Bringing Dead Stars Back to Life

This is the third in a series of six articles on astronomy research at Harvard.

In the year 1006, the heavens grew suddenly bright as a spectacular astronomical explosion produced a new star as bright as the quarter moon and casting shadows on the ground.

In 1054, 1572, and 1604, a similar massive explosion incited turmoil and foreboding when a formerly dim star grew immensely bright.

Supernovae, often considered the most awe-inspiring of all astronomical phenomena, also happen to be some of the rarest, as only six have been recorded in the last 2000 years. Yet, it is one of the few astronomical occurances that can be observed "by a man in the street or a Harvard undergraduate that happens to be around at the right time," says Frederick D. Seward, one of the world's experts on such phenomena.

Seward, who does his research at the Harvard Smithsonian Center for Astrophysics, located near the QRAC, recently startled the astronomical field by locating and photographing the third known optical supernova remnants, also known as pulsars.

A violent explosion--a supernova-- often characterizes a star's death, producing, at its brightest, radiation 10 billion times that of the sun and leaves behind a collapsed core of neutrons known as a pulsar.

Scientists who study such phenomena, however, are at a considerable disadvantage primarily because they are forced to rely on ancient Chinese and Medieval records for the bulk of their data.

Seward and his colleagues at the Center for Astrophysics use the data of ancient supernovae and simultaneously employ the latest astronomical technology to reconstruct the history of stars that exploded hundreds of years ago.

"The stuff the earth is made of was created in a supernova billions of years ago," explains Stephen S. Murray. "In fact most of our elements come from supernovae," he adds.

By focusing on the remnants of supernovae, they are coming closer to determining the--types of stars that explode, how they self-destruct, and the importance of their remnants.

"These are the largest known releases of energy. There's a chance of finding something really now, something unexpected and unexplained," Seward says.

When a massive star ends its normal life, it collapses by blowing off its outer layers, producing a very dense cloud of neutrons, leaving a very dense core.

The remnants of pulsars rotate and emit radiation at their magnetic poles. Whenever one of the poles turns toward the line of light from the Earth, a pulse of radiation is received. The phenomenon is comparable to the pulse of light emitted by a lighthouse beam.

Remnants have a lifetime of about 20,000 years, Seward explains, and expand and fade into interstellar space as they age.

Although the pulsars often emit weak signals, scientists use radio signals to learn more about them. Scientists also get data from recently taken satellite photographs of the phenomena.

While they have spotted hundred pulsars through radio emmissions, only two were ever actually photographed until Seward and his colleagues in recent months located a third optical pulsar. Moreover, the recently located pulsar is easily observeable.

The pulser photograph is Seward's latest astronomical contribution. "He's really gotten the field off the ground. He's the recognized elder statesman," Murray says.

Using satellite compiled data dating back to 1979, the scientist has determined that supernovae explosions have produced massive quantities of chemicals such as sulpher, calcium, argon and silicon.

The death of a far-off star may seem of little consequence to life on Earth, but Seward points out that a supernova may have played a crucial role in the planet's evolutionary evolutionary history.

"The cosmic rays of a nearby supernova may have caused the extinction of the dinosaurs," he says. But, he adds, there are currently no stars close enough to place the planet in danger.

Looking toward the future, supernovae study may lead to a whole new realm of physics, Seward says. For example, pulsars contain gravitational fields more powerful than can possibly be created on Earth.

"It's using space as a natural lab that lasts millions of years," says Paul Gorenstein of the Center for Astrophysics.

In fact, the gravitational field around a pulsar is so strong that "It would literally lear you apart before you could even get close. It would pulverize any solid object into dust before reaching the surface," Seward says