U.S. astronomers have determined flares seen after a gamma-ray burst are apparently a continuation of the burst itself.

Gamma-ray bursts release in seconds the same amount of energy the sun will emit during its expected 10 billion-year lifetime. That energy comes from the core of a massive star collapsing to form a black hole or neutron star.

Early in its mission, the National Aeronautics and Space Administration's Swift satellite's X-ray Telescope discovered the initial pulse of gamma-rays -- known as prompt emission -- is often followed by short-lived but powerful, X-ray flares, suggesting a GRB's central engines remain active long after the prompt emission.

In the latest study, Hans Krimm and colleagues at the Universities Space Research Association and the Goddard Space Flight Center demonstrated X-ray flares are indeed a continuation of the prompt emission.

"This pattern points to a continuous injection of energy from the central engine, perhaps fueled by sporadic in-fall of material onto a black hole," said Krimm. "The black hole just keeps gobbling up gas and the engine keeps spewing out energy."

The research is to appear in the Aug. 10 issue of the Astrophysical Journal.