The star had been in hiding. A galaxy sat halfway between it and us, eclipsing it from the Earth's point of view. But when it went supernova last September, astronomers caught the image of the concealed explosion anyhow, all thanks to a cool trick of physics.

Because of a bizarre effect called gravitational lensing explained by Einstein's theory of general relativity, scientists caught four separate images of the supernova in a single picture. Stranger still, the faraway supernova—it lies more than 4.4 billion light years from home—was naturally magnified by 5,000 percent when the scientists first saw it.

This quad-imaged supernova is an extraordinary rarity. So far, it is the only one we have ever seen. It was discovered by sheer chance during a survey of supernovas and other exotic cosmic bodies led by Ariel Goobar, an astronomer at Stockholm University. The scientists unveiled the find in a paper published today in the journalScience.

A zoomed-in view of the gravitationally lensed supernova iPTF16geu. The insets shows a view of the foreground lensing galaxy and on the far right the resolve multiple images of the lensed supernova as observed with the Hubble Space Telescope and the Keck/ Joel Johansson

A Gravitational Lens

So, how could we spot a supernova that's hidden behind a galaxy billions of light years away? And how could we see it four times in a single picture?

In his 1915 theory of general relativity, Albert Einstein outlined how gravity can bend space itself. Like a bowling ball warping the fabric of a tightly pulled sheet, super-massive bodies like galaxies can bend the shape of space to an extreme degree.

The case of our supernova is a cool example. While there's an intervening galaxy eclipsing our direct view of the supernova, that galaxy is also bending the space around it, and that changes the path of any light streaming just around its galactic edges. Thanks to the incredible mass of the galaxy, this effect is so strong that some of the light is bent right back toward Earth. So: When we look just to the left, right, top and bottom of this galaxy, we're actually getting a peek at what's behind it. In a single picture, the supernovae shows up four times. (Another famous example of this effect is a quad-imaged quasar called The Einstein Cross.)

This gravitational lens is also magnifying the supernova, making it appear as if it were 50 times larger than it is.

This effect, galled a gravitational lens, is also magnifying the supernova, making it appear as if it were 50 times larger than it is. This magnifying effect is a bit more straightforward. The supernova is magnified for the same reason that any run-of-the-mill binoculars make distant objects look bigger. Both take light and bend it toward a single point.

The chance of finding a quad-imaged, gravitationally lensed supernova is absurdly small for two reasons. For one, compared to the lifespan of stars, supernova are but brief flickers in the night sky. This one was visible for a little over a month. Secondly, a supernova (or any other object, for that matter) will be gravitationally lensed toward the Earth only if the cosmic alignment is just right. It has to be almost perfectly in line behind a massive body.

To find what scientists unveiled today, you need to find a brief, unexpected flash from a point of origin you can't even see before it happens—and it has to be exactly in line with something super-massive from our perspective. Really, it's no wonder that we've only ever seen three gravitationally lensed supernova before, and only one (today's) that forms four distinct images.

iPTF image of the field where the SN iPTF16geu was found. The insets show zoomed-in patches around the supernova and its host galaxy Joel Johannson

Cosmic Mile Markers

Palomar Observatory in Southern California discovered the strange supernova in September 2016 through a computerized optical telescope that compares snapshots of the sky to find strange new light sources. But because humans (read: grad students) have to slowly sift through what the computer has found to separate interesting discoveries from mistakes, the supernova wasn't caught by human eyes until six days later. Shortly after, the astrophysical community was alerted to the fascinating find, and images of the supernova were snapped by telescopes across the world and in orbit, including the Hubble Space Telescope.

The supernova is more than just a rare and spectacular find. It's also a valuable tool for understanding the makeup of our universe. Supernovae come in flavors, and Goobar's is one called a type Ia supernova. This type of supernova are valuable to scientists because they all look extremely similar.

"The basic idea type is that you can show me two of these supernova, and they're going to look very, very similar. Similar in their peak brightness, similar in how they fade, just very similar properties all around," says Robert Quimby, an astronomer at San Diego State University with the research team.

The supernovas are so uniform because all type Ia supernova start the same way. Simply put, they're Earth-sized cores of former stars that slowly siphon off another star's gas until, boom, they take on too much and detonate in a runaway nuclear meltdown.

Because they all look so similar, says Quimby, they can be thought of as cosmic mile markers. If you see one that's bright, you know it's close. If you see one that's faint, you know that it's far away. And figuring out exactly how far away is a simple calculation, because you know how bright it should be. This gravitational lensing effect, which magnifies the image of the supernova, gives the scientists an opportunity to glean even more information from this cosmic mile marker.

This content is created and maintained by a third party, and imported onto this page to help users provide their email addresses. You may be able to find more information about this and similar content at piano.io