The Milky Way’s closest galactic neighbor, the Andromeda galaxy is one of only a few galaxies that can be seen by the naked eye from Earth. The Andromeda galaxy is thought to be between 3 billion and 10.01 billion years old (more on this later!). One slightly alarming fact is that Andromeda and the Milky way are predicted to collide in the future – but don’t worry too much, it’s estimated to collide in 3.75 billion years at which point the sun will be a red giant and Earth will be gone. Hubble helped us determine that Andromeda is moving towards us at about 250,000 miles per hour – a speed that could get you from Earth to the Moon in only one hour.
Scientists used to believe that Andromeda was around two or three times the size of our own galaxy, however, new scientific research shared in 2018 suggests this is not the case. It turns out that Andromeda is roughly the same size as the Milky Way and we had previously overestimated the amount of dark matter in the Andromeda galaxy. The study was authored by Prajwal Kafle from the University of Western Australia.
“By examining the orbits of high-speed stars, we discovered that this galaxy has far less dark matter than previously thought, and only a third of that uncovered in previous observations.”
This is somewhat curious since Andromeda does have substantially more stars than our own galaxy. There is thought to be around one trillion stars in the Andromeda galaxy, significantly more than the Milky Way’s 200 to 400 billion stars.
Andromeda, or Messier 31 as it is otherwise known, is located 2.5 million light years from Earth. The galaxy gets its name from the area it is located, within the constellation of Andromeda – named after Princess Andromeda from Greek mythology. It is not totally correct to say Andromeda is the galaxy closest to our own, but it is the closest spiral galaxy to our own. There is actually a dwarf galaxy that lies within the Milky Way that is the closest galaxy to us. This dwarf galaxy is called Canis Major Dwarf Galaxy, it lies 30,000 light years from our solar system, and we’ve only known about it for around a decade.
Both the Milky Way and Andromeda lie within a region astronomers refer to as the “local group.” Frustratingly, it is difficult to find a straight answer to how many galaxies are within our local group since different scientific institutions cite different numbers, however, it lies somewhere between 30 and 60.
Using computer simulations, Astronomers have determined that Andromeda likely formed from the collision of two smaller galaxies billions of years ago. A team of researchers in China and France worked together to model the formation of the galaxy. This is no easy feat of computing and requires some impressive processing power. The researchers used eight million particles to simulate the gas, stars, and dark matter that is Andromeda. Researchers concluded that 10 billion years ago the matter that is now Andromeda was two separate galaxies. Around 8.75 billion years ago they began to collide, finally completing their collision 1.8 to 3 billion years ago. This means Andromeda as we know it is younger than our solar system which is close to 4.6 billion years old.