What do we know about the Great Attractor?

The Great Attractor is a vast, diffuse region of gravitational anomaly in intergalactic space that exerts a significant pull on our Milky Way galaxy and thousands of other galaxies. It represents a massive concentration of mass, influencing the motion of galaxies across a significant portion of the universe.

Understanding the Great Attractor

The Great Attractor is not a single object but rather a vast, diffuse region where a substantial amount of mass is concentrated. This gravitational "hot spot" pulls galaxies, including our own Milky Way, towards it at millions of miles per hour. Scientists observe its presence not directly, as it's largely obscured, but through its profound gravitational influence on the surrounding cosmic landscape.

Key Characteristics and Discovery

Our understanding of the Great Attractor has evolved over time, with significant breakthroughs in mapping its influence and location.

• Discovery: The location of the Great Attractor was finally determined in 1986, marking a pivotal moment in understanding large-scale cosmic structures.
• Distance: It is situated between 150 and 250 million light-years (Mly) away from the Milky Way. The more recent and widely accepted estimate places it at approximately 250 Mly (79 Mpc) from our galaxy.
• Direction: This massive gravitational center lies in the direction of the constellations Triangulum Australe (The Southern Triangle) and Norma.
• Obscuration: A significant challenge in studying the Great Attractor is that it lies behind the plane of the Milky Way galaxy, an area known as the "Zone of Avoidance." This region is heavily obscured by our galaxy's dust and gas, making direct optical observation difficult and requiring alternative methods like X-ray astronomy.

What Causes the Gravitational Pull?

The immense gravitational pull attributed to the Great Attractor is not caused by a single, colossal object but by a vast accumulation of galaxies and dark matter.

• Supercluster Concentration: It is thought to be the gravitational center of a collection of several massive superclusters, including:
  • The Norma Cluster
  • The Hydra-Centaurus Supercluster
  • The Shapley Supercluster, which is often considered a major component or even the core of the Great Attractor's influence, lying behind it from our perspective.
• Laniakea Supercluster: Our own Milky Way galaxy is part of the larger Laniakea Supercluster, which encompasses tens of thousands of galaxies. The Great Attractor itself is effectively the gravitational bottom of this vast cosmic "valley," drawing all galaxies within Laniakea towards it.
• Dark Matter: A substantial portion of the Great Attractor's mass, and thus its gravitational effect, is believed to be composed of dark matter. This invisible substance makes up about 27% of the universe's mass-energy content and contributes significantly to the large-scale structure of the cosmos.

Cosmic Flows and Our Motion

The Great Attractor is a prime example of how large-scale gravitational forces dictate cosmic flows. Galaxies are not just expanding away from each other due to dark energy, but are also simultaneously experiencing gravitational pulls from local mass concentrations. The Great Attractor is responsible for a significant component of the "peculiar velocity" of the Milky Way and its neighboring galaxies – their motion relative to the general expansion of the universe. This means our galaxy is being pulled towards this region at a speed of hundreds of kilometers per second.

Key Facts Summary

For a concise overview, here are the key facts about the Great Attractor: