  High-time-resolution X-ray observations of compact objects provide direct
access to strong-field gravity, to the equation of state of ultra-dense matter
and to black hole masses and spins. A 10 m^2-class instrument in combination
with good spectral resolution is required to exploit the relevant diagnostics
and answer two of the fundamental questions of the European Space Agency (ESA)
Cosmic Vision Theme "Matter under extreme conditions", namely: does matter
orbiting close to the event horizon follow the predictions of general
relativity? What is the equation of state of matter in neutron stars? The Large
Observatory For X-ray Timing (LOFT), selected by ESA as one of the four Cosmic
Vision M3 candidate missions to undergo an assessment phase, will revolutionise
the study of collapsed objects in our galaxy and of the brightest supermassive
black holes in active galactic nuclei. Thanks to an innovative design and the
development of large-area monolithic Silicon Drift Detectors, the Large Area
Detector (LAD) on board LOFT will achieve an effective area of ~12 m^2 (more
than an order of magnitude larger than any spaceborne predecessor) in the 2-30
keV range (up to 50 keV in expanded mode), yet still fits a conventional
platform and small/medium-class launcher. With this large area and a spectral
resolution of <260 eV, LOFT will yield unprecedented information on strongly
curved spacetimes and matter under extreme conditions of pressure and magnetic
field strength.
