The mystery of dark matter, the non-luminous matter particles undetectable with telescopes, has only deepened when a new study attempted to shed light on the dark, invisible material.
Dark matter, a key actor in the standard cosmological model, is assumed by most astronomers to be consisting of exotic particles clumping together, and its gravitational forces attract normal matter into the cluster to form galaxies. It is thought to make up for 25 per cent of the universe. According to NASA's website, dark matter is not in the form of stars and planets that we see, for observations show that there is far too little visible matter in the universe to make up the 25% required by the observations. And dark matter is not in the form of dark clouds of normal matter, matter made up of particles called baryons.
While dark matter neither emits or scatters light, its existence can derived only from the gravitational effects on visible matter.
After completing this study, we know less about dark matter than we did before, the study's lead author Matt Walker, a Hubble Fellow at the Harvard-Smithsonian Center for Astrophysics, said.
When astronomers observed two Milky Way neighbor dwarf galaxies, Fornax and Sculptor, the results seemed to go against what the standard cosmological model suggests - that the density of the dark matter should sharply increase toward the centers of galaxies. Using computers to simulate the process of galaxy formation, the astronomers found the dark matter scattered over several hundred light-years across in a rather uniform manner.
The new measurements contradict a basic prediction about the structure of cold dark matter in dwarf galaxies. Unless or until theorists can modify that prediction, cold dark matter is inconsistent with our observational data, said Walker.
If a dwarf galaxy were a peach, the standard cosmological model says we should find a dark matter 'pit' at the center. Instead, the first two dwarf galaxies we studied are like pitless peaches, said Jorge Peñarrubia of University of Cambridge, Walker's co-author.
Dwarf galaxies, made of up to 99 per cent dark matter and 1 per cent stars, are ideal targets in unfolding dark matter's mystery. Fornax and Sculptor, each holding one to ten million stars, in contrast to around 400 billion in our galaxy. The small number of stars allows the astronomers to take a comprehensive sample of approximately 1,500 to 2,500 stars and examine their location, speed and basic chemical composition.
Stars in a dwarf galaxy swarm like bees in a beehive instead of moving in nice, circular orbits like a spiral galaxy, said Peñarrubia. That makes it much more challenging to determine the distribution of dark matter.
The new measurements suggest two options: normal matter impacts dark matter more severely than previously thought, or dark matter is not cold, or slow-moving, as widely accepted today.
More studies on dwarf galaxies are expected until the team can determine which is true.
The findings were published in The Astrophysical Journal.