How Space Collisions Work

Thanks to photographs from space telescopes and computer modeling, astronomers are able to search for and observe the existence of both galactic and stellar collisions. Scientists originally believed these types of space collisions, also known as mergers, to be fairly rare, but research in the early 21st century has found them to be fairly common. As experts understood more about the beginning of the universe and the Big Bang theory, they realized that galactic collisions were even more common in the early stages of time. Because the universe was much smaller, galaxies were huddled closer together, and, shooting out from the origin of the Big Bang, were likely to collide into others during their journey throughout space. Even our own galaxy, the Milky Way, carries with it debris from early collisions with other massive bodies, and astronomers expect the Andromeda galaxy, our nearest large neighbor, to swallow us up sometime in the distant future.

A space collision might sound like perfect material for an expensive Hollywood summer blockbuster, but watching one take place would actually be much less exciting than you'd think. Even though galaxies and stars move toward each other at hundreds of miles per hour, their mergers can take millions of years to form. Instead of exploding like massive bombs, space collisions act like smooth, undefined balls of gas. Once two stellar bodies meet, the massive gravity of each one will distort the shape of the other, usually resulting in a droplet shape. On April 24, 2008, for instance, the Hubble Space Telescope captured images of Arp 148, the aftermath of two galaxies colliding. While one galaxy took on the typical ring shape, its neighboring galaxy was stretched thin like a tail.

One common type of collision is between two neutron stars. Neutron stars are actually corpses of old stars -- when a star reaches the end of its life, it explodes, and a mass equivalent to the amount found in our sun condenses into an area the size of a city. When two are created in close proximity, they form what's called a binary pair and orbit each other, eventually merging after hundreds of millions of years. The combined masses of the dead stars are so heavy the event creates a black hole in space, and split second flashes of light brighter than a billion suns give off huge magnetic fields. Gravitational waves from a near neutron star pair could have the effect of displacing the oceans by about 10 times the diameter of an atomic nucleus -- a seemingly small amount, but quite large if we're talking about all the water in the ocean. Although there are only six known pairs of neutron stars on a path for collision, scientists believe there are many more out in space and that these types of mergers could happen as frequently as once or twice a year.

What about space collisions on a much smaller scale, such as one between an asteroid and the Earth? To read about asteroid impacts and the possibility of life surviving, see the next page.

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We've seen it countless times in the movies: An asteroid hurtling through space threatens life on Earth, and the heroes of the film are forced to come up with a way to stop its course and save the human race.

But what if the heroes didn't pull it off, and an asteroid actually smashed into the Earth? Would living organisms be able to survive an impact, or would the damage cause mass extinction?

Fortunately for anything with the usual biological processes, the chances of survival are a bit higher than you might think. Many experts believe the dinosaurs were wiped out by a deadly asteroid impact several millions of years ago, but many species survived the disaster, and we, of all animals, eventually made it to the top of the food chain.

Surviving a global catastrophe on the surface of the Earth is one thing, but are there any other options for struggling life forms following a devastating collision? In 2008, an international group of students from Germany, Russia, the United Kingdom and the United States published a research paper that tested the extraordinary possibility of bacteria surviving after impact with an asteroid. The study posed the interesting question of whether or not living organisms could either 1) be lifted outside of Earth's atmosphere on rocky debris and pulled back down to Earth or 2) be transferred, again via rocky debris, onto another potentially hospitable planet like Mars.

The students acknowledged the extreme difficulty of what's known as lithopanspermia, or the transfer of life from one planet to another by impact-expelled rocks. Any microorganisms attached to debris would not only have to survive the blast, they'd have to survive the ejection into space, the long journey (anywhere between 1 and 20 million years) from one planet to the next, radiation from the sun's rays and re-entry into the new planet's atmosphere.

They also point out that, in spite of the difficulty, the 40 Martian meteorites discovered on Earth suggest the trip has happened before. The students decided to test the particularly tough, radiation-resistant cyanobacteria called Chroococcidiopsis, usually found in hot deserts around the world. Using high explosives and high-pressure air guns to replicate the effect of an impact shock, they subjected the resistant bacteria, along with several others, to a lot of pressure. They arrived at the conclusion that survival is possible, but the bigger the blast, the better -- a large enough impact, somewhere between 5 and 50 GPa of pressure (diamonds form under about 10 GPa), would need to blow out the atmosphere to make escape less harmful for the organisms.

For lots more information on dazzling destructive bodies of energy floating through space, see the next page.