Q&A: Black Holes

Q:
What is ADAF (Advection Dominated Accretion Flows)?

A:
An advection dominated accretion flow is one in which the infalling (or accreting) matter falls into a black hole without radiating away much of its energy, less than one percent. This can happen if the density of the infalling matter is low, so the particles make few collisions or their way beyond the event horizon. If the matter is falling onto a neutron star instead, or is spiralling slowly in a thick disk toward a black hole, it can radiate away ten to a hundred times more energy than in the advection case. Astronomers study the radiation pattern to deduce what kind of accretion flow they are observing, and whether a black hole or neutron star is present.