A Nebula is a Giant Cloud of Dust and Gas
A nebula is a giant cloud of dust and gas in space. Some nebulae come from the gas and dust thrown out by the explosion of a dying star, such as a supernova. Other nebulae are regions where new stars are beginning to form. Nebulas play a crucial role in the life cycle of stars. In an astronomical context, it refers to any celestial object which appears cloud-like when viewed through a telescope.
When telescopes weren’t as powerful as today, this term encompassed galaxies such as our neighbor Andromeda, often called the “Andromeda nebula.”
Nebulas are Found in the Space Between Stars
However, with the benefit of modern telescopes, we know that galaxies aren’t cloud-like but are made up of billions of stars. It means astronomers now reserve the word nebula for genuine clouds — of gas and dust — in our galaxy.
Nebulas are often found in the space between stars, known as the interstellar medium. On average, this region contains only around one atom per cubic centimeter. However, in certain places, the density can be significantly higher than this — high enough to become visible through a telescope.
The result is what we call a nebula is a giant cloud, and they are among the most spectacular sights in astronomy. Many of the most iconic Hubble telescope images, such as the “Pillars of Creation,” are images of nebula.
There are several different types of the nebula, depending on how they form and their composition. Most nebulae are primarily made of gas, which can glow with its light, creating the colorful displays we are familiar with.
But other nebula — such as the so-called “dark nebula” — are much dustier in their composition, and rather than glowing, this dust blocks the light from more distant objects beyond it.
Nebula Plays a Crucial Role
Nebula plays a crucial role in the life cycle of stars, both at their birth and death. Stars are born in dense clumps of gas, dust, and other material inside diffuse emission nebulae, also frequently referred to as “stellar nurseries.”
Hubble’s Pillars of Creation is in this category, as is the famous Orion Nebula — which you may have seen through binoculars or a small telescope.
The principal force at work here is gravity. It causes the tenuous interstellar medium to condense into a nebula, and gravity, which causes clumps inside the nebula to collapse into stars.
At the other end of a star’s life, we encounter a different type of emission nebula. Stars like the sun end their lives as highly compact white dwarfs. But as they shrink into this phase, they release clouds of gas, forming a so-called “planetary nebula.” It is a misleading name because such a nebula has nothing to do with planets.
Unlike diffuse emission nebula, these have a more clearly defined appearance. They are usually circular, which reminded William Herschel of a planet when he first observed them in the 1780s.
Not all stars end their days in the relative serenity of a planetary nebula. A much more massive star than the sun will eventually explode as a supernova. The debris from that explosion forms yet another kind of nebula called a supernova remnant. The most famous of these is the Crab Nebula, which is all that remains of a spectacular supernova observed by Chinese astronomers in 1054.
What do Nebulae Look Like?
Astronomers use very powerful telescopes to take pictures of faraway nebulae.
Space telescopes such as NASA’s Spitzer Space Telescope and Hubble Space Telescope have captured many images of faraway nebulae.
Nature of Nebulae
To capture the spectacular nature of nebulae, telescopes, such as the Hubble Space Telescope and the James Webb Space Telescope ( JWST) use infrared radiation to create an image.
The visible light emitted by stars forming in and around a nebula can be blocked by the dense cosmic clouds of gas and dust that make up a nebula. Therefore, scientists must look to other wavelengths of light emitted from the nebula, such as infrared radiation.
Infrared cameras onboard the JWST have relieved some of the most detailed images of nebulae, such as the Southern Ring planetary nebula.
The Southern Ring nebula — also known as NGC 3132 — is around 2,500 light-years away from Earth and home to a dying star at its core.
The JWST has captured one of the most detailed nebula images using its Near-Infrared Camera (NIRCam) and the Mid-Infrared Instrument (MIRI). JWST has captured layers of gas and dust within the Southern Ring Nebula. Each layer has been created by expelling cosmic matter from the central dying star.
