Using a new mapping technique that takes into account the motions -- and not just the distances -- of nearby galaxies, astronomers discovered that the Milky Way is located in the suburb of a massive, previously unknown super-cluster they named Laniakea, a term from Hawaiian words meaning “immeasurable heaven.”
Actually, Laniakea’s girth is measurable, though difficult to conceptualize. The super-cluster spans 520 million light-years in diameter, more than five times larger than the cluster previously believed to be the Milky Way’s cosmic home.
A light-year is the distance that light, moving at a speed of 186,000 miles per second, travels in one year. One light-year is about 5.88 trillion miles.
Astronomers were able to identify the boundaries of Laniakea by charting the flow of more than 8,000 galaxies surrounding the Milky Way. By that yardstick, they discovered that the Milky Way, along 100,000 other galaxies, is sailing toward a region named the Shapley super-cluster.
Other nearby galaxies are being gravitationally tugged in other directions. The new map of the local universe delineates the flow lines where the galaxies’ paths diverge, establishing for the first time regions of space under the influence of particular super-clusters.
In addition to Laniakea, the local universe includes galaxy complexes Shapley, Hercules, Coma and Perseus-Pieces.
“We don’t have the distance information to see the far sides of ... our (super-cluster) neighbors and we haven’t seen far enough to understand what’s causing this full motion of our galaxy,” astronomer and lead researcher Brent Tully, with the University of Hawaii, told Discovery News.
“That’s really the goal, to look out far enough -- probably three times farther than we are right now, probably requiring many thousands of more distance measurements, to map this larger region,” he said.
Astronomer Elmo Tempel, with Tartu Observatory in Estonia, said he was surprised that the Milky Way’s super-cluster wasn’t found sooner.
“Laniakea is the biggest structure in the local universe. Usually, the biggest structures are discovered first,” Tempel wrote in an email to Discovery News.
Tully and colleagues used recently published measurements of direct distances between galaxies, including for the first time galaxies that are farther away. That enabled them to calculate velocities at a bigger scale than previous studies.
“The discovery of Laniakea is definitely interesting and hopefully will initiate studies that will map the local universe in more detail,” Tempel wrote.
“Super-clusters and galaxy filaments are structures that are present in the distribution of galaxies. However, we do not know much about these structures and we do not know how these structures affect the formation and evolution of galaxies, including our Milky Way. This study will give us new perspective (on) how to analyze these problems in observations,” he wrote.
The research and a related commentary by Tempel appear in this week’s Nature.