Our picture of cosmic evolution could be challenged by the discovery of a massive galaxy that appears to be lacking dark matter.
Dark matter, which makes up about 85% of the matter in the universe, appears to be absent from the galaxy NGC 1277, which is part of the Perseus cluster. galaxies. The galaxy, located 240 million light-years from Earth, is the first Milky Wayconglomerate-sized conglomerate of stars, planets, dust and gas devoid of dark matter.
“This result does not correspond to currently accepted cosmological models, which include dark matter,” said discovery leader and researcher at the University of La Laguna, Sebastién Comerón, in a statement. statement.
Related: What is dark matter?
Black matter is effectively invisible because it does not interact with light like the everyday matter that makes up stars, planets, and us. Its presence can however be inferred by its gravitational interactions. The existence of this shadowy substance was first postulated when astronomers observed massive galaxies spinning so fast that they would separate if not for the gravitational influence of an invisible mass holding them together.
This fact has led scientists to theorize that all large galaxies are shrouded in a dark matter envelope, and this has become an important assumption in the development of theories of galactic evolution. But the discovery of a galaxy that appears to contain no dark matter challenges that assumption.
Examining a Galaxy of Antisocial Relics
Considered a cosmic relic, NGC 1277 is unusual among galaxies because it has had little interaction with other surrounding galaxies. Galaxies like this are thought to be the remnants of giant galaxies that existed in the primitive universe. As such, these relic galaxies are essential in helping astronomers understand how the first galaxies form.
To help in this line of research, Comerón and his colleagues observed the relic galaxy NGC 1277 with an instrument called an integral field spectrograph. This allowed them to map the motion of the galaxy and determine its mass and how that mass is distributed.
This revealed that the total mass distribution of NGC 1277 – which is expected to include dark matter – was the same as the mass distribution of its daily matter content, i.e. stars, dust, gas and planets. This means that within the radius of the galaxy there cannot be more than 5% dark matter content, but the results are more consistent with a total absence of dark matter in NGC 1277.
This is surprising, because currently favored models of cosmic evolution, including the cosmology standard modelsuggest that NGC 1277 should be composed of 10% to 70% dark matter.
“This discrepancy between the observations and what we expect is a puzzle, and perhaps even a challenge for the standard model,” said Ignacio Trujillo, team member and researcher at the University of La Laguna.
Where did the dark matter of the relic galaxy go?
The scientists behind this revelation have some ideas as to why NGC 1277 is so deficient in dark matter.
“The first is that the gravitational interaction with the surrounding medium within the cluster of galaxies in which this galaxy is located has eliminated dark matter,” said Anna Ferré-Mateu, a member of the team and researcher at the University of La Laguna. “The other is that dark matter was driven out of the system when the galaxy formed by the fusion of protogalactic fragments, which gave rise to the relic galaxy.”
The team is not completely satisfied with either explanation and will therefore continue to investigate NGC 1277 with the William Herschel Telescope (WHT) at the Roque de los Muchachos Observatory on the Canary Island of La Palma.
If these future investigations confirm that this relic galaxy does not have the most mysterious form of matter in the universe, scientists believe that this will not completely call into question the existence of dark matter. Conversely, the team believe they would challenge alternatives to dark matter models, the so-called modified theories of gravity.
“Although dark matter from a specific galaxy may be lost, a modified law of gravity must be universal; it cannot have exceptions,” Trujillo said. “So a galaxy without dark matter is a refutation of this kind of alternative to dark matter.”
Conclusive answers will have to wait, however, Comerón acknowledged. “The puzzle of the formation of a massive galaxy without dark matter remains a puzzle,” concluded the scientist.
The team’s research is published in the journal Astronomy and astrophysics.