Watch the video above: Brad Tucker from The Australian National University explains how astronomers were able to see a supernova four times.
TORONTO – Imagine being able to look back in time at a particular event that took place. Say, for example, the birth of a child. Now imagine being able to see that happen over and over again.
Well, astronomers were excited to have been able to have done just that. Not with a child, but with a supernova, or a powerful stellar explosion.
Using the Hubble Space Telescope, astronomers spotted a supernova that occurred about nine billion years ago. They didn’t just see it once, but four times.
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“I was so excited when I spotted the four images around the galaxy. It was a complete surprise,” explained Patrick Kelly from the University of California, who discovered the supernova during a routine search as part of the project Grism Lens Amplified Survey from Space (GLASS).
Gravitational lensing
How is it possible to see something occur multiple times? The effect is caused by gravitational lensing.
In 1915, Einsten published his general theory of relativity, which in part stated that massive objects can distort space-time. In this case, a large galaxy in the foreground is bending the light from a supernova that is in another galaxy behind it.
“So the light is seen in four images configured like a cross around the elliptical galaxy,” said Anja von der Linden, postdoc at the Dark Cosmology Centre at the Niels Bohr Institute at the University of Copenhagen in a release. “It is called an Einstein Cross after Albert Einstein, who first predicted the phenomenon of gravitational lensing 100 years ago.”
Gravitational lensing is common. Hubble has spotted the warping of galaxies as the light passes through large clusters. And this Einstein Cross has also been seen before, but not with a supernova. The lensing has also made this supernova appear 20 times brighter than it actually is.
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Using Einstein’s theory, we know that time on Earth passes more slowly compared to that just a few thousand kilometres above the planet (to get really nit-picky, it’s different from your feet to your head, but the difference is incredibly minute). That’s because of Earth’s mass, paltry compared to the mass of the galaxy that’s causing this gravitational lensing.
In fact, you likely don’t realize this, but you see this scientific principle in action every day. GPS satellites have to account for this, called time-dilation, with their atomic clocks having to make up for the difference in time.
Scientists are also excited by this new observation because it can tell them more about dark matter, an invisible, yet massive force that astronomers believe accounts for most of the mass in our universe (what we see — the planets, stars, galaxies etc. — only accounts for five per cent of the universe’s mass). This could be used to measure the rate at which the universe is expanding.
The paper is published in the March 6 edition of Science which marks the 100th anniversary of Einstein’s General Theory of Relativity.
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