The curvature of spacetime around a huge mass has provided the most detailed measurement yet of the cosmic distribution of dark matter.
With the help of gravitational lenses, a team led by cosmologist Kaikitaro Inoue from Kindai University in Japan has mapped mysterious forms of matter at the smallest scale ever seen, with a resolution of just 30,000 light years. .
It may seem large, but when you consider the area of the Milky Way, 100,000 light years in diameter, it’s more impressive. Researchers have successfully mapped something we can’t even see across more than 7.5 billion light-years, down to a scale less than one-third the size of a galaxy. That’s amazing.
This analysis relied on the fortuitous alignment of cosmic objects known as gravitational lenses. Space-time bends around a giant body, just as a depression forms under your body when you sit on a trampoline. When you roll a marble on a trampoline mat, the marble curves along a rounded surface instead of in a straight line.
A similar thing happens to light flowing through space when it encounters the curved spacetime around large objects such as galaxies and galaxy clusters. So, for example, if there is a distant galaxy behind one of these objects, the light from the more distant galaxy will be distorted and expanded as it travels through the curved spacetime.
One reason this is great is because it allows scientists to study distant galaxies in much more detail than they could without the lens. But how the light is distorted and blurred can also reveal the distribution of gravity within the foreground lens.
As it turns out, this is a great way to find out where dark matter is hiding. We don’t know what dark matter is. Since they do not emit light, they cannot be detected directly. What we do know is that there is an invisible mass in the universe that creates excess gravity. We can detect that gravitational influence, so we can track where the mass is lurking.
This still doesn’t tell us what dark matter is, but figuring out where it is can help us understand how it works. In the case of gravitational lensing, if we subtract all the normal matter (i.e. galaxies) from the mass distribution deciphered from the distorted light of background objects, what remains is dark matter.
This is what Inoue and his colleagues did using a gravitational lensing galaxy called MG J0414+0534. This galaxy is so far away that it took about 11.3 billion years for its light to reach us. If you sit a little closer, the lens galaxy in the foreground distorts the light and splits it into four images.
The positions of these segmented images are not completely explained by lensing of the visible portion of the foreground galaxy. So researchers used the powerful Atacama Large Millimeter/Submillimeter Array and new analysis techniques to subtract the contribution of the visible part of the lenticular galaxy to the distorted light from MG J0414+0534, and to detect the dark matter in the lenticular galaxy. We have created a more detailed map of. .
The resulting map supports the theory that there are large clumps of dark matter within and between galaxies, as predicted by the cold dark matter theory. For the first time, this theory has been shown to be consistent even on scales smaller than galaxies.
Researchers say this represents a powerful new tool to aid the quest to understand dark matter. Efforts to constrain its properties have been hampered by the inability to resolve its distribution at scales smaller than galaxies. Doing so could help scientists narrow down their options as to the identity of the mysterious ubiquitous mass.
This research astrophysical journal.