Free Astronomy Magazine January-February 2016

31 JANUARY-FEBRUARY 2016 ASTRONAUTICS longer come into contact with the walls of the cavities housing them, in which they will fluctuate as if they were in a perpetual free fall. A complex system of laser beams will bounce on the cubes’ surfaces and mea- sure their position with an accuracy in the order of a billionth of a millimetre (picome- tre). At the end of its path, each laser beam will be recombined and any variation in the cubes’ position will result in phase changes of the light, which, depending on the case, will be dimmer or brighter. This is relatively simple to perform in lab- oratories on the ground, but a technology of this kind becomes tricky to handle in ian point L1, located between the Sun and our planet, about 1.5 million km from the latter. L1 is a region of space where the gravitational pull of the Sun and Earth on a body compensates, keeping the body in permanent equilibrium. The probe will not actually remain in a stable position, but it will orbit around L1 at distances between 250,000 and 400,000 km. Its arrival in L1 is scheduled for mid-February, while the op- erational phase will start in early March. After its arrival, inside the LISA Technology Package, i.e. the laboratory containing the actual experiment, will be released the two cubes, which from that moment should no T his animation shows how gravitational waves are ex- pected to move. This would consist in the rhythmic ex- pansions and contractions of space-time, capable as they pass of increasing and decreasing the distance between bodies floating freely in the cosmos. [ESA–C. Carreau] D egenerate stars systems, such as the one shown here, con- sisting of a white dwarf (the larg- est) and a pulsar, are one of the scenarios in which researchers ex- pect copious pro- duction of intense and continuous gravitational waves. [ESO/L. Calçada]