Nebulae are among the most fascinating celestial bodies contributing to stellar evolution. The word ‘nebula’ comes from Latin meaning “ vapor, mist, fog, exhalation or smoke.” Precisely, a nebula is a giant cloud in space made up of dust and gas particles, primarily hydrogen and helium. In the astronomical context, a nebula refers to any cosmic object that appears cloud-like when seen through a telescope. They come in various sizes and shapes; some have diameters that are hundreds of light-years. In the life cycle of stars, they play a crucial role by acting as the nursery for new stars.
Formation of Nebula:
To understand the evolution of galaxies and the life cycle of stars, it is important to know the complex formation process of nebulae. A nebula is basically composed of dust, hydrogen, and some other ionized gasses. It either forms through the clouds of interstellar gas or through the aftermath of a supernova. The process of formation of a nebula occurs in the following steps:
- The interstellar dust and gas particles begin to get close and form clumps. As more and more particles clump up together, their gravitational influence grows stronger and stronger. As a result, more particles are drawn toward this clump, and after a huge span of time, a large gaseous cloud is formed in space, known as a nebula.
- Over time, some parts of these gaseous clouds become a lot denser than other parts. With the accumulation of more and more matter, a point is reached when this material starts collapsing upon itself.
- Due to high gravity and large year mass nuclear reaction starts and the major component, hydrogen, starts fusing to convert into helium. Subsequently, a star is formed within an enormous gaseous cloud.
Composition Of Nebula: What Are Nebulas Made Of?
There are various factors like age, location, and physical conditions upon which the composition of nebulae depends. In some nebulae, the predominant component is hydrogen while in others helium, nitrogen, oxygen, and carbon are the main constituents. Nebulae can be emissary, dark, or reflective depending upon the nature of the gas and dust particles in it. These particles can either have lost or gained electrons i.e. ionized, which results in the emission of light of various wavelengths showing characteristic patterns and colors in nebulae.
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Who discovered the nebula?
In 964, a Persian astronomer Abd al-Sufi noticed “a little cloud” and wrote about the Andromeda Galaxy. Later in 1054, the formation of a Crab nebula during a supernova was observed by the Chinese and Arabic astronomers. Afterward, nebulae became more noticed in the 17th century with the advancements in optics. Nicolas Claude Fabri de Pieresc discovered the Orion Nebula in 1610. Orion Nebula was also noticed by Johann Baptist Cysat in 1618. A well-known astronomer Christian Huygens did the first explicated observation in 1659. Edmond Halley worked on 6 nebulae after about 50 years.
Where are nebulae located?
Nebulae are often located in the space between stars. The nearest known nebula to the Earth is the Helix nebula which is formed through the remains of a dying star.
Can we see a nebula?
Some nebulae are visible through the naked eye. The Orion nebula is present between the stars in the constellation Orion’s sword. Many of the nebulae can be seen with telescopes but it depends upon the number of stars that illuminate the dust clouds that are essential for their formation. The galaxies and star clusters look alike. However, it is difficult to figure out the dissimilarity between them. Some advanced telescopes for space like Hubble and Spitzer have a lot of images of nebulae.
Types of nebula
Nebulae have various shapes and sizes formed through different processes. They are categorized into:
Supernova remnants:
The explosion of massive stars in a supernova sends dust particles and gas into space leading to the formation of this type of nebula named a supernova remnant. The Crab Nebula is an example of a supernova remnant.
Planetary nebulae:
When a medium-sized dying star ejects ionized gasses, a vibrant shell is formed named as planetary nebula. In fact, stars like the Sun run out of fuel, shed their outer layers, and the remaining core emits radiation. An example of a planetary nebula is the Ring Nebula.
Emission nebulae:
Emission nebulae have a characteristic glow due to ionized gasses, particularly hydrogen and helium. They are formed around the stars that are continuously emitting radiations and ionizing the surrounding gasses. Hence, this type of nebulae is named so because they emit light. Orion Nebula is an example of emission nebulae.
Dark nebulae
Dark nebulae block the light from the nebulae behind them and stars, which is why they look like dark patches in the sky. For example, Horsehead Nebula.
Reflection nebulae:
As the name indicates, the radiation is not emitted by reflection nebulae. However, the gas and dust particles scatter the light coming from nearby stars. For example, Witch Head Nebula.
Other types of nebulae whose images have been captured by astronomers are Helix Nebula, Omega Nebula, Dumbbell Nebula, North America Nebula, Cone Nebula, California Nebula, Thor’s Helmet Nebula, Soul Nebula, Lagoon Nebula, Wizard Nebula, Rosette Nebula, Trifid Nebula, and Veil Nebula.
How do stars form in a nebula?
As we have already discussed, nebulae are made up of different gasses and dust particles. Although these are so scattered out in the nebulae, gravity slowly begins pulling together the clumps of these gas and dust particles. These clumps get larger enough and gravity gets stronger. Ultimately, these clumps become so huge that they collapse from their own gravitational pull. Thus, the material at the core of the cloud heats up due to this collapse which is the beginning of a new star.
Role of Nebulae in the Universe
Nebulae have several key functions in stars and galaxies’ formation which is why they are referred to as stellar nurseries. These dense regions are the birthplaces of many stars where gas and dust particles collapse due to gravity which leads to the formation of protostars that eventually convert to full-fletched stars. Apart from playing a role in star formation, there are several other roles of nebulae. i.e. recycling of matter, cosmic element synthesis, and galactic evolution.