Scientists Explain How Light from Stars Cleared Cosmic Fog

The opaque and dense fog between galaxies in the early universe could have been cleared by high-energy light from massive stars, according to a new study.

The study was published recently in the Astrophysical Journal Letters.

About 400,000 years after the big bang, the universe was cooled enough for electrons and protons to come together to form a fog of neutral hydrogen gas. The general belief among astronomers is that early star-forming galaxies might have provided sufficient amount of the required kind of high-energy radiation to evaporate the dense hydrogen fog in interstellar regions. However, they have not been able to find the manner in which that radiation could escape a galaxy.

Now, a dwarf galaxy near our own Milky Way, undergoing a burst of intense star formation and generating massive amounts of ultraviolet radiation, has been reported to have been discovered by astronomers from the University of Michigan.

The researchers used special filters to see where and how the galaxy's extreme ultraviolet radiation, or UV light, was interacting with nearby gas. They found that the UV light is, indeed, evaporating gas in the interstellar medium. And it was doing so along a narrow cone emanating from the galaxy.

The researchers said that within starburst galaxies, a superwind from these massive stars could clear a passageway through the gas in the galaxy, allowing the radiation to escape. They also noted that the shape of the cone was able to help in explaining why similar processes in other galaxies had been difficult to detect.

This feature is relatively narrow. The opening that is letting the UV light out is small, which makes this light challenging to detect. We can think of it as a lighthouse. If the lamp is pointed toward you, you can see the light. If it's pointed away from you, you can't see it, said the study's lead author, Jordan Zastrow of the University of Michigan.

The findings are expected to help astronomers understand how the earliest galaxies affected the universe around them.