Volume 5, Issue 35 February 2008
Tracking Space Transients
Professor of astronomy Joshua Bloom studies gamma-ray bursts and other transient objects such as supernovae. Image credit: courtesy Josh Bloom
To watch the most powerful explosions in the universe, it helps to be quick on the draw. In seconds to minutes, the titanic blasts known as gamma-ray bursts can release more energy than our sun in 10 billion years. The initial flash of gamma rays is followed by a stream of electromagnetic radiation flowing from the site. The energy bathes nearby stars, nebulae, and galaxies in a brilliant afterglow, providing a floodlit view of the blast's environment.
Joshua Bloom, a Berkeley professor of astronomy, compares the analysis of a gamma-ray burst to a crime scene investigation. "If you blow something up over the course of a second, what you have left is this forensics scene. You have to look for the fingerprints of something that isn't there anymore," he says.
Bloom uses this technique to help explain the origins of these phenomenal explosions. At first, scientists divided gamma-ray bursts into just two types. Long-duration bursts, which persisted for more than two seconds, were followed by a second violent explosion called a supernova, produced by a collapsing star forming a black hole. The origins of short-duration bursts, however, remained unknown because astronomers had not yet closely pinpointed such events on the sky.
Some gamma-ray bursts are the explosive results of a massive star collapsing to form a black hole.
Gamma-rays are released in two jets along the star's axis of rotation. The burst may last from a few milliseconds
to a few minutes.
Image credit: Nicolle Rager Fuller/NSF
In 2005, Bloom observed the afterglow of the first well-localized short burst. The eagle eye's view allowed his team to discern that it had occurred near an elliptical galaxy, a conglomeration of mostly red and old stars. He deduced that the brief blast was likely due to the collision of two neutron stars-the extremely dense, massive remnants of collapsed stars-or a neutron star and a black hole.
From that point on, the tidy two-class burst hypothesis began to break down. Bloom's team has recently observed a short burst from a nearby galaxy which likely came from the surface of a neutron star. They have also observed two long bursts lacking supernovae, implying that there is greater diversity in the mechanisms producing gamma-ray bursts than was once believed.
Bloom's research group manages the robotic telescope PAIRITEL. Bloom has developed a system to allow fully robotic telescopes like PAIRITEL to observe fleeting sky phenomena soon after they appear. Image credit: Joshua Bloom
According to Bloom, the key to advancing the study of gamma-ray bursts and other transient phenomena is using many telescopes to observe these events at the same time. This approach is better able to characterize transients that appear unusual or are near enough to yield a good view. "You're potentially finding a diamond in the rough that you then need to devote more resources to very quickly," he says. "The big progress in gamma-ray bursts came when we got other telescopes around the world looking at them in other wavelengths."
The trick has been enlisting observing help in a timely fashion. To announce news of a blast, scientists once had to make time-consuming phone calls and emails to other astronomers. Bloom has helped develop a way to accelerate this process. He has created a language for today's robotic telescopes to automatically describe and broadcast sightings of gamma-ray bursts and other transient objects to other telescopes. Based on these Real-time Virtual Observatory Event (VOEvent) bulletins, robotic telescope facilities can more quickly respond to important astronomical happenings. The language has already yielded results such as the discovery of new planets around distant stars.
Bloom also seeks to standardize the reams of data being stored by robotic telescopes to allow easy analysis of their digital images. Within these databases, Bloom sees the potential of scientific pay dirt-insights into bursts or other transient events that may have been recorded during other studies of the sky. "It used to be when you wanted to understand this type of object you went and got some telescope time. Now in many cases you don't have to take the data-it already exists," Bloom says. Learning how to mine existing data records, he says, "is a skill that most astronomers don't yet have as part of our formal training, but we desperately need to build this toolbox for future generations."
Infrared images of two supernovae captured by PAIRITEL.
Image credit: Joshua Bloom
Data-mining techniques combined with real-time observations of the dynamic sky is where Bloom sees great opportunity for new discoveries. Referencing the career advice given to Dustin Hoffman's character in the movie "The Graduate," Bloom says that "transients, for astronomers, is the new plastics-it's where it's at."