Astronomers in Mexico have identified seven large extragalactic radio sources, which are also known by the name giant radio galaxies.
The radio galaxy Centaurus A [Image by NASA/CXC/CfA/R.Kraft et al.; MPIfR/ESO/APEX/A.Weiss et al.; ESO/WFI]
When we think of galaxies, we think of bright swirls of gas, stars, and planets. We mostly think of the light that they emit. However, all the galaxies in the entire universe actually also emit radio wave signals. Part of the radio wave they emit is the light we see. However, there are some galaxies that emit such powerful radio signals that their radio signature is more visible than their light. By mapping out the radio signals, astronomers can also detect these radio signals the same way they detect light from these other galaxies.
The radio galaxy Hercules A [Image by NASA/ESA/S. Baum and C. O'Dea (RIT) - R. Perley and W. Cotton (NRAO/AUI/NSF)/Hubble Heritage Team (STScI/AURA)
The galaxies that emit more visible radio signals are what scientists call radio galaxies. When these galaxies stretch out to about a million parsecs, with a linear length of 3.3 million light years at least, they’re called giant radio galaxies.
A new study describes how researchers analyzed images taken from two recent radio surveys: the Jansky Very Large Array (JVLA) 1-2 GHz Snapshot Survey and the 150-MHz LOFAR Two-metre Sky Survey Preliminary Data Release (LoTSS-PDR). Data from these images provided the researchers with more than 2,000 features, which indicate the presence of giant radio galaxies.
“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 researchers wrote.
Will researchers find more radio galaxies in the future?
The largest radio galaxy of the seven newly-discovered galaxies, designated J1301+5105, is 8.44 million light years wide, and it’s now among the largest known radio galaxies. The largest radio galaxy ever discovered, designated J1420-0545, measures about 16 million light years wide.
Meanwhile, the smallest newly-discovered galaxy is 3.35 million galaxies wide, measuring just above the threshold for it to be considered a giant radio galaxy.
These findings prove that there are more giant radio galaxies in the universe than previously thought. The researchers also showed that observation and the analysis of images can make it possible to discover several of these giant radio galaxies.
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