The Andromeda Galaxy is also known as “M31” and is a spiral galaxy and the closest neighboring galaxy to our Milky Way. As Andromeda moves through the universe it is bringing along 14 dwarf galaxies, including M32, M110, and M33 (Triangulum Galaxy) It’s one of the few galaxies that we can see from Earth, and that’s saying a lot since it is 2.5 million light-years away from us.

Andromeda may be our neighbor, but it’s not our friend. Andromeda is moving closer to us and is expected to collide with the Milky Way in around 4.5 billion years. When that happens it’s thought that two galaxies will merge, creating a giant elliptical galaxy.

There are only ten galaxies that we can see with the naked eye and Andromeda is one of them. It’s a pancake-shaped disk spiral galaxy and when viewed in regular light the Andromeda galaxy’s rings look more closely like spiral arms. It takes ultraviolet light viewing to be able to distinguish that they are actually rings. Astronomers believe that these rings are the result of a collision over 200 million years ago between the Andromeda galaxy and its neighbor, M32.

The Hubble Telescope assembled 7,398 images that were taken over 411 individual telescope pointings to create one of the best and largest pictures of the Andromeda galaxy. It totals 1.5 billion pixels that show over 100 million stars and thousands of star clusters. To give you a comparison of this accomplishment, it would be like taking a picture of a beach and identifying individual grains of sand.

Andromeda Statistics:

  • Galaxy Type: Spiral
  • Diameter: 220,000 light-years
  • Mass: 1,230 billion M
  • Constellation: Andromeda
  • Group: Local Group
  • Number of Stars: 1 trillion


Due to the fact that the Andromeda galaxy has been viewed by cultures all over the globe, it’s impossible to say who actually discovered it. In 964, Abd al-Rahman al-Sufi, a Persian astronomer wrote in his “Book of Fixed Stars” that the galaxy appeared to look like a “small cloud.” This is the first known documentation of the Andromeda galaxy.

Great Andromeda Nebula

In 1764, Charles Messier labeled the galaxy as M31 and incorrectly gave credit to what was then called a “nebula” to Simon Marius, a German astronomer, who was the first to observe the galaxy in a telescope. Isaac Roberts is given credit in 1887 for taking the first photographs of the Andromeda galaxy.

In the early 1900s astronomers had thought that the Milky Way was the entire universe and that the strange areas that they called the “nebula” existed inside the Milky Way. By the 1920s American astronomers Heber Curtis and Harlow Shapley began what is called the Great Debate to question the assumptions because Curtis had found novae in the Andromeda galaxy and was stating that it was a galaxy separate from the Milky Way.

It wasn’t until 1925 that this “debate” ended when Edwin Hubble identified a special kind of star that would help with distance calculations within Andromeda. Prior to that time, Shapley had indicated that the Milky Way was only 100,000 light-years across and Hubble’s new figures countered that information by saying that the novae in the Andromeda galaxy was too far away to be inside the Milky Way. Hubble’s research continued as he used Doppler shift measurements of the galaxies to figure out that the universe was expanding.

In the 1940s, Walter Baade officially doubled the distance to Andromeda as he became the first to observe stars individually that existed in the galaxy’s central region. The 1950s radio maps of Andromeda created even more accuracy after radio emissions were detected at Jodrell Bank Observatory by Cyril Hazard and Hanbury Brown.


The Andromeda galaxy is 260,000 light-years across and images taken from our high tech telescopes show blue-white bands that make up the areas that hold the large young newer stars. The cooler dust shows up as dark blue-grey lines, and the cloudy dense cocoon areas are where new star formations are occurring. When the stars are born they will ignite their core’s nuclear fusion and the dust will be blown away with stellar winds. The orange-white ball in the center area is a collection of the older, cooler stars that were created a long time ago.

Andromeda, like the Milky Way, is a spiral galaxy that has a concentration of matter in the middle that causes a bulge. This bulge is encircled by a disk of dust, stars, and gas and has a large halo. Even though Andromeda has more stars that our Milky Way galaxy, it’s actually smaller in size. Scientists believe that the Milky Way contains more dark matter than Andromeda, making our galaxy larger.

The Hubble Space Telescope images have detailed a lot more information showing densely packed stars in the Andromeda galaxy that extend from the hub’s innermost area. The images include lanes of dust and stars that sweep out to the outer disk. The yellow-colored stars that are in the center of Andromeda are the cooler stars.

Interesting Information:

The middle bulge of the Andromeda galaxy is larger than the one in the Milky Way galaxy. Scientists believe that this explains why 7 of the 35 known black hole candidates are so close to that galaxy’s center. All seven are within 1,000 light-years of the center. 8 of the 9 black hole candidates identified in the Andromeda galaxy were associated with globular clusters. These are clusters in the center of Andromeda that are star concentrations of the past. Scientists haven’t been able to find even one black hole in any of the globular clusters of the Milky Way.

Exploration and Study:

NASA’s Chandra X-ray Observatory has been critical in the discovery of 26 black hole candidates in the Andromeda galaxy. This makes Andromeda’s black hole count the largest number found so far in any galaxy outside of the Milky Way. A team at the Harvard-Smithsonian Center for Astrophysics used Chandra over a period of 13 years to accomplish 152 observations. This expanded the 9 black holes that were previously known to 26 new black hole candidates. The new black holes were placed in the stellar-mass black hole category, which are black holes that are 5-10 times the mass of the sun and are created due to the collapse of a massive star.

