The mystery behind the unusual “see-through” galaxy discovered using Nasa’s Hubble telescope has only deepened, the US space agency said on Friday. When astronomers first discovered the giant cosmic cotton ball, it looked like the galaxy didn’t have much dark matter, the invisible glue that makes up the bulk of the universe’s matter.
All galaxies, according to Nasa, appear to be dominated by dark matter and astronomers looked for a simpler explanation after they uncovered the oddball galaxy. In a Hubble Space Telescope snapshot of the galaxy, its ancient stars were so spread out that distant galaxies in the background could be seen through it.
“So, finding a galaxy lacking the invisible stuff is an extraordinary claim that challenges conventional wisdom. It would have the potential to upset theories of galaxy formation and evolution,” Nasa said in a statement.
The US space agency said that the ultra-diffuse galaxy, first reported in 2018, is almost as wide as the Milky Way but it “contains only 1/200th the number of stars as our galaxy.” The ghostly galaxy, named NGC 1052-DF2, or DF2, doesn’t appear to have a noticeable central region, spiral arms, or a disk. Determining the amount of the galaxy’s dark matter depends on accurate measurements of how far away it is from Earth.
“I think people were right to question it because it’s such an unusual result. It would be nice if there were a simple explanation, like a wrong distance. But I think it’s more fun and more interesting if it actually is a weird galaxy,” said Pieter van Dokkum, lead researcher of the Hubble observations.
Also Read | ‘Cosmic masterpiece’: New Nasa image shows ‘violent energy’ of Milky Way ‘downtown’
To bolster their original finding, the researchers followed up their initial study. They observed about 5,400 ageing red giant stars using Hubble to calculate a more accurate distance to the galaxy. The red giant stars reach the same peak brightness, so they are reliable yardsticks to measure distances to galaxies.
The researchers estimated that DF2 is 72 million light-years from Earth, which places the galaxy farther than the original Hubble 2018 estimate of 65 light-years distance. Nasa said that the distance measurement solidifies their claim that DF2 lacks dark matter. The galaxy contains at most 1/400th the amount of dark matter that the astronomers had expected.
“So the mystery of why DF2 is missing most of its dark matter still persists,” Nasa added.
