What happens when galaxies collide?
Our Milky Way galaxy is on a collision course with the nearby Andromeda galaxy. In about 4 billion years, the two galaxies will meet in a spectacular merger. When galaxies collide, their stars usually pass by each other without incident. But the collisions dramatically change the galaxies’ shapes and structures. The galaxies’ gas and dust interact and trigger new bursts of star formation.
Collisions between large spiral galaxies like the Milky Way and Andromeda are rare in the recent universe. The last major merger in our galaxy’s history occurred over 12 billion years ago. Galaxy interactions were more common in the early universe when galaxies were closer together.
What will happen when the Milky Way and Andromeda collide?
As the Milky Way and Andromeda galaxies hurtle toward each other at 250,000 mph, their outer edges will first stretch and intertwine like taffy. Tidal forces will tear long streamers of gas and stars from the galaxies’ disks.
After the initial collision, the galaxies will swing past each other and then fall back together for a direct bull’s-eye hit. During this second collision, the two central black holes will merge in an explosive event. Most of the stars in both galaxies will remain intact. But about 3-5% of the stars will be flung out in long streams and tidal tails.
The Milky Way and Andromeda will fuse together over the course of billions of years. The new, larger galaxy is nicknamed Milkomeda or Milkdromeda. Its shape will resemble elliptical galaxies, which have puffy, spherical structures.
What will happen to the Earth?
When the Milky Way and Andromeda collide, there is only a slim chance that our solar system will be directly disturbed. The stars in the merging galaxies are so far apart that collisions between stars are extremely rare. However, the collision will shake up the precise orbits of planets in both galaxies.
There are several ways the Earth could potentially be affected:
1. Oort Cloud disruption
The Milky Way’s disk is surrounded by a giant halo of icy bodies called the Oort Cloud. When Andromeda passes through this region, the Oort Cloud will be severely disrupted. Some comets will be hurled inward toward the Sun and planets. If a rogue comet enters the inner solar system, it could have dire consequences for life on Earth.
2. Increased solar flares
The Sun’s activity rises and falls on an 11-year cycle. Collisions between galaxies generate shockwaves that can trigger increased solar activity, including more frequent solar flares and coronal mass ejections. Powerful solar outbursts emit bursts of x-rays, UV radiation, and energized particles that can damage Earth’s atmosphere, power grids, and satellites.
3. Tilted orbits
The gravity of the passing Andromeda galaxy may alter the tilt of our solar system. Earth’s axial tilt, or obliquity, determines our seasons. If the tilt changes substantially, Earth’s climate will be dramatically affected. The oceans and continents could shift orientation, leading to widespread environmental changes.
4. Distant supernovae
Galaxy collisions trigger massive star formation as gas clouds collide and collapse. The most massive newborn stars end their lives as supernovae explosions just a few million years after their birth. A nearby supernova could inflict damage on Earth’s ozone layer, allowing increased UV radiation to reach the surface. Supernovae also produce cosmic rays that can mutate genes and damage electronics on Earth.
5. Supermassive black hole turbulence
When the black holes from the Milky Way and Andromeda merge, the resulting black hole will devour surrounding gas and unleash powerful jets of radiation. If one of these jets is pointed directly at Earth, it could obliterate our ozone layer and expose the planet to harmful cosmic and UV radiation.
Will life on Earth survive?
While the Milky Way-Andromeda collision will bring interesting changes to our galaxy, life on Earth is likely to persevere through the event. Here are some reasons why:
Long timescale
The galaxies’ collision will unfold over billions of years, giving life plenty of time to adapt and evolve to changing conditions. Catastrophic events like stars passing close to the solar system are unlikely.
Sun’s lifespan
Our Sun will continue its stable fusion for another 7 billion years after the galaxy collision, providing Earth with the steady energy source required for life. Only later, as the Sun ages, will its luminosity increase and threaten Earth’s habitability.
Earth’s resilience
Life on Earth has already survived many galactic incidents, including supernova explosions, gamma ray bursts, and encounters with black holes. As long as the planet itself remains intact, life can endure many cosmic challenges.
Advanced civilization?
Intelligent life may have evolved substantially in the next 4 billion years and developed technological solutions to threats from the galaxy collision. An advanced civilization could use techniques like stellar engineering to stabilize the solar environment.
Conclusion
While the collision between the Milky Way and Andromeda galaxies raises concerns about disruptions to our solar system, life on Earth will likely continue throughout the slow merger process. The Sun’s lifespan exceeds the duration of the collision. Although some cosmic incidents could threaten habitability, life has proven resilient when facing similar events in Earth’s past. An advanced technological civilization may also develop strategies to mitigate risks from the merging galaxies. Overall, the galaxy collision is unlikely to completely sterilize Earth, allowing life to endure this cosmic transformation.
| Potential threat | Consequences for Earth |
|---|---|
| Oort Cloud disruption | Increased comets entering inner solar system |
| Increased solar flares | Atmospheric and satellite damage from radiation |
| Tilted orbits | Dramatic changes to Earth’s seasons and climate |
| Distant supernovae | Ozone layer damage and increased radiation |
| Black hole turbulence | Potential to destroy ozone layer and expose surface to radiation |
| Factor | Impact on Earth’s Habitability |
|---|---|
| Timescale of collision | Gives life time to gradually adapt; catastrophes less likely |
| Sun’s lifespan | Steady energy source available throughout collision process |
| Earth’s resilience | Life has survived other cosmic events like supernovae and gamma ray bursts |
| Advanced civilization | Intelligent life may devise solutions to mitigate hazards |