Blazar hunters: searching the night sky
The quest to unravel the mystery of the evolution of the universe as seen from the eyes of two astronomers in Bengaluru
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At around 11pm one Friday in April 2014, Vaidehi Sharan Paliya, 31, a doctoral student at the Indian Institute of Astrophysics (IIA), one of Bengaluru’s, and India’s, most respected research institutions, received what’s called an astronomer’s telegram—an email that sends out alerts on time-sensitive events occurring in the universe.
This telegram was from Russia and it spoke of an extraordinarily bright object that had caught Russian astronomers’ attention.
Days earlier, on 13 April, MASTER, a robotic telescope at the Amur Observatory in Russia, had detected this hitherto unobserved celestial object during its daily scheduled survey. Alerted by this, the Russian astronomers kept an eye on it. By 19 April, it had increased in brightness several fold. Indeed, for a brief period, it was the brightest object in the sky.
On 24 April, Paliya scanned existing scientific literature for any information about this object. The only information he could find, based on its location in the night sky, was that the object emitted gamma rays—electromagnetic radiation of very high energy.
Paliya had a hunch that the object could be a blazar, a type of active galactic nuclei (AGN) galaxy (or a galaxy of the early universe). Blazars have an extremely bright and luminous core and emit gamma rays.
To confirm his hunch, Paliya knew, he would have to launch a scientific investigation based on data from telescopes. And time was of the essence. Saturday was a holiday not just for his institute, but for other research institutions around the world. The object itself could fade in days.
Paliya spoke to his doctoral adviser C.S. Stalin, who in turn reached out to a collaborator in England, Andy Fabian, an eminent astrophysicist. Fabian advised them to write a proposal to the US space agency Nasa for a so-called target of opportunity observation. The proposal, if accepted, would give Paliya and Stalin the opportunity for the object to be observed on high priority.
On Monday, 27 April, Stalin and Palia submitted their request to scientists in charge of SWIFT, a Nasa satellite. SWIFT carries out observations on behalf of astrophysicists around the world. The world of modern astrophysics isn’t dominated by men peering into telescopes, but by telescopes that capture data that is then studied by scientists such as Paliya and Stalin. The duo were doubtful whether they would get time on SWIFT. Space telescopes are much in demand.
By 6pm, the scientists at SWIFT approved the request. Paliya and Stalin had time on the satellite. By 8pm, SWIFT had studied the object and sent the data it collected to the Indian scientists. Paliya stayed up till 3am the following day studying the data using algorithms written for the purpose. The object was still emitting gamma rays. At his request, scientists at SWIFT sanctioned and conducted two more observations, on 28 and 29 April.
Meanwhile, Paliya and Stalin reached out to other observatories for more data from telescopes. Scientists in the UK, with access to the NuSTAR telescope, covered the X-ray spectrum for them on 8 May. They also sought and got data from the TNG telescope in Italy. And from the IIA’s own observatory in Ladakh, from where the Himalayan Chandra Telescope covered the optical spectrum for them.
The data was conclusive. The object was a blazar.
The origin of the universe
Blazars are some of the furthest known objects in the universe. For astronomers distance is time, so blazars are from a very distant past. They (and other distant galaxies) hold the secrets to the evolution of the universe.
The discovery of these extragalactic or faraway cosmic objects was made possible by a serendipitous invention, the radio telescope. In 1931, a physicist named Karl Jansky was working to identify and investigate sources of noise or static that may interfere with transmission of shortwave radio signals.
An employee of Bell laboratories in New Jersey, he designed a 100ft antenna to record different types of radio signals. The antenna would rotate, scanning the sky for 20 minutes—it came to be nicknamed Jansky’s merry-go-round—and while studying its recordings, Jansky came across an unusual noise, a faint but persistent hiss.
He had found the first cosmic radio waves from the Milky Way galaxy. His antenna turned out to be the first and most basic form of a radio telescope. His findings were widely reported, including in The New York Times, and the field of radio astronomy took off in the 1940s. With radio telescopes, astrophysicists could see further and deeper into the universe. Many distant radio sources were identified with the help of radio telescopes.
In 1963, in the hallowed corridors of the Mt Palomar Observatory at the California Institute of Technology, Maarten Schmidt, an astronomer, discovered the most distant object observed till then. Named 3C 273, the object was first identified as a radio source in the late 1950s. But it was so bright that it was thought to be a star.
Using the observatory’s 200 inch telescope, Schmidt realized that the bright spectral lines were from different wavelengths, called redshift in scientific parlance. As the light emitted by a cosmic object takes longer to reach Earth, the wavelength gets stretched, and the light appears redder. The farther away an object, the greater the redshift.
