Andromeda Milky way Galaxies the Differences Similarities of two Neighbors

The Milky Way and Andromeda (M31) galaxies made news in May when NASA officials confirmed that the two are headed for a cosmic collision within the next four billion years – an additional two for it to merge and then another two billion for when Andromeda’s companion, Triangulum galaxy (M33) also makes an impact.

Andromeda is our closest galactic neighbor in this sea of galaxies. Scientists have said for years that there are many similarities between the Milky Way and Andromeda, especially throughout our evolution during the first billion years.

But before our two galaxies have their destined clash, merge and form one elliptical galaxy, what are the similarities and differences do the Milky Way and Andromeda share? Here are some interesting facts about the neighbors.


Andromeda is more than 2.2 million light years away from us, but it is honing in on our galaxy.  It is between 70 and 80,000 light years across and 222,000 light years in diameter. This was measured through the observations of 3,000 of its stars.  Meanwhile, the Milky Way is approximately 100,000 light years in diameter and only 1,000 light years thick.


The Milky Way maintains a galaxy of more than 200 billion stars and most of the stars located in the disk of our galaxy. Andromeda, meanwhile, has five times as many stars as its neighbor with one trillion stars.


Although it is difficult to spot planets in sister galaxies, there have been planets discovered in Andromeda.  The four extrasolar planets are: Upsilon Andromeda b (AKA: HD69830 b), Upsilon Andromeda c (AKA: HD69830 c), Upsilon Andromeda d (AKA: HD69830 d) and HD 8673 b.

With the vast amount of stars in our galaxy and even Super-Earths, it is possible that one day life could be found in the Milky Way.  Every year, astronomers discover these exoplanets and 54 of them, thus far, are placed in the habitable zone or Goldilocks Zone.  It is estimated that there are 50 billion planets; 500 million of them could be located in the habitable area.

Black holes

Scientists believe supermassive black holes are located in the center of each galaxy. Therefore, it is safe to assume that Andromeda shares a similarity in maintaining not only a black in its epicentre, but also the number of black holes.


In 2006, a group of researchers at the California Institute of Technology stated the Milky Way and Andromeda galaxies had similar origins throughout its first several billion years. It detailed the study of the motions and metals of roughly 10,000 stars in Andromeda and concluded they were metal-poor – if both are poor then they both had similar upbringings.

Indeed, there are differences between the two galaxies, but eventually, in the next four billion years, the two will form and no longer will scientists (if they are still around) have to differentiate between the two.