Photo-erosion is the dispersion of the outer layers of a prestellar core by ionizing radiation of a nearby star

Star

A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...

, thus preventing these layers from accreting onto the protostar

Protostar

A protostar is a large mass that forms by contraction out of the gas of a giant molecular cloud in the interstellar medium. The protostellar phase is an early stage in the process of star formation. For a one solar-mass star it lasts about 100,000 years...

 at the centre of the core, and thereby reducing the mass of the developing object so instead of forming a star, it may form a free-floating brown dwarf

Brown dwarf

Brown dwarfs are sub-stellar objects which are too low in mass to sustain hydrogen-1 fusion reactions in their cores, which is characteristic of stars on the main sequence. Brown dwarfs have fully convective surfaces and interiors, with no chemical differentiation by depth...

 or planetary-mass object.