Somehow David Schlegel, M.S. ’91, Ph.D. ’95, a senior scientist at Lawrence Berkeley National Laboratory, keeps a straight face when he says one of his research goals is to tell the history of the universe.
In his latest work, published in The Astrophysical Journal, Schlegel and his collaborators document a “one in a billion” gravitational lens cluster called the Carousel Lens that can shed light on the location and density of dark matter and how dark energy has affected the accelerating expansion of the universe.
A gravitational lens is a large mass of the universe comprised of a celestial body, like a cluster of entire galaxies, and mostly dark matter, a mysterious substance not made of any particles we’re familiar with from high school chemistry, such as protons and electrons. The lenses are detectable via telescope images of the sky that can see objects up to 12 billion light-years away.
A few years ago, a group of Schlegel’s undergraduates began using machine-learning algorithms to scan the largest two-dimensional image of galaxies ever created, produced by combining hundreds of thousands of images from three telescopes over 1,400 nights. Schlegel thought they might luck into finding a gravitational lens or two, which appear as multiple bright shapes encircling a central shape (the “lens” curves light, making the same shape appear more than once in different locations).
“I thought, ‘I don’t expect they’ll find very much, but they’ll learn something.’ As it turned out, these students are very good, and they really ran with it. In fact, they’ve cataloged more [gravitational lenses] than everyone else in the world combined,” says Schlegel.
The undergrads, led by William Sheu ’21, documented seven gravitational lenses representing seven galaxies and a small foreground group of galaxies. In the above image, the four lensing “L” galaxies appear at the center and are located about 5 billion light years from Earth, while the galaxies numbered 1–7 are anywhere from 7.6 to 12 billion light years away.
A lot can be done with this one discovery. By examining the locations of the galaxies relative to each other, astronomers can determine the location of dark matter and investigate how dark energy, the repulsive force pushing the universe apart, has literally built the universe over 13.7 billion years.
“In a sense,” says Schlegel, “this is like a Rosetta Stone for us, deciphering the universe.”
