What is a Nebula?
A Nebula is named from the Greek word for “cloud”. Nebulae (plural) come in many shapes and sizes and have a way of captivating those that observe and photograph these deep sky objects in space.
Most nebulae are enormous in size. Some are even hundreds of light-years in diameter. Nebulae do contain some mass. They have a greater density than the space surrounding them. Yet many nebulae are less dense than any vacuum we have created on Earth.
“a nebula is a cloud of gas and dust in outer space, visible in the night sky either as an indistinct bright patch or as a dark silhouette against other luminous matter.”
Nebulae usually consist of Hydrogen and Helium, as these are the most common and stable compounds in the Universe. The formation of a nebula can occur when a star undergoes a significant change, such as excess fusion in its core.
Types of Nebulae
HII regions and dark nebulae are where stars can form. They are made mostly of hydrogen and helium, with traces of other gases and infusions of dust grains. hey are found largely in the spiral arms of our galaxy. Our own solar system was born in such a region more than 4.5 billion years ago. The best-known molecular clouds are the Orion Nebula, the Eta Carinae Nebula, The Eagle Nebula (also, known as the Pillars of Creation), the Tarantula Nebula in the Large Magellanic Cloud, the Horsehead Nebula, the Coal Sack, and the Lagoon Nebula. Most of them, except for the Coal Sack, are bathed in the light of the stars that formed within them. The Coal Sack is an example of a dark nebula that obscures nearby stars, and may be forming stars within.
Supernova remnants are the final remains of massive stars that have blown themselves apart at the ends of their lives. These are expanding clouds of gas and dust with neutron stars or even black holes marking the final resting place of the star. The most famous supernova remnant is the Crab Nebula in Taurus. Its explosion appeared in our skies in the year 1054 AD. It contains a pulsar — a spinning neutron star — surrounded by filamentary clouds of material blasted out when its progenitor star exploded.
Planetary nebulae are the leftovers of stars like the Sun. They consist of a cloud of gas and dust surrounding a slowly cooling white dwarf star. The best-known planetary nebula is the Ring Nebula in the constellation Lyra. It was once a sun-like star that gently blew its outer atmosphere to space as it aged. What’s left of that atmosphere is a ring-shaped cloud that glows from the radiation of the dwindling white dwarf star.
Facts About Nebulae
- Most nebulae contain the “stuff of stars and planets”, including gases, dust, and complex molecules.
- As stars die and lose their materials to space, their gases and dust mix with clouds of gas, creating the complex nebulae we see.
- Nebulae are always in motion, even though they look quiescent in images. The clouds mix and churn, which creates magnetic fields.
- There are several types of molecular clouds: dark globules, emission nebulae, and reflection nebulae. Emission nebulae glow as their gases are heated. Reflection nebulae are mostly dust which reflects the light from nearby stars.
- Our Sun and planets formed in a nebula some 4.5 billion years ago.
- Nebulae exist in other galaxies. Astronomers have observed them in all spirals as well as the nearby Magellanic Clouds.
