Our Milky Way galaxy is a man-eating galaxy.
The Andromeda Galaxy has grown by engulfing other galaxies. But it may also be destined to collide and merge with an even larger galaxy. Galactic collisions are normal, and NASA believes this collision is inevitable (in a few billion years). However, a new study argues that with our current knowledge of the Andromeda Galaxy, such a future collision is not yet certain, and that the odds are 50/50.
You might wonder what would happen if our disk-like spiral galaxy were to one day collide with the Andromeda galaxy, which is more than twice the size of the Milky Way. Astronomers predict that such a cosmic collision would eventually produce a giant egg-shaped galaxy.
A NASA scientist saw the first Voyager images, and he was horrified by what he saw.
But what will happen to the stars and planets in our Milky Way galaxy? And what will be the fate of Earth?
Hypothetical view from Earth of the distorted Milky Way and Andromeda galaxies (right) after the initial collision.
Credit: NASA
The Milky Way and Andromeda Collide
A galactic collision like this doesn’t seem like a good idea.
After all, these objects are packed with at least hundreds of millions of stars, millions of black holes, and possibly trillions of planets. If you were standing on a rocky world like Earth, would catastrophe be imminent?
Thankfully, no.
Galaxies collide because they have unimaginable gravitational forces that attract each other. “During its lifetime, a galaxy is very likely to encounter another galaxy that is similar or smaller,” Diego Muñoz, an astrophysicist at Northern Arizona University, told Mashable.
But these impacts would not spell doom for our solar system: “The solar system will probably remain largely unaffected.” Munoz said.
Mashable Lightspeed
“The solar system will probably be largely unaffected.”
That’s mainly because the universe is so vast, with huge distances between stars, and they’re relatively small. “In fact, if you shrink the sun down to the size of a grain of sand, the nearest star would be a few miles away, so a close encounter with another star, even during a merging galaxy, is extremely unlikely,” planetary scientist Sally Dodson Robinson of the University of Delaware told Mashable.
Furthermore, stars and their solar systems cannot compete with the gravity of larger galaxies. Solar systems orbit the central core of a galaxy, just as our solar system orbits the Milky Way every 240 million years. Even if galaxies merge, solar systems will not be attracted to each other.
A graphic of the Milky Way galaxy, with the Sun shown below the galactic center.
Credit: NASA / JPL-Caltech / R. Hurt (SSC / Caltech)
The star-filled center of the Andromeda Galaxy, also known as M31.
Credit: NASA / ESA / B. Williams and J. Dalcanton, University of Washington, Seattle
But collisions between older galaxies can cause the galaxies’ gas to collide and condense, generating stellar activity. The resulting heavy gas clouds can collapse and stimulate the formation of new stars.
“There will be some fireworks,” Nelson Caldwell, an observational astronomer at the Harvard-Smithsonian Center for Astrophysics, told Mashable.
What will change after a galactic collision?
A galactic collision won’t whip planets and stars around like billiard balls, but it will change things, some visibly.
As billions of stars merge, objects will rearrange. Stars and their planetary systems may move to new locations. For example, the sun may end up much further from the center of a new egg-shaped, “elliptical” galaxy, Munoz said.
And if we could actually see into space, our view of the universe would be dramatically different. “The planets would continue to orbit as they always have, but the constellation patterns seen from each planet would change,” says Dodson-Robinson. Andromeda, as visually depicted by NASA, would also gradually become a striking presence dominating our night sky. The giant galaxy, only faintly (but impressively) visible in the sky today, would grow bigger and bigger, eventually colliding with the Milky Way and stimulating vibrant star formation.
Eventually, billions of years from now, the view from Earth, or an Earth-like planet, may look like the bright center of a giant elliptical galaxy, as shown below.
A giant elliptical galaxy formed after the merger of the Milky Way and Andromeda galaxies, as seen virtually from Earth.
Credit: NASA
Of course, these changes in the sky aren’t sudden; they happen over billions of years. A very long-lived civilization might be able to observe these incredible cosmic changes, but our relatively short human lifespans don’t. “No human can see things moving,” Jackson Taylor, a doctoral student at West Virginia University who studies pulsars, exoplanets, and gravitational waves, told Mashable.
However, according to the popular new study mentioned above, it is not certain that this cosmic event will occur, as both the Milky Way and Andromeda galaxies belong to the “Local Group” of galaxies, and two in particular (M33 and the Large Magellanic Cloud) may exert gravitational influences that would prevent such a collision. Researchers argue that there are still too many unknowns to say for sure what will happen in billions of years. After all, just like with today’s weather forecasts, small errors or inaccurate assumptions will magnify over time, resulting in significant deviations from the original predictions.
“Looking at the system as a whole, uncertainties in the current positions, motions, and masses of all galaxies leave room for significant variation in outcomes, and we find that there is nearly a 50% chance that the merger of the Milky Way and Andromeda will not occur in the next 10 billion years,” wrote the researchers, whose paper is undergoing peer review – a sound process of scientific scrutiny.
But even if humans can avoid self-destruction and survive for billions of years on our shape-shifting continents, we may never witness such a merger — at least not from Earth. In about 5 billion years, the old sun will expand so much that it will become a red giant, boiling our oceans or engulfing us entirely.
“The sun is probably older,” Muñoz noted, “but that’s a different question.”
