nebula

Astronoma

2022

We explain what a nebula is, what types exist and their characteristics. Also, what is the Orion Nebula.

"Helix" is a planetary nebula discovered in 1824.

What is a nebula?

Nebulae are brightly colored, cloud-like concentrations of gas and stardust. They are important to him universe because within some of them the stars (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 the earth, which are measured in light years.

However, it is possible to have detailed images that show its majesty, thanks to scientists operating with complex and sensitive instruments, such as the telescope Hubble spacecraft.

Type of nebulae

Nebulae come in different shapes and sizes, and are divided into four types:

  • The reflection nebulae. They are those that reflect the light from nearby stars (stars that don't emit enough radiation). Present colors in bluish tones due to the way the light is scattered by the particles of dust from the nebula. For example, the nebula "Pleiades" (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 atoms of hydrogen that receive ultraviolet radiation from stars. For example, the "Omega" nebula.
  • The absorption nebulae. Also called "dark nebulae", they are not directly visible. They are those that do not emit light and that hide the stars they contain. The first astronomer to discover this type of nebula was the German William Herschel. For example, the "horse head" nebula.
  • 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

Nebulae are composed of gas (hydrogen and helium predominate) and dust. They reach a diameter of hundreds of light years length. They are formed with the explosion of supernovae, that is, they are the consequence of the last stage of life of stars.

When a star has no more fuel to burn (the gases), its core begins to collapse under its own weight and that generates an abrupt expulsion of the outer layer that expands into space, which gives rise to varied and striking forms: nebulae.

For example, the fate of Sun it is to become a "planetary" type nebula and end its days as a "white dwarf". In about five billion years, the Sun will deplete its hydrogen reserve and become a giant red star, expanding beyond the orbit from the earth.

Hundreds of millions of years later, it will emanate half of its mass into outer space, so it will be seen (from distant star systems) as a great planetary nebula, where before existed the Solar system.

Another very significant and interesting feature is that some of the nebulae can give rise to stars and planetary systems. Stars are formed 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, nebulae perform a process in which they shrink). There is a fragmentation of the matter into smaller groups and each of them can heat up to start a nuclear reaction that turns into 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 to other objects in the Solar System.

In addition to nebulae, there are groups of ancient stars (among 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 between nebulae or in different spaces in galaxies.

Orion Nebula

The Orion Nebula is also called Messier 42 or M42.

The Orion Nebula, also known as Messier 42 or M42, is one of the brightest and can be seen in the night sky (despite being about 1,400 light-years from Earth). It was discovered by the Frenchman Nicholas Peiresc in 1610.

It is located south of the Orion belt and is made up of hundreds of newborn stars and a group of young stars, called Trapezium, that are approximately two million years old.

Its appearance presents colors varied: reddish (consequence of the radiation of the electromagnetic emission of hydrogen), bluish with violet tints (consequence of the reflection of the stars of spectral type that are in the center of the nebula) and greenish (consequence of the transition of electrons Over the atoms oxygen).

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