Starless hydrogen ring around distant galaxy discovered by researchers at NCRA, Pune
The galaxy (named AGC 203001), is located about 260 million light-years away from earth
A team of astronomers from the National Centre for Radio Astrophysics (NCRA), Pune, discovered a “mysterious” ring of hydrogen gas around a distant galaxy, using the Giant Metrewave Radio Telescope (GMRT), said Omkar Bait on Thursday, who is the lead author of the study published in the journal Monthly Notices of the Royal Astronomical Society.
Bait along with professor Yogesh Wadadekar, and five others, all co-authors, who were part of the study, said that the ring is much bigger than the galaxy it surrounds, and has a diameter about four times that of our Milky Way.
The galaxy (named AGC 203001), is located about 260 million light-years away from earth.
Bait, who led the study, is a PhD student at NCRA-TIFR working under the supervision of Wadadekar while Sushma Kurapati, also a PhD student in NCRA-TIFR played a role in the radio observations along with scientists Pierre-Alain Duc (Universite de Strasbourg, Strasbourg, France); Jean-Charles Cuillandre (PSL University, Paris, France); Peter Kamphuis (Ruhr University, Bochum, Germany) and Sudhanshu Barway (Indian Institute of Astrophysics, Bengaluru).
“There is only one other such known system with such a large neutral hydrogen ring. The origin and formation of such rings is still a matter of debate among astrophysicists. Neutral hydrogen emits radio waves at a wavelength of about 21cm. This radiation from neutral hydrogen atoms has allowed us to map the amount and distribution of neutral hydrogen gas in our Milky Way galaxy and in other galaxies in the Universe. Typically, large reservoirs of neutral hydrogen gas are found in galaxies which are actively forming new stars. However, despite showing no signs of active star formation the galaxy AGC 203001 was known to have a large amount of hydrogen, although its exact distribution was not known,” said Bait.
The unusual nature of this galaxy motivated astronomers in NCRA-TIFR to use the GMRT to conduct high resolution radio observations of this galaxy to find out where in the galaxy this gas lies.
The GMRT observations revealed that the neutral hydrogen is distributed in the form of a large off-centered ring extending much beyond the optical extent of this galaxy, said Bait, while adding, “It was more puzzling when we found that the existing optical images of the ring showed no sign of it containing stars. In collaboration with two French scientists, Pierre-Alain Duc and Jean-Charles Cuillandre, the NCRA team obtained a very sensitive optical image of this system using the Canada-France-Hawaii-Telescope (CFHT) in Hawaii, USA. However, even these images do not show any sign of starlight associated with the hydrogen ring.”
“There is no clear answer today as to what could lead to the formation of such large, starless rings of hydrogen. Conventionally, galaxy-galaxy collisions were thought to lead to the formation of such off-centered rings around galaxies. However, such rings also generally contain stars. This is contrary to what is found in this ring. Figuring out how this ring was formed remains a challenge for astronomers. Encouraged by this discovery, our team is now conducting a large survey to map the neutral hydrogen around several more similar galaxies. If some of them also show rings like this, it should help us to better understand the formation of such elusive rings,” said professor Wadadekar.
The, journal in which the study was released, publishes the results of research in positional and dynamical astronomy, astrophysics, radio astronomy, cosmology, space research and the design of astronomical instruments.