A galaxy without dark matter

A galaxy without dark matter

A galaxy without dark matter

Given the object's large size and faint appearance, astronomers classify NGC 1052-DF2 as an ultra-diffuse galaxy.

In a first, scientists have discovered a galaxy that is nearly completely devoid of dark matter - the mysterious substance believed to make up most of the universe.The galaxy, known as NGC1052-DF2, has been classified as an an ultra-diffuse galaxy, a relatively new type of galaxy that was first discovered in 2015.

Dark matter, which is invisible, is thought to comprise about a quarter of the universe's combined mass and energy and about 80 percent of its total mass, but has not been directly observed.

Measurements made with Keck and Gemini Observatory, both on Maunakea, the Hubble Space Telescope and others showed that NGC 1052-DF2, an ultra-diffuse galaxy, followed a different path. "It's so rare, particularly these days after so many years of Hubble, that you get an image of something and say, 'I've never seen that before.' This thing is astonishing, a very big blob that you can look through".

Van Dokkum said NGC1052-DF2 is so sparse that "it is literally a see-through galaxy". Based on their observations, they found the mass to be what you'd expect to see from the stars alone, suggesting that the galaxy has no dark matter.

Astronomers have discovered a unique galaxy, from which dark matter appears to be completely missing. These ideas, however, still do not explain how this galaxy formed.

Scientists say that there is about five times the amount of dark matter in a galaxy than regular matter. However you wouldn't expect that galaxy to be as big as this object (it's nearly the size of the Milky Way), and you'd also expect to see some other remnants around from the merger event.

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In recent decades, astronomers have believed that invisible, mysterious dark matter is the dominant aspect of any galaxy.

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". They no longer rule out that there are probably more ways to create a galaxy than just starting from a dark matter core.

Parsing what that means isn't easy, but it does lead to one clear, if counterintuitive, conclusion, the team argues: "Alternatives to dark matter have trouble with this object", van Dokkum said.

And, yet, scientists using telescopes atop Maunakea found one galaxy that has nearly none at all. When van Dokkum and his team found NGC 1052-DF2, they expected to see something similar.

This might seem counterintuitive, but DF2 actually supports the existence of dark matter, which some theories argue doesn't exist. The galaxy was then renamed NGC1052-DF2.

The galaxy is about 65 million light-years away in the constellation of Cetus and is about the same size as the Milky Way. It may have been formed from gas interaction blowing out or into a larger galaxy. For example, they can look at how fast stars cruise around a galaxy. Mysterious "dark matter" makes up the rest. The image also served as a confirmation that galaxies are interconnected through a cosmic web of dark matter.

Assuming the results are right, there are a few theories to explain how galaxies like NGC 1052-DF2 could come together untouched by dark matter's hidden hand. Galaxies like the Milky Way have some 30 times more dark matter than normal matter. The leading dark matter theory predicts that this "sea" of particles moves around a galaxy in deep, plunging orbits like comets around the sun. NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope.

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