A Star Is Burst

by Bryan Gaensler

The following article first appeared in Issue 2 of Cosmos Magazine, published in August 2005, and is Copyright ©2005 Luna Media Pty Ltd. It may not be reproduced or distributed without written permission from the publisher.

For a fraction of a second in December, a dying remnant of an exploded star let out a burst of light that outshone the Milky Way's other half-trillion stars combined, astronomers announced on Friday.

- The New York Times, 20 February 2005

I receive a lot of email. And I confess that often I'm not too good at reading or replying.

So on the morning of 29 December last year, when a colleague from NASA sent me a message entitled "URGENT!", I didn't exactly jump to attention. It took me about an hour to get around to reading this email, at which point I learnt that "SGR 1806-20 just emitted a giant flare".

This is a concise way of saying that about 50,000 light years away, a bizarre type of star called a "magnetar" - only about 20 km across, but much heavier than the Sun and with a magnetic field a 1,000 trillion times stronger than the Earth's - had emitted an enormous pulse of gamma-ray radiation.

How enormous? Well it took us a few days to realise just what we were dealing with, but we now know that SGR 1806-20 had generated a kind of "solar flare on steroids", resulting in the brightest explosion in the history of astronomy. Brighter than the powerful gamma-ray bursts produced when distant black holes are born, brighter than the once-in-a-century supernova explosions recorded by the ancient Chinese and often visible in broad daylight, brighter even than the full Moon. This little magnetar gave off more energy in 0.2 seconds than the Sun does in about 200,000 years.

I didn't understand how such a thing could happen. But I knew what to do next. I quickly organised for the Very Large Array (VLA) in New Mexico - a group of 27 interlinked dishes that is the world's most powerful radio telescope - to point at the coordinates of this star. I was hoping we might still be able to detect the faint radio glow produced as the debris from this cataclysmic explosion slammed into surrounding interstellar gas.

To be honest, I wasn't hopeful of seeing much, having chased after various explosions of all types before, and having never really seen much. The VLA staff also were not particularly enthusiastic, giving us just an hour of observing time; and we had to wait until 3 January, after the New Year break.

Unlike the film Contact, when Jodie Foster sat in the VLA control room directing observations, trained operators do the actual observations in New Mexico, while astronomers like me monitor the action from the comfort of their computers - in my case, from my office in Boston. And since radio telescopes can operate in broad daylight, the observations would take place at the very civilised hour of 2.15pm.

The allotted date was a Monday, the first weekday of the year. I spent most of the day preparing my classes for the new semester: an ordinary day at work.

But then 2.15pm arrived, and like a precision choreography, all 27 giant dishes in the desert country swung into position, pointing at the precise area of the sky where the blast had been detected. I put some NASA colleagues on speakerphone, so I could tell them what I was seeing.

The data soon began to flow over the Internet onto my hard drive. I could hear the excitement in my colleagues' voices over the telephone, but personally I didn't really expect to see much.

The observations finished an hour later, at 3.15pm. I'm a fast typist and by 3.20pm I had analysed the data and had a picture of this part of the sky. Disappointingly, there was a ridiculously bright source of radio emission right in the middle of the image, blocking out this part of the sky. Had I pointed at the wrong place? Or had the Sun, which was very close by in the sky, somehow messed things up? I checked the coordinates of this annoying source, and suddenly realised that we were looking right at the position of the magnetar. This was no faint radio glow, this was a monster!

"Um ...," I said to the rest of my team over the speaker-phone. "I may have made a mistake, but I think thereƕ something there, and it's really, really bright."

I had a few independent checks I could do, which I started to run through. Meanwhile, another team in California, with whom we had been asked to share our data, sent out a message over the Internet saying that they were seeing this too. It had to be real.

The next few weeks are still a blur. Emails and phone calls flew out to telescopes in Parkes, Narrabri and Canberra in Australia; Netherlands, England, India, the Caribbean and Hawaii. Astronomers everywhere who were still on vacation were tracked down and told to train every telescope they could find on the position of this magnetar.

Months later, the results are still streaming in. We've used our telescopes to measure the detailed structure of the initial explosion, we've watched material fly outward from the star's surface at almost half the speed of light, and we've scratched our heads as the source quickly faded away but then suddenly became brighter again. The story is still unfolding.

I now have a whole new cohort of scientific collaborators from all over the world, most of whom I'm yet to actually meet. And I've been flooded with phone calls from the public convinced that this bizarre exploding magnetar somehow produced the Asian tsunami of December 26 last year (it didn't; the tsunami occurred a day earlier).

And now I read my email promptly. Especially the ones marked "urgent".

Bryan Gaensler is an Assistant Professor of Astronomy at Harvard University and the 1999 Young Australian of the Year. He is a member of the Editorial Advisory Board of Cosmos.

This article is Copyright ©2005 Luna Media Pty Ltd. It may not be reproduced or distributed without written permission from the publisher.

Last updated: 06-Mar-2006
Bryan Gaensler