How do emission nebulae form

It is illuminated by a pulsar which was created by the supernova. Nebulae are often the sites of star formation. In fact, all stars, planets, and solar systems are formed from nebulae.

A nebula may lie undisturbed for many millions or billions of years as it waits for just the right conditions. Eventually, the gravity from a passing star or the shock wave from a nearby supernova explosion may cause swirls and ripples within the cloud. Matter begins to coalesce into clumps and grow in size. As these clumps get larger, their gravity increases. Gravity continues to pull in matter from the nebula until one or more of the clumps reach critical mass.

The clumps are forming protostars. As gravity squeezes even tighter, the core temperature eventually reaches 18 million degrees. At this point, nuclear fusion begins and a star is born. The solar wind from the star will eventually blow away all of the excess dust and gas.

Sometimes other smaller clumps of matter around the star may form planets. This is the beginning of a new solar system. Several nebulae have been found to be stellar nurseries. The Eagle Nebula, and the Orion Nebula are both sites of active star formation.

There are a few nebulae that can be seen with the naked eye and many more that can be detected with a good pair of binoculars. A telescope is required to bring our fine details. Unfortunately, the human eye is not sensitive enough to bring out the rich colors of most nebulae. It is the photograph that does the most justice to these incredible objects.

Until recently, time exposures on film were the best way to bring a nebula's true colors. Today, digital photography has simplified the process. New tools like the Hubble space telescope are giving us views of nebulae that have never been seen before.

Areas of active star formation have been identified in many galaxies that were once thought to be inert. But how exactly does a nebula form in the vast and apparent vacuum of space?

Read on and find out! Nature abhors empty space, after all! A nebula subsequently begins to form when a few atoms get close enough to clump together. Naturally, the more atoms that clump up, the stronger their gravitational influence then becomes. This in turns allows them to draw even more particles towards them and after eons of time you get a large gaseous cloud forming in space.

Furthermore, some parts of the cloud may become even denser than other areas. As more and more matter accumulates, the material mostly hydrogen may then reach a point when it start to collapse in upon itself. At some critical point the sheer mass and high gravity then start a nuclear reaction and hydrogen starts fusing to make helium.

Unfortunately the name planetary nebula is very misleading since these nebulae have nothing to do with planets. During the first observation of these objects they resembled Uranus. In the astronomer Herschel, who observed them, named these - at that time unknown structures - planetary nebulae.

Since then the name has not been changed even though we now know that a planetary nebula is an emission nebula, not a planet or a nebula connected to a planet. Two other types of nebulae that can be observed are supernova remnants and reflection nebula.

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In this case, the excited gas is not necessarily dominated by HII , but can also contain significant amounts of ionised helium HeII; blue emission and doubly-ionised oxygen OIII ; green emission.

Since much more energy is required to ionise helium than hydrogen, the bluest areas of planetary nebulae are the hottest and indicate the areas of highest excitation. The Orion Nebula M42 is possibly the most famous emission nebula. Massive stars located in the heart of the nebula are bombarding the gas with UV radiation causing it to glow. The Ring Nebula is a planetary nebula showing regions of ionised nitrogen red , oxygen green and helium blue.