We explain what a nebula is, what types exist and their characteristics. Also, what is the Orion Nebula.
What is a nebula?
The nebulae are cloud-like concentrations of gas and stellar dust with striking colors. They are important for the universe because stars are formed within some of them (as a consequence of condensation and aggregation phenomena of matter). In other cases, they only contain remains of extinct stars.
Nebulae can be found anywhere in interstellar space. In our galaxy (the Milky Way), nebulae are found at great distances from Earth which are measured in light years.
However, it is possible to have detailed images in which its majesty can be appreciated, thanks to scientists who operate with complex and sensitive instruments, such as the Hubble space telescope.
Type of nebulae
Nebulae have different shapes and sizes, and are divided into four types:
- Reflection nebulae They are those that reflect the light of nearby stars (stars that do not emit enough radiation). They present colors in bluish tones due to the way light is scattered by the dust particles of the nebula. For example, the “Pleiades” nebula (or also called “seven sisters”).
- The emission nebulae They are the most common, those that emit their own light due to the alteration of the hydrogen atoms that receive ultraviolet radiation from the stars. For example, the “Omega” nebula.
- Absorption nebulae. Also called “dark nebulae”, they are not directly visible. They are those that do not emit light and hide the stars they contain. The first astronomer to discover this type of nebulae was the German William Herschel. For example, the “horsehead” nebula.
- The planetary nebulae. They are those that emit the light of the stars they contain, after they expel their outermost layers of gas (their last stage of life). This type of nebula is shaped like a ring or bubble. For example, the “Helix” nebula.
Characteristics of nebulae
The nebulae are composed of gas (hydrogen and helium predominate) and dust. They reach a diameter of hundreds of light years in length. are formed by the explosion of supernovae that is, they are the consequence of the last stage of life of the stars.
When a star has no more fuel to burn (gases), its core begins to collapse under its own weight and this generates an abrupt expulsion of the outer layer that expands into space, giving rise to varied and striking shapes: the nebulae
For example, The destiny of the Sun is to become a “planetary” nebula and end her days as a “white dwarf.” In about five billion years, the Sun will exhaust its hydrogen reserve and become a giant red star, expanding beyond Earth's orbit.
Hundreds of millions of years later, half of its mass will emanate into outer space, so it will be seen (from distant star systems) as a large planetary nebula, where the Solar System once existed.
Another very significant and interesting feature is that some of the nebulae can give rise to stars and planetary systems. Stars form from gas and dust found in some nebulae, such as the Pillars of Creation and the Eagle Nebula.
There, gas and dust accumulate due to their own gravitational effect (that is, the nebulae undergo a process in which they shrink). A fragmentation of matter into smaller groups occurs and each of them can heat up to start a nuclear reaction that becomes a new star.
The rest of the matter that fails to become a star is part of the material that will give rise to a planet or other objects in the Solar System.
In addition to nebulae, there are groups of ancient stars (some of the oldest in the universe) called “globular clusters,” which orbit the galactic nucleus (the center of rotation of our galaxy).
These clusters are attracted to each other by the force of gravity, so they form spherical regions. Hence the origin of its name, from Latin globulus which means “small sphere.” That is why we can find stars or groups of stars among nebulae or in different spaces of galaxies.
Orion Nebula
The Orion Nebula, also known as Messier 42 or M42, is one of the brightest and can be observed in the night sky (despite the fact that it is located about fourteen hundred light years from Earth). It was discovered by the Frenchman Nicholas Peiresc in 1610.
It is located south of Orion's belt and is made up of hundreds of newborn stars and a group of young stars, called Trapezium, which are approximately two million years old.
Its appearance presents varied colors: reddish (consequence of the radiation from the electromagnetic emission of hydrogen), bluish with violet tints (consequence of the reflection of the spectral type stars found in the center of the nebula) and greenish (consequence of the transition of some electrons on oxygen atoms).
Continue on: Orion Nebula
References
- «The most spectacular nebulae in the universe» in MuyInteresante.es
- «Planetary nebulae» in Blog.nuestroclima.com
- “The nebulae” at Astrobitacora.com
- “Supernova” on Wikipedia.org
- “Orion Nebula” at NationalGeographic.com.es
- “Birth of a star” on ESA.int
- «The dust, gas and stars in the Orion Nebula» in Observatorio.info
