NOVA

Talitha Williams

The more astronomers looked, the more dark matter there seemed to be. But how much is there? And where exactly is all this mysterious stuff? Astrophysicist Priya Natarajan is trying to find out.

Priya Natarajan

I have worked my entire career trying to understand the nature of dark matter.

Williams

But how do you understand what you can't see? Luckily, this invisible dark matter gives itself away because it has a habit of playing tricks with light.

Natarajan

In 2014, with the Hubble Space Telescope, a very intriguing kind of object was observed.

Williams

It appeared to be a galaxy with four exploding stars, called supernovae, going off at the same time.

Natarajan

Like, four evenly spaced supernovae.

Williams

In reality, there was only one supernova. But it somehow shows up in four different places. What's going on?

Natarajan

This configuration of four, evenly spaced multiple images is called an Einstein Cross. It was predicted by Einstein. When in reality, one supernova went "boom," and we had a little gift. The paths of light rays are bent into a configuration with four distant images of the same supernova.

Williams

Somehow, the light from that one supernova traveled along several bending pathways-arriving at four different spots in the sky.

Natarajan

The phenomenon of light bending is something we actually encounter every day and it's all around us. So for example, if you look at graph paper through the bottom of a wine glass. You know that this is a regularly-spaced grid but because of the light bending, you actually see a stretching of the grid pattern.

Williams

In the cosmos, what bends light is gravity distorting the fabric of space. It's called gravitational lensing and it can produce spectacular results-smears, rings, smiley faces. It can even make a supernova show up in four different places at once. For Priya, these aren't just fascinating illusions. They are crucial clues in the dark matter mystery. Since gravity is what bends the light in these images, and dark matter creates gravity, the distortions can reveal where dark matter is in the universe.

Natarajan

And so it's the dark matter that is producing this huge amount of distortion.

Williams

So, Priya is gathering a giant database of these distortions all in her quest to map out dark matter throughout the universe. And Priya and maps? Well, they go a long way back.

Natarajan

We're going to one of my favorite places where I fulfilled all of my childhood fantasies. The map room at the Beinecke Rare Book Library.

Williams

Priya's quest grew from an obsession that's gripped her since she was a young girl.

Natarajan

I was obsessed with all kinds of maps and atlases when I was young. I'm crazy about maps. These mappers of yore, when they ran out of data or knowledge, it was marked as "terra incognita." Mythical places that await exploration.

Williams

The places young Priya most wanted to map, were not on Earth, but in the heavens.

Natarajan

There was something about the cosmos being a little bit out of reach that really attracted me.

Williams

As soon as she got her first computer, she used it to create a star chart.

Natarajan

It was a hard problem and I sat down for six weeks and I wrote the program. These were not things that no one had figure out before, right. But I was figuring them out for the first time. I was hooked.

Williams

Today, Priya is fulfilling her dream of exploring the frontiers of the universe. She's one of several researchers writing computer programs that use gravitational lensing to map the location of dark matter.

Natarajan

This is one of the largest maps of dark matter. The red regions are where you have an excess of dark matter. If we zoom in to a dark matter simulation, it looks rather like these fibers-almost like neurons.

Williams

Using computer simulations of the early universe, astronomers now think that dark matter formed a giant web.

Natarajan

Where the matter filaments cross, at these nodes, you form these clusters of galaxies.

Williams

Astrophysicists now realize dark matter must have played a central role early on, drawing together ordinary matter, and allowing galaxies to form. We wouldn't be here if it weren't for the powerful pull of dark matter.

Natarajan

Our current understanding of dark matter is literally it shapes the universe that we see.