'Bizarre' ghost galaxy discovery stuns scientists

A Hubble Space Telescope image of the galaxy NGC1052-DF2. (Image: NASA; ESA; P. van Dokkum)

Scientists have been stunned by the discovery of a so-called ‘ghost galaxy’ that appears to contain virtually no dark matter, once thought to be a key building block for galaxies.

A team of astronomers from the University of Toronto, Yale University, San Jose State University, University of California Observatories, the Harvard-Smithsonian Center for Astrophysics and the Max Planck Institute in Germany made the discovery. The unique galaxy is about 65 million light-years away.

A light-year, which measures distance in space, equals 6 trillion miles.

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Galaxy NGC1052-DF2, or DF2, is roughly the size of our own Milky Way galaxy, but has only 1/200th of the stars, according to the experts. The Milky Way has hundreds of billions of stars, according to NASA, and enough gas and dust to make billions more stars. Our galaxy also has at least 10 times as much dark matter as all its stars and gas combined.

DF2 was first spotted with the Dragonfly Telephoto Array, a powerful telescope built by experts from the University of Toronto and Yale University. Follow-up observations were made using the W.M. Keck Observatory in Hawaii and NASA’s Hubble space telescope.

The absence of dark matter in DF2 surprised scientists, who published their findings in the journal Nature Communications Thursday. NASA notes that dark matter, an invisible substance, is the “underlying scaffolding” upon which galaxies are built. “It's the glue that holds the visible matter in galaxies — stars and gas — together,” it explained, in a statement on the discovery.

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Experts have described DF2 as “ghostly” as a result of its lack of dark matter and scant stars. This means that distant galaxies are visible through DF2.

“We thought all galaxies were made up of stars, gas and dark matter mixed together, but with dark matter always dominating,” said Prof. Roberto Abraham from the University of Toronto and co-author of the paper, in a statement. “Now it seems that at least some galaxies exist with lots of stars and gas and hardly any dark matter. It is pretty bizarre.”

“This invisible, mysterious substance is the most dominant aspect of any galaxy,” added Pieter van Dokkum, Yale’s Sol Goldman Family Professor of Astronomy, and lead author of the paper, in a statement. “So finding a galaxy without it is unexpected. It challenges the standard ideas of how we think galaxies work, and it shows that dark matter is real. It has its own separate existence apart from other components of galaxies. This result also suggests that there may be more than one way to form a galaxy.”

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Astronomers are now hunting other distant galaxies with similar attributes. “We’re currently undertaking a survey to find more objects like DF2,” said Abraham. “Dragonfly is good at finding these sorts of objects. Maybe we’re only seeing the tip of the iceberg.”

In a separate research project, scientists recently announced the discovery of 15 new planets, including a “super-Earth” that may have liquid water on its surface. Earlier this year, astronomers also confirmed that planets in galaxies beyond the Milky Way had been spotted for the first time.

Follow James Rogers on Twitter @jamesjrogers