A groundbreaking discovery has been made by a team of scientists led by researcher Sebastién Comerón at the IAC and the University of La Laguna (ULL). Their study focused on the galaxy NGC 1277, a massive galaxy several times larger than our Milky Way, which appears to lack dark matter. This finding challenges the widely accepted cosmological models that include dark matter as a significant component of galaxies.
Dark matter is an invisible form of matter that does not interact with normal matter but exerts a strong gravitational pull on stars and nearby gas, which makes its presence indirectly observable. In standard model cosmology, massive galaxies are expected to contain substantial amounts of dark matter. NGC 1277, being a prototype “relic galaxy” with no interactions with neighboring galaxies, is a rare and intriguing target for study. Relic galaxies are believed to be remnants of giant galaxies formed in the early universe.
The team used an integral field spectrograph to observe NGC 1277 and create kinematic maps, revealing the mass distribution within the galaxy up to a radius of approximately 20,000 light years. Surprisingly, they found that the mass distribution was consistent with just the stars’ distribution, suggesting that there might be little to no dark matter present within the observed radius. Cosmological models predict that a galaxy of NGC 1277’s mass should contain at least 10% dark matter, possibly even up to 70%.
Two possible explanations were offered for the lack of dark matter in NGC 1277. One theory suggests that gravitational interactions with the surrounding medium within the galaxy cluster it belongs to might have stripped away the dark matter. The other hypothesis proposes that dark matter was expelled during the galaxy’s formation through the merging of protogalactic fragments, eventually giving rise to the relic galaxy.
However, the scientists found both explanations unsatisfactory, leaving the mystery of how a massive galaxy formed without dark matter unresolved. To further investigate this enigma, the team plans to conduct new observations with the WEAVE instrument on the William Herschel Telescope at the Roque de los Muchachos Observatory on La Palma, Canary Islands.
If the absence of dark matter in NGC 1277 is confirmed, it could seriously challenge alternative models for dark matter, particularly theories that suggest a modification of gravity on large scales. Such modifications should be universal and consistent across all galaxies, making the discovery of a dark-matter-free galaxy a contradiction to these alternative theories.
The study’s implications are groundbreaking, and the team’s findings have been published in the esteemed journal Astronomy & Astrophysics.