Astronomers Spot Distant Galaxy Surrounded By Mysterious Hydrogen Gas Ring

A galaxy called AGC 203001 is about 260 million light-years away from us, and a team of astronomers from the National Centre for Radio Astrophysics in Pune, India discovered something rather mysterious about it. Using the Giant Metrewave Radio Telescope (GMRT), they discovered that AGC 203001 is surrounded by a massive ring of hydrogen gas that is unlike other hydrogen gasses in other galaxies.

AGC 203001

The astronomers’ GMRT observations revealed that the hydrogen gas around AGC 203001 is distributed in the form of an off-centered gas ring that is so massive it is much bigger than the galaxy it is surrounding. In fact, the gas ring has a diameter of about 380,000 light-years or approximately four times the size of the Milky Way.

Typically, such large amounts of neutral hydrogen gas around galaxies are found in ones that are actively forming stars. However, the astronomers found that AGC 203001 actually presented no signs of active star formation, something that was confirmed by sensitive optical images of the system using the Canada-France-Hawaii-Telescope (CFHT) in Hawaii, USA.

Specifically, CFHT observations did not find any evidence of starlight associated with the hydrogen ring.

Mysterious Gas Rings

Such gas rings are very rare, and in fact, the Leo Ring is the only other system with a similar extended hydrogen ring.

Typically, off-centered gas rings around galaxies are believed to be formed by collisions between galaxies, but such rings generally show signs of star formation. Given their findings, the astronomers also present various possible explanations for AGC 203001’s mysterious gas ring, from the host galaxy being a hydrogen-rich one to a strong shock during a collision that eventually prevented star formation.

That said, there is so far no clear answer to what might have caused the hydrogen gas ring to form, and the astronomers note that such rare rings are still poorly understood. As such, in future studies, they aim to conduct large surveys to map the neutral hydrogen around other similar galaxies. This way, if they find more of such hydrogen gas rings, it would help them better understand the mechanisms that cause them to form.

The study is published in the Monthly Notices of the Royal Astronomical Society.