A Los Alamos-led team of international researchers offers a novel way of studying the nurseries of the very first stars formed after the Big Bang. The team discovered that reverberations of the visible light from giant explosions called gamma-ray bursts can reveal clues to the early environment just after the Big Bang.
“Just as geologists use seismic waves generated by explosive charges to study the nature of the surrounding rocks, this new discovery will allow astronomers to use the relationship of the gamma-ray burst explosion’s light to that generated by the impact of the blast on the surroundings to study the collapsing star’s environment,” said Tom Vestrand of Space Science and Applications (ISR-1).
To capture the gamma-ray burst’s light reverberations and develop their theory, the team compared light measurements from ground-based instruments with data from two NASA satellites. The research was described in the July 13 issue of the journal Nature.
“A significant number of gamma ray bursts are generated by the death of massive stars that were born and died before the Universe was 10 percent of its current age. So the reverberations from these explosions provide unique clues about the environments of some of the very first stars,” he said.
The team used the Laboratory’s system of autonomous robotic telescopes called RAPTOR (RAPid Telescopes for Optical Response) and simultaneous observations of gamma rays by instruments on NASA’s Swift satellite and a Russian instrument on NASA’s Wind Satellite.
RAPTOR was built by the Los Alamos Thinking Telescopes team headed by Vestrand, an astrophysicist. The project was funded by Los Alamos’ Laboratory Directed Research and Development Program.
RAPTOR is a network of robotic observatories. Each observatory typically consists of a wide-field telescope array and a narrow-field telescope mounted on a platform that can swivel to any point in the sky in less than 6 seconds. The telescope platforms are the fastest ever built.
To observe the GRBs’ unpredictable, fleeting flashes of light, the RAPTOR telescopes must always be ready to respond to an event that could happen anywhere in the sky in the next minute or next month. When a flash occurs, observations must begin during the critical first minute of the explosion. Human operators with conventional telescopes don’t have the attention span and response for that -- the only practical option is to do it robotically. When an event does occur, the autonomous RAPTOR robotic telescopes can whip around and begin detailed observations in just a few seconds.
Gamma-ray bursts are brief, intense, flashes of gamma-ray emission, and the most distant ones are now known to signal the birth of a black hole through the cataclysmic collapse of a massive star. While the intense gamma rays are emitted only during the explosion, the new observations show that visible light is emitted both by the explosions and the glowing embers of surrounding material impacted by the blast.
Although today’s picture of the first critical minute of a gamma-ray burst is much more complete than it was only 12 months ago, these cataclysmic explosions continue to surprise astronomers. For example, in a recent event the RAPTOR system autonomously discovered a bright outburst of the visible light almost an hour after a faint triggering burst of gamma rays.
“This tells astronomers that the distant Universe still is hiding powerful explosions that can be discovered only by monitoring millions of steady optical sources,” said Przemek Wozniak of ISR-1. To meet this “needle in a haystack” challenge, astronomers, engineers, and computer scientists at the Laboratory are working together on advanced systems called “thinking” robotic telescopes that merge robotic hardware, modern database technology, and detection algorithms based on “machine learning.”
“We are world leaders for this advanced technology thrust that aims to build autonomous thinking sensors and I believe it is likely to have a profound impact on how we help our Nation build instrumentation to recognize and respond to increasingly complex threats,” said Vestrand.
