The LISA Gravitational Observatory

LISA will be a large-scale space mission designed to observe one of the most elusive phenomena in astronomy – gravitational waves.

LISA is an all-sky monitor and will offer a wide view of a dynamic cosmos using gravitational waves as new and unique messengers to unveil the Gravitational Universe. It can provide the closest ever view of the infant Universe at TeV energy scales, has known sources in the form of verification binaries in the Milky Way, and can probe the entire Universe, from its smallest scales near the horizons of black holes, all the way to cosmological scales. The LISA mission will measure source parameters with astrophysically relevant sensitivity in a band from below 10−4 Hz to above 10−1 Hz.  Among the sources that will be studied by LISA we can mention: astrophysical black holes, extrem mass ratio inspirals, compact galactic binaries, super-massive black hole binaries.

LISA is the 3rd Large (L3) Mission of the current ESA program, scheduled for launch in the early ‘30s.

The LISA instrument consists of 3 spacecrafts at the vertices of a huge, 2.5 Gm in side, triangle. These will be the end stations of 3 different interferometers (two independent) with picometer sensitivity.  As the constellations rotates, while trailing behind the Earth in its orbit, it will scan the entire sky, simultaneously measuring both polarisations of the gravitational waves.

One of the key technologies that the mission relies on is the realization of nearly perfect free fall of its test masses: this was tested in the LISA-Pathfindermission of 2016-17, where residual forces were reduced to the fN/√Hz level.  Among these disturbances, we mention spurious electrostatic forces:  cosmic rays produce a build-up of charge on the test masses that, in turn, can generate noise  force. The masses need therefore to be discharged by a non-contact method.

LISA activity in the Roma Tor Vergata INFN unit is at present focused, in collaboration with groups of TIFPA- University of Trento and  University of Florida, on the development and testing of an improved Charge Management System, capable of modifying the charge status of the test masses via photoelectric effect with photons generated by deep UV LEDs.