New confirmations that the galaxy NGC 1052-DF2 contains very little dark matter

The galaxy NGC1052-DF2 (Image NASA, ESA, Z. Shen and P. van Dokkum (Yale University), and S. Danieli (Institute for Advanced Study))
The galaxy NGC1052-DF2 (Image NASA, ESA, Z. Shen and P. van Dokkum (Yale University), and S. Danieli (Institute for Advanced Study))

An article published in “The Astrophysical Journal Letters” reports a precise measurement of the distance of the galaxy NGC1052-DF2 that was used to confirm that it’s almost devoid of dark matter, a notable anomaly. A team of researchers led by Pieter van Dokkum of Yale University used the Hubble Space Telescope to observe the red giants on the outskirts of NGC1052-DF2 using them as “standard candles” taking advantage of the fact that they all reach the same peak in brightness. Understanding why so few of the gravitational effects attributed to dark matter are detected in this galaxy may offer new clues to its nature.

An article published in March 2018 in the journal “Nature” reported research on the ultra-diffuse galaxy NGC 1052-DF2. Measuring the velocity of 10 globular clusters within it allowed estimating its overall mass. The surprise came from the fact that the estimate indicated the presence of dark matter 400 times lower than expected. In practice, the results indicate that NGC 1052-DF2 contains very little dark matter.

Pieter van Dokkum, who led the team that conducted that research, and some of his team members continued to study the galaxy NGC 1052-DF2. A precise measurement of this galaxy’s distance is important because the brightness we detect depends on it and the brightness allows us to estimate the mass of the stars within it. The gravitational effects that are generally detected in a galaxy are much stronger than those justified by the common matter present, hence the dark matter theory. If a galaxy is closer than estimated, it means that the stars inside it are less massive than estimated and that the amount of dark matter inside is greater than estimated.

The new results based on the brightness of the red giants on the periphery of the galaxy NGC1052-DF2 confirm the conclusions published in 2018. Meanwhile, Pieter van Dokkum and his collaborators discovered another galaxy almost devoid of dark matter in the same group, NGC1052-DF4. In both cases, one hypothesis is that the dark matter was snatched by a neighbor.

According to the researchers, these results confirm the existence of dark matter. This may seem paradoxical but the reasoning is that if the hypothesis of a modified gravitational law were correct, the effects should be detected in the galaxies NGC1052-DF2 and NGC1052-DF4 as well. Instead, the results indicate that something is missing in those galaxies. Other alternative models can be tested, meanwhile, research will continue to try to explain these anomalous cases and in the hope of finding other galaxies with very little dark matter to increase the available data.

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