You're watching FreeSchool!
Space: it's vast and full of secrets. Of all the incredible objects scientists have found,
out among the stars, some of the most spectacular are nebulae. Scattered throughout the galaxy,
these vast clouds have captivated the minds of astronomers and stargazers for centuries.
Nebulae are the birthplace of stars and planets. They hold clues to the formation and evolution of
our galaxy. And, these vast cosmic clouds have a serene and mesmerizing beauty.
Although most nebulae are completely invisible to the naked eye, modern telescopes are able to
give us close-up views of some of the most breath-taking objects in the universe.
A nebula, named for the Greek word for 'cloud,' is in fact an interstellar cloud of dust and gas.
They are made mostly of hydrogen and helium, but they may also contain other gases and cosmic dust.
The exact composition of a nebula can vary depending on its location and the processes
that formed it. Like the clouds in the sky, nebulae come in interesting shapes, like flowers,
insects,
animals, or people.
This is how many of them get their names.
There are four main types of nebulae. First, there are star-forming regions,
also known as stellar nurseries. In these huge areas of hydrogen gas,
gravity pulls the material together into larger clumps, which in turn attract more material.
More and more gases squeeze together harder and harder, making it grow hotter and hotter.
When it becomes hot enough, it will be a new star.
Whatever is left over may become planets, circling it.
An example of a star-forming region and one of the most famous nebulae in the sky is the
Orion Nebula. The Orion Nebula is the most active area of star formation in our galaxy.
Although it is visible to the unaided eye, it is only a vague glow.
Through a telescope, the extent of its wonder becomes visible.
The Orion Nebular is 15 light years across, and is made mostly of hydrogen.
When you look at this nebula, you are looking at stars being born.
This nebula gets its glow from something called the Trapezium,
a cluster of four stars, each thousands of times brighter than our sun.
Their energy has cleared a space in the gases around them.
You can see that see that other stars are being born inside the nebula, too.
These ovals are blankets of dust surrounding newborn stars.
The rings inside are probably new planetary systems being formed around these stars.
1300 light years away, the Orion Nebula is only a little glow in Orion's sword.
Second, there are planetary nebulae. This kind of nebula doesn't really
have anything to do with planets, but when early astronomers saw them through their telescopes,
they looked so round and bright that they thought they must be planets.
Planetary nebulae are formed by the slow death of ordinary stars.
Near the end of their life, some stars begin to shed their outer layers into space.
These layers are mainly made of hydrogen gas, but as the star begins to die other
elements are produced as well, including oxygen, carbon, and iron.
The hot core of the dying star illuminates the material, causing it to glow.
As the layers of gas and dust expand, they create
beautiful and colorful clouds that may manifest in many different shapes.
One of the most famous examples of a planetary nebula is the Helix Nebula,
also known as the "Eye of God." It is located about 700 light-years away from Earth and is
one of the closest planetary nebulae to us. From a distance, it looks like a giant, glowing eye.
Up close, the Helix Nebula is a fantastic sight,
with intricate patterns and thousands of streamers of bright gas extending toward its center.
This beautiful object is known as the butterfly nebula, and it is another example of a planetary
nebula. Although it looks peaceful, and like a delicate butterfly from afar,
it is actually made of raging clouds of gas, heated to more than 36,000 degrees Fahrenheit.
For comparison, that is more than three times hotter than the surface of the sun!
The gas is also in motion - moving at more than 600,000
miles an hour. At that speed, you could go from the earth to the moon in just 24 minutes!
One last famous example of a planetary nebula is the Cat's Eye Nebula.
It is a bit further away from Earth, at about 3,000 light-years, but it is still one of the
brightest planetary nebulae in the sky. The Cat's Eye Nebula is made up of several rings of gas,
each with a different color and pattern. The central star is so hot that it has
ionized the gas around it, creating a bright blue color in the middle of the nebula.
The third kind of nebulae are called supernova remnants.
Sometimes when a star dies it doesn't die slowly - it dies with a bang!
A supernova is a huge explosion that spreads the material from the star across a huge expanse
of space. The leftovers form a nebula, which may over time collect and form new stars.
The Crab Nebula is an example of a supernova remnant.
This nebula is especially exciting because we know when the star that created it exploded!
Nearly 1,000 years ago, Chinese astronomers noticed a bright new star in the sky.
It stayed there for almost two years, and then slowly vanished. Modern astronomers
studying the Crab Nebula realized that the bright, temporary star described in the ancient record was
an excellent match for the the supernova that would have created the Crab Nebula.
Knowing when the star went nova allowed scientists to
learn a great deal about the way this type of nebula develops.
In addition to the Crab Nebula, there are many other supernova remnants found throughout our
galaxy, each with their own unique characteristics and properties. Some of the most famous supernova
remnants include the Veil Nebula, the remnant of a supernova that occurred around 5,000 years ago,
and the famous Tycho's Nova, a nebula formed by a supernova which was observed in 1572.
The fourth kind of nebulae are dark nebulae. A dark nebula, also called an absorption nebula,
is a cloud of gas and dust that is only visible because of bright nebulae and stars behind it.
Typically much denser than bright nebulae,
dark nebulae are difficult to observe because they do not produce their own light.
Like a shadow or a silhouette, they take their shape from the light we do not see.
One of the most famous dark nebulae is the Horsehead Nebula.
It is easy to see where this nebula got its name! The Horsehead Nebula is made of
thick dust clouds, so dense that they block the light of stars behind them.
Just because the cloud is dark, does not mean that it is cold.
Looking at the nebula through an infrared camera that allows us to look at the heat it gives off,
we can see that the Horsehead Nebula is very hot, indeed.
There are even bright spots visible, which shows where new baby stars are forming.
No matter what type they are, nebulae are among the most dazzling celestial
objects to be found in the sky. They are a window into the life cycle of the universe.
In the end, the same raw materials that form stars are left behind when stars die,
to form in turn new stars - and the cycle begins again.