Andromeda the Milky Way versus Sol
Will the Galaxies Collide before the Sun Blows up?
The question itself raises other questions. How old is the sun and how long will it live? How far away from each other are the two galaxies and how fast do they travel?
How big are the two galaxies and are they on a collision course? Is the collision course direct or at an angle? What is a collision?
The Milky Way
The center of our galaxy, the Milky Way, is about 26,000 lights years away from Earth. In celestial terms distance is very big and is calculated in light years; however, the center of the galaxy is not a point but a central disk 12,000-18,000 light years across. It contains 20% of the visible mass and 38% of the total mass of the galaxy. Also we know that the Milky Way is about 100,000 light years across (from one arm to another.)
To determine how many stars are in a galaxy astronomers use the term solar mass. The total solar mass in the Milky Way is about 400 billion +/- 200 billion. We can say there are about 400 billion stars like our sun in the galaxy (not including dark matter.)
Andromeda
The Andromeda galaxy (M31) has about 300 billion +/- 150 billion solar masses. Andromeda, while having fewer stars, is about 5 times bigger in diameter than the Milky Way or 500,000 light years across and 2.2 million light years from Earth.
The Sun
Our sun, Sol, is a middle of the road type G star with an absolute magnitude of +4.85. It is about 5 billion years old and half way through its life. It will end its life as a Dead White Dwarf Star. But this second half of the sun’s life is quite important for life on Earth. Approximately 4.5 billion years from now the sun will start to expel its atmosphere and become a red giant. At that point there is dispute whether the sun will engulf the earth or the weaker mass of the sun will allow the earth to escape the sun’s gravity. In either case the atmosphere on Earth will be blown into space and the oceans will dry up. The earth will become a very inhospitable place at best.
The sun will continue for many millions of years blowing its atmosphere into space creating a planetary nebula, but life on earth will cease to exist.
The Collision
Andromeda and the Milky Way are approaching each other at a relative speed of 0.047% the speed of light. Two scientists Cox & Loeb of Harvard figured that the two will start to get here about 2.3 billion years from now.
But what is a collision? Such a fundamental question has actually a far reaching answer. People think that a collision means things physically hitting each other. In galactic terms that is not always the meaning. The two galaxies will definitely come “between” each other but space is extremely large. The collision that is spoken of here is with reference to the gravitational effect of one object upon another, in this case two galaxies.
As we said above the galaxies are huge and have billions of stars and planets in each one but they also have much more empty space than solid matter as we tend to think of it. While the actual galactic “collision” will last about 2.8 billion years there will be few if any actual stellar impacts, according to Astrophysical Theorist Dr. Chung-Pei Ma. "Galaxies are mostly empty [space], so the stars and dark matter mostly just pass each other by. The chance of two stars hitting each other is tiny."
The results
The gravitational forces of the two galaxies will reshape into a single galaxy. Cox and Loeb have called this new, resultant super galaxy Milkomeda. During the first encounter with Andromeda our sun will still be turning hydrogen into helium so advocates can say the collision will occur first. However, as shown in the University of Toronto time lapse video of the galactic collisions, it will take nearly 5 billion years from now for the two galaxies to completely merge. Our sun will have become a red giant long before that. So supporters of the sun’s demise can argue their position as well.
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