By Jof Enriquez
Mexican astronomers have discovered seven new giant radio galaxies (GRGs) through visual inspection of two large-scale radio surveys, which may reveal the existence of more of these massive extragalactic radio sources.
Jonatan Rentería Macario of the Autonomous University of Zacatecas, and Heinz Andernach of the University of Guanajuato, pored over images collected from the JVLA 1-2 GHz Snapshot Survey of SDSS Stripe82, and the 150-MHz LOFAR Two-metre Sky Survey Preliminary Data Release (LoTSS-PDR). They identified more than 2,000 extended features that they used to pinpoint the seven new GRGs.
A GRG is a radio galaxy with a projected linear size larger than one Megaparsec (1 Mpc = 3.09e22 m = 3.3e6 light years). To put it into perspective, the smallest GRG is equivalent to about 33 Milky Way galaxies put side-by-side in a line.
Among the newly discovered group of GRGs, the smallest one was around 3.35 million light years, and most were between 4.08 and 5.09 million light-years. The largest one, designated J1301+5105, has a projected linear size of about 8.44 million light years, which makes it one of the biggest of its kind, according to Sputnik News. In comparison, the largest GRG ever found so far, designated J1420-0545, is nearly twice that long, with a projected linear size of 16 million light years.
"Our results show that current and forthcoming low-frequency surveys with excellent sensitivity to low surface brightness features have a large potential to discover significant amounts of giant radio galaxies, as well as sources of complex or currently unknown types of morphologies," the authors wrote in their paper published on arXiv.org.
Further analysis of survey data could reveal more GRGs, especially radio-faint and distant ones, the researchers said.
Even though thousands of radio galaxies are already known, only about 300 GRGs have been discovered so far, due to their sheer expanse and weak radio luminosity. Astronomers, however, are highly interested in finding more of them to better understand the dynamics and evolution of these extragalactic radio sources.
In July, Indian astronomers discovered 25 GRGs, which indicate these stellar objects may be common than previously thought.
“The fundamental conclusion is that there are probably quite a few of these in the universe,” said Ed Churchwell, emeritus professor of astronomy at the University of Wisconsin-Madison, reported Newsweek.
“A good analogy might be that we know quite a lot about trees, but it's still interesting if someone finds a few very large examples of a particular species of tree,” Steve Croft, from Berkeley’s SETI Research Center, told Newsweek via e-mail.