Laird teamed up with NASA, which gave $70,000 in funding for the project. The scientists determined that a supernova — a massive star explosion — would have to be much closer than previously thought to have devastating effects on the earth.
“I was initially disappointed when we came up with a regular result. Actually, of course, no news is sometimes good news,” Laird said.
Past studies indicated that a supernova 55 light years, or 55 times the distance light travels in a year, from Earth could release gamma and cosmic rays that would be harmful to the ozone layer. Laird and his colleagues found that the number could be lowered to 26 light years.
For Laird´s part of the study, he used the Space and Physics Lab at the University of Kansas to create a model. He used gamma rays from the most recent supernova, SN1987a, which occurred outside the Milky Way galaxy in 1987.
“We knew how far away it was. So we used physical laws,” Laird said. “As we moved it closer in our model, you could see what the impact would be.”
Neil Gehrels, an astrophysicist for NASA´s Goddard Space Flight Center, said he selected Laird for the project because he was one of the best in the country.
John Cannizzo, a contractor for Goddard Space Flight Center, has worked on the project for the last two years. He studied the effects of supernovae on the ozone layer.
“The main upshot of this is that it looks like supernovae don´t have a very powerful effect on the depletion of the ozone,” Cannizzo said.
Laird said if a supernova reached a distance of 26 light years from Earth, it could result in a 50 percent depletion of the ozone layer.
“It´s not an absolute distance. We think it´s in the ballpark,” Laird said.
The odds of a supernova reaching 26 light years is one in 670 million.
For Laird and his colleagues, seven years of research is drawing to an end. Their research will be published in the March 10 edition of the Astrophysical Journal.
“It is exciting because we are telling our colleagues and the public about the results now,” Gehrels said. “It´s interesting to hear their comments and reactions.”
Two weeks ago, they presented their findings to the American Astronomical Society.
“We only got five minutes,” Laird said. “We got several questions, more than most presenters.”
— Edited by Christy Dendurent