One hundred years ago, astronomy was a small field, limited by the number of observations scientists made while peering through a telescope. With the advent of space telescopes like the Hubble Space Telescope — and the fast computers to analyse inhuman amounts of data — the field has exploded, and the latest results from Hubble are just one example.
Friday, a team of scientists published an image in the journal Science that is unlike anything ever seen before. The image, shown above, is of a powerful type of cosmic explosion called a supernova. And thanks to the crazy way in which gravity manipulates space, Hubble has caught this exact same supernova four times over, indicated by the arrows in the photo above.
A supernova occurs when a massive star — far more massive than our sun — ends its life in a brilliant and explosive display of light. The light from this particular supernova took 9 billion years to reach Earth.
The reason we can see four different images of the supernova is because of the way that gravity distorts the fabric of space. In 1916, Albert Einstein’s general theory of relativity first predicted this behaviour, called gravitational lensing, and astronomers have seen numerous examples of it.
Never before have astronomers seen this kind of effect for a supernova, and the rare image could help improve estimates of dark matter, the elusive, invisible material that makes up a quarter of everything in the universe.
The way gravitational lensing works is when an extremely massive object, like a galaxy cluster, curves the space around it — like the way a bowling ball would curve a trampoline. If you stand on one side of the trampoline and role a marble across to your friend on the opposite side, the marble’s path would not be straight but instead would follow the curve made by the bowling ball.
The same thing happens for light travelling through space. The bowling ball in this case is a galaxy cluster called MACS J1149.5+223 and is located 5 billion light years from Earth. Below is an image showing how the closer galaxy cluster bends light from the supernova toward Earth.
“The massive galaxy cluster focuses the supernova light along at least three separate paths,” Jens Hjorth, from the Dark Cosmology Centre in Denmark and a co-author on the paper, said in a statement released by the European Space Agency. “And then when one of those light paths happens to be precisely aligned with a single elliptical galaxy within the cluster, a secondary lensing effect occurs.”
This secondary lensing effect actually magnifies the supernova so that it appears 20 times brighter than its natural brightness.
Although astronomers can see all four spots of light at the same time right now, it won’t always be the case.
Each speck of light took a different amount of time to reach Earth because it traveled along a different path through space. Therefore, when the light from the supernova blinks out, astronomers will see the dots disappear one at a time.
And by measuring how long it takes between each disappearing act will give the team a better idea of how much dark matter is around the galaxy cluster. Galaxy clusters are thought to form in massive cocoons of dark matter, but it’s difficult to determine just how massive. Rare events like this will help astronomers nail this mystery down and better understand where clumps of dark matter form in the universe and how they affect the way galaxy clusters form and evolve.
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