Dark Matter Should Be Everywhere, but This Mysterious Galaxy Has None

Mindy Sparks
March 28, 2018

They found that dark matter is either very sparse or isn't there at all. You typically don't find one without the other. But this is the first time a galaxy that appears to have no dark matter was ever discovered. Now, however, researchers have found a galaxy that seems to have no dark matter at all. In the new study, Yale researchers calculated the mass of the galaxy based on the movements of 10 star clusters inside it, and found that the visible stars can account for nearly all of its mass.

Stacy McGaugh, an astrophysicist at Case Western Reserve University in OH who has worked on both dark matter and MOND and did not work on the paper, disagreed with the idea that this galaxy refutes MOND or bolsters the case for dark matter. Is DF2 a mutant due to its proximity to a much more dominant galaxy, NGC 1042? For example, when two galaxies merge, streams of gas can collide, while the dark matter is thought to pass through without interacting. It is an exceptional find since galaxies are commonly thought to contain more dark matter than the ordinary matter that makes up a galaxy's stars, gas and dust.

Astronomers have found a distant galaxy where there is no dark matter.

Theories that challenge dark matter's existence will need to explain away the new claim about galaxy NGC 1052-DF2 to survive. Scientists only know dark matter exists because they can observe how it pushes and pulls things they can see, like stars.

He also raised the possibility that another galaxy nearby was tweaking NGC 1052-DF2's motion through an element of MOND called the "external field effect".

The Dragonfly team of Roberto Abraham (far left), Pieter van Dokkum (far right), and University of Toronto and Yale graduate students pose with one half of the Dragonfly array at its home site in New Mexico.

Van Dokkum, Abraham, and their colleagues determined the lack of dark matter by measuring the velocity of clusters of stars called globular clusters within DF2 and found they were moving slower than expected. Instead, the clusters were moving at about 28,000 kilometres per hour. Stars and clusters in the outskirts of galaxies containing dark matter move at least three times faster. From those measurements, the team calculated the galaxy's mass. This would allow the gas to form stars away from clumps of dark matter. Gemini revealed that the galaxy does not show signs of an interaction with another galaxy.


They're hoping that these weird objects will help guide theorists like Ostriker and Bullock to better understand what dark matter is. In Dragonfly images, the object had size and structure, but in data from the Survey, the same area looked more like a collection of pinpoints of light than a typical galaxy.

DF2 also lacks the amount of gas and dust prevalent in other galaxies. "It is literally a see-through galaxy". But it doesn't look like an elliptical galaxy, either. It has no dense, central region and no black hole. Based on the colors of its globular clusters, the galaxy is about 10 billion years old. In an email to ZME Science, lead author Pieter van Dokkum explained that there are a few ideas as to how this type of galaxy might come to be, but none of them can truly explain things satisfactorily, and they're not sure how to interpret this discovery. But more detailed observations by the Dragonfly Telephoto Array, a DIY-style observatory cobbled together from Canon camera lenses to study faint, extended objects in the sky, caught van Dokkum and his team's interest. The galaxy is on one end of two extremes, the other anchored by Dragonfly 44, another unusual galaxy discovered by the same team in 2016. "How you actually go about forming one of these things is completely unknown".

But the researchers do have some ideas.

Lying some 63 million light-years from the Milky Way, the elliptical galaxy NGC1052-DF2 seems to be completely made up of normal matter, defying all expectations. Despite it being so elusive, its effects have been identified through several different methods, and there is very strong evidence to suggest that dark matter does exist.

Most paths to explaining NGC 1052-DF2's formation implicate its galactic neighbors. In addition to the dearth of dark matter, DF2 is unusual in another way: it is roughly the size of our Milky Way Galaxy, but contains only 1/200 the number of stars. They are analyzing Hubble images of 23 other diffuse galaxies. Dragonfly has seen other objects that look similar to DF2, says van Dokkum, but they haven't been investigated yet.

While NGC 1052-DF2 doesn't break any fundamental rules of the dark matter theory, Bauer said the galaxy is surprising and unexpected enough to force astrophysicists to develop some new models of how galaxies come together.

The observation also raises questions about how galaxies formed in the first place. "Maybe this is what you would get".

Other reports by Iphone Fresh

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