Target Dark Matter
A large part of our universe is said to consist of dark matter - most cosmologists share this opinion. But it is well known that it is difficult to observe invisible things and to prove their existence. Now the proof seems to have worked for the first time.
All cosmology is based on the assumption that gravity behaves the same throughout the universe. Just as the sun and earth attract each other in the solar system, the same gravitational force should hold the individual celestial bodies together in galaxies or even clusters of galaxies. The observation, however, taught otherwise. To explain the binding in such large structures either far more matter is required than has been spied so far, or the theory of gravitation devised by Albert Einstein was flawed.
To save Einstein's work, theorists came up with dark matter. Invisible to the telescopes, it should bring the missing gravity and thus avert a changing gravity. The concept was confirmed many times, whether it was about the star movements in spiral galaxies or the dynamics of entire galaxies. But in the end it remained a pure product of thought, without being able to prove its existence. However, astronomers around Douglas Clowe now believe that they have finally unmasked the mysterious mass.
You owe this sensation to a gigantic scenario in space – the collision of two clusters of galaxies. These clusters of galaxies contain most of the usual matter in the form of diffuse hot gas. Only a tenth is in stars. According to the theory, gas and stars are bound by the gravity of dark matter, which exceeds the mass of normal matter many times over. Without them, the fast-moving galaxies and hot gas would be rapidly diverging.
If two clusters of galaxies penetrate each other, the gas in them is subjected to tensile forces similar to air resistance. These slow down the hot gas. The galaxies, however, move on almost unhindered, leaving the gas behind. At that moment, about a hundred million years after the actual collision, the Chandra X-ray satellite was able to view the merging galaxy cluster 1E 0657-56. The images show that the hot gaseous mixture of hydrogen and helium formed into a cloud resembling a projectile as a result of the shock wave from the collision.
The optical images of the galaxies and their surroundings provided the astronomers with less elaborate, but all the more interesting results. So-called gravitational lensing effects were observed on these. The light emitted by distant galaxies is bent by the gravity of an object in front of it. The spectra of the light deflected in this way then allow conclusions to be drawn about the mass distribution of the gravitational lens, in this case galaxy cluster 1E 0657-56. The more the light was deflected, the heavier the cluster.
The scientists found much more matter in the vicinity of the galaxies than in the gas cloud that remained behind. Thus, the gas cannot have been the most massive component in the galaxy cluster - instead, this role is attributed to dark matter, which, unlike the gas, has not slowed down. This would also confirm the previous assumption that it interacts with other particles - whether from ordinary or also dark matter - exclusively via gravitation.
This spatial separation of luminous and invisible matter thus indicates the existence of two fundamentally different types of matter. For astronomers, a strong clue to dark matter.
Now the "only" question is what it actually consists of.