Galaxies colliding and interacting with each other is a relatively common cosmic occurrence. When galaxies collide, they interact, pulling gaseous material and particulates around, potentially changing the morphology of the two separate galaxies. You can see the visual effects here.
When galaxies collide they can cause huge changes in the individual galaxies’ shapes. All galaxies are moving outward because of the lingering force of the great explosion, but they also have different pulls and spins causing them to sometime collide. Gaseous material in the galaxies is pulled apart by the force of collision and the shape of the galaxies is altered. There sometimes are new stars formed or new galaxies broken off from the force as well.
There are hundreds of billions of galaxies in the Universe, moving in all directions, each of them composed of huge amounts of energy and matter. In fact, the average galaxy houses more than 100 billion stars and star formations and ranges from 1,500 to 300,000 light-years across. Most galaxies are separated from the nearest galaxy by hundreds or thousands of light-years, but with so much matter moving around, there are bound to be collisions.
Although we are not affected on Earth (yet), a galactic collision is not a small matter. During a collision, a huge amount of energy is released, and the gases and gravitational pulls of each galaxy mix up, which some astronomers think creates a breeding ground for more stars. It does not happen quickly, like a car crash, but can actually take up to a billion years for a collision of galaxies to neutralize.
Scientists can’t watch a collision happen due to the huge time frame required. Instead, they take pictures using high-power telescopes, including the Hubble Telescope, of current galactic collisions. This allows them to gather data and generate a computer model for collisions and to make video simulations from the models.
A collision, even though a huge amount of energy is released, is typically not an explosive event. The distance between stars in galaxies is so huge—imagine grains of sand each separated by one or several football fields—that in most cases they just slip together and become one. The probability of stars actually coming into contact with each other is very small.
But this is not always the case. Many galaxies have supergiant black holes at their centers, and if these black holes were to collide during a galactic merger, it would cause a violent explosion so powerful that it could wobble space-time. In fact, astronomers have discovered a galaxy in which two supergiant black holes are on a collision course, and they believe that when they merge, stars will be ejected from the galactic center and a huge amount of gravitational energy will be released.
Galaxies have a hierarchy. That is, large galaxies get bigger, and small, “dwarf” galaxies get absorbed. Astronomers call this process “Galactic Cannibalism”. When a dwarf galaxy comes into contact with a large galaxy, the tidal pull of the larger one pulls it inward, which causes the dwarf galaxy to be completely shredded, leaving only remnant streams of stars as reminders of its old self. There is evidence that our Milky Way Galaxy has dined on dwarfs in the past, and the nearby Andromeda Galaxy is absorbing them as well. Here is a photo of a dwarf galaxy being digested by the Andromeda Galaxy:
Our Milky Way
Galactic collisions and cannibalism are commonplace in the cosmos. And our home, the Milky Way, is no exception to the rule. It is currently gobbling small galaxies, and we’re on a course to run straight into one of the largest galaxies nearby.
Using infrared imagery, scientists from the University of Massachusetts and the University of Virginia, have discovered evidence that our galaxy is currently tearing apart the nearby Sagittarius dwarf galaxy . For the last two billion years, the Milky Way has been breaking down Sagittarius, which at one ten-thousandth the size of the Milky Way, never had a chance. Now, astronomers believe that it is at a critical stage in its absorption—a point of no return.
Further in our future—about 4 billion years from now—our galaxy will collide with the Andromeda Galaxy. Astronomers are uncertain what exactly will happen to Earth and life, if there is still life by then, but most think that because of the spacing between stars, it will be a relatively benign collision, and our two galaxies will merge together as one. The gases from each galaxy will mix up, creating a new stars and nebulas in a sky that might look something out of Van Gogh’s mind. Here’s a video of what it might look like.
All images courtesy of nasaimages.org
Video from http://www.youtube.com/watch?v=dJRc37D2ZZY
A number of things may happen when galaxies collide. Material may be blasted outward, and many new stars may form as a result of the collision. Colliding galaxies tend to merge with each other, and after many millions of years form new galaxies called ellipticals.
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