Nebula

Space is big! Science is cool! So let’s talk about it. 

What Is Nebulae ?

    A nebula is an enormous cloud of dust and gas occupying the space between stars and acting as a nursery for new stars. The roots of the word come from Latin nebula, which means a “mist, vapor, fog, smoke, exhalation.” Nebulae are made up of dust, basic elements such as hydrogen and other ionized gases. 

Who discovered it?

     The first mention of it may have been in 964 by Persian astronomer Abd al-Rahman al-Sufi who wrote about the Andromeda Galaxy noticing "a little cloud".

 Early Arabic and Chinese astronomers also noticed the creation of the Crab Nebula as a result of a supernova in 1054.   

It wasn’t until the 17th century and advances in optics that nebulae became more observed. In 1610, Nicolas-Claude Fabri de Pieresc discovered the Orion Nebula, which was then observed in 1618 by Johann Baptist Cysat. The first detailed observations, though, waited for famous scientist Christiaan Huygens in 1659. Huygens, by the way, also was the first to come up with a standard formula for centripetal force, which he published in 1659. So a big year for Huygens.                                                                    

  Can I see it?

    Some nebulae are bright enough to be seen with the naked eye. The Orion Nebula is one of these, located between the stars in the constellation Orion’s sword. Many others are visible through telescopes, depending on how many stars are around them to illuminate the dust clouds that form the nebulae. However, it’s often hard to differentiate between star clusters, galaxies and nebulae due to their similar makeup.

      

How do stars form in a nebula?

In this image of the Carina Nebula, you can spot tiny yellow and white dots inside pink dust clouds. Those tiny dots are newly-formed stars! Credit NASA/JPL-Caltech/University of Colorado

Nebulae are made of dust and gases—mostly hydrogen and helium. The dust and gases in a nebula are very spread out, but gravity can slowly begin to pull together clumps of dust and gas. As these clumps get bigger and bigger, their gravity gets stronger and stronger.

Eventually, the clump of dust and gas gets so big that it collapses from its own gravity. The collapse causes the material at the center of the cloud to heat up-and this hot core is the beginning of a star.

Where are nebulae?

Nebulae exist in the space between the stars—also known as interstellar space. The closest known nebula to Earth is called the Helix Nebula. It is the remnant of a dying star—possibly one like the Sun. It is approximately 700 light-years away from Earth. That means even if you could travel at the speed of light, it would still take you 700 years to get there!                                                                                                                                                                              

 

Types Of Nebulae :

* Emission Nebula / Star-Forming Region

Also known as “stellar nurseries”, these massive collections of hydrogen gas are pulled together by gravity to form incredible formations like the “Pillars of Creation” found within the Eagle Nebula.

In these star-forming regions, the formations of gas, dust, and other materials cluster together to form denser regions. The density attracts matter and eventually becomes dense enough to create the formation of stars. The remaining material is then believed to form planets and other planetary system objects.

Emission Nebulae are those that emit radiation from ionized gas and are often called HII regions because they are largely composed of ionized hydrogen. The Orion Nebula is an emission nebula and star-forming region.

Not only is it the brightest nebula in our sky, but it is also the most active star-forming region in our Galaxy. This nebula can easily be observed up-close with a small telescope. It occupies an area that is twice the diameter of our full Moon.

As gravity continues to merge these materials together, the region becomes hot enough to create a new star. The remaining materials may form into Planets that will orbit the star, just as our Solar System was formed.

The Orion Nebula is an emission nebula and star-forming region. It is the most active star-forming region in our Galaxy, and can easily be observed up-close with a small telescope.

* Planetary Nebulae 

When early astronomers observed these round, compact nebulae in the night sky – they thought that they must be planets. In reality, planetary nebulae have nothing to do with planets.

Planetary nebulae are formed when a star dies, and create dramatic formations of radiating cosmic gas. Some great examples of planetary nebulae in the night sky include the Ring Nebula, the Dumbbell Nebula, and the Helix Nebula.

Planetary Nebulae involves a low-mass star entering the final stage of its life. This is called the Red Giant phase, where the star slowly loses its outer layers due to helium flashes from their interior.

When the star has lost enough material its temperature increases. In turn, the UV radiation that is emitted ionizes the surrounding material that has been thrown off.

The gas is expanding outwards at an incredible speed, and this movement has been documented in the following time-lapse of V838 Monoceros's captured over time by Hubble.

* Supernova Remnant

    A supernova remnant is a cosmic explosion that has spread the materials from a star across a huge expanse of space. The remnants of this explosion have formed into a nebula, and this nebula type creates some of the most incredible formations in space.

    Some nebulae are formed as the result of supernova explosions and are hence classified as Supernova Remnant Nebulae. In this case, short-lived stars experience implosion in their cores and blow off their external layers.

    This explosion leaves behind a “remnant” in the form of a compact object – i.e. a neutron star – and a cloud of gas and dust that is ionized by the energy of the explosion.

    The Veil Nebula is a prime example of Supernova Remnant, as seen as this image captured using a small telescope in my backyard. The Veil Nebula includes several filamentary nebulae, including Pickering’s Triangle. 

* Dark Nebula

    A Dark Nebula is a cloud of gas and dust that is revealed due to the bright areas of interstellar material and stars behind it. The nebula is silhouetted against a bright background to create interesting shapes and formations.

    There are also what is known as Dark Nebulae, opaque clouds that do not emit visible radiation and are not illuminated by stars but block light from luminous objects behind them. Much like Emission and Reflection Nebulae, Dark Nebulae are sources of infrared emissions, chiefly due to the presence of dust within them.

    Examples of dark nebulae include the Coalsack Nebula and the Horsehead Nebula. This nebula is composed of thick clouds of dust that block the bright emission nebula gas behind it.

    Most nebulae are of vast size; some are hundreds of light-years in diameter. A nebula that is visible to the human eye from Earth would appear larger, but no brighter, from close by. The Orion Nebula, the brightest nebula in the sky and occupying an area twice the angular diameter of the full Moon, can be viewed with the naked eye but was missed by early astronomers. Although denser than the space surrounding them, most nebulae are far less dense than any vacuum created on Earth – a nebular cloud the size of the Earth would have a total mass of only a few kilograms. Many nebulae are visible due to fluorescence caused by embedded hot stars, while others are so diffused that they can be detected only with long exposures and special filters. Some nebulae are variably illuminated by T Tauri variable stars. Nebulae are often star-forming regions, such as in the "Pillars of Creation" in the Eagle Nebula. In these regions, the formations of gas, dust, and other materials "clump" together to form denser regions, which attract further matter, and eventually will become dense enough to form stars. The remaining material is then believed to form planets and other planetary system objects.

The "Pillars of Creation" from the Eagle Nebula. Evidence from the Spitzer Telescope suggests that the pillars may already have been destroyed by a supernova explosion, but the light showing us the destruction will not reach the Earth for another millennium.