Issue 18.1: February/March 2015
Department

The Super-Dupercluster

Where exactly are we? Right here.
Story by Rachel Davies.

For as long as we’ve existed, humans have stared up at the night sky in wonder. There’s nothing like being reminded of how tiny we are in comparison with the vastness of space to put life into perspective, and over the last hundred years we’ve learned much more about the nature of what we’re seeing and our place in the universe—more than at any other time in human history.

It wasn’t until the 1920s that we learned that the galaxies we spied in the heavens aren’t part of our own Milky Way, but separate island galaxies. Around the same time, we found evidence that the universe is expanding and proposed the Big Bang Theory. In the 1930s we noticed that the detectable mass of a galaxy can’t generate enough gravity to keep itself together and hypothesized the existence of an unseen mass called dark matter; today dark matter, along with with dark energy, is believed to make up the lion’s share of the mass of the universe, with all visible matter weighing in at a puny 5 percent of what’s out there: Apparently everything the human eye can actually see is just a fraction of a massive, mysterious entity that physicists are working night and day to understand.

We’ve also observed that there are more stars in the universe than grains of sand on Earth and studied how these stars—along with clouds of gas and dust, planets, exoplanets, moons, asteroids, supernovas and black holes—form galaxies. These galaxies in turn group together into “superclusters”—the largest structures in the known cosmos. And in September of last year, thanks to the work of modern space explorer Professor R. Brent Tully and his cohorts in France and Israel, we were presented with a map of our home supercluster. It’s called Laniākea, which translates to “immeasurable heavens,” and it’s much bigger than anyone imagined.

“I wanted for sure to give it a Hawaiian name,” explains Tully. He is sitting in his tiny office in the Institute for Astronomy at the University of Hawai‘i at Mānoa, where he has been on the faculty since 1975. Every surface is covered with stacks of papers. On the edge of a desk teeters a much-thumbed edition of The Nearby Galaxies Catalog, a tome he authored in 1988 that describes the locations of the three thousand galaxies closest to our Milky Way. Glorious color images of heavenly bodies are pinned to the walls. Use a little imagination and Tully’s tiny office could be the captain’s quarters of a ship. Certainly he is a pioneering explorer and mapmaker. Here in modern times, he’s at the vanguard of understanding what’s out there in the oceanic immensity of space.

Tully embraces the metaphor of a seafaring explorer, noting that the name Laniākea was chosen to recognize the achievements of the Polynesian voyagers who discovered the Hawaiian Islands in the middle of the vast Pacific Ocean. “I don’t have to risk my life,” he says, “but I feel a kinship with the ancient explorers. And philosophically this kind of work has that kind of import. It’s about where we live. It’s about trying to understand our environment and make it familiar.”

The known universe has the structure of a vast, interconnected web. In some parts of the web there are large voids, in others dense clusters of galaxies. Tully’s work involves discovering what defines and separates those galaxies and clusters. Mapping the precise boundaries of Laniākea involved a solid decade of calculating the distances to eight thousand galaxies, measuring farther out than ever before and then tracking the movements and flow of those galaxies in relation to each other.

Previously, superclusters had been defined simply as areas where there were lots of galaxies, but the data Tully and his group collected revealed a new and more precise way of defining superclusters: by the movement of galaxies within them. The group discovered that all of the galaxies in the region we now call Laniākea flow toward each other, the way water on one side of a mountain will flow into one watershed. The edge of a supercluster is the place where gravitational flow lines diverge; when this happens galaxies drift in a different direction and into other, neighboring superclusters. To give me a visual sense of it all, Tully pushes a button on his office computer, and on his screen the Laniākea Supercluster springs to life. We watch a video that shows what Tully calls Laniākea’s “basin of attraction,” toward which galaxies are flowing, including our own Milky Way, which is a barely discernible dot way out in the suburbs near the boundary of Laniākea and its neighboring super-cluster, Perseus-Pisces. Seen in 3-D, Laniākea is shaped slightly like a hat. “Yes,” Tully agrees, “I always think it looks like one of those old warrior’s helmets.”

Laniākea is vast. Tully and his team determined that Laniākea comprises a region one hundred quadrillion (ten to the seventeenth power) times the mass of our sun and five hundred million light-years across. It contains more than one hundred thousand galaxies. It’s a hundred times larger than the Virgo Cluster (which was previously considered our home supercluster), and Laniākea also encompasses the Hydra-Centaurus and Pavo-Indus clouds.