The Andromeda Galaxy as seen by NASA

A wide-field view of the Andromeda galaxy was taken from the Burrell Schmidt telescope of the Warner and Swansey Observatory in Arizona. Additional details of Andromeda’s core and the spiral arm dust were taken from an image by Vincent Peris, an astrophotographer. Scientists combined the images to show the different bands of red, green, and blue in the visible light area of the electromagnetic spectrum.

Important Events:

  • 2011: Using infrared wavelengths, scientists were able to track the star birth and death rates in the Andromeda galaxy.
  • 2013: Astronomers identify a ring of dwarf galaxies around the Andromeda galaxy.
  • 2013: Using NASA’s Chandra X-ray Telescope, scientists found 26 black hole candidates in the Andromeda galaxy.
  • 2015: Hubble Space Telescope identifies material around the Andromeda galaxy that is described as a “halo”. The halo is 1,000 times more massive and 6 times larger than past size measurements. The increased size allows scientists to speculate whether the Milky Way galaxy has a halo and if so, the two halos may already be merging as the galaxies get closer together.
  • 2015: The Hubble Space Telescope completes a mosaic picture of the Andromeda galaxy that is made up of 7,398 exposures that were taken over 411 telescope pointings. Scientists made note that the image offers update details showing over 100 million stars in the Andromeda galaxy along with dust structures and features that were previously not seen.
  • 2016: Using NASA’s NuSTAR (Nuclear Spectroscopic Telescope Array), scientists discover an additional 40 black holes in the Andromeda galaxy.
  • 2017: Discovery of gamma-ray radiation that could be an indicator of dark matter in the Andromeda galaxy and used to identify dark matter in the Milky Way galaxy.
  • 2017: Scientists were surprised when they found two supermassive black holes in the Andromeda galaxy that had a close orbit to each other. The discovery was the “most tightly coupled” supermassive black holes that had been found to that date.
  • 2017: Using NASA’s NuSTAR (Nuclear Spectroscopic Telescope Array) astronomers found a probable pulsar in the Andromeda galaxy, which is a fast-spinning dead star that had been observed earlier.

In 4 billion years the Milky Way and Andromeda galaxies will collide. The collision will change the structure and contents of the two galaxies. They are racing closer to each other at a rate of around 70 mi/112 km per second. The merger will probably take another 2 million years to complete. Based on that time schedule, it will be well after the date when our own sun ends its life by turning into a red giant and expanding to consumer the terrestrial planets, including Earth.

Facts about Andromeda Galaxy for Kids:

  • Andromeda may be the largest galaxy in our Local Cluster but it isn’t as massive as the Milky Way. Scientists think this is due to the Milky Way containing more dark matter.
  • Astronomers use the Andromeda galaxy for detailed study in an attempt to understand the evolution and origin of galaxies.
  • The Andromeda galaxy is moving closer and closer to the Milky Way galaxy at a speed of 100-140 km per second.
  • Andromeda galaxy’s spiral arms are being twisted or distorted due to the gravitational interactions that it has with two other neighboring galaxies: M32 and M110.
  • The Andromeda galaxy has around 450 globular clusters that orbit around and in it, making some of them among the highest density population of globulars that have ever been recorded so far.
  • The double nucleus of the Andromeda galaxy is extremely crowded. It contains a huge star cluster at the very center as well as a supermassive black hole that is hidden at the core.
  • Scientists believe that the Andromeda galaxy’s ring of dust and two spiral arms may be due to interaction with the smaller M32 galaxy when M32 took a plunge into the heart of the Andromeda galaxy.
  • While you need a really good location that is away from all bright lights, the Andromeda galaxy is the most distant object in the celestial skies that you can view with the naked eye.

Pop Culture:

When it comes to popular fiction, the Andromeda galaxy is one of the galaxies that has been the focus of stories, film, television, and even games. Some of the more popular include:

  • Superman: Birthright a comic that had Kryton orbiting an M3 star in the Andromeda galaxy.
  • Skrull, a Marvel Comic, is an empire made up of about a thousand worlds inside the Andromeda galaxy.
  • The BBC television series of 1961 entitled A for Andromeda focused on a radio signal received from the direction of the Andromeda galaxy. It followed with another series sequel called The Andromeda Breakthrough.
  • The 1963 television series, The Outer Limits, had an episode entitled The Galaxy Being about a radio station engineer that is in contact with a peaceful alien from the Andromeda galaxy that is somehow transported by accident to Earth.
  • A Star Trek episode in 1968 called “By Any Other Name” involves the starship Enterprise being hijacked by aliens in an empire from the Andromeda galaxy. Another episode of the series called “I, Mudd,” has an android that states that their creators were humanoids from the Andromeda galaxy.
  • In Gene Roddenberry’s Andromeda, the Systems Commonwealth claimed territory in the Andromeda galaxy.
  • Doctor Who fans will remember the two episodes involving the Andromeda galaxy in “The Ark in Space” and “Evolution.”
  • Monty Python’s Flying Circus Series 1, Episode 7 included a comedy sketch about aliens from the Andromeda galaxy.
  • The film “Guardians of the Galaxy” primarily takes place in the Andromeda galaxy.