A team of astronomers from the TIFR-National Centre for Radio Astrophysics (NCRA) has discovered a rare ring of hydrogen gas surrounding a lenticular galaxy, that is located about 260 million light-years away from Earth.
Interestingly, radio emissions from AGC 203001 galaxy originate from a time when dinosaurs thrived on Earth and were observed in December 2017, thanks to the advanced telescopes now available for sky-gazing.
This discovery made use of the Pune-based Giant Metrewave Radio Telescope (GMRT) and Canada-France-Hawaii-Telescope (CHFT) in Mauna Kea, Hawaiian Islands.
Astronomers highlight that the detection of such a galaxy with a hydrogen ring is rare, more so because there were no stars within it. Generally, condensed hydrogen gas acts as a primary source for star formation in any galaxy.
“The optical image of the galaxy AGC 203001 showed no signs of any stars, which is astounding. One of the reasons could be that hydrogen gas is very low in density and its vast expanse could make it unconducive for star formation,” said Yogesh Wadadekar, senior scientist and co-author of the research published on Thursday in the Monthly Notices of the Royal Astronomical Society.
The newly-discovered ring is only the second of its kind ever detected and has a diameter of about four times that of the Milky Way.
Besides stumbling upon such a galaxy with gaseous hydrogen mass settled outside the disc, lead author of the study, Omkar Bait, added that the size of AGC 203001 was as big as the Milky Way.
“The gaseous matter of this galaxy is less than one-100th in mass than what is present within our Milky Way. Whereas, the gas found within the ring is only one-fifth times the total mass found inside the Milky Way,” said Bait, who will soon submit this discovery as his doctoral work.
Scientists still do not know the reasons for this star-less and off-center hydrogen ring around a galaxy.
“Scientifically, a collision between two galaxies leads to such an off-center ring with stars in it. But this was not found in our discovery,” explained Bait, adding, “We now plan to carry out surveys and study radio emissions of nine similar galaxies that have been shortlisted with similar criteria.”
If more such off-center rings are traced, scientists feel that the overall process of the formation of such rings will be better interpreted. “The objective remains to understand the origin of the gas and improve the overall understanding of star formation,” said Wadadekar.
While the Indian team set out to exploit the high sensitivity and high-resolution offered by GMRT, they later collaborated with Pierre-Alain Duc, University of Strasbourg and Jean-Charles Cuillandre of PSL University in France to obtain the CFHT optical image. This study also includes Sushma Kurapati, another Ph.D. student in NCRA-TIFR, who played a role in the radio observations, along with Peter Kamphuis, Ruhr University, Germany and Sudhanshu Barway from Indian Institute of Astrophysics, Bengaluru.
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