The mysterious nature of dark matter has deepened further with a new study that shows it is uniformly distributed across several hundred light-years in two nearby dwarf galaxies—the Fornax and the Sculptor.
Dark matter is invisible, yet its gravitational pull helps bind galaxies together. These two Milky Way neighbors only contain between one and 10 million stars, compared with about 400 billion in our galaxy.
Two astronomers investigated the location, velocity, and chemical composition of around 2,000 stars in these dwarf galaxies, which make ideal study candidates as they contain about 99 percent dark matter and 1 percent normal matter—stars.
“After completing this study, we know less about dark matter than we did before,” said lead author Matt Walker at the Harvard-Smithsonian Center for Astrophysics (CfA) in a press release.
The standard cosmological model of the universe, Lambda-Cold Dark Matter (CDM), comprises slow-moving clumps of dark matter at the centers of galaxies.
“Our measurements contradict a basic prediction about the structure of cold dark matter in dwarf galaxies,” Walker said. “Unless or until theorists can modify that prediction, cold dark matter is inconsistent with our observational data.”
Determining the distribution of dark matter in dwarf galaxies is challenging.
“Stars in a dwarf galaxy swarm like bees in a beehive instead of moving in nice, circular orbits like a spiral galaxy,” co-author Jorge Peñarrubia at the UK’s University of Cambridge said in the release.
The data contradicted the Lambda-Cold Dark Matter model whereby dark matter distribution is expected to increase sharply towards the galaxy centers.
“If a dwarf galaxy were a peach, the standard cosmological model says we should find a dark matter ‘pit’ at the center,” Peñarrubia said. “Instead, the first two dwarf galaxies we studied are like pitless peaches.”
This research suggests that dark matter is not cold or that its interaction with normal matter is stronger than realized. The astronomers plan to elucidate this conundrum by studying other dwarf galaxies, especially those that contain even more dark matter.
Dark matter is invisible, yet its gravitational pull helps bind galaxies together. These two Milky Way neighbors only contain between one and 10 million stars, compared with about 400 billion in our galaxy.
Two astronomers investigated the location, velocity, and chemical composition of around 2,000 stars in these dwarf galaxies, which make ideal study candidates as they contain about 99 percent dark matter and 1 percent normal matter—stars.
“After completing this study, we know less about dark matter than we did before,” said lead author Matt Walker at the Harvard-Smithsonian Center for Astrophysics (CfA) in a press release.
The standard cosmological model of the universe, Lambda-Cold Dark Matter (CDM), comprises slow-moving clumps of dark matter at the centers of galaxies.
“Our measurements contradict a basic prediction about the structure of cold dark matter in dwarf galaxies,” Walker said. “Unless or until theorists can modify that prediction, cold dark matter is inconsistent with our observational data.”
Determining the distribution of dark matter in dwarf galaxies is challenging.
“Stars in a dwarf galaxy swarm like bees in a beehive instead of moving in nice, circular orbits like a spiral galaxy,” co-author Jorge Peñarrubia at the UK’s University of Cambridge said in the release.
The data contradicted the Lambda-Cold Dark Matter model whereby dark matter distribution is expected to increase sharply towards the galaxy centers.
“If a dwarf galaxy were a peach, the standard cosmological model says we should find a dark matter ‘pit’ at the center,” Peñarrubia said. “Instead, the first two dwarf galaxies we studied are like pitless peaches.”
This research suggests that dark matter is not cold or that its interaction with normal matter is stronger than realized. The astronomers plan to elucidate this conundrum by studying other dwarf galaxies, especially those that contain even more dark matter.
The study has been accepted for publication in The Astrophysical Journal.
You can read the research paper here.
