Gravity with a lens effect

The gravitational lens effect can bend, intensify, split and even fan the light into a ring. (Image: Pitris / iStock)

Ghost images in curved spacetime: In the November issue, bild der Wissenschaft reports on the exciting history of the discovery of the gravitational lens effect and its versatile use as a tool in astrophysics. What Albert Einstein originally thought to be undetectable, now provides insights into various secrets of the universe.

The gravitational lens effect is based on the effect of large masses on light. Similar to optical lenses, gravity can deflect radiation and lead to amazing effects. A galaxy, for example, can act as a gravitational lens in the universe. With its gigantic gravity, it influences the light of a source that, from our point of view, lies behind the galaxy. Due to the gravitational lens effect, the position of a star can appear shifted. The force of gravity can bend, intensify, split and even fan the light into a ring. This is how cosmic chimeras can arise – ghost images billions of light years away.

As the bdw astronomy expert Rüdiger Vaas reports in the first article of the three-part title topic, the two discoverers considered the effect 100 years ago for abstract theory and such observations to be unlikely. But in this case Albert Einstein and the British astrophysicist Arthur Eddington should be wrong: in 1979, astronomers detected the first mirage in the sky, which is fooled by a gravitational lens. Since then hundreds of these gravitational phenomena have been discovered in many variations and more are being added.

A helpful effect with an exciting story of discovery

This is no longer just a matter of confirming the theory: the gravitational lens effect found its way into applied research. Astrophysicists and cosmologists use it as an extremely versatile tool to fathom the secrets of the near and far universe. The distortion of light caused by gravity can enlarge distant objects and make them more visible, but it can also provide information about the properties of the “lens”. Vaas explains how the gravitational lens effect is used, for example, in the search for exoplanets, black holes, primeval galaxies, dark matter and the indicators of the cosmos.

In the sub-article “Einstein and the dishwasher”, the author reports on the downright crazy history of the discovery of the gravitational lens effect. Albert Einstein suspected early on that gravity changes light and can lead to distorted images. But he initially shied away from the publication of his theories and first had to be urged to do so by the amateur astronomer Rudi W. Mandl. But colleagues had already gotten ahead of him, reports Vaas.

In the third part, the author then turns to the further history of the gravitational lens effect. Despite Einstein’s doubts, astronomers succeeded in calculating it more precisely and eventually formulated predictions for possible observations on very different scales. Afterwards, however, it took decades before many of these forecasts turned out to be correct, reports Vaas in the article “Ghost images in the sky”.

You can find out more in the November issue of bild der Wissenschaft, which will be available in stores from October 20th.

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