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Starts With A Bang

Mostly Mute Monday: A distant galaxy cluster and the power of Einstein’s gravity

The ability for mass to bend and magnify background light is a unique feature of General Relativity. But it can fool us, too.


“Gravitational and electromagnetic interactions are long-range interactions, meaning they act on objects no matter how far they are separated from each other.” –Francois Englert

A century ago, Einstein put forth a new theory of gravity: General Relativity. The solar eclipse of 1919 finally confirmed that mass gravitationally bent light around it.

Images credit: New York Times, 10 November 1919 (L); Illustrated London News, 22 November 1919 (R).

But only much later was the phenomenon of gravitational lensing confirmed: where a distant galaxy cluster acted as a lens, magnifying and distorting the background galaxies behind it.

In 2014, the Hubble Space Telescope imaged an ultra-massive galaxy cluster found by the Sloan Digital Sky Survey, and unveiled what appeared to be a spectacular, multiply-imaged distortion of blue, star-forming background galaxies.

Image credit: NASA, ESA, and G. Tremblay (European Southern Observatory).

The multiple images of similar structures, the distortions and the similar colorations all pointed to gravitational lensing.

Image credit: NASA, ESA, and G. Tremblay (European Southern Observatory).

But a careful analysis of the data showed that while the outer arcs are indeed lensed background galaxies…

Image credit: K. Sharon et al., 2014, via http://arxiv.org/abs/1407.2266.

the brightest blue lights, interconnecting the two giant ellipticals at the cluster’s center, come from the merger of the galaxies and the surrounding gas themselves.

Image credit: NASA, ESA, and G. Tremblay (European Southern Observatory).

What we’re looking at is a combination of the stars and galaxies of the foregrounds cluster, some 4,000 times as massive as the Milky Way, a transient burst of star formation, and only a few background objects.

Despite our excellent intuition, there’s no substitute for good data.

Image credit: NASA, ESA, and G. Tremblay (European Southern Observatory).

Mostly Mute Monday tells the story of a single astronomical phenomenon or object in visuals, images, video and no more than 200 words.

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