By Sahana Ghosh & Gokul Bhagabati
Celebrating Dhanteras? Have you ever wondered where did the gold in your jewellery come from? A cosmic cooking pot may hold the answer.
This emerged when scientists detected for the first time light tied to a gravitational-wave event, thanks to two merging neutron stars located about 130 million light-years from Earth in the constellation Hydra.
"For the first time ever, we measured spacetime ripples (gravitational waves) and light from the same source in the universe," Karan Jani, an Indian-born astrophysicist and part of the LIGO (Laser Interferometer Gravitational-wave Observatory) team that made this discovery, told IANS.
Crashing neutron stars may be the universe's dominant source for many of the heaviest elements, including platinum and gold.
"The collision provides us clues on how heavy elements like gold and platinum are produced in our cosmos," Jani said.
"Each element of gold that we love to show off in our jewellery, has reached our Earth after traveling from such collision of neutron stars from millions of light years from galaxies far far away. Yes, all of us carrying the pride of wearing gold are carrying relics from such cosmic events," he added.
On August 17, LIGO in the US, working with the Virgo Interferometer in Italy, detected gravitational waves passing the Earth. This event following the neutron star merger was named GW170817.
About two seconds later, two space observatories, NASA's Fermi Gamma-ray Space Telescope and European Space Agency's INTErnational Gamma Ray Astrophysics Laboratory (INTEGRAL), detected a short gamma-ray burst from the same area of the sky.
Several scientific papers describing and interpreting these observations have now been published in the journal Science, Nature, Physical Review Letters and The Astrophysical Journal.
Neutron stars are one of the smallest stars in the universe and form when a star much more massive than the Sun runs out of nuclear fuel and collapses to form an extremely dense and small object.
It is heavier than the Sun but its diameter is the size of an average city like Kolkata.
Such is the density of these bodies that a spoon of neutron star material can be as heavy as Mount Everest.
"The process (merger of neutron stars) leaves signatures in both gravitational and electromagnetic waves whose detection and exploration can potentially revolutionise our understanding of the universe," said Dibyendu Nandi, head, Center of Excellence in Space Sciences India (CESSI) at IISER Kolkata.
"The very high energy released in this process sustains exotic phenomena that may have produced a major fraction of the gold in the universe," he said.
As many 40 scientists from 13 Indian institutions are part of the LIGO-Virgo discovery paper, according to Tarun Souradeep, LIGO India spokesperson.
This discovery is also extremely significant given that this is the first time that both gravitational and electromagnetic waves from a cosmic event were detected together, said Nandi.
"We now get to see both sides of the coin," Nandi told IANS.
The neutron stars merged in a galaxy called NGC 4993.
"This detection is significant in three remarkable ways - first, it allows us to independently test Einstein's General Theory of Relativity as we recorded two different forms of radiation - gravitational waves and light - originating from the same astrophysical source," Jani said.
"Secondly we were able to constrain the expansion of our universe and subsequently measure the age of our universe, and thirdly the collision provides us clues on how heavy elements like gold and platinum are produced in our cosmos," he added.
Indian scientists contributed to the fundamental algorithms crucial to search for inspiraling binaries in noisy data from multiple detectors, computing waveforms for these signals by solving Einstein's equations, tests of Einstein's theory and many other aspects of the data analysis, said Souradeep.
In addition, several Indian telescopes such as AstroSat, Giant Metrewave Radio Telescope (GMRT) and the Himalayan Chandra Telescope (HCT) participated in the search for electromagnetic flashes.
The sensitive CZTI instrument on AstroSat helped narrow down the location of the gamma-ray flashes. HCT obtained optical images at locations of neutrinos detected by other telescopes at the same time as the burst, and showed that they were unrelated to the gravitational-wave trigger.
The Indian team in LIGO includes scientists from CMI Chennai, ICTS-TIFR Bangalore, IISER Kolkata, IISER Trivandrum, IIT Bombay, IIT Gandhinagar, IIT Hyderabad, IIT Madras, IPR Gandhinagar, IUCAA Pune, RRCAT Indore, TIFR Mumbai and UAIR Gandhinagar.
Astronomers from IISER Pune, IIT Bombay, IUCAA Pune, TIFR Mumbai, PRL Ahmedabad, IIT Hyderabad, IIA Bangalore, NCRA-TIFR Pune, ARIES Nainital and IIST Trivandrum participated in the electromagnetic follow-up of this event using a variety of telescopes.
Previous detections of gravitational waves have all involved the merger of two black holes, a feat that won the 2017 Nobel Prize in Physics earlier in October.
(Sahana Ghosh can be contacted at email@example.com; Gokul Bhagabati can be contacted at firstname.lastname@example.org)