Two galaxies have been photographed merging about 230 million light years from Earth, and one expert says “it will never look like a normal galaxy again.”
The image, taken with the Hubble Space Telescope and released by NASA and the European Space Agency late last month, was originally thought to show a single, abnormal galaxy in the Hercules constellation.
But astronomers now say it actually depicts two galaxies in the process of forming a “new” galaxy after they were drawn together by gravity. “We now see them merging into a single structure,” NASA said in a news release.
A galaxy is made up of hundreds of billions of stars, held together by gravity. Billions of galaxies exist and they often cluster together in very large groups.
“Every now and then the galaxies will be attracted to each other by gravity and they will essentially collide,” explained Randy Attwood, executive director of the Royal Astronomical Society of Canada.
The merger of two or more galaxies is a process that can take millions of years, Attwood explained.
He told the Toronto Star that galaxies usually look like pinwheels with spiral arms or glowing balls and they generally maintain a uniform shape.
“This one looks like something very strange is happening because the arms are sort of all over the place,” he said about the galaxies colliding in the Hubble image.
“It will never look like a normal galaxy again.”
So what happens when two galaxies collide?
NASA said some stars will lose their original orbits as a result of the collision and Attwood added that some may even be thrown out of their system altogether.
But Barbara Ryden, a professor of astronomy at Ohio State University, told the Star that these collisions rarely result in stars directly hitting each other.
That’s because the space between stars measures about 10 million times the diameter of a single star. “It’s like two swarms of flies flying towards each other and the flies don’t collide,” Ryden said.
Galaxy collisions cause big clouds of interstellar gas to hit each other, Ryden explained, and “when two gas clouds collide it becomes unstable, it starts to fragment and collapse and form new stars.”
The U.S. space agency predicts that the Milky Way, the galaxy in which the Earth, sun and the rest of our solar system resides, will have a “head-on collision” with the neighbouring Andromeda galaxy in about four billion years.
Astronomers say, though, that while the event will fling the sun into a new region of our galaxy, the “Earth and solar system are in no danger of being destroyed.”
Ryden said that observing galaxy collisions can tell astronomers more about how the collisions occur and possibly even lead them to a greater understanding of dark matter, a matter they cannot see with telescopes but which they estimate makes up a significant portion of our universe.
The angle and speed at which galaxies collide and their original shape and composition influence how the resulting galaxy will take shape.
“When you collide two nice, neat, spiral galaxies together . . . what you get is this big, blobby galaxy that’s called an elliptical galaxy,” Ryden said.
The galaxy in the Hubble image appears chaotic, but it will soon settle down into “an elliptical blob,” she said.
“Right now there are lots of bright stars because you have star formation, but those, too, will die out. So you’re looking at a snapshot of this very dynamic process.”