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Astronomers find six dark galaxy candidates -- galaxies with few stars

By Brooks Hays
Astronomers find six dark galaxy candidates -- galaxies with few stars
The dark galaxy candidates were identified with the help of the Very Large Telescope, located in Chile. Photo by ETH Zurich

May 23 (UPI) -- Scientists have found six new dark galaxy candidates -- galaxies with few or no stars. As one can imagine, these starless, or near-starless, candidates aren't very bright, making them extremely hard to find.

Astronomers are interested in understanding how galaxies form, as well as how stars emerge from the diffuse gas of the intergalactic medium. Dark galaxies promise insights into these mysteries. Unfortunately, dark galaxies are still only hypothetical.

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If confirmed, dark galaxies could offer astronomers a glimpse of galaxies before star formation begins in earnest. The theoretical galaxy consists of gas and dark matter, but has yet to develop the ability to form stars with any regularity.

To study dark galaxies, scientists first have to find them, and a team of astrophysicists at ETH Zurich have developed a technique for doing so. To locate the six dark galaxy candidates detailed in their new paper -- published in the Astrophysical Journal -- the scientists used quasars as a flashlight.

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Quasars are extremely luminous supermassive black holes. Their accretion disks emit ultraviolet light. The high-energy rays trigger a fluorescent emission in hydrogen atoms called the Lyman-alpha line. The pulses from quasars make nearby dark galaxies briefly visible.

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Scientists have previously used a similar technique to look for dark galaxies, but researchers ETH Zurich targeted quasars farther away than has previously been possible. They also rendered the nearby dark galaxy candidates in a full spectral profile.

"Our integral field survey provides a nearly uniform sensitivity coverage over a large volume in redshift space around the quasars as well as full spectral information at each location," researchers wrote in their paper.

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Their efforts revealed six strong dark galaxy candidates out of a total of 200 Lyman-alpha emitters.

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