Scientists have found dark matter in small clumps
The small clumps of observed dark matter can help us in knowing more about the particles that form them.
Scientists have observed new insights into the nature of dark matter and how it behaves. The new observation using new techniques and the Hubble Space Telescope confirms one of the predictions of the widely accepted theory called 'cold dark matter'. The theory suggests that all galaxies are formed and embedded within clouds of dark matter.
What is dark matter and why it matters:
Dark material is one of the explanations behind the expanding nature of the universe. Scientists theorise it as consisting of slow-moving 'cold' particles coming together to form hundreds of various celestial structures.
How is dark matter detected?
Dark matter is invisible but makes up most of the mass of the universe. It acts as a scaffolding that helps in the formation of galaxies. Scientists detect the presence of dark matter by observing its effect on stars and galaxies.
Where can it be found?
The concentration of dark matter has been detected around large- and medium-sized galaxies but detecting small dark matter formation is difficult. So, scientists have developed theories related to "warm dark matter" that can be imagined as fast-moving particles that form smaller concentrations. But the new theory suggests something different.
Leader of the Hubble survey, Anna Nierenberg says, "Ours provides the strongest evidence yet for the presence of small clumps of cold dark matter. By combining the latest theoretical predictions, statistical tools and new Hubble observations, we now have a much more robust result than was previously possible."
How has dark matter been detected?
Instead of looking at other stars and galaxies for the influence of dark matter, the team targeted eight quasars.
Quasars are bright spots of light far away from the earth. They give more energy than 100 normal galaxies combined. These lights are expected to be coming from galaxies that have black holes at their centre. They observed that the warped light acts as a magnifying lens.
The dark matter clumps:
The dark matter clumps were observed along the line of sight of the quasars and around the lensing galaxies. These observed clumps are 1/10,000th to 1/100,000th times the mass of the Milky Way's dark matter halo. Scientists say that these tiny groupings don't contain even small galaxies.
Therefore, it would have been impossible to detect these dark matter clumps using a transition method that looks into embedded stars.
Gravitational lensing produced four distorted images of each observed quasar. Gravitational lensing is a phenomenon where the light from distant galaxies gets distorted by the gravitational pull of other celestial bodies. These distorted images helped in conducting a more detailed analysis of the dark matter.
Scientists found that dark matter clumps changed the brightness and position of the distorted quasar image. They compared the measurements with a new predicted image of a quasar that has not been distorted by the dark matter.
A team member Daniel Gilman says, "Imagine that each one of these eight galaxies is a giant magnifying glass. Small dark matter clumps act as small cracks on the magnifying glass, altering the brightness and position of the four quasar images compared to what you would expect to see if the glass were smooth.”
The unique emission from the quasars in the background are best seen in infrared light and the earth's atmosphere is opaque in comparison to the infrared light we need to observe. The Hubble space telescope allows us to make these measurements in a galaxy system.
The detection of small structures in the study provides more information about dark matter's nature. "The particle properties of dark matter affect how many clumps form," Nierenberg explained. "That means you can learn about the particle physics of dark matter by counting the number of small clumps,” he added.
But still, we are clueless about the particles that make dark matter.
"At present, there's no direct evidence in the lab that dark matter particles exist," Birrer said.
"Particle physicists would not even talk about the dark matter if the cosmologists didn't say it's there, based on observations of its effects. When we cosmologists talk about dark matter, we're asking 'how does it govern the appearance of the universe, and on what scales?