Schmidt’s 3C 273 came to be known as a quasar, short for quasi-stellar radio source, since it looks like a star, but was not one. Since then, thousands of quasars have been found, some much farther away than 3C 273.
The discovery of quasars challenged the then prevailing view of the universe. According to the Steady State Theory, the universe was considered more or less uniform. If the theory of Steady State were true, then all types of galaxies would have to be distributed evenly through the Universe, some close and some far away. But quasars were and are only found at great distances, which mean they only existed in the distant past. We are seeing them now as light from an object a billion light years away takes a billion years to reach us.
The great astronomer Edwin Hubble was the first to convince the scientific community that the universe is not in steady state and is actually expanding. His work suggested that the universe had a beginning, when all galaxies were closer, but were now speeding away, giving rise to the Big Bang Theory
Schmidt’s discovery of quasars was another important piece of evidence in favour of the Big Bang Theory, which is still in vogue. In 1978, blazars were categorized as a separate subset of quasars at a conference in Pittsburgh. The term was coined by Ed Speigel, a professor of astronomy at Columbia University, based on a slight difference in the orientation of the object.
Scientists like Stalin are trying to unravel the mysteries of the universe by studying these distant speeding galaxies. And Stalin has a plan, a challenging one that no one has attempted before.
Blazar hunters
Stalin—as evident from his name—is from Tamil Nadu. In the 1960s, the rationalist Dravidian movement encouraged people to name their children after political leaders (preferably left-leaning ones) and scientists. Names such as Livingstone, Kennedy, Lenin and Armstrong are common among people of a certain vintage from the state.
On a sultry day in July, I meet him at his office on the serene campus of the IIA. Outside, in Koramangala, the heaving Bengaluru neighbourhood where the institute is based, life goes on at a frenetic pace. On campus, we could well be in a different planet.
Stalin sits in his austere office, files neatly piled up on the desk, wearing a light blue checked shirt, with sleeves rolled up to the elbow and cream coloured trousers. From the small town of Kanyakumari in Tamil Nadu to a scientist at one of the country’s leading research institutes in astrophysics, his journey has been uneventful but memorable.
Edwin Hubble once said, “Astronomy is something like the ministry. No one should go into it without a calling." But for Stalin, there was no divine call, just a case of fortuitous timing.
After his completing an undergraduate degree in Kanyakumari, Stalin enrolled in a master’s programme in physics at the Madurai Kamaraj University. Back then, he says, teachers were the biggest influence on students. During his master’s programme, he met V.R. Venugopal, a scientist on sabbatical from the Tata Institute of Fundamental Research (TIFR), Mumbai.
Coaxed and inspired by him to try his hand at research, Stalin sent an application for the visiting research programme at TIFR for postgraduate students.
He was accepted and his tenure at TIFR kindled his interest in research. Stalin went onto pursue a doctoral degree at the Aryabhatta Institute of Observational Sciences, Nainital. There, he spent hundreds of nights under the open skies studying quasars.
Quasars are powered by a central black hole and Stalin’s aim was to observe the differences between the central black holes and their immediate surroundings in two types of quasars—ones that emit copious amount of radiation in the radio band and those that emit little or no radio emission.
The Aryabhatta observatory is located on Manora peak, in a sparsely inhabited town, 9km from Nainital, in the Himalayas, 2,000m above sea level. Stalin had to often sit alone in the observatory, braving the cold. In addition, there was the danger of wild tigers and leopards, so he carried a stick with a pointed edge, called a bhalla locally, to protect himself.
After his doctoral degree, Stalin went to study quasars in more detail during post-doctoral stints at Paris and Pune. Qualified as an expert in quasars, it was but a natural progression for Stalin to turn his attention to blazars.
Like quasars, blazars are powered by supermassive black holes which lie at the centre of the galaxy. The blazar discovered by Stalin and Paliya is powered by a black hole that is 250 million times the size of the sun and emits 500 times as much energy.
Like a huge whirlpool, the monstrous gravity of the black hole pulls the surrounding matter in the form of dust and gas towards itself. As this dust and gas settles, they form a disk around the black hole. This accretion disk, as it is known, releases copious amounts of electromagnetic radiation.
Perpendicular to the accretion disk, spurts of powerful jets carrying plasma shoot out in either direction from the core of the active galactic nuclei. In blazars, these jets point toward the Earth, allowing scientists to observe the high energy radiation, the gamma rays emitted from the jet region. It isn’t clear how these jets are formed.
