Sunday, January 5, 2020

Rare hydrogen gas ring found in distant galaxy with no new stars by Pune astronomers

Astronomers at the Indian National Centre for Radio Astrophysics (NCRA) in Pune have found a galaxy with a large ring of hydrogen wrapped around it, but no stars.

Galaxies comprise of gas, solar systems, cosmic dust and stars. The galaxy observed by the researchers, AGC 203001, is located 260 million light-years away from Earth and shows no signs of star formation at all. This feature was peculiar to astrophysicists considering what is a well-know and widely-accepted model of galaxies and hydrogen rings — a prominent ring of hydrogen gas means more star formation is actively taking place in it.

The pair of strange, luminescent creatures at play in this image are actually galaxies — realms of millions upon millions of stars. This galactic duo is known as UGC 2369. The galaxies are interacting, meaning that their mutual gravitational attraction is pulling them closer and closer together and distorting their shapes in the process. A tenuous bridge of gas, dust, and stars can be seen connecting the two galaxies,, during which they pulled material out into space across the diminishing divide between them.  Interaction with others is a common event in the history of most galaxies. For larger galaxies like the Milky Way, the majority of these interactions involve significantly smaller so-called dwarf galaxies. But every few aeons, a more momentous event can occur. For our home galaxy, the next big event will take place in about four billion years, when it will collide with its bigger neighbour, the Andromeda Galaxy. Over time, the two galaxies will likely merge into one — already nicknamed Milkomeda. Image: ESA/Hubble/NASA

Moreover, the ring is massive — about four times as wide as the Milky Way galaxy, making this starless hydrogen ring only the second of its kind observed in the universe (apart from the huge Leo Ring found in 1983), as per a study in the Monthly Notices of the Royal Astronomical Society. Looking at AGC 203001's large ring in the visible light spectrum astronomers found no readings of stars or starlight from the ring.

Another feature scientists noted was the off-centre position of the ring with regard to the galaxy. While researchers thought this happens by collision with an 'intruder' galaxy, but still results in large amounts of star formation in the resulting hydrogen rings, which wasn't what they noticed with the ring discussed in this paper.

"A collision between two galaxies leads to such an off-centre ring with stars in it. But this was not found in our discovery," lead author of the study, lead author of the study Omkar Bait explained, adding, "We now plan to carry out surveys and study radio emissions of nine similar galaxies that have been shortlisted with similar criteria."

The team of astronomers set out to use the high-sensitivity, high-resolution imaging offered by the Giant Metrewave Radio Telescope (GMRT), and got some fine focus data from the Canada-France-Hawaii-Telescope (CFHT) in Hawaii. There isn’t any clear explanation for why AGC 203001 is starless with a massive hydrogen ring. But scientists intend to take notes and compare AGC 203001 to many other hydrogen gas-rich galaxies where no new stars form.



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