New study gives evidence for dark-matter free galaxies


A few years ago, when Pavel Mancera Piña–a PhD scholar at the University of Groningen–along with his colleagues discovered galaxies with little to no dark matter, they were told: “measure again, you’ll see that there will be dark matter around your galaxy.” Dark matter is a form of matter that makes up about 27 per cent of the universe’s mass.

The team used a sophisticated radio telescope called Very Large Array in New Mexico for their study and spent days re-analysing their observations. Their results recently published in the Monthly Notices of the Royal Astronomical Society which confirms that there is no trace of dark matter in the galaxy AGC 114905, located about 250 million light-years away.

When asked if this is the first evidence of a dark-matter free galaxy, Mancera Piña explained: “In recent years, a research group at Yale University has suggested that two galaxies (DF-2 and DF-4) have little or zero dark matter. Some of these claims are seen with skepticism by some other astronomers. Our previous study in 2019 showed six galaxies candidates to have very low dark matter content. In our new paper, we show in detail how one of these six galaxies, AGC 114905, seems indeed to have no room for dark matter, using very high-quality data.”

The researchers list two possible explanations for this lack of dark matter. One is that the AGC 114905 galaxy could have lost or been stripped of its dark matter by nearby larger galaxies.

The other assumption is around the angle at which they think they are observing the galaxy. “We observe galaxies projected at different angles in the sky. Depending on this angle, we should apply a correction to the velocity at which we observe the gas moving. We have measured the inclination of AGC 114905 and applied the corresponding correction,” explained Mancera Piña in an email to indianexpress.com.

However, he cautioned that if for some reason the measurement is off and the inclination of the galaxy is actually lower, they would need to factor in a larger correction that could level some more room for dark matter. But the researchers are confident that their measurements are robust.

The team has planned to obtain more data for more gas-rich ultra-diffuse galaxies like AGC 114905, in particular those that were studied in the 2019 paper in order to see if all of them show the same unusual dark matter properties.





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