Where does this come from, and can I check it?

Their gravity bends light from objects behind them into arcs. The figure is taken from NASA Hubble, which is linked in full on this page. Every fact on Mondo Knows names its source rather than repeating an unsourced claim.

Is this really a space fact?

Yes. It sits on the Space shelf, one of 2,600 sourced facts grouped into space, animals, the human body, history, science and more. Category pages collect every fact in the same field.

What else can I read about it?

The links under the fact point to a quiz, game, puzzle or calculator on the same subject, and the shelf below shows related facts. The wording here is original, and quoted phrases are marked as quotations.

Mondo Knows Facts

Galaxy clusters act as magnifying lenses

Their gravity bends light from objects behind them into arcs General relativity predicts that mass curves space, so light paths bend near heavy objects. Astronomers use the effect to see galaxies otherwise too faint and far. The technique gave the first estimates of dark matter in clusters. It sits in Mondo's space collection, one of 200 facts that each trace back to the reference below.

Where this comes from

NASA Hubble

Facts that can change over time are reviewed and updated. If something here looks wrong, Mondo would rather know than be confidently incorrect.

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Science trivia

More facts like this

The Milky Way will collide with the Andromeda GalaxyIn four billion years our home galaxy will merge with its nearest large neighbour The observable universe contains septillions of starsAstronomers estimate there are more stars in space than sand grains on Earth The Hubble Deep Field uncovered thousands of distant galaxiesFocusing on a tiny patch of dark sky revealed deep cosmic history The Milky Way belongs to a cluster of over fifty galaxiesThe Local Group spans ten million light-years and is led by Andromeda Galaxies across the universe are arranged in a vast cosmic webGravity arranges billions of galaxies along dark matter filaments and voids A teaspoon of neutron star matter weighs a billion tonnesThe material is compressed to the density of an atomic nucleus

Tags: gravity, lensing, galaxies

Galaxy clusters act as magnifying lenses: the short answers

Where does this come from, and can I check it?: Their gravity bends light from objects behind them into arcs. The figure is taken from NASA Hubble, which is linked in full on this page. Every fact on Mondo Knows names its source rather than repeating an unsourced claim.
Is this really a space fact?: Yes. It sits on the Space shelf, one of 2,600 sourced facts grouped into space, animals, the human body, history, science and more. Category pages collect every fact in the same field.
What else can I read about it?: The links under the fact point to a quiz, game, puzzle or calculator on the same subject, and the shelf below shows related facts. The wording here is original, and quoted phrases are marked as quotations.