“It Shouldn’t Exist” –The Galaxy With No Dark Matter


Galaxy without Dark Matter


“It really is quite uncomfortable. It shouldn’t exist; it shouldn’t be real,” Marla Geha, an astronomer at Yale University , said in 2018 of a small, strange galaxy a small galaxy that seems to contain none of the invisible stuff known as dark matter. “Yet if you look at the data, that’s the conclusion you’re drawn to.” Astronomers have long noticed an invisible elephant in the room — so-called dark matter, which seems heavier than all the visible stars, gas and dust in the cosmos by a ratio of 6-to-1.

Since dark matter it interacts gravitationally like regular matter, there has been speculation that some galaxies may contain lots of dark matter, but very little visible matter. These “dark galaxies,” such as Triangulum II, a small galaxy on the edge of our Milky Way, wouldn’t be particularly bright, but they would be distinguished by their strong gravity.

In contrast, galaxy NGC 1052–DF2, a half-transparent smear of light 65 million light-years away in the constellation Cetus, hosts some 200 million suns’ worth of stars, and negligible amounts of gas and dust. And that’s it. According to the 2018 study by Yale astronomer Pieter van Dokkum and colleagues, the galaxy’s visible matter accounts for its entire mass, a commonsense conclusion that turns out to be deeply strange.

The Weirdness of Dark-Matter Free Galaxies

Today, a group of researchers from the Instituto de Astrofísica de Canarias (IAC) cleared up the 2018 mystery: The existence of NGC 1052–DF2 “sans dark matter.”

According to an article published in the Monthly Notices of the Royal Astronomical Society (MNRAS) a group of researchers at the Instituto de Astrofísica de Canarias (IAC) has solved this mystery via a very complete set of observations of KKS2000]04 (NGC1052-DF2). Galaxies with no dark matter are impossible to understand in the framework of the current theory of galaxy formation, because the role of dark matter is fundamental in causing the collapse of the gas to form stars. In 2018, a study published in Nature announced the discovery of a galaxy that apparently lacked dark matter.

The researchers, perplexed because all the parameters that depended on the distance of the galaxy were anomalous, revised the available distance indicators. Using five independent methods to estimate the distance of the object, they found that all of them coincided in one conclusion: The galaxy is much nearer than the value presented in the previous research.

The original article published in Nature stated that the galaxy is at a distance of some 64 million light years from the Earth. However, this new research has revealed that the real distance is much less, around 42 million light years.

Thanks to these new results, the parameters of the galaxy inferred from its distance have become “normal,” and fit the observed trends traced by galaxies with similar characteristics.

“We Have No Idea of Why They Exist” –Weird Dark-Matter-Free Galaxies 

The most relevant datum found via the new distance analysis is that the total mass of this galaxy is around one-half of the mass estimated previously, but the mass of its stars is only about one-quarter of the previously estimated mass. This implies that a significant part of the total mass must be made up of dark matter. The results of this work show the fundamental importance of the correct measurement of extragalactic distances. It has always been one of the most challenging tasks in astrophysics—how to measure the distances to objects that are very far away.

The Daily Galaxy, Max Goldberg, via Instituto de Astrofísica de Canarias (IAC)

Image credit: Galaxy missing dark matter via Arxiv.org

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