New studies confirm existence of galaxies with little to no dark matter

A survey image taken with the Dragonfly Telephoto Array shows objects within the field of the elliptical galaxy NGC 1052. Image: P. Van Dokkum (Yale University)/STScI/ACS

A survey image taken with the Dragonfly Telephoto Array shows objects within the field of the elliptical galaxy NGC 1052. Image: P. Van Dokkum (Yale University)/STScI/ACS

Scientists had raised doubts about the discovery of a galaxy two years ago, dubbed NGC 1052-DF2, that appeared to contain no dark matter

Researchers from Yale University claim to have found stronger evidence to confirm that galaxies with little or no dark matter do really exist.

Dark matter is a mysterious, hypothetical form of matter, thought to dominate the makeup of galaxies. It is believed to account for about 85 per cent of the matter in the known Universe. 

Scientists also believe that dark matter is possibly composed of some elusive subatomic particles, such as axions, that are yet to be discovered by scientists.

About two years ago, Yale researchers discovered a weird galaxy, dubbed NGC 1052-DF2 (or DF2), which seems to contain almost no dark matter. It was the first time that any such galaxy had been found in the Universe.

While many scientists praised the finding at the time, some also raised doubts about the accuracy of the results.

Now, Yale researchers have come up with two new studies, whose results confirm that their initial observations about NGC 1052-DF2 were correct.

In the first study, researchers took more precise measurements of DF2 using the Keck Cosmic Web Imager installed on W. M. Keck Observatory. With these measurements, the team found that the globular clusters present within DF2 were moving at a speed that matched well with the mass of the DF2's normal matter. The clusters would have moved at much faster speeds had there been dark matter within the galaxy.

In the second study, the researchers discovered another galaxy with very little or no dark matter. It was spotted using the Keck Observatory's Low Resolution Imaging Spectrometer and was labelled NGC 1052-DF4 (or DF4) by the research team.

According to scientists, these two galaxies can be classified as ultra-diffuse galaxies (UDGs), which are similar to the Milky Way in terms of size, but have between 100 to 1000 times fewer stars. Because of that, they appear translucent and are difficult to observe in the Universe.

The new observations suggest that there could be more such galaxies in the Universe.

Yale researchers are currently conducting a wide-area survey using the Dragonfly Telephoto Array in a bid to identify more UGDs. They also plan to examine potential candidates using the Keck telescopes.

The detailed findings of the studies are published in The Astrophysical Journal Letters.

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