplosions or by collisions between neutron stars.It might appear that the elementary-particle aspect of astroparticlephysics has been completed by the discovery ofthe b quark (Lederman 1977) and t quark (CDF collaboration1995). There are now six known leptons (ν e , e − ; ν µ ,µ − ; ν τ , τ − ) along with their antiparticles (¯ν e , e + ; ¯ν µ , µ + ;¯ν τ , τ + ). These are accompanied by six quarks (up, down;charm, strange; top, bottom) and their corresponding six antiquarks.These matter particles can be arranged in threefamilies or ‘generations’. Measurements of the primordialdeuterium, helium, and lithium abundance in astrophysicshad already given some indication that there may be onlythree families with light neutrinos. This astrophysical resultwas later confirmed beyond any doubt by experiments at theelectron–positron collider LEP 11 in 1989 (see also Fig. 2.1).The standard model of elementary particles, with its threefermion generations, was also verified by the discovery ofgluons, the carriers of the strong force (DESY 12 , 1979), and11 LEP – Large Electron–Positron collider at CERN in Genevaγ burstertop and bottom quarksgluons