Using a Chinese super telescope, an international team of scientists has discovered a huge cloud of atomic gas that is 2 million light years wide, about 20 times the size of the Milky Way, in which our solar system is located.
The cloud surrounds the “Stefan Quintet,” according to Xu Cong, an astronomer with the Chinese Academy of Sciences National Astronomical Observatories and lead author of the new research.
The Stefan Pentagram is a compact group of 5 bright galaxies in the constellation of Pegasus.
Atomic gas is the primary material from which stars and galaxies are formed, and each “Stefan Five” galaxy is made up of millions of star clusters, four of which actually interact, while the fifth is further from Earth.
The discovery is a mystery and will require astronomers to rethink how gas behaves at the edges of groups of galaxies, according to the Space News website.
Because atomic hydrogen is freer to float through galaxies than other components of an atomic gas cloud, it easily disperses when objects in the galaxy interact with each other. The scattered hydrogen in Stefan’s pentagram is a time capsule that can tell scientists of such events that could be nearly a billion years old.
The cloud is a particularly surprising discovery because astronomers expected ultraviolet light to alter the nature of hydrogen in the cloud.
Ultraviolet light ionizes atoms in a cloud of atomic gas, which means they gain or lose electrons and end up being charged. But the gas observed in the “Stefan pentagon” is not ionized.
The lack of ionization indicates that the gas may be left behind by the formation of galaxies. Aside from the stars, diffuse clouds of atomic hydrogen still exist alone, which could be byproducts of the reactions that formed a galaxy.
It is also possible that the cloud surrounding Stephan’s Pentagram was triggered by an ancient collision between two galaxies.
Although the explanation for the uniform gas is still unknown, the answer could change what we think we know about how galaxies are born and continue to evolve.
