Look closely at this image, and you might think you’re seeing triple.
A new James Webb Space Telescope photo showcases three copies of the same galaxy cluster hosting a supernova, the brightest and most violent type of space explosion known.
The cosmic triplets aren’t artifacts of a defective telescope but a quirk of nature called “gravitational lensing,” something predicted in Albert Einstein’s General Theory of Relativity over a century ago.
How does gravitational lensing work?
Gravitational lensing happens when a celestial object has such a massive gravitational pull that it warps the time and space around it. NASA often uses the analogy of a bowling ball placed on a foam mattress or trampoline to illustrate how the fabric of spacetime bends. Light that would otherwise travel straight curves and gets distorted as it passes through the warped spacetime.
Gravitational lensing even has the potential to replicate objects, the way a funhouse mirror can create multiple irregular images.
In this case, the galaxy cluster RX J2129, located 3.2 billion light-years from Earth in the constellation Aquarius, is acting like a colossal magnifying glass in the sky. This natural phenomenon allows scientists to see even more distant objects in the cosmos, making them appear brighter. The extra prescription strength of a gravitational lens can help extend the view of Webb, the world’s most powerful space telescope, to see even earlier galaxies.
Gravitational lensing even has the potential to replicate objects, the way a funhouse mirror can create multiple irregular images.
Astronomers are now adept at spotting the telltale effects of gravitational lensing, but that wasn’t always the case. Four decades ago, the concentric arcs of light and stretched celestial objects could be downright confusing. In 1987, an enormous blue arc thought to be hundreds of trillions of miles long was first considered one of the largest objects ever detected in space. The arc was found near the galaxy cluster Abell 370, with another similar object near galaxy cluster 2242-02.
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Later that year, scientists at Stanford University and the National Optical Astronomy Observatory in Arizona sorted out that they were, in fact, optical illusions, distorted by Abell 370. The New York Times’ published a story about the “bizarre” implication of Einstein’s theory, titled “Vast Cosmic Object Downgraded to a Mirage.”
What is a ‘Type Ia’ supernova?
Credit: ESA / NASA / CSA / P. Kelly
The supernova featured in the new image was first discovered using the Hubble Space Telescope. During those Hubble observations, researchers suspected it was a faraway example of a so-called Type Ia supernova. Those involve a white dwarf, the dense remnant of a star that can’t burn nuclear fuel at its core anymore. The white dwarf then strips stellar material away from a nearby star.
When the feeding star reaches about 1.4 times the mass of the sun, it blows up, no longer able to sustain its weight.
There’s a reason scientists are using the Webb telescope, a collaboration of NASA, the European Space Agency, and the Canadian Space Agency, to revisit it. These supernovas have fairly consistent luminosity, so they make handy measurement tools for astronomers: The distance of a Type Ia supernova from Earth is proportional to how bright or dim it appears.
The supernova’s light could help astronomers figure out how much RX J2129 is enhancing background objects. And, in turn, that information about its magnification strength could give researchers a sense of how massive the galaxy cluster is.
