The afterglow from the neutron-star merger located about 138 million light years away, that sent gravitational waves rippling through the universe, has continued to brighten, scientists have found. New observations from NASA’s orbiting Chandra X-ray Observatory indicate that the gamma ray burst unleashed by the collision first detected in August last year is more complex than scientists initially imagined.
“Usually when we see a short gamma-ray burst, the jet emission generated gets bright for a short time as it smashes into the surrounding medium – then fades as the system stops injecting energy into the outflow,” said Daryl Haggard, astrophysicist at McGill University in Canada. “This one is different; it’s definitely not a simple, plain-Jane narrow jet,” said Haggard. The data could be explained using more complicated models for the remnants of the neutron star merger.
One possibility is that the merger launched a jet that shock-heated the surrounding gaseous debris, creating a hot ‘cocoon’ around the jet that has glowed in X-rays and radio light for many months. The X-ray observations jibe with radio-wave data reported last month by another team of scientists, which found that those emissions from the collision also continued to brighten over time.
While radio telescopes were able to monitor the afterglow throughout the fall, X-ray and optical observatories were unable to watch it for around three months, because that point in the sky was too close to the Sun during that period. “When the source emerged from that blind spot in the sky in early December, our Chandra team jumped at the chance to see what was going on,” said John Ruan, a postdoctoral researcher at the McGill Space Institute new paper.
“Sure enough, the afterglow turned out to be brighter in the X-ray wavelengths, just as it was in the radio,” said Ruan, lead author of the study published in the Astrophysical Journal Letters. That unexpected pattern has set off a scramble among astronomers to understand what physics is driving the emission. The neutron-star merger was first detected on August 17 by the US-based Laser Interferometer Gravitational-Wave Observatory (LIGO).
The European Virgo detector and some 70 ground- and space-based observatories helped confirm the discovery. The discovery opened a new era in astronomy. It marked the first time that scientists have been able to observe a cosmic event with both light waves – the basis of traditional astronomy – and gravitational waves, the ripples in space-time predicted a century ago by Albert Einstein’s general theory of relativity.
Mergers of neutron stars, among the densest objects in the universe, are thought to be responsible for producing heavy elements such as gold, platinum, and silver.