Milky Way - Andromeda Collision

Our galaxy, Milky Way and its nearest large neighbor the Andromeda galaxy (M31), are on a collision course. Billions of years from now, the merger will transform the structures of both galaxies and creates a new arrangement of stars we have dubbed MILKOMEDA (Milky Way + Andromeda). The merger will radically transform the night sky.

Currently, the Milky Way's thin disk of stars and gas appears as a nebulous strip arching across the sky. As Andromeda grazes the Milky Way, a second strip of stars will join the one that presently graces the night sky in summer. After the final merger, the stars will no longer be confined to two narrow lanes, but instead, scattered across the entire sky.

In the research, Astrophysicist have explore the Milky Ways fate by simulating the Milkomeda's birth in a super computer. The simulations are at sufficient level of detail (resolution) to learn a lot about the coming merger and how it will change our perspective on the universe. Although we won't be here to witness the event, this is the first research on Earth that has a chance of being cited 5 billion years from now.

The Andromeda Galaxy
It is the largest galaxy among the local groups and a neighbor of Milky Way, located just next of Alpha Centauri, nearly 2.5 million light years away. Fourteen satellite galaxies accompany Andromeda, including the two visible on this image: M32 [above Andromeda] and NGC 205 [below Andromeda].

Evidence of the dynamic connection between the Milky Way and the Andromeda comes from their relative motions. The galaxies are barreling towards each other at nearly 270,000 mph (190,000 km per hours). This is because, the spectral lines of Andromeda's light appear to be blueshifted - displaced toward the blue end of the spectrum - by the Doppler effect. In contrast, most galaxies in the universe are flying away from the Milky Way.

Nearly 50 years ago, Franz Kahn and Lodewijk Woltjer pioneered the "timing argument". This hypothesis held that the Milky Way and Andromeda formed close to each other, during the dense in the early stages of the universe.

Subsequently, the general expansion of the universe pulled the two galactic neighbors apart. Later, the Milky Way and Andromeda reversed their out/vard trajectories owing to mutual gravitational attraction. Since then, they have completed nearly a full orbit around each other.

The timing argument, combined with estimates of the galaxies' relative velocities and other factors, indicates the local Group's total mass is about 3 trillion times the sun's mass. It also suggests the Milky Way and Andromeda will make a close pass in about 4 billion years.

FROM EARTH - we see the Milky Way from an insider's perspective. Depending in the time of year, an Earth-bound observer can see 3 or 4 different arms of the spiral.

CHANGE OF FORTUNE:
The Sun's peaceful orbit around the center of the Milky Way - which it has traverse nearly 20 times since it birth - will forever change. Its new path will be far more chaotic owing to the rapid fluctuations in gravity induced by the merger. What would this mean for Earth and its residents?

Research suggest that the Milky Way and Andromeda will begin to interact strongly 2 billion years from now, and then complete the merger in about 5 billion years. The latter date is especially notable because it coincides with the sun remaining life span. Currently, our sun is about halfway through its lifetime and eventually will begin to expand. As it does so, it will consumes all its available hydrogen and evolve toward a red giant phase within 5 billion years. In short, the sun will be in its death throes on Milkomeda's birthday.