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Scanning For Very Big Bangs

April 29, 2010
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Swift has only one X-ray patient. But that “patient” is the entire universe.

Swift is a NASA satellite. It’s working on a long-term X-ray survey of the whole sky, and that’s just one of its jobs. No wonder it hasn’t completed the task after more than five years in orbit.

Swift was launched in November 2004. Along with X-raying the sky, its duties include monitoring black holes and neutron stars for surges of high-energy radiation, and making ultraviolet studies of exploding stars.

But its main assignment is to look millions, even billions of years back in time.

The spacecraft primarily studies gamma-ray bursts (GRBs), which are enormous, mysterious explosions way out in the depths of space. Earlier this month, Swift found its 500th GRB. “On the one hand, it’s just a number, but on the other it’s a remarkable milestone,” Neil Gehrels, Swift’s lead researcher at Goddard Space Flight Center in Greenbelt, Maryland, told ScienceDaily. “Each burst has turned over a new piece of the puzzle, and a clearer picture is emerging.”

Gamma rays are the highest-energy form of light. GRBs are brief but ferociously intense releases of mind-boggling amounts of energy. Scientists think they come from the collapse of a massive star into a black hole or the collision and merger of two compact but massive objects (either two neutron stars or a neutron star and a black hole).

A typical GRB produces as much energy in a few seconds as our sun will generate in its entire 10-billion-year expected lifetime. So far, fortunately for us, all GRBs have happened far, far away. The closest one that Swift has noticed occurred about 100 million light-years away. None has ever been observed in our Milky Way galaxy. Then again, we here on Earth didn’t even know GRBs existed until 1967, when they were discovered by military satellites that were looking for secret nuclear tests.

How powerful are these cosmic cataclysms? On March 19, 2008, Swift detected one from 7.5 billion light-years away that was actually visible, briefly, to the naked eye. As we all remember from our school days, a light-year is the distance that light travels in one year. That had to be a very big bang indeed.

The most distant GRB that Swift has found came from 13.04 billion light-years away, meaning that we’re just now catching up on what happened in that corner of space 13.04 billion years ago. “The burst is beyond the farthest confirmed galaxies and quasars, making it the most distant object we know in the universe today,” said Derek Fox, a Swift team member at Penn State.

The best scientific guesses currently place the age of the universe at 13.75 billion years, give or take a few million. So Swift is giving us glimpses into the universe’s early days, relatively speaking. That’s a pretty cool job of imaging.

Related seminar: The Business of Radiology


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