  Supermassive black holes, with masses of 10^6 to more than 10^9 solar masses,
are among the most spectacular objects in the Universe, and are laboratories
for physics in extreme conditions. The primary goal of ARISE (Advanced Radio
Interferometry between Space and Earth) is to use the technique of Space VLBI
to increase our understanding of black holes and their environments, by imaging
the havoc produced in the near vicinity of the black holes by their enormous
gravitational fields. The mission will be based on a 25-meter space-borne radio
telescope operating at frequencies between 8 and 86 GHz, roughly equivalent to
an orbiting element of the Very Long Baseline Array. In an elliptical orbit
with an apogee height of 40,000-100,000 km, ARISE will provide resolution of 15
microarcseconds or better, 5-10 times better than that achievable on the
ground. At frequencies of 43 and 86 GHz, the resolution of light weeks to light
months in distant quasars will complement the gamma-ray and X-ray observations
of high-energy photons, which come from the same regions near the massive black
holes. At 22 GHz, ARISE will image the water maser disks in active galaxies
more than 15 Mpc from Earth, probing accretion physics and giving accurate
measurements of black-hole masses. ARISE also will study gravitational lenses
at resolutions of tens of microarcseconds, yielding important information on
the dark-matter distribution and on the possible existence of compact objects
with masses of 10^3 to 10^6 solar masses.
