April 30, 1991

Article at Reuters

Supernova explosion will light up night sky, astronomers say

The strange star Eta Carinae, surrounded by the Homunculus Nebula, surrounding imaged red and near-ultraviolet wavelengths

By Wilson da Silva

SYDNEY – If the strange star of Eta Carinae blows up, as astronomers believe it will, its explosion will light up the night sky from the Mediterranean Sea to Antarctica.

The cataclysmic event will even be visible during the day, and will release more energy than all of the world’s nuclear weapons detonating at once. Such an event, called a supernova, has astronomers rubbing their hands with glee.

 “It really can’t control itself, it’s obese,” said astronomer Dr David Allen of the Anglo-Australian Observatory. “When it hiccups, it throws off as much material as our sun contains.”

But when could it happen?

“It could be tomorrow, it could be 100,000 years from now,” said Allen.

Although five million times brighter than the sun, Eta Carinae is surrounded by dust and gas which obscures and dims it, making it too faint to see with the naked eye.

Yet in the centre of this stellar storm the star, the most massive known, is seething away, waiting to go supernova.

“It’s quite obvious it’s going to explode,” said Allen, who in 1979 first pinpointed the star’s location in space. “It will be visible during daylight, and it’s plausible that it will cast shadows at night.”

Astronomers believe the dust and gas presently surrounding Eta Carinae was expelled in the 1830s when the unstable star suffered a convulsion, thought to be periodic, and spat out billions of cubic kilometres (miles) of hot gaseous material every second.

Doctor David Malin, also of the observatory, said the star’s last convulsion in the 1830s cleared the dust around the star, turning it from invisible to the second brightest in the sky for many months and puzzling astronomers of the time.

It later faded as the material cooled and darkened, accruing near the star and blocking its light again.

Allen and Malin have monitored the star for more than a decade from the observatory’s telescopes in the dark skies of northern New South Wales. The star, located near the Southern Cross constellation, almost never sets from their skies.

As in the case of the 1987 supernova that thrilled scientists around the world, the southern star makes Australia one of the best vantage points.

But Malin says once detonated, it will be visible low in the horizon as far north as the Mediterranean Sea.

The 1987 supernova, the first visible to the naked eye since 1604, turned from invisible into a bright pinpoint of light and made international headlines.

But compared with Eta Carinae, the so-called 1987A supernova is regarded as an “ordinary” one. Before exploding, 1987A was some 20 times the size of the sun, while Eta Carinae is between 100 and 150 times its size – far too massive to be stable.

It consumes three quadrillion (3,000,000,000,000,000) tonnes of hydrogen every second. When it blows, it will be the biggest ever recorded. It is also some 20 times closer to us than 1987A and will put on a more spectacular light show.

But the Earth is safe from the detonation, Malin said. Eta Carinae is so far away its rays take thousands of years, travelling at the speed of light, to reach us.

“It’s a very healthy 7,000 light years away,” said Malin. “It could have gone off already in which case we’ll have to wait 7,000 years to see it. Or it could have happened a long time ago, and we will see it flare up tomorrow.”