Astronomers have identified as many as six dark galaxy candidates located some 12 billion light-years away from Earth. Unlike other galaxies that bustle with stellar bodies and have a lot of stars, the dark galaxies are almost devoid of stars. They are inefficient at forming and igniting stars.
The star-less dark galaxies are filled with great amount of matter and gas. They are very difficult to detect and study as they emit little visible light. It is believed that these systems formed an integral part of the galactic formation, as they are expected to be around from during the early days of our universe.
The research team led by physicists at ETH Zurich used a combination of an old technique and new technology to make the discovery. The team found the dark galaxies by leveraging capabilities of quasars which make for some of the brightest objects in our universe. The light that these objects emit is the result of the friction produced in the accretion disk of gas and stars surrounding it.
Quasars give off intense ultraviolet light that fluoresces nearby hydrogen atoms, giving an emission called Lyman-alpha line. The resulting light allows the astronomers to see if any dark galaxy, full of hydrogen, is located in close proximity of the quasar.
“The signal from any dark galaxies in the vicinity of the quasar gets a boost, making them visible,” the researchers noted.
Back in 2012, astronomers detected several possible dark galaxies by applying the same technique using European Southern Observatory’s Very Large Telescope. In 2014, the same telescope was upgraded with Multi Unit Spectroscopic Explorer or the MUSE instrument, which helped the astronomers peer into the neighborhood of quasars and find the six galaxies.
The researchers identified 200 sources of Lyman-alpha light and distinguished the six potential dark galaxy candidates from among them. They observed each of the six quasar fields for ten hours.
The study was published in the Astrophysical Journal.