Dark nights spawn chase of brightest

Power cuts hatched dream of boy who tracks universe's most luminous body

By G.S. Mudur
  • Published 6.07.15
Vaidehi Paliya in the Himalayan Chandra Telescope complex in Ladakh

New Delhi, July 5: Vaidehi Sharan Paliya recalls how, as a 10-year-old boy, he would gaze at the stars in the night sky each time power cuts threw his rural home in Ayodhya into pitch darkness.

Those nights laid the seeds for an interest in astronomy that, five years ago, prompted him to quit an automobile engineering job for research and, last year, drew him to the mystery of the most luminous object ever seen in the universe.

Alerted by a midnight digital telegram from Russia, Paliya, a researcher at the Indian Institute of Astrophysics, Bangalore, activated a global campaign to study the puzzling object.

The campaign has led Paliya and fellow astronomers to label the object as a blazar, a super-massive monster black hole at the centre of a distant galaxy that is shooting enormous blobs of plasma in the form of jets aimed directly towards the Earth.

Their observations and calculations suggest that the blazar is powered by a black hole with a mass over 250 million times that of the Sun, and is releasing energy about 500 billion times as much as that emitted by the Sun.

Astronomers have so far catalogued about 1,800 blazars, but this object located about 10 billion light years away displayed such a massive energetic outburst on April 19 last year that for several hours it was the most luminous object in the universe.

"Blazars are known to emit flares, but this one abruptly turned into the most luminous beacon ever observed, showing a luminosity unbelievably high," Paliya, 31, told The Telegraph.

He was on his desk at the IIA close to midnight on April 24 last year when he received the alert, sent through a messaging service called The Astronomer's Telegram, from a research group at the Sternberg Astronomical Institute, Moscow University.

Astronomers use such telegrams to announce interesting observations so that others too can study the fast-changing events. This telegram was titled "Possibly the most powerful persistent object in the Universe..." and called on the astronomical community to initiate multi-wavelength observations.

Paliya and associate professor Chelliah Subramoniam Stalin at the IIA collaborated with other astronomers with an interest in blazars from the Institute of Astronomy in Cambridge, Brera Astronomical Observatory in Italy, Shanghai Astronomical Observatory in China, and the University of Calicut.

The astronomers used the Himalayan Chandra Telescope in Ladakh, an Italian telescope on the Canary Islands, and three Nasa telescopes in space: NuStar, Swift and Fermi Gamma Ray Space Telescope. They have published their findings in The Astrophysical Journal.

"We were able to observe the object only during the decaying phase of its flare," Stalin told this newspaper.

"But its energy emission patterns suggest it is a blazar, and the sudden eruption may have something to do with changes in the magnetic fields associated with its fast-moving jets of plasma."

Astronomers said the blazar appeared unique because it brightened by a huge amount within days.

"The spectrum of this particular blazar differs strongly from (those of) other blazars at similar distances, so it is telling us about a different aspect of their behaviour, (a) potentially different physics," Michael Parker, a research scientist at the Institute of Astronomy in Cambridge, said.

Blazars are associated with what astronomers call active galatic nuclei - galaxy cores that are extraordinarily luminous and are powered by monster black holes. A black hole is the remains of a massive star that has exhausted its fuel and collapsed under gravity to such a dense object that not even light can escape it.

While all galaxies are believed to have black holes at their cores, active galactic nuclei are distinguished by the enormous amount of electromagnetic radiation generated as matter spirals into their black holes.

At times, the matter falling into these black holes is thrown outward into fine beams along the axis of rotation of the black hole, creating what astronomers call jets of plasma. Astronomers define blazars as active galactic nuclei whose jets are pointed towards the Earth.

The IIA team members have now selected a sample of 50 blazars for more detailed observations.

"We'd like to understand the physical mechanisms that drive their jets," said Paliya, who studied mechanical engineering at the Institute of Technology, Varanasi, and joined an automobile manufacturing company before quickly moving to the IIA.

"Blazars are among the farthest of objects known. It's exciting to try and figure out what is going on so far away."