Map shows Milky Way’s corner of the universe.
Scientists have redrawn the cosmic map of our corner of the universe, using new tools to define which galaxies interact with our own. The so-called supercluster of galaxies that contains the Milky Way has been named “Laniakea,” which means “immense heaven” in Hawaiian.
Defining regions in an infinite universe is tricky business: Clusters of dozens of galaxies, called local groups, are further bound into clusters containing hundreds of galaxies. The Laniakea supercluster, described in a paper published in this week’s Nature, is 500 million light-years in diameter and contains 100,000 galaxies — and we sit at the very edge of it. Together, those galaxies carry 100 million billion times the mass of our sun.
How can such a massive number of galaxies be connected? While some areas of space are basically empty, others contain highly concentrated star power. In these areas, the supercluster galaxies are drawn toward each other in intricate ways. According to R. Brent Tully, an astronomer at the University of Hawaii, Manoa, and lead author of the study, galaxies in the cosmos can be compared to water on Earth.
“We have finally established the contours that define the supercluster of galaxies we can call home,” Tully said. “This is not unlike finding out for the first time that your hometown is actually part of a much larger country that borders other regions.”
“Within a land form, water flows in certain directions,” Tully said. “The water knows, even if the land is very flat, which way is downhill.” Instead of downhill valleys that attract water flow, our universe has something called the Great Attractor. This region serves as a gravitational focal point, influencing the motion of galaxies in the supercluster.
In the new study, Tully and his colleagues provide the first clear definition of a supercluster. By mapping the flow of more than 8,000 galaxies that surround our own, they figured out where the clusters diverged. In other words, they pinpointed at what point galaxies started to be drawn toward a different “valley” than we are.
Superclusters are among the largest structures in the interconnected web of galaxy clusters that account for much of the matter in the universe. Tully and his colleagues said the extent of superclusters should be defined by their gravitational spheres of influence. They used the Green Bank Telescope and other radio telescopes to map out the motions of galaxies.
The Green Bank Telescope is the world’s largest fully steerable radio telescope. It’s part of the National Radio Astronomy Observatory site in Green Bank, W.Va.
It’s possible that scientists will eventually map an even more super cluster. “We’ve found the local region, but we already see that our base of attraction is actually being pulled toward another base of attraction,” Tully said. “We don’t really understand why.”
To solve that mystery, researchers will look two to three times farther than they did when they mapped Laniakea. That, he said, will be a huge undertaking — they’ll have to chart tens of thousands more heavenly bodies.