Blazars are extremely variable at all wavelengths; their emission of energy and spectra change on timescales ranging from a few hours to many years. Understanding the relationship of variability at different wavelengths could explain the physical mechanism powering these galaxies and identify the nature of the jets.
Paliya and Stalin want to study this variability. For this, they have earmarked 55 blazars, carefully selected from the known repertoire of blazars, covering a wide range of redshift, some relatively near and some far.
Kavalur
As I stand expectantly under the imposing metallic dome, I feel a sudden jerk. The floor below me shakes for a second and the dome begins to slide open, vertically and horizontally to the cloudy skies above, with a low whirring sound. The stately telescope turns portentously, aiming at an imaginary object in the sky.
“At night, when you are all alone here, this can be pretty terrifying," chuckles Paliya.
I am at the Vainu Bappu Observatory, in the village of Kavalur, Tamil Nadu. The observatory’s prized possession is a 2.3m wide telescope, also named after Vainu Bappu, the first director of the IIA.
For the study of the 55 blazars they have identified, Stalin and Paliya are making use of the optical telescope at the IIA’s observatory in Kavalur, Tamil Nadu.
Kavalur is roughly three hours from Bengaluru. A narrow road off the Bengaluru-Chennai highway through open fields interspersed with tiny houses leads to the base of the Jawadi hills. As the road ascends the Jawadi hills, monkeys saunter along the sides of the road, looking for morsels from vehicles passing by. The observatory itself is in a 100 acre cloistered campus atop the Jawadi hills, 700m above sea level.
Like a hotel, an observatory is all about location. It needs to be at a high altitude, where the air column is less, the weather is fairly controlled, and with the promise of clear skies. And it should be in a secluded place, away from towns so that the light from the ground does not interfere with the night observations.
When Bappu scouted around for a place to host the observatory, he surveyed all of south India before settling on Kavalur. The location is also close to the equator, so both the northern and southern skies can be observed.
Inside the well-landscaped and manicured campus is the Vainu Bappu telescope, a 2.3m wide telescope made indigenously (it was inaugurated in 1986 by prime minister Rajiv Gandhi). A pristine white cylindrical building with a white metallic dome houses the telescope. Inside, curved walls are adorned with framed images of galaxies taken with the telescope over the years. The telescope is held in place with steel rods and pipes just below the dome. A glass enclosure on one side contains the computer controls for the telescope. The telescope is highly sensitive to temperature and moisture so the dome is normally only opened during the nights, and only if there is no threat of rain, not even a drizzle.
As with all optical telescopes, the mirror is the main component that allows astrophysicists to gather light spectra of the cosmic objects. The mirror, manufactured by the IIA, weighs 3.5 tonnes and was carried from Bengaluru to Kavalur carefully in a truck escorted by vehicles on either side. At the time of installation, it was the largest telescope in Asia (the position has now been usurped by a Chinese telescope).
The observatory is a second home to Paliya. Today, he is dressed in a T-shirt, track pants and sports a cowboy hat. There is a big tilak on his forehead, beads around his neck and he’s carrying a long stick.
Paliya and Stalin are ideal partners. Paliya’s infectious enthusiasm is balanced by Stalin’s calm and composed mien. They spar verbally on everything from cosmology to food and politics.
Paliya wants to make a systematic study of the optical spectra of the 55 blazars. He hopes to record the optical spectrum of each blazar on three different nights. He needs a total of 165 clear nights—if the weather gods so wish, he could be done in a year.
But the 2.3m telescope is always in demand. It is open to scientists and amateur astronomers from all over India and it is not easy to have time allotted there. So Paliya has turned his attention to the latest possession of the institute, a smaller, more compact and less powerful telescope. Installed on 19 April 2014, this 1.3m telescope is only accessible to the institute’s students and faculty members as of now.
Manufactured by an American company, DFH, this telescope works exactly like the Vainu Bappu telescope. All the observer has to do is feed in the night coordinates of the target to be observed and the appropriate exposure time on the computer. Once the dome is opened, the telescope automatically turns, aims itself at the target in the sky and records the optical spectra.
Paliya says there could be thousands of blazars in the universe, but they are so faint that with current observational capabilities we cannot detect them. However, if they become brighter for some reason, much like the blazar noticed by the Russians did, they can be discovered.
There’s a theory that this brightening or so-called active state is something that happens to all galaxies. This is a stage when they emit a lot of radiation and spurt powerful jets, but as time passes (at cosmological scale) they fade and become dormant—much like ike our own Milky Way.
If Stalin and Paliya are successful in their endeavour studying blazars, they can gain an understanding of not only the evolution of the universe, but also of where it is heading.
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