We see the things we see—everyday objects, stars, planets in the solar system, and so on—because photons reveal their existence. These visible objects make up a small percentage of the universe. Most of our universe contains things we can’t see—dark matter and dark energy. That’s the world of Dr. Priyamvada Natarajan.
Although studying invisible objects may seem like a magical art, it isn’t. Dark matter and dark energy have an effect on their surroundings. It is possible to figure out the size and distribution of dark matter by looking at their effects. It’s sort of like "seeing" magnetism. If you watched a video of a nail moving across a flat table, seemingly on its own power, you’d probably conclude there is a magnet under the table. The movement of the nail would give you a clue as to the size and placement of the magnet. That’s the sort of approach that Dr. Natarajan uses.
Take a look at the large image to the left—the blue arc surrounding the white dot. That’s a photo taken by the Hubble space telescope. The blue arc is an Einstein ring, which is an example of gravitational lensing. Gravity can bend space so much that light doesn’t travel in a straight line. Thus gravity acts like a lens, but instead of focusing the object, it distorts the shape. (Think of looking through someone else’s eyeglasses.) That blue arc is not actually a blue arc. To find out what it really is, Dr. Natarajan “surgically cleans up” the image. The operation not only shows what the original image looks like, but helps her deduce the size and distribution of dark matter.
The three smaller images on right of the larger one are her “surgical” results. The top image is the real object. The middle object is galaxy that has a dark matter halo. The bottom image is what results when the dark matter halo distorts the light from the blue image at the top.
“ALL THAT WE KNOW of the universe we get from observing photons... But dark matter, which makes up 90 percent of the total mass in the universe, is called dark because it neither emits nor reflects photons—and because of our ignorance of what it is.” ~Priyamvada Natarajan
To find out more details about Dr. Natarajan’s research, watch: Solving Dark Matter and Dark Energy, a talk given for Seminars About Long-term Thinking hosted by The Long Now Foundation.