GRO J1655-40: Evidence for a Spinning Black Hole
In the center of a swirling whirlpool of hot gas
is likely a beast that has never been seen directly: a
black hole.
Studies of the bright light emitted by the
swirling gas frequently indicate not only that a
black hole is present, but also likely attributes.
The gas surrounding GRO J1655-40, for example, has been found to display an unusual flickering
at a rate of 450 times a second.
Given a
previous
mass estimate for the central object of seven times the mass of our
Sun, the rate of the
fast flickering can be
explained by a black hole
that is rotating very rapidly.
What physical mechanisms actually cause the flickering -- and a slower quasi-periodic
oscillation (QPO) -- in
accretion disks surrounding
black holes and
neutron stars remains a topic of much research.
