NASA has announced that its Swift telescope has detected its 1,000th gamma-ray burst (GRB). The Swift GRB mission was launched in November 2004, 11 years ago, to help astronomers better pin down the sources and mechanism of GRBs. The first GRBs were spotted in the 1967s (by satellites looking for secret nuclear-weapon tests), and it was only in the early-1990s that astronomers figured out they were extremely powerful blasts of energy that signalled the births of blackholes.
Since its launch, Swift has significantly contributed to the study of GRBs with its precision and longevity. The flashes of gamma-rays that this space-borne telescope studies last only for a few seconds, making it impossible for astronomers to pinpoint and study their sources accurately until more advanced engineering became available. Swift was launched in November 2004 to a low-Earth orbit – and from there, it was able to home in on GRBs bare seconds after they occurred, take multiple readings of its source, and relay the data to Earth so ground-based telescopes could get in on the action.
In the last decade, it has made 1,000 such observations – a truly staggering number for that’s the birth of 1,000 blackholes and 1,000 studies of the birth of blackholes.
Blackholes are born when very massive cosmic bodies – like giant stars – implode under the might of their own gravity. Sometimes, instead of giant stars, the dead cores of two stars that weren’t massive enough collide and merge, forming a blackhole. In both cases, matter from these bodies is expelled violently while jets of particles shoot out from the star’s dying core at almost the speed of light. These jets spike through the expelled matter, and as they reach the surface, they emit gamma-rays, the most energetic form of radiation possible. This burst of radiation, the GRB, is very bright and is focused in the shape of two jets pointing away from the star in opposite directions. Sometimes, a bright flash of light also accompanies the burst because the radiation ionises a nearby (unfortunate) cloud of gas.
The dying star then blows up as a supernova.
Like cosmic bombs
We can study GRBs only when they’re pointed in the direction of the Swift telescope; we don’t observe those pointed in other directions. This means the 1,000 GRBs spotted by Swift are from the minority of blackholes whose beams were pointed at it, and that possibly millions of blackhole births were missed in the same time we took to spot a grand. These gravitational monsters are everywhere and everywhen.
The most telling thing about a GRB’s power is the distance from which its flash can be spotted. Swift’s 1,000th GRB, dubbed GRB 151027B, was spotted on October 27 at a distance of more than 12 billion lightyears – from a time when the universe was less than a billion years old. On April 29, 2009, Swift spotted GRB 090429B at a distance of 13.4 billion lightyears, making it likely the death of one of the first stars in the universe. If there’s something more awesome, it’s that in March 2008, GRB 080319B became the most distant object to be seen by the naked eye: across 7.5 billion lightyears. Scientists would soon calculate that that amount of energy equals the entire energy of the Sun (and “nature’s brightest explosion”).
GRBs typically release about 1,000 times the mass-energy of Earth. They come in two broad varieties: short and long. The long bursts last for at least two seconds and come from heavy stars that are about to go supernova. The shorter bursts, which sometimes last for a few milliseconds, are thought to originate from two the merger of two neutron stars. These ‘stars’ aren’t really stars in the truest sense but are the cores of dead stars that weren’t heavy enough to collapse all the way into blackholes. Still, they’re very, very dense, and when they collide and merge, they emit the short GRB pulse.
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Because of these tremendous energies, it’s important to know how often GRBs occur and where. If one goes off too close to Earth, the radiation could significantly alter the biochemistry of life on Earth (much smaller doses of high-energy radiation are known to cause cancer) and literally carve off the ozone layer. Based on Swift data, scientists estimate that for a galaxy the size of the Milky Way, GRBs occur no more frequently than once every 100,000 years. Moreover, the GRB that’s gone off closest to Earth till date was 130 million light years away, observed in March 2014.
… That’s still scarily close, so more power to Swift! India is also a major host of gamma-ray telescopes in the world, and participates in the better characterising the initial observations that Swift makes. These include the HAGAR Telescope at the Indian Astronomical Observatory, and the Major Atmospheric Cherenkov Experiment telescope, which is the world’s second-largest high-altitude gamma-ray telescope. Both are situated in Ladakh. The site itself is a favourite to install such telescopes because “it has very clear and dark skies almost throughout the year, and a large number of photometric and spectroscopic nights”, according to Pratik Majumdar, Saha Institute of Nuclear Physics, Kolkata. Another gamma-ray telescope is set to come up here in 2018.