A massive galaxy with little to no dark matter is puzzling scientists

A massive galaxy that behaves like it has next to no dark matter within it could challenge the current understanding of how the universe works.

This illustration depicts a conventional galaxy (ESO 325-G004) on the right and NGC 1277 on the left on the weighing scale. (instituto de astrofísica de canarias/ NASA)

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An international group of researchers has discovered the first evidence of a massive galaxy with little to no dark matter. The existence of this galaxy calls into question the current standard model of how astronomers believe the universe works.

Dark matter is a form of matter that scientists believe accounts for nearly 85 per cent of all the matter in the universe. It gets its “dark” moniker from the fact that it does not interact in any way with electromagnetic fields, including light and radio waves. It does not absorb, reflect, or emit radiation, which makes it nearly impossible to detect. This is why no experiment has directly detected dark matter successfully.

But then how do we know it exists? Calculations based on observations of various galaxies in the universe show that they would behave differently if they did not contain dark matter. Also, even though dark matter does not directly interact with light, it does have mass. And when there is a large amount of mass, it can bend the space-time continuum, and therefore, light. This “gravitational lensing” done by many galaxies also points towards the evidence of dark matter.

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But a team of scientists have found that the galaxy NGC 1277 does not contain dark matter, or contains very little of it, according to the Instituto de Astrofísica de Canarias in the Canary Islands in Spain.

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In the current standard model of cosmology, massive galaxies contain significant quantities of dark matter. NGC 1277 is a “relic galaxy,” which means a galaxy that shows no interactions with its neighbours.

“The importance of relic galaxies in helping us to understand how the first galaxies formed was the reason we decided to observe NGC 1277 with an integral field spectrograph. From the spectra we made kinematic maps which enabled us to work out the distribution of mass within the galaxy out to a radius of some 20,000 light years,” said Sébastien Comerón, lead author of a study published in the journal Astronomy & Astrophysics, in a press statement.

After studying the mass distribution in the galaxy, the researchers discovered that the mass came from just the distribution of stars. Based on this, they deduced that there cannot be more than 5 per cent of dark matter in the galaxy. In fact, the observations are consistent with the complete absence of dark matter as well.

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But based on the standard cosmological model, galaxies with the mass of NGC 1277 should have at least 10 per cent of its mass coming from dark matter. According to co-author Ignacio Trujillo, this difference between the observations and the predictions is a “puzzle, and maybe even a challenge” for the standard model.

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Dark Matter