Black holes can actually lose mass. Stephen Hawking theorized in 1974 that black holes radiate small numbers of particles (mainly photons), a process known as “Hawking Radiation”. This “evaporation” process can lead the black hole to shrink over time and ultimately to vanish completely. However, it is a staggeringly slow process: it would take about 10^67 years for a black hole the mass of the Sun to evaporate, significantly longer than the 14 billion years the Universe has existed.
Department of Astrophysics,
IMAPP, Radboud University,
P.O. Box 9010,
6500 GL Nijmegen, The Netherlands
Institute for Theoretical Physics (ITP),
Max-Planck-Institut für Radioastronomie (MPIfR),
Auf dem Hügel 69, D-53121