Sunday, April 13, 2008

Galactic Collisions: Andromeda and Milky Way

Welcome back to What's Up?

It's been yet another cold month, but don't fret as the stars are still shining, nebulae glowing, with Saturn and Mars bright in the sky, and Jupiter rising in the early morning sky around 1:30am by the end of the month.

This month we're going to venture far beyond the solar system, out into deep space to explore galactic collisions.

Imagine a massive galaxy, containing hundreds of billions of stars zooming toward another large galaxy. Most people would view something like this as a destructive event, but these titanic collisions are actually more of a creative event because the gravitational forces of each of the galaxies disturb nebulae within them to collapse into dense clumps that form stars.

Galaxies where extreme star birth occurs are called "star-burst" galaxies. One of the more well know galaxies of this type is M82, which can be found just north-east of the Big Dipper with a telescope.

Astronomers prefer to call galactic collisions mergers because that's what ends up happening: the galaxies merge into a single, large, disorganized accumulation of stars called an elliptical galaxy, such as the galaxy Virgo A.

Virgo A is a massive galaxy. It has gobbled up many smaller galaxies to become the large elliptical galaxy it is today whereas the Milky Way is a fairly large galaxy that contains up to about 300 billions stars, Virgo A contains a few trillion!

At the present time galaxy mergers are by no means common. Only one in every few hundred galaxies in the process of merging, or interacting with another nearby galaxy. A great example of interacting galaxies is the Tadpole Galaxy, which is a spiral galaxy with a long "tail" of dust and gas streaming away from it.

Although it may not be common to see merging galaxies today in the present universe, it was probably much more common in the past because the universe was much smaller than it is today. This cramped early universe experienced many such collisions and interactions with other galaxies. Using large telescopes, like the Hubble telescope, astronomers can get snap-shots of different mergers and get a general idea of what happens.

Very recently, with the power of computers increasing drastically, astronomers have been using supercomputers to make simulations of what would happen if two or more galaxies were to collide, or orbit around each other slowly coming closer and closer until they eventually merge.

For a visual of, merging galaxies with a little bit of interactivity, you can watch such a simulation at: "". You can do your own simulation at "" and be able to put in what galaxy types, size, etc. you have in the simulation.

An interesting event for the future of our galaxy is the possibility of it merging with the Andromeda Galaxy. The Andromeda Galaxy is the closest large galaxy to us. You can see it for yourself because it is one of the brightest galaxies in the sky. You can even see it with the naked eye during Fall-evening viewing!

This galaxy and our own are heading towards each other at an astounding rate, but their distance apart is so great that the galaxies won't merge for about 3 or 4 billions years. Don't worry about our solar system being destroyed by this incoming galaxy, that will be colliding with us at a speed of one million miles per hour, because stars rarely collide because they are space so far apart within a galaxy.

Since things in the universe are spaced so far apart it may be very difficult to visualize the distances between things. Imagine the Milky Way and Andromeda as each being the size of a CD. Now hold them eight feet apart. That is about their sizes relative to the distance between them.

Once you've put those CDs away we'll take a peek at what's up in the sky.

There will be a new moon on April 6. This new moon will fill to full by April 20.

Between the new and full moon is the Russian Soyuz rocket launch on April 16th. This will be the 17th mission to the International Space Station.

I'd like to give a special mention to the astronauts aboard the last shuttle mission to the International Space Station in March for setting up Canada's enormous space robot Dextre. This robot will take take over the dangerous task of assembling the space station and doing routine repairs.

I also applaud everyone who participated in Earth Hour on March 29th and turned out their lights for one hour. I that everyone is more aware of light pollution's detrimental effects on our beautiful night sky.

Until next month, just look up!

Hey Kids...
You, too, can check out the thin crescent moon. It will be very thin and faint on April 4, the hardest day to find the moon. You will need to get up early, a bit before 6am armed with a pair of binoculars to look for the moon low on the eastern horizon(where the sun rises). Make sure to be careful about the rising sun because looking at the sun through binoculars can easily blind you in an instant! Also this month, starting April 8 or 9, watch as the moon's phase slowly changes from night to night throughout the month.

Andrew Reeves lives near Kinkora and is a member of the Athena Community Astronomy Club. His column appears the first Saturday of each month. To learn more about astronomy or the club go to or contact him at