Look up in the sky -- It's a bird, it's a plane, it's a hybrid gamma-ray burst!
No, it's not a superhero. It's a new space phenomenon discovered by Penn State astronomers and astrophysicists that is bringing 15-year-old theories into question.
"We're scratching the surface of an entirely new phenomenon," said Peter Meszaros, Eberly College of Science chairman of astronomy and astrophysics and professor of physics.
The hybrid gamma-ray burst (GRB) -- known as GRB 060614 for the date it of its discovery on June 14, 2006 -- was spotted with the help of the Swift satellite. The Swift is a NASA satellite mission dedicated to the study of GRBs that is operated by the mission operation center in State College, said Derek Fox, assistant professor of astronomy and astrophysics at Penn State.
GRBs are exploding stars that emit as much energy in a few seconds as the sun produces in 10 billion years, Meszaros said. Scientists were particularly interested in the sighting of the new GRB because it deviated from previous classification of what used to be called long and short GRBs.
The type two GRB -- formerly classified as the long GRB -- is thought to be a 100-second explosion caused by the collapse of a star that has a mass 10 times more than the sun. The collapse occurs when the massive star's nuclear fuel is depleted, Fox said. The collapse is followed by a bright display of light called a supernova.
The one-second explosion from the type one GRB -- formerly classified as the short GRB -- is thought to be caused by the merging of two neutron stars or from a neutron star merging with a black hole and is not followed by a supernova, Fox said.
Unlike the type one and type two GRBs, the explosion of the hybrid GRB lasted 100 seconds but was not followed by a supernova, Fox said, thus falling into neither of the previously eblished categories.
"In order to get a supernova you have to explode and heat up about a solar mass of gas, so if you don't have that much gas being accelerated at high velocities, then you won't get a supernova," Fox said. "We're pretty sure that whatever happened with the hybrid gamma-ray burst, there wasn't a large mass of hot expanding gas."
Meszaros said one possible cause of the hybrid GRB is the existence of an unknown space object that caused the burst, and if this is so, a third class of objects will have to be recognized. He speculated that the GRB could have been a type two GRB whose explosion was abnormally long.
"[The discovery] can be very important because we're detecting a type of object which previously didn't know was there," Meszaros said. "If it's a new type of [star that causes GRBs], it means we have a better idea of how many stars are formed and what kind [of stars] -- kind of an inventory of the universe and what's out there."
Bing Zhang, a former Penn State professor who is now an assistant professor at the department of physics and astronomy at the University of Nevada, Las Vegas, was involved in the discovery and believes the new GRB is a more energetic type-one burst.
"If we make this GRB eight times less energetic, then we [would] produce a short GRB just like we had before," Zhang said.
Whereas the classification of GRBs was previously decided by a single characteristic -- duration of the burst or presence of supernovae -- the classification of GRBs has changed with the sighting of the hybrid GRB, Zhang said. Now a list of criteria is used to determine how a GRB should be classified, he said.
The emergence of the hybrid GRB opens the door to more study of black holes, phenomena that result from the presence of a large amount of mass in a small space such that the gravitational field becomes so strong that light cannot escape, Fox said.
"Black holes are objects of fundamental interest because their properties reveal the nature of gravity, which is one of the fundamental forces of the universe," Fox said. "We think that GRBs are the first cries of a black hole, so the conclusion would be that there's some way to make a black hole that we haven't thought of yet."
