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It used to be when scientists predicted the time and date of when a star would explode, they might be off by a million years. Armed with a new theory, a research team has just reduced the margin of error to less than a day.
In accurately forecasting that a supernova would be observed April 8, the theorists also provided strong support for their "cannonball" model for mysterious and potentially dangerous space emissions known as gamma ray bursts.
In recent years, astronomers have connected the bright light generated by exploding stars, called supernovae, to intense bursts of gamma rays that frequently appear to emerge from the same location. The events are thought to be a combined sign of the formation of a dense neutron star or black hole. But little is known about the connection. Most researchers insist they don't know which comes first, the gamma-ray burst (GRB) or the supernova. Further clouding the picture, not all supernovae generate noticeable GRBs.
Now a team of theoretical physicists at CERN and the Technion Institute of Technology in Israel has provided strong evidence that both emissions are the simultaneous result of the supernova. The gamma-ray burst (GRB) is initially the more intense, and the characteristic supernova light, seen in various wavelengths, ramps up slowly and peaks a few days later.
Arnon Dar and his colleagues believe that gamma-ray bursts are fueled by huge cannonball-like clumps of matter shooting out along the axis of rotation of an exploding star, then colliding with other material. The intensity of an event depends on simply whether the cannonballs are pointed at Earth or not. In fact, he says, most GRBs almost surely go unnoticed.
The cannonball theory, which has been controversial over the past couple of years, led to modestly successful predictions recently for events that turned out to be difficult to observe in detail. The experience emboldened Dar's team, however.
So when NASA's High-Energy Transient Explorer satellite (HETE) spotted one of the brightest and closest GRBs ever seen -- it was a "mere" 2 billion light-years away -- on March 29, the theorists worked quickly to develop and publish a forecast. Meanwhile, astronomers around the world were monitoring the event with several telescopes.
"We made the prediction on April 1 and updated it on April 3," Dar told SPACE.com yesterday. "We posted a professional paper in the astro-ph archives [a Web site monitored by other scientists] on April 6 and submitted it to the Astrophysical Journal Letter on that day."
Dar's co-authors are Shlomo Dado and Alvaro De Rujula.
In the paper, reviewed by SPACE.com, the team predicted the supernova's signature light would be evident on April 8. It was, and an exploding star called SN 2003dh has now been officially catalogued.
In an e-mail interview, De Rujula explained the group's thinking in more detail.
The cannonballs ejected by a supernova are ordinary matter weighing nearly as much as Earth and travelling at speeds approaching that of light. The cannonballs, along with other radiation zooming out in two directions along an exploded star's axis of rotation, fuel a well-known afterglow of radiation in wavelengths on the electromagnetic spectrum from lower-energy radio and visible light to higher-energy X-rays and gamma rays.
"The gamma-ray burst and the supernova happen simultaneously and the afterglow is the sum of the radiations from a jet of cannonballs and the supernova itself," De Rujula said. The initial afterglow commonly associated with the gamma-ray burst decreases over time, while the supernova emission increases and peaks usually within two weeks.
"Because our theory works so well, we can predict when the afterglow becomes dim enough for the supernova not to be outshined," De Rujula said. "In this case we dared to predict the exact date of the supernova discovery -- we knew many people were looking -- and we got it right!"
The accurate forecast means the theorists' cannonball model -- which has not been accepted by all supernova experts -- cannot be called wrong. More study will be required to prove if it is right, but "perhaps this means that there is some truth to the model," De Rujula said.
If the model is on track, then gamma-ray bursts are not really as dramatic as often depicted. Rather, a burst packs but a fraction of a supernova's total output, De Rujula said. It appears intense because it's pointed at Earth. "If you point a small pointing laser into your eye, it is also the strongest radiation you have ever seen," he said.
Gamma-ray bursts are just supernovae playing high-energy accelerator physics, as De Rujula sees it.
"Exactly how they do it, we have no idea whatsoever," he said. "But once they eject cannonballs, we can follow their effects in detail."
In an interview in 2001, Dar explained why it is fortuitous that GRBs almost always come from outside the Milky Way Galaxy. The radiation from such an event, were it to originate nearby, could produce a lethal dose of byproducts -- particles called muons -- upon striking Earth's atmosphere, he said.
"Most of the species on Earth -- on the ground, underground and in the oceans, seas and lakes down to tens of yards (meters) -- will be extinct directly by these penetrating muons," Dar said. He and others have suggested that past mass extinctions on Earth might be attributable to such events.
