Kolkata: A team of four Indian astronomers from West Bengal discovers 53 new rare giant radio quasars, 20 to 50 times bigger than the Milky Way. A research paper named “Unveiling New Giant Radio Quasars from the TGSS Sky and Their Large-scale Environment,” published in the The Astrophysical Journal Supplement Series, tells of this.
A team of four Indian astronomers, led by prominent astronomer Dr Sabyasachi Pal of Midnapore City College, recently discovered 369 radio quasars exhibiting enormous radio jets that stretch from approximately 0.2 to nearly 7.2 million light-years using data from the TIFR GMRT Sky Survey (TGSS) at 150 MHz. Of the newly discovered astronomical objects, 53 have been identified as giant radio quasars.
How Bengal’s Astronomers Mapped the Universe’s Longest Radio Jets
Under the leadership of Dr Pal, two young scientists, Dr Souvik Manik from Midnapore City College and Dr Netai Bhukta from Sidho-Kanho-Birsha University, conducted much of the work. Dr Sushanta K Mondal from Sidho-Kanho-Birsha University also contributed significantly to this project. The researchers used the TGSS data because its low observing frequency, wide sky coverage, and high sensitivity of the GMRT (the Giant Metrewave Radio Telescope) make it ideal for identifying such gigantic radio-emitting structures in the distant universe.
Quasars are supermassive black holes, typically containing ten million to a billion times the mass of the Sun, surrounded by intensely luminous disks of gas and dust, and are found at the centers of distant galaxies. Only a small fraction of quasars emit strong radio waves, and most of these radio sources appear compact at radio wavelengths. However, a tiny subset of these rare radio-emitting quasars exhibit enormous radio jets that shine brightly in radio wavelengths, stretching across several million light-years, known as giant radio quasars.
Why Giant Radio Quasars Hold Clues to Black Hole Evolution
Their projected jet lengths span several million light-years. Young scientist Dr Souvik Manik added, “The sizes of these radio jets are not comparable to our solar system or even our galaxy; we are talking about twenty to fifty Milky Way diameters placed side by side.” Galaxies that emit radio signals are called radio galaxies. Each radio galaxy has one or more supermassive black holes at its center. Jets of charged particles are emitted in two directions from the region near these black holes, which are mainly visible at radio wavelengths. The jets from these radio galaxies are sometimes larger than the Milky Way.
At the center of these systems lies a supermassive black hole that draws in the surrounding gas and dust through an accretion disk. As this material spirals inward, it becomes extremely hot and ionized, producing intense magnetic fields in the inner regions of the disk. These fields are believed to channel and accelerate streams of high-energy plasma away from the black hole’s poles, forming powerful relativistic jets that shoot out in opposite directions and travel vast distances through space. Over time, these jets inflate into enormous lobes of radio-emitting plasma that extend far beyond the visible boundaries of their host galaxies. “Their enormous radio jets make these quasars valuable for understanding both the late stages of their evolution and the intergalactic medium in which they expand, the tenuous gas that confines their radio lobes millions of light-years from the central black hole,” said Dr Pal.
Chaotic Early Universe Explains Extreme Jet Asymmetry, Say Researchers
Dr Pal also tells us that the addition of 53 new giant radio quasars significantly expands the known population of such rare objects. The main significance is the size of the newly assembled sample, which is larger than many earlier catalogs. Interestingly, the enormous sizes of these quasars also provide clues about how long jets remain active and how quickly they expand.
Many leading astronomers and research groups have highlighted that uncovering such a powerful and distant quasar provides an important opportunity to study the formation and evolution of supermassive black holes at megaparsec scales as well as the conditions of the early universe and its surrounding environment, jet evolution, and the physical conditions of the young cosmos. Several teams have also remarked that the discovery demonstrates the continued scientific value of archival radio surveys and the capabilities of low-frequency radio telescopes in revealing rare, high-redshift objects.
“It appears that the environment plays a major role in shaping how these radio jets evolve,” comments Dr Bhukta. “In denser regions, the jets might be slowed down, bent, or disrupted by the surrounding gas, while in emptier regions, they can grow freely across the intergalactic medium.” Although most quasars launch two opposing radio jets, the team observed that these jets are often unequal in length or brightness, a feature known as radio jet asymmetry. Regarding this, “This asymmetry tells us that these jets are battling against an uneven cosmic environment,” explained Dr Mondal. “On one side, the jet may be ploughing into denser clouds of intergalactic gas, slowing its growth, while the other side expands freely through a thinner medium.” The team also found that giant quasars at higher redshifts tend to show greater asymmetry than lower-redshift sources. This could be because the early universe was more chaotic and filled with denser gas that distorted the jets’ paths. This observation offers insight into how galaxies and their environments evolved during that era.
Dr Pal informs us that follow-up observations are already underway using the upgraded GMRT and the Very Large Array for further advanced studies. They’re also conducting optical or infrared spectroscopy for precise redshifts and X-ray observations to probe the hot gas around the host galaxies. In this way, discoveries of many new giant quasar models directly strengthen the black hole theory and indirectly improve the modern cosmological models.
