Astronomers have been trying to unlock the secrets to the existence of dark matter in the universe for years and, according to a recent report, they may finally be one step closer to the answer.
After studying four colliding galaxies using the Multi Unit Spectroscopic Explorer (MUSE) instrument on the Very Large Telescope (VLT) in Chile, a team of scientists from England's Durham University have discovered the first evidence that dark forces and dark bosons might actually exist. They combined the data gathered using MUSE with imaging from the Hubble Space Telescope to observe the Abell 3827 cluster, a collection of four galaxies in direct collision with one another.
To find out the exact location of the invisible dark matter, the scientists made use of gravitational lensing, a naturally occurring phenomenon in space first predicted by Albert Einstein in his general theory of relativity.
Lensing happens when the mass of dark matter causes spacetime to distort around the galaxies, which in turn scatters and distorts the rays of light coming from the far away galaxy. This method is also used to locate outer planets near distant stars.
"We used to think that dark matter just sits around, minding its own business, except for its gravitational pull," Richard Massey, the study's chief author from Durham University, said.
"But if dark matter were being slowed down during this collision, it could be the first evidence for rich physics in the dark sector—the hidden Universe all around us."
The researchers found that Abell 3827 has a high amount of dark matter, which is why the space around the four galaxies warps significantly.
They observed that the light that travels to Earth from distant objects in the galaxy pass through the warped area, creating evidence of lensing including arcs of light and double images. This result is used by scientists to measure the unseen matter in Abell 3827.
According to the findings, the dark matter in at least one of the galaxies in the Abell 3827 cluster had separated it from its stars and other visible matter by about 5,000 light-years. The researchers believe that the dark matter in this specific galaxy somehow interacted with dark matter from another, causing it to decrease in speed and create a separation between this galaxy and the normal matter in its area.
This phenomenon is similar to how two photons pass each other. Both particles release photon that is absorbed by the other, causing them to recoil from one another.
One theory suggests that since dark matter is not affected by normal electromagnetic force, a new "dark force" from a dark photon is what possibly caused the repulsion observed in one of the galaxies in Abell 3827.
Astronomers admit that there is still much to learn about dark matter, but they finally know that it exists, and it is believed to be the one keeping galaxies from fragmenting as they rotate.
"We know that dark matter exists because of the way that it interacts gravitationally, helping to shape the Universe, but we still know embarrassingly little about what dark matter actually is," astronomer Liliya Williams of the University of Minnesota said.
"Our observation suggests that dark matter might interact with forces other than gravity, meaning we could rule out some key theories about what dark matter might be," Williams added.
As of the moment, scientists are yet to observe similar self-interacting dark matter in other galaxies. They are now trying to find out more about the origin of dark matter by testing high levels of energy using the Large Hadron Collider. They have also initiated the Dark Energy Survey to create dark matter maps.
The Durham University study is published in the journal Monthly Notices of the Royal Astronomical Society.
Photo: NASA Goddard Space Flight Center | Flickr