A Nebula is a fascinating place in the universe, it is not just a massive dust cloud whereas it is the birthplace of the stars in our universe. They have intrigued humanity over centuries and it is the best place to study the stellar life cycle. Studying this curious phenomenon, we might understand the universe and our place in it. Even our neighbouring Andromeda galaxy was first thought to be a Nebula. So what are these captivating Nebulas and how are they formed? Are they visible in our dark sky?
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| The Orion Nebula |
What are Nebulae?
A Nebula is a giant star cloud of dust in space which are formed from the gas and dust created by the supernova explosion of stars and they also act as the birthplace for new stars. The Nebulas are an astronomically dense structure that is opposite of a star. We can't understand the lifecycle of the star without understanding the life cycle of the nebulas. The Orion Nebula is probably the most famous nebula and it is also present in our backyard (the Milky Way Galaxy) thereby visible to the naked eye. They are mostly made up of hydrogen and helium and these Nebulas are found in interstellar space.
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| The Bubble Nebula |
The French scholar Nicolas Claude Fabri de Pierces was the first to observe the Orion Nebula using a telescope. Later in the 19th century, Edwin Hubble helped classify the nebulas based on the light spectrum they emit in the cosmos and he also found out that the luminescence of the nebulas is due to the emitted by the nearby stars. The closest known nebula to our solar system is the Helix nebula which is approximately 700 light-years away from Earth. The amazing images of the different varieties of nebulas are taken from the powerful space telescopes of NASA like the Spitzer telescope and the Hubble space telescope.
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| The Helix Nebula, which is closest to our solar system |
Even the Andromeda Galaxy was first considered to be a nebula, but after close observations from our space telescope, it was found to be a galaxy. The Nebulas are not very dense clouds, in fact, the nebula which is about the size of the Earth would only weigh around a few kgs. Most of the nebulas are visible in the sky because of the light emitted from the surrounding stars, but some of the nebulas are dim and so they can only be observed by long exposures or using the ultraviolet spectrum to capture the image of the Nebula which will be done in the James Webb space telescope.
How Nebula is formed?
There are different ways in which a Nebula forms in the universe. Some of the nebulas are formed as the result of the supernovas or the death of the star. The concentrations of the cloud are uneven throughout the entire nebulae, the low-density regions remain shattered and the high-density region of the nebula remains as think pillars forming the famous Eagle nebula's pillar of creation. But not every cloud collapses and forms a star, some of the clouds in the Nebulas also give rise to the Planets, asteroids, comets and even some remains as specks of dust. There are a variety of nebulas found in the observable universe.
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| The Eagle Nebula's Pillar of Creation |
There are several Nebulas observed in our observable universe and we categorize them into 4 major types:
The Region containing partially ionized gas in which the star formation typically happens. These are mostly found in spiral and irregular galaxies. They also come in a variety of sizes.
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| The Ring Nebula is a planetary nebula that is about 2000 light-years away from Earth. Image: Hubble space telescope |
Planetary nebulas form at the demise of the intermediate-mass star. Even the death of our sun will give rise to a planetary nebula. The planetary nebulas are the final stage of stellar evolution.
As the name suggests, these are the wreckage of the supernova explosion of a star. The materials are ejected into the cosmos after the explosion and the interstellar medium carries along with the remnants of the explosion forming the supernova remnant nebula.
Dark Nebulas are very dense clouds of stardust that don't allow visible light to pass through them and hence the stars and galaxies in the back are not visible. They don't have a defined boundary.
How do Stars form in Nebulas?
Nebulas are also called the 'nurseries for the Stars' because they act as a nursery for young stars in the universe. In a particularly dense area in the nebula, the dust clouds collapse and a massive star are formed at the centre of the cloud. This process emits ultraviolet radiation, which actually ionizes the particles in the vicinity. This is the primary way of the formation of the star, but some stars are formed because of the supernova explosion. After the death of the star, the materials of the star are ejected into the cosmos which gets ionized in the Nebulas and a solid core is produced which in turn becomes the base of the star.
Can Nebulas be seen from Earth?
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| The Image of the Orion Nebula, which is 1500 light-years away from Earth taken by the Hubble Space Telescope. Source: NASA |
Most of the images taken of the nebulas are taken using infrared imaging or using false colour as they could not be taken via normal cameras because of the clouds of dust obstructing our view of the nebulas. Some of the nebulas can also be spotted in the sky with our naked eye and the Orion nebula is visible in the dark sky. But it is difficult to distinguish between the star clusters and the nebulas using our naked eye. The Nebulas are huge in diameter spanning over hundreds of light-years and therefore they are visible in the night sky, but they appear dimmer as they only reflect the starlight.
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