Credit: Nature Video / Laniakea: Our home supercluster
Somewhere in the universe is a small, blue planet, the third drop from a star called the Sun. Just one of billions of stars in a spiral galaxy known as the Milky Way. But where in the universe is the Milky Way?
A team of scientists gather data on more than 8,000 of the galaxies that surround us, they mapped each galaxies position and movement in space. And for the first time, they’ve shown that the Milky Way is part of a much larger system of galaxies - a super cluster that they have named Laniakea. The Milky Way is nested in the furthest reaches of this structure on the outskirts.
The entire universe can be seen as an intricate network of galaxies - a cosmic web. Some areas are almost empty dark voids, others are densely packed with galaxies in regions known as super clusters. Super clusters are the biggest structures found in the universe. But scientists have struggled to define where one ends and another begins. To map our home super cluster, a team led by Brent Tully at the University of Hawaii studied the motions of the galaxies around us in unprecedented detail.
Even though the entire universe is expanding rapidly gravity is also at work pulling against this acceleration. By discounting cosmic expansion, the team worked out which galaxies are being pulled towards us - shown in blue and which are being pulled away - shown in red. This enabled them to create a map of cosmic flows - the paths that galaxies migrate along, targeted a tiny pace by the force of gravity. Using this motion they came up with a new way to map the distribution of matter in the universe. Delving into a home super cluster you can see that most galaxies are being pulled towards a dense center. This is known as the Great Attractor. Our galaxy is among those sliding towards this patch of space which dominates our region of the universe.
Let’s take a different view. Each circle represents a galaxy. Again we can see most galaxies being pulled towards the Great Attractor in the direction of the arrows. Between the Great Attractor and us - the Milky Way is a relatively empty area a blue void. And next to us is Virgo - a large and dense cluster whose bright galaxies have been observed from Earth for centuries. Until now astronomers group us - the Milky Way and its surrounding galaxies with Virgo and nearly a hundred other clusters in a super cluster that stretches a hundred million light-years across. But using this new technique we can see that this is just the tip of the iceberg. This cluster of clusters is merely an appendage of a much larger super cluster more than one hundred times bigger and more massive.
Credit: SDvision interactive visualization software by DP at CEA/Saclay, France
How did the team know how to redraw the boundaries of this cosmic map? Here’s our super cluster in black and a neighboring structure Perseus-Pisces in red. Scientists defined the boundary as the points where the flows of galaxies diverge, like water dividing at a watershed. This is where neighboring structures share apart.
This is the first clear definition of a super cluster. Laniakea means immeasurable heaven in Hawaiian, a fitting name for the vast community of galaxies that we are a part of. So now we know that on the edge of a super cluster would Laniakea in a galaxy called the Milky Way around a star we call the Sun there is a small blue planet - our home.
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