What Is the Local Group?
The Local Group is the small galaxy neighborhood that includes the Milky Way, Andromeda, the Triangulum Galaxy, and dozens of smaller dwarf galaxies.
When people ask how does the local group move, they are usually asking how this entire collection of galaxies travels through space relative to the cosmic background and nearby large-scale structures.
This motion is not simple drifting.
It reflects gravity from massive nearby systems, the expansion of the universe, and the combined motion of every galaxy inside the group.
How Does the Local Group Move?
In broad terms, the Local Group moves as a gravitationally bound system through the universe while also containing galaxies that orbit around shared centers of mass.
Its overall motion is measured relative to the cosmic microwave background, a relic radiation field that provides a useful universal reference frame.
Astronomers have found that the Local Group is not stationary with respect to the universe at large.
It is moving at hundreds of kilometers per second, and that motion is influenced by major gravitational attractors such as the Virgo Cluster, the Great Attractor, and the Shapley Concentration.
What Drives the Motion of the Local Group?
Several physical effects shape the movement of the Local Group:
- Gravitational attraction from nearby galaxy clusters and superclusters.
- Cosmic expansion, which stretches space on very large scales.
- Internal orbital motion of galaxies inside the Local Group.
- Dark matter, which adds most of the mass and gravitational pull.
These factors combine to produce a complex motion pattern.
The Local Group is not simply flying through empty space; it is embedded in the cosmic web, where galaxies follow filaments and flow toward denser regions.
What Is the Local Group Moving Toward?
The Local Group is generally moving toward the Virgo Cluster and, on larger scales, toward the direction associated with the Great Attractor.
These are not single objects in the everyday sense but large mass concentrations that influence the motion of galaxies across vast distances.
At the same time, the Milky Way and Andromeda are moving toward each other because of their mutual gravity.
This inward motion is separate from the group’s overall journey through space.
How Fast Is the Local Group Moving?
Measurements indicate that the Local Group moves at roughly 600 kilometers per second relative to the cosmic microwave background.
That is an extremely high speed by human standards, but on cosmic scales it is a normal consequence of gravity acting over millions and billions of years.
It is important to separate this bulk motion from the internal velocities of individual galaxies.
For example, the Milky Way and Andromeda are approaching one another at about 110 kilometers per second, while many dwarf galaxies have their own smaller orbital or streaming motions.
How Do Astronomers Measure the Motion?
Astronomers use several tools to determine how the Local Group moves:
- Redshift and blueshift to measure whether galaxies are moving away or toward us.
- Cosmic microwave background dipole to identify the Local Group’s motion relative to the rest frame of the universe.
- Distance measurements using standard candles such as Cepheid variables and Type Ia supernovae.
- Proper motion studies from observatories such as the Hubble Space Telescope and Gaia.
The cosmic microwave background dipole is especially important.
Because the background radiation appears slightly hotter in the direction of motion and slightly cooler in the opposite direction, astronomers can infer the speed and direction of the Local Group with high precision.
Does the Local Group Expand with the Universe?
The answer is partly no and partly yes.
Inside the Local Group, gravity is strong enough to hold galaxies together, so the group does not participate in universal expansion the way empty space between distant galaxy clusters does.
Beyond the scale of the Local Group, however, cosmic expansion becomes dominant.
This means nearby bound systems stay intact, while distant galaxies continue to recede as space itself expands.
The Local Group sits at the boundary where local gravity and global expansion compete.
What Role Does Dark Matter Play?
Dark matter is essential for understanding the Local Group’s motion.
Most of the mass in the Local Group is not visible matter from stars, gas, and dust.
Instead, it is thought to reside in dark matter halos surrounding the Milky Way, Andromeda, and dwarf companions.
These halos help bind the group together and influence internal orbits.
They also affect how the Local Group responds to external gravitational fields.
Without dark matter, the observed motions of galaxies in the Local Group would be difficult to explain.
How Is the Milky Way Moving Within the Local Group?
The Milky Way is not the center of the Local Group.
It is one major galaxy among several, and its motion reflects both the group’s bulk travel and its local gravitational interactions.
Key features of the Milky Way’s motion include:
- Movement toward the common center of mass shared with Andromeda.
- Participation in the Local Group’s overall motion through the cosmic web.
- Small velocity changes caused by nearby dwarf galaxies and dark matter substructure.
Because of this, the Milky Way is constantly changing position relative to the rest of the group, even though the entire system is moving together.
Why Does the Motion of the Local Group Matter?
Studying this motion helps astronomers map mass in the universe, including invisible dark matter and large-scale gravitational structures.
It also improves measurements of galaxy distances, galaxy formation, and the history of cosmic expansion.
The motion of the Local Group is also a useful test of cosmological models such as the Lambda Cold Dark Matter model, which describes how structure grows in the universe.
If observed motion does not match predictions, it can point to missing mass, measurement errors, or new physics.
What Will Happen Next?
Over the next several billion years, the Local Group will continue moving through the cosmic web while the Milky Way and Andromeda gradually approach one another.
Their future merger, sometimes called Milkomeda in popular writing, will reshape the internal structure of the group.
Even as that local collision unfolds, the broader Local Group will keep responding to the gravity of surrounding matter on scales far larger than any single galaxy.
That dual motion—internal interaction and external drift—is the key to understanding how does the local group move.
Key Terms Related to Local Group Motion
- Cosmic microwave background: ancient radiation used as a universal reference frame.
- Redshift: stretching of light to longer wavelengths from motion or expansion.
- Blueshift: compression of light toward shorter wavelengths from approach.
- Gravitationally bound system: a structure held together by gravity.
- Dark matter halo: the invisible mass surrounding galaxies.
- Cosmic web: the large-scale filamentary structure of matter in the universe.