10 Spiral Galaxy Facts – How They Form

Spiral galaxies provide us with some of the best views in our night sky, and many of the most well known galaxies are actually spirals. They’re named as such because of their swirling appearance, which means that they end up looking like a throwing ninja star.

Unlike irregular galaxies, a spiral galaxy can usually be easily identified – this is made even easier with high powered equipment like the Hubble Space telescope.

Spiral Galaxy Facts

  1. There are many different examples of galaxies that are spirals, including the Triangulum Galaxy, the Whirlpool Galaxy and the Pinwheel Galaxy.
  2. Until 2005, we defined the Milky Way as a spiral galaxy. However, upon closer inspection we confirmed that it us actually a barred spiral galaxy.
  3. The center of a spiral galaxy is something we call the Bulge, which is a very large group of stars, giving a super bright appearance.
  4. Along with the other types of galaxy, the Spiral galaxy was first defined by Edwin Hubble in 1936.
  5. Spiral galaxies are further classified by how tight their arms are e.g. A-type have tight arms, whereas C type have loose arms.
  6. The former oldest spiral galaxy in our universe is called BX422. It is thought to be around 11 billion years old, two billion years older than any others. This was replaced in 2020 by the Wolfe Disk galaxy, which is more than 12 billion years old.
  7. The larger a galaxy is, the faster that it spins – larger galaxies can spin twice as fast as smaller ones.
  8. Large spiral galaxies can spin their arms at a speed of more than 1.25 million miles (2 million km) per hour.
  9. The closest spiral galaxy to our Milky Way is the Andromeda galaxy.
  10. The first galaxies were actually discovered in the 17th Century, although they were not called galaxies until much later by Edwin Hubble.

What is the structure of a spiral galaxy?

When we’re considering a spiral galaxy, we generally look for different parts that make up its structure. We have the bulge. which is a high concentration of stars right in the middle of the galaxy. Another important part of a galaxy is its arms, which are regions of stars that give it its spiral appearance.


As well as this, we also potentially have a bar of stars in its center – however, this is only the case for barred spiral galaxies. Many time a spiral galaxy won’t actually have this in its center, in which cases, it’s a regular or ordinary spiral.

When a galaxy like this has very well defined spiral arms, then we refer to it as a grand design spiral galaxy. It’s usually very easy to identify these types of spiral arms, in comparison to a multi-arm spiral galaxy, which may be much more difficult to identify.

Most Asked Questions about Spiral Galaxies

Do elliptical galaxies evolve into spiral galaxies?

It was first thought by Edwin Hubble that the elliptical galaxy actually evolved into a spiral galaxy. However, this was later disproven by astronomers (this happens with quite a lot of stuff from past theories, as we get more and more data and ability to study theories from astronomers of the past).

What are the two types of spiral galaxy?

If you see someone talking about the two different types of spiral galaxy, they’re generally referring to the difference between a spiral galaxy and a barred spiral galaxy. However, there are more classifications of spiral galaxy within each type.

How is a spiral galaxy formed?

The first thing we need to understand about the arms of the spiral is that they are not connected – they are just stars grouped together to give this appearance. It’s thought that these arms of a spiral galaxy are actually density waves, which are like sound waves, that move around the galaxy much slower than it’s stars.

What are the characteristics of a spiral galaxy?

Spiral galaxies tend to be very easy to identify from other types of galaxy. They have a big bright spot in the middle, which we called the bulge – this is a big group of stars that are within close proximity of each other. Outside of this is the spiral, or the arms of the galaxy, which are typically spirally around the bulge in the center.

What is an example of a spiral galaxy?

There are many different spiral galaxies that are visible in our night sky. In fact, more than 75% of all the visible galaxies are spirals! Probably the best example of a true spiral galaxy is the Pinwheel galaxy, which is a face-on spiral galaxy.


All in all, spiral galaxies are the most abundant in our night skies, with many people thinking they’re the most attractive galaxies too. With many of our most well known galaxies being spirals, it makes sense that they are the most well known within astronomy.

The largest spiral galaxies should be very easy for you to see in the sky too, as large galaxies with spiral structures at their very center are then surrounded by dark matter, which can make the spiral itself appear to be even more massive.

Leave a Comment