science & techESA/Hubble

A massive galaxy cluster acts as a natural magnifying glass for light from the early universe

the gist

Gravitational lensing happens when a massive object bends the space around it, so light from objects behind it follows curved paths. Here a foreground galaxy cluster, named SDSS J0915+3826, works like a giant magnifying glass, amplifying light from galaxies whose light has taken up to 11.5 billion years to reach us. Astronomers used this natural lens to measure the sizes, brightness and star formation rates of individual clumps inside those distant galaxies. Those galaxies formed when the universe was young, so they offer a rare close look at its early history.

how it works

Mass bends spacetime, and light follows the bent path. A massive cluster therefore focuses and stretches the light of galaxies directly behind it, making them appear brighter and larger than they really are.

so what

Lensing lets telescopes study objects too faint or distant to see otherwise, turning clusters into natural telescopes. It has become a key method for mapping dark matter and studying the first galaxies.

ESA/Hubble · CC BY 4.0

Image: ESA/Hubble & NASA Acknowledgement: Judy Schmidt ( geckzilla.com )