As we watch the video, we talk about how the universe’s time scales and dimensions present a huge challenge to human comprehension: It’s a massive stretch for humans to get our heads around the sheer, mind-boggling immensity. A landmark moment in human history occurred in 1972, when Apollo 17 photographed the Earth from outer space, and for the first time we looked upon our blue-green planet hanging in the darkness. Since then we have seen a growing array of fantastic images of the universe that surrounds us. But still … one hundred quadrillion times the mass of the sun? How do we take that in?

Tully is always on the lookout for ways to stretch his own capacity to understand it. He describes a “eureka moment” in 1992, in a tiny room called The Cave at the University of Illinois. There Tully donned virtual reality goggles and found himself out in space among the stars and galaxies that he had been mapping; 3-D images of those stars and galaxies were projected across the walls, floor and ceiling of the room, and the images were tracked to the goggles so that they moved as he moved. Suddenly Tully was a giant inside a universe he had previously observed only through a telescope. Remembering, he grins widely. “I could stride across millions of light-years,” he recalls. “Here’s the Milky Way floating by, here’s the Virgo Cluster, there’s the Great Attractor region. And I could walk around in there. There it really was!”

So how big is the universe then? Fasten your seat belts: Tully has calculated that there are millions of superclusters like Laniākea. And that’s just as far as we can see, which is as far as light has traveled in the 13.7 billion years since the Big Bang. How big the universe is beyond that nobody knows. It’s likely that it’s abundantly, unfathomably and indescribably larger, perhaps even a multiverse of innumerable big bangs and universes similar to our own. “If astronomy has anything to offer the world apart from pretty pictures, “says Tully, “it’s to introduce to us this idea of billions of years and hundreds of millions of light-years of distance. Things that are beyond our normal experience and intuition but are a real part of where we live.”

Vancouver-born Tully was in graduate school in Maryland in 1964 when he found himself drawn to astrophysics, attracted to the opportunities afforded by the field’s lack of popularity, particularly within the wide-open and fledgling area of extragalactic study. He did his thesis on the Whirlpool Galaxy, also called Messier 51, looking at the forces that create its spiral structure, and he has been working with the movement of stars and galaxies ever since. In 1977 he developed the now-standard Tully-Fisher method of calculating distances to other galaxies. In 1988 he published his Nearby Galaxies Catalog, describing the locations of galaxies in the area that stretches out one hundred million light-years around the Earth. He has contributed to the online Extragalactic Distance Database, acted as science advisor for Nova and other television shows, and worked on the 3-D modeling software programs “Deep Space Explorer” and “Starry Night,” which enable you to fly among the thirty thousand galaxies nearest to Earth. When prodded, he bashfully draws our attention to the two career awards that he garnered in the last few months: the Viktor Ambartsumian International Prize from Armenia, and the Gruber Cosmology Prize from Yale. The award statues balance side-by-side atop a paper-strewn filing cabinet.

When Tully came to the University of Hawai‘i thirty-nine years ago, he joked that there were more dentists in Hawai‘i than astrophysicists in the entire world. “There was so little known. I’ve been really lucky to be part of what’s become a golden age of astronomy,” he beams. This initially small pool of extragalactic explorers has grown into a collaborative and passionate international community. Tully’s fellows on the Laniākea project include its co-initiator Helene Courtois, associate professor at the University of Lyon and head of the Cosmology-Euclid group at the Institut de Physique Nucleaire de Lyon. “She infused energy into the project,” explains Tully. “She made it happen.” The other members are Yahuda Hoffman, data analyst and theoretician from Jerusalem’s Racah Institute of Physics, and Daniel Pomarède from France’s Institute of Research into the Fundamental Laws of the Universe, who created movies and images from the data. “It’s been very helpful to us to have the capability of seeing the data,” Tully says of Pomarède’s work. “It’s complicated. What we are looking for is the unexpected.”

What’s next for Tully? The astronomer suggests that we need to look out another factor of two or three in distance to better understand the forces acting upon our galaxy and supercluster. The technology does exist to do this, but it’s a big job, requiring a huge amount of manpower and resources. “Come back in ten to fifteen years,” Tully grins.

As I leave his office, the corridors of the Institute for Astronomy buzz with excitement. Professors and students are hurrying to their weekly colloquium meeting, and a hum of various languages fills the air. The French word for galaxy emerges clearly from the throng. Along the corridors images of nebulas, stars and galaxies are pinned up, and through open doorways whiteboards with incredibly complex equations can be spied. Someone with an American accent laughingly laments the state of the office coffee machine: Due to technical difficulties, there won’t be enough coffee for the meeting. It’s somehow reassuring that even pioneers using the most advanced technology to measure the mind-bending vastness of the cosmos can still get thrown by a coffee maker on the fritz. HH

Story by Rachel Davies. Photos by