In a galaxy 4 billion light-years away... astronomers find ‘smoking gun' trail after gamma-ray blast

Posted by pt91 at Aug 05, 2013 10:54 AM |
University of Leicester astronomers find evidence for a new kind of cosmic explosion, called a kilonova - which has been theorised before, but never seen
In a galaxy 4 billion light-years away... astronomers find ‘smoking gun' trail after gamma-ray blast

Gamma-ray Burst 130603B . Credit: NASA, ESA, N. Tanvir (University of Leicester), A. Levan (University of Warwick), A. Fruchter (STScI), J. Hjorth (University of Copenhagen), R. Hounsell (STScI), K. Wiersema (University of Leicester), and R. Tunnicliffe (

Issued by University of Leicester Press Office on 5 August 2013

University of Leicester astronomers have discovered the fading remains of a huge celestial explosion, known as a Short-duration Gamma-ray burst and thought to be responsible for producing many heavy elements in the Universe such as gold and platinum.

Professor Nial Tanvir, of the Department of Physics and Astronomy at the University of Leicester, led a team of astronomers who used Hubble to study a recent short-duration burst in near-infrared light.

The Hubble study may represent the first detection of a so-called kilonova, a stellar explosion that is roughly 1,000 times brighter than a nova (the eruption of a white dwarf), but about 1/1,000 less luminous than a typical supernova (the self-detonation of a massive star).

Astrophysicists have predicted that kilonovas are created when a pair of super-dense neutron stars in a binary system spiral together. This event happens as the system emits gravitational radiation, tiny ripples in the fabric of space-time. The energy dissipated by the waves causes the two objects to spiral closer together. In the final milliseconds, as the two objects merge, the death spiral kicks out highly radioactive material. This material heats up and expands, emitting a burst of light.

On June 3 NASA’s Swift Space Telescope picked up the extremely bright gamma-ray burst, catalogued as GRB 130603B, in a galaxy located almost 4 billion light-years away. Although the initial blast of gamma rays lasted just 1/10 of a second, it was about 100 billion times brighter than the subsequent kilonova flash.

The visible-light afterglow was detected at the William Herschel Telescope and its distance was determined with the Gran Telescopio Canarias, both located in the Canary Islands.

“We quickly realized this was a chance to use Hubble to hunt for a kilonova in near-infrared light,” Tanvir says. The calculations suggested that the light would most likely be brightest in near-infrared wavelengths about 3 to 11 days after the initial blast. The researchers needed to act quickly before the light faded, so they requested Director’s Discretionary Observing Time with Hubble’s Wide Field Camera 3.

On June 12-13 Hubble searched the location of the initial burst, spotting a faint red object. An independent analysis of the data from another research team confirmed the detection. Subsequent Hubble observations three weeks later, July 3, showed that the source had faded away, proving that it was the fireball from an explosive event.

“Previously, astronomers had been looking at the aftermath of short-period bursts largely in optical light, and were not really finding anything besides the light of the gamma-ray burst itself,” explains Andrew Fruchter of the Space Telescope Science Institute in Baltimore, Md., a member of Tanvir’s research team. “But this new theory predicts that when you compare near-infrared and optical images of a short gamma-ray burst about a week after the blast, the kilonova should pop out in the infrared, and that’s exactly what we’re seeing.”

In addition to confirming the nature of short GRBs, the discovery has two important implications. First, the origin of many heavy chemical elements in space has long been a puzzle. Kilonovas are predicted to form such elements in abundance, spraying them out into space where they could become part of future generations of stars and planets.

Second, the mergers of compact objects are also expected to emit intense gravitational waves, first predicted by Albert Einstein. Gravity waves have not yet been discovered, but new instruments under development may make the first detections within a few years. “Now it seems that by hunting for kilonovas, astronomers may be able to tie together the events giving rise to both phenomena,” Tanvir says.

ENDS

For more information contact Professor Nial Tanvir on nrt3@le.ac.uk

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