Other researchers argue that our atmosphere would instead protect life on Earth and that there is almost no danger. Either way, recent calculations by another science team showed that a properly aimed explosion near enough to threaten Earth occurs just once in a billion years
http://www.space.com/scienceastronomy/supernova_warning_030417.html
In accurately forecasting that a supernova would be observed April 8, the theorists also provided strong support for their "cannonball" model for mysterious and potentially dangerous space emissions known as gamma ray bursts.
In recent years, astronomers have connected the bright light generated by exploding stars, called supernovae, to intense bursts of gamma rays that frequently appear to emerge from the same location. The events are thought to be a combined sign of the formation of a dense neutron star or black hole. But little is known about the connection. Most researchers insist they don't know which comes first, the gamma-ray burst (GRB) or the supernova. Further clouding the picture, not all supernovae generate noticeable GRBs.
Now a team of theoretical physicists at CERN and the Technion Institute of Technology in Israel has provided strong evidence that both emissions are the simultaneous result of the supernova. The gamma-ray burst (GRB) is initially the more intense, and the characteristic supernova light, seen in various wavelengths, ramps up slowly and peaks a few days later.
Arnon Dar and his colleagues believe that gamma-ray bursts are fueled by huge cannonball-like clumps of matter shooting out along the axis of rotation of an exploding star, then colliding with other material. The intensity of an event depends on simply whether the cannonballs are pointed at Earth or not. In fact, he says, most GRBs almost surely go unnoticed.
The cannonball theory, which has been controversial over the past couple of years, led to modestly successful predictions recently for events that turned out to be difficult to observe in detail. The experience emboldened Dar's team, however.
So when NASA's High-Energy Transient Explorer satellite (HETE) spotted one of the brightest and closest GRBs ever seen -- it was a "mere" 2 billion light-years away -- on March 29, the theorists worked quickly to develop and publish a forecast. Meanwhile, astronomers around the world were monitoring the event with several telescopes.
"We made the prediction on April 1 and updated it on April 3," Dar told SPACE.com yesterday. "We posted a professional paper in the astro-ph archives [a Web site monitored by other scientists] on April 6 and submitted it to the Astrophysical Journal Letter on that day."
Dar's co-authors are Shlomo Dado and Alvaro De Rujula.
In the paper, reviewed by SPACE.com, the team predicted the supernova's signature light would be evident on April 8. It was, and an exploding star called SN 2003dh has now been officially catalogued.
In an e-mail interview, De Rujula explained the group's thinking in more detail.
The cannonballs ejected by a supernova are ordinary matter weighing nearly as much as Earth and travelling at speeds approaching that of light. The cannonballs, along with other radiation zooming out in two directions along an exploded star's axis of rotation, fuel a well-known afterglow of radiation in wavelengths on the electromagnetic spectrum from lower-energy radio and visible light to higher-energy X-rays and gamma rays.
"The gamma-ray burst and the supernova happen simultaneously and the afterglow is the sum of the radiations from a jet of cannonballs and the supernova itself," De Rujula said. The initial afterglow commonly associated with the gamma-ray burst decreases over time, while the supernova emission increases and peaks usually within two weeks.
"Because our theory works so well, we can predict when the afterglow becomes dim enough for the supernova not to be outshined," De Rujula said. "In this case we dared to predict the exact date of the supernova discovery -- we knew many people were looking -- and we got it right!"
The accurate forecast means the theorists' cannonball model -- which has not been accepted by all supernova experts -- cannot be called wrong. More study will be required to prove if it is right, but "perhaps this means that there is some truth to the model," De Rujula said.
If the model is on track, then gamma-ray bursts are not really as dramatic as often depicted. Rather, a burst packs but a fraction of a supernova's total output, De Rujula said. It appears intense because it's pointed at Earth. "If you point a small pointing laser into your eye, it is also the strongest radiation you have ever seen," he said.
Gamma-ray bursts are just supernovae playing high-energy accelerator physics, as De Rujula sees it.
"Exactly how they do it, we have no idea whatsoever," he said. "But once they eject cannonballs, we can follow their effects in detail."
In an interview in 2001, Dar explained why it is fortuitous that GRBs almost always come from outside the Milky Way Galaxy. The radiation from such an event, were it to originate nearby, could produce a lethal dose of byproducts -- particles called muons -- upon striking Earth's atmosphere, he said.
"Most of the species on Earth -- on the ground, underground and in the oceans, seas and lakes down to tens of yards (meters) -- will be extinct directly by these penetrating muons," Dar said. He and others have suggested that past mass extinctions on Earth might be attributable to such events.
Other researchers argue that our atmosphere would instead protect life on Earth and that there is almost no danger. Either way, recent calculations by another science team showed that a properly aimed explosion near enough to threaten Earth occurs just once in a billion years
http://www.space.com/scienceastronomy/supernova_warning_030417.html
