Astronomers observe intra-group light, an elusive glow between distant galaxies

tech.hindustantimes.com:

An international team of astronomers have turned a new technique onto a group of galaxies and the faint light between them known as 'intra-group light' to characterise the stars that dwell there.

Lead author of the study published in MNRAS, Dr Cristina Martinez-Lombilla from the School of Physics at UNSW Science, said "We know almost nothing about intra-group light.

"The brightest parts of the intra-group light are ~50 times fainter than the darkest night sky on Earth. It is extremely hard to detect, even with the largest telescopes on Earth -- or in space."

Using their sensitive technique, which eliminates light from all objects except that from the intra-group light, the researchers not only detected the intra-group light but were able to study and tell the story of the stars that populate it.

"We analysed the properties of the intra-group stars -- those stray stars between the galaxy groups. We looked at the age and abundance of the elements that composed them and then we compared those features with the stars still belonging to galaxy groups," Dr Martinez-Lombilla said.

"We found that the intra-group light is younger and less metal-rich than the surrounding galaxies."

Not only were the orphan stars in the intra-group light 'anachronistic' but they appeared to be of a different origin to their closest neighbours. The researchers found the character of the intra-group stars appeared similar to the nebulous 'tail' of a further away galaxy.

The combination of these clues allowed the researchers to rebuild the history -- the story -- of the intra-group light and how its stars came to be gathered in their own stellar orphanage.

"We think these individual stars were at some points stripped from their home galaxies