ASTRONOMY

Spectacular death throes of a star

ANNE STEACY March 9 1987
ASTRONOMY

Spectacular death throes of a star

ANNE STEACY March 9 1987

Spectacular death throes of a star

ASTRONOMY

At 11 p.m. on Feb. 23, inside a small observatory on a barren mountaintop in northern Chile, Ian Shelton noticed a surprisingly bright star on an astral photograph he had just taken through a 10-inch telescope with a lense the diameter of a dinner plate. Intrigued, he walked outside —and discovered that the star that appeared on the freshly developed picture was bright enough to be seen without a telescope. Then, after using his more powerful 24-inch telescope to confirm the sighting, Shelton telephoned the Harvard Smithsonian Center for Astrophysics in Cambridge, Mass., and about 14 hours later officials at the centre announced that the 29year-old researcher at the isolated observatory owned by the University of Toronto had spotted the most significant supernova, or exploding star, recorded since the German astronomer Johannes Kepler sighted a similarly bright star 383 years ago. As a result, the new celestial phenomenon now bears its Winnipeg-born discoverer’s name: Supernova Shelton 1987 Number 1.

A supernova occurs when a star exhausts all its available thermonuclear fuel. With its fuel exhausted, the star’s core collapses. Then, immediately after, the star disintegrates in a gigantic explosion ignited by intense heat from gases being sucked into the centre. Said U of T astronomer Robert Garrison, director of the Chilean observatory: “It is like a nuclear explosion on a cosmic scale.” Before exploding, the supergiant star was 100 times the size of the Earth’s sun, but it is now tens of thousands of times larger. The death of the star recorded on sky charts as CPD-69°202 has the potential to provide astronomers with new information about the universe.

In fact, what Shelton spotted last week was an event that took place 150,000 years ago, but it took that long to become visible on Earth. Although the star is 150,000 light-years from Earth, in cosmic terms it is

close. It is in a galaxy known as the Large Magellanic Cloud. Scientists have many photographs of the star taken before Shelton’s discovery—and astronomers expected it to continue its existence for millions of years. Said

Garrison: “We had no sign it was ready to go. It is going to upset stellar evolution studies a lot.”

The fact that Shelton was even in Chile, 7,380 feet above sea level on the summit of Las Campanas mountain, is in itself an accomplishment against the odds. On April 1, 1985, officials at the federal government’s Natural Sciences and Engineering Research Council cut a $130,000 grant to the university’s astronomy department by 30 per cent. The department had used the annual grant to maintain the observatory, and it considered closing the operation down. But Garrison said that department members have contributed portions of their own personal research grants, as well as money solicited from alumni and other sources, to keep the observatory open. Said

Garrison: “It is not an accident that it was a Canadian who found the supernova. We had the foresight to put the observatory there and the guts to keep it going. And Ian had the background and good scientific judgment to know

it was something important and what to do with it.”

Still, in order to stay within the annual $100,000 operating budget, the university has postponed some maintenance work at the observatory. For one thing, Garrison said, gears and controls on the 24-inch telescope were manufactured during the 1960s and need to be replaced. Said the 50-yearold astronomer —who has himself discovered several previously unknown kinds of stars, including a pure helium star in 1973: “It is possible that the telescope could have been down at that critical time.”

In that event, the supernova would now bear another astronomer’s name. Indeed, several U.S. astronomers work only half a kilometre from Shelton’s post, operating an observatory for the Washington,

D.C.-based Carnegie Institute. But their 100-inch telescope (10 times larger than the one with which Shelton made his discovery) was trained on more distant galaxies. As a result, they missed the sudden eruption of the giant star—as did other European and U.S. astronomers with large, expensive telescopes trained on the southern sky from nearby mountains. And in Australia—where Garrison says that there are several avid supernova searchers— the sky was too light to spot the supernova when Shelton took the most significant photograph of his life. Now, says Garrison, all astronomers who are in a position to see the supernova are co-operating and gathering data to be published in scientific journals. Said Garrison: “Astronomy is a very international thing. It is nice that a Canadian found it, but we can forget about nationalism from here on in.”

On the night that Shelton made his historic discovery, he had planned to take photographs of a comet due to appear in the early-morning skies. And to test the astrograph—a photographic telescope built in 1905 that uses 14-inch-square glass plates—he happened to aim the old apparatus at the Large Magellanic Cloud. Then, he took the picture that made his name known to astronomers around the world.

Before his discovery, Shelton spoke to Garrison twice a week by shortwave radio. Since then they have been talking to each other twice a day. Shelton continues to monitor the brightness and colors of the pinkish-purple supernova for at least 16 hours a day. Said Garrison at week’s end: “This is an astronomer’s dream. His initial exhilaration is passing, and he is settling down into more of a routine. But this is his life—he loves it.”

According to Garrison, the supernova is ideally placed to help researchers measure distances in the universe. Scientists have calculated the distance to Shelton’s supernova and can now use it as a fixed reference point to calculate the distance to other supernovas in more distant galaxies by measuring their brightness. The star’s death throes will likely be most visible this week as the destruction of the supernova reaches its climax and burns with a brightness that is 100 billion times greater than the light emitted by the original star. For the next two months the phenomenon will appear to residents of the Southern Hemisphere as the brightest star in the night sky. Shelton will keep watch from his rocky lookout post—and savor a discovery that placed his name among the stars.

— ANNE STEACY in Toronto