Explaining Gravitational Lensing Without Dark Matter

Investigators know that massive galaxies and clusters can be used as gravitational lenses in surveying whatever space structures are behind them. But astrophysicists are now looking for methods to explain the mass of the “lenses” without turning to dark matter for the solution.

The main phenomenon underlying gravitational lensing is light distortion. The clusters and massive galaxies that act as lenses are so heavy, that their gravitational pull is tugging on light passing through and around these objects.

This literally bends the light, distorting and magnifying the image of all bodies lying beyond that particular cluster or galaxy. In most regards, the objects act as gigantic lenses in space, hence the name.

But astrophysicists have calculated that the amount of lensing – how much the light is bent when under the influence of clusters and galaxies – cannot be explained by the visible mass of the objects alone.

Some have proposed using dark matter for explaining this phenomenon, which is known as the “over-concentration problem.” Though using the spacial form of matter is easier, experts want to see if they can explain the differences in other manners.

The problem is that the amount of lensing massive space objects are capable of producing is a lot larger than experts calculated based on the mass the objects contain. This mystery cannot be readily solved without introducing dark matter into the mix.

Experts have recently developed a new method for detecting galaxy clusters for future studies, which is called the Sunyaev-Zel’dovich (SZ) effect. It revolves around searching for distortions in the Cosmic Microwave Background (CMB) by looking for inverse Compton scattering patterns.

Using this technique, what astronomers are seeing are interactions between CM photons and highly-energized electrons in the giant structures.

This allows investigators to see both clusters visible in the optical portion of the electromagnetic spectrum, as well as clusters that may have red-shifted into the radio spectrum.

Researchers are currently using SZ effect measurements to determine if the amount of mass in the clusters can be predicted without using dark matter. If so, some assumptions about how clusters form may need revising.

One of the most interesting consequences of the new studies was the discovery of the fact that the current dark matter model cannot account for the amount of dark matter that actually exists in the clusters, if we're to consider the possibility.

More of the stuff can be found in clusters than the Lambda-Cold Dark Matter model holds, which means that the model may need some revising, Universe Today reports.