By Jonny Lupsha, Wondrium Staff Writer
The Andromeda Galaxy is headed straight for us—but it’s all good. Between its speed and distance from us, we still have four billion years before its first close pass. The Hubble Space Telescope provides details.
What would happen if two spiral galaxies had a near-miss? If we can find a way to live another four billion years, we can have front-row seats. The Andromeda Galaxy is currently approaching the Milky Way, but at just 0.04% the speed of light and from a distance of 2.5 million light-years away. It’s believed that it will make a close pass by us, then have a larger collision at a later time.
This event will dramatically change the shape and character of our galaxy. In his video series Experiencing Hubble: Exploring the Milky Way, Dr. David Meyer, Professor of Physics and Astronomy at Northwestern University, explains the process the merging galaxies will undergo.
Ships Passing in the Night
What will the night sky look like in four billion years?
“At this time, Andromeda will be nearing its first close pass of the Milky Way,” Dr. Meyer said. “As a result, it will be a huge feature on the night sky rivaling the entire Milky Way in brightness. At this point in time, the spiral structure of both galaxies will not yet have been affected much by their gravitational interaction.”
As Andromeda passes by the Milky Way, their gravitational attraction will pull tidal tails of stars and gas out of each galaxy. This has actually already happened to another pair of spirals known as Arp 273, located in the constellation of Andromeda 300 million light-years away. Hubble captured a picture of them that spans 230,000 light-years across, showing their distorted spirals. The outer arm of the larger galaxy, according to Dr. Meyer, is now a huge ring with “blue bursts of star formation” scattered around it.
“As viewed from Earth after this first pass, the resulting night sky is likely to feature a warped Milky Way studded with blue bursts of star formation,” he said. “The gas and stars from Andromeda will be tidally stretched across the sky with ongoing starbursts throughout.”
When Worlds Collide
Based on existing evidence of colliding galaxies as well as computer simulations, in about 6 billion years, the night sky as viewed from Earth will be like the best fireworks show imaginable. And it will last millions of years. But why?
“As Andromeda and the Milky Way collide directly, it will take that long for their gas to be consumed by the resulting starburst,” Dr. Meyer said. “Locally, the Sun will be evolving from a red giant to a white dwarf. Given the vast star spacing in the two galaxies, it is very unlikely that the planetary orbits in the solar system will be disrupted by their collision.”
Of course, the Sun is currently a yellow dwarf and will have to evolve to a red giant, first. That will begin to take place around the same time that Andromeda and Milky Way first pass each other. In all likelihood, when that happens, all the water on Earth will boil away, leaving our planet a hot and lifeless rock. However, what will happen to our solar system when the galaxies collide?
“There is about a 10% chance that it will be thrown on a tidal tail into extragalactic space,” Dr. Meyer said. “It is less likely that it will be thrown near or into the merged supermassive black hole at the new galactic center. Due to the vast space between the stars, there is essentially no chance that it will collide with a star from Andromeda.
“Thus, most likely, it will be thrown into a large elliptical orbit around the new galactic center.”
Experiencing Hubble: Exploring the Milky Way is now available to stream on Wondrium.