updated 11/25/2010 2:28:15 PM ET 2010-11-25T19:28:15  When
certain stars collapse, they release overwhelming blasts of
energy called gamma-ray bursts the most powerful explosion in
the universe. But the cosmic leftovers of these violent
outbursts have been a mystery until now.  Two new studies
suggest that when  gamma-ray bursts  explode, some can leave
behind black holes like cosmic gravestones, while others may end
up as spinning neutron stars.  Gamma-ray bursts occur when some
massive stars reach the ends of their lives and exhaust their
supplies of fuel for nuclear fusion in their cores. Without the
pressure from fusion pushing outward, gravity wins.  In the
ensuing dramatic collapse, a flood of high-energy, short-
wavelength gamma-ray light is released. They are sometimes
associated with supernovas another explosive way stars die   but
are separate events.  Bursts for black holes  One of the new
studies found that for a certain class of the brightest, most
powerful gamma-ray bursts, only black holes will