With the naked eye in a dark sky location, it is possible to see both a nebula and a galaxy. With a telescope, you can see many more of each. They both appear to be of a similar size. This may lead some to ask, are nebulae bigger than galaxies?
In this article, we will delve into this question. We will first answer the question directly. Once that is out of the way we’ll look into what each of them are and how they are different.
So let’s answer the question.
Are Nebulae Bigger Than Galaxies?
The simple answer is no; nebulae are not bigger than galaxies. In fact, they are much smaller.
The Milky Way is thought to be approximately 100,000 light-years across. Our galaxy has a couple of accompanying galaxies. One of them, the Small Magellanic Cloud, is just 18,900 light-years across. The largest known galaxy is 16,000,000 light-years across.
In comparison, nebulae are several light-years to hundreds of light-years across. Nebulae are one of the constituents of galaxies. They are the matter from which stars are born; more about later.
So now that we have answered the question let’s explore information about nebulae and galaxies. We will also have a brief look at the types of each.
What is a Nebula?
A nebula is a diffuse cloud of gas and/or dust. They can either emit light, reflect light, or block light. As this indicates, there are various types of nebulae, as listed below.
Types of Nebulae
- Emission Nebulae: These are clouds of gas that emit their own light. They are found in association with large stars. The light from such stars excites the atoms in the gas. This occurs when electrons in the atoms move to higher energy levels. This excited state is unstable, so the electrons spontaneously return to lower energy levels. As a result, the emitted light may differ from the original light. The gas in these clouds is dominated by hydrogen but can include other gasses such as oxygen and sulfur. In natural color, these nebulae normally appear to be red.
- Reflection Nebulae: As with emission nebulae, we can see light from them. However, reflection nebulae do not emit any light. They reflect the light of other objects, mainly stars. This type of nebulae is blue in color.
- Dark Nebulae: No light can be seen from this type of nebulae. Their presence is detected due to them blocking the light from objects behind them. They contain a high percentage of dust.
Below are examples of each of the three main types of nebulae. Be aware that within the main types, there are sub-types. Also, some nebulae contain more than one type of nebulae. For example, the Trifid Nebula has emission and reflection nebulae (as shown below).
How do Nebulae Form?
Nebulae are formed from clouds of interstellar gas and dust or from the remains of pre-existing stars that have gone through a supernova (What is a nebula?). In the former case, the cloud was initially cold. In this cold state, reflection and dark nebulae can be formed. The gas can also be excited due to the formation of stars in close proximity to form emission nebulae.
Incidently the initial cold clouds of gas and dust are the material of which stars are made. Newly formed stars may be the source of the energy of emission nebulae. Clouds of gas and dust are often referred to as stellar nurseries. Solar systems may subsequently form with the stars from the same material.
Once a star has gone through a supernova, gas and dust are ejected into space. The stellar corpse radiates energy that excites the ejected gas to form an emission nebula. This process produces what is called a planetary nebula.
Which Nebula is Closest to Earth
The closest nebula to Earth is a planetary nebula called the Helix Nebula. It is about 660 light-years from Earth. The star that formed it is believed to have gone into supernova about 10,600 years ago. The nebula is about 2.87 light-years across.
What is a Galaxy?
A hundred years ago, many scientists believed that everything in the night sky was contained within the Milky Way. The spiral structures of galaxies were thought to be spiral nebulae. Other scientists argued that they were structures much like our own galaxy.
Early in his career, Edwin Hubble studied the ‘spiral nebulae’ and provided definitive evidence of what they were. He noticed that they contained a certain type of variable star. These variable stars can be used to calculate their distance. When the calculations were completed, it was found that they were at a distance far in excess of what the size of our galaxy was thought to be (Hubble Views the Star That Changed the Universe).
We now know galaxies are large collections of millions to billions of stars and associated gas and dust. At their cores supermassive black holes are commonly found. They are held together by gravity. The observed motion of galaxies suggests that they contain significant amounts of matter that we have yet to identify. This matter is what we call dark matter.
Types of Galaxies
Galaxies are classified by their structure. Edwin Hubble devised the classification scheme. He was one busy man!
Galaxies are grouped into elliptical galaxies and spiral galaxies. The ellipticals are round to oval-shaped with no spiral structure. Obviously, the spiral galaxies have spiral structures. Spiral galaxies are further divided into normal spirals and barred spirals. The normal spirals have a round central bulge, with the barred sprals having an elongated central bulge.
A separate group contains irregular galaxies with shapes not covered in the other groups.
For more information, see Why Are Galaxies Flat?
How do Galaxies Form
Galaxy formation is an area of active research. There are a couple of competing ideas. In the early history of the universe, it is thought that the primordial gas collapsed and started rotating. Top-down theories propose that galaxies form directly from huge clouds of gas to form galaxies. The opposing bottom-up theories propose that gas formed much smaller bodies that merged to form galaxies.
Whichever theory is correct, galaxies continue to develop. Further mergers concentrated matter further and allowed for the development of structures within galaxies.
An important aspect of galaxy formation is that their supermassive black holes develop simultaneously.
Which Galaxy is Closest to Earth
The closest galaxy to Earth is a satellite of our own galaxy. It is called the Sagittarius Dwarf Spheroidal Galaxy and is 65,230 light-years from Earth.
If we ignore the dwarf galaxies that orbit our galaxy, the closest is the Andromeda galaxy. This galaxy is so close that it is visible with the naked eye under dark skies. It is 2.5 million light-years from Earth and getting closer. On its current path, it will collide with our galaxy. This collision will cause many nebulae to form in both galaxies due to the compression of interstellar gas. However, it is nothing to worry about because that will not occur for another 4.5 billion years. That is nearly as long as our Sun has before it dies to, perhaps, form a planetary nebula.
If you could see the full extent of the Andromeda galaxy, its length would be about five and a half times that of a full Moon. The first image in this post is of Andromeda.
Final Thoughts
So there you have it. Nebulae are not bigger than galaxies. In fact, they are significantly smaller and are one of the constituents of galaxies.
However, nebulae are very important. They lead to the formation of new stars and, ultimately, solar systems like our own.
We hope that you have a good understanding of both nebulae and galaxies.
Now that you have some understanding of how the Sun was formed, you may like to know how the Sun produces energy.
I found astronomy while working in dark rural locations. Initially, I explored the night sky and learnt the constellations before purchasing a pair of binoculars to further my knowledge of the sky.
My first telescope was a 200 mm Newtonian reflector on an equatorial mount. I found that this telescope had a steep learning curve but was a rewarding experience.
As time progressed, I became interested in astrophotography. This resulted in purchasing a 110 mm refracting telescope and a dedicated monochrome-cooled astronomical camera. This resulted in another very rewarding steep learning curve that far surpassed the experience with my first telescope.
I have joined Telescope Guru to share my knowledge of telescopes and astronomy.
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