If you want to determine your place in the universe, start with your cosmic address. They live on Earth -> Solar System -> Milky Way -> Local Cluster -> Virgo Cluster -> Virgo Supercluster -> Laniakea. Thanks to new deep-sky surveys, astronomers now believe that all of these places are part of an even larger cosmic structure in the “neighborhood” called the Shapley Concentration.
Astronomers call the Shapley concentration the “basin of attraction.” This is a region loaded with mass that acts as an “attractor”. It is a region with many clusters and groups of galaxies and the largest concentration of matter in the local universe. All of these galaxies and dark matter give the concentration its gravitational influence. There are many such basins in the universe, including Laniakea. Astronomers are working to study them in more detail, which should help create a more accurate map of the largest structures in the universe.
A section of the Laniakea Supercluster, a local attraction. This structure contains many galaxies and clusters, including our own Milky Way Galaxy. Image credit: Interactive visualization software SDvision from DP at CEA/Saclay, France.
A group led by University of Hawaii astronomer R. Brent Tully measured the motions of about 56,000 galaxies to understand these basins and their distribution in space. “Our universe is like a giant web in which galaxies lie along filaments and cluster at nodes where gravitational forces pull them together,” Tully said. “Just as water flows in watersheds, galaxies flow in cosmic basins of attraction. The discovery of these larger basins could fundamentally change our understanding of cosmic structure.”
Cosmic currents and mapping structures
Tully's team is called CosmicFlows and studies the movements of these distant galaxies in space. The team's “redshift” studies revealed a possible shift in the size and extent of our local galactic gravitational pull. We already know that we “live” in Laniakea, which is about 500 million light-years across. However, the movements of other clusters suggest that there is a larger “attractor” directing the cluster flow. The CosmicFlows data suggests that we could be part of the Shapley concentration, which could be ten times the volume of Laniakea. It is about half the size of the largest structure in space, the “Great Wall,” a chain of galaxies that stretches over 1.4 billion light-years.
The 2dF Galaxy Redshift Survey discovered several superclusters. Inside is the structure known as the Sloan Great Wall. Courtesy of the 2dF Galaxy Redshift Survey.
The Shapley concentration was first observed as a “cloud” in the constellation Centaurus in the 1930s by astronomer Harlow Shapley. This supercluster appears along the direction of movement of the local group of galaxies (where we live). For this reason, scientists speculated that it could influence the peculiar motion of our galaxy. Interestingly, the Virgo Supercluster (as well as the Local Group and the Milky Way) appears to be moving toward the Shapley concentration. The surveys that Tully and others are conducting should confirm this movement toward what she is attracted to.
Exploring ever larger structures in the universe
Where do these attractions come from? In some ways, they are as old as the universe and its cosmic web of matter, which Tully refers to. The seeds for the web and these basins of attraction were planted approximately 13.8 billion years ago. After the Big Bang, the young universe was in a hot, dense state. As it expanded and cooled, the density of the matter began to fluctuate. There were tiny differences in these density fluctuations. Think of them as the earliest “seeds” of galaxies, galaxy clusters, and even larger structures we see in the universe today.
This detailed map of the cosmic microwave background was created from seven years of data. It shows the “seed” structures of galaxies in the early universe. Photo credit: NASA
As astronomers study the sky, they find evidence of all of these different structures. Now they have to explain it. The idea that the Shapley concentration is the large basin to which our Laniakea belongs means that current cosmological models do not fully explain its existence.
“This discovery presents a challenge: Our cosmic surveys may not yet be large enough to map the entire extent of these vast basins,” said UH astronomer Ehsan Kourkchi. “We still look through giant eyes, but even those eyes may not be big enough to capture the full picture of our universe.”
Measurement of attractors
The main player in all of these galaxies, clusters and superclusters is gravity. The more mass, the more gravity influences movements and distribution of matter. For these basins of attraction, Tully's research team examined their effects on the movements of galaxies in the region. The basins exert a kind of “tug of war” on the galaxies that lie between them. This affects their movements. In particular, redshift surveys like the ones Tully's team is conducting will map radial motion (along the line of sight), velocities (how fast they move), and other associated motions. By mapping the velocities of galaxies in our local universe, the team can define the region of space where each supercluster dominates.
Of course, these movements are difficult to define. That's why the team carries out different types of measurements. They don't just map the luminous matter in galaxies. You also have to take into account the suspected existence of dark matter. There are other complications too. For example, not all galaxies are the same – that is, they differ in their shape (morphology) and density of matter. Astronomers can get around this by measuring the so-called “galaxy velocity.” This is the difference between its actual speed and the expected “Hubble flow” speed (which reflects gravitational interactions between galaxies).
The results of the Tully team's surveys are expected to provide increasingly precise 3D maps of these regions of space. This includes their structures as well as their movements and speeds. These maps, in turn, should provide greater insight into the distribution of all matter (including cold dark matter) throughout the universe.
More information
Identification of basins of attraction in the local universe (journal)
Identification of basins of attraction in the local universe (arXiv pdf)
The Shapley Supercluster: the largest concentration of matter in the local universe (PDF)
Like this:
Load…
Comments are closed.