Planetary nebula refers to any class of bright nebulae that are expanding shells composed of luminous gases. The origin of these glowing gases is flying stars in the universe. When you observe planetary nebulae through a telescope, you will see that they have a relatively compact appearance that is different from the regular formation of nebulae. Usually, a nebula has chaotic patchy shapes of other nebulae. Planetary nebulae are called so because they resemble planetary disks. The first planetary nebulae were discovered in the 1700s.
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Planetary Nebula Definition
Planetary Nebula is a small object having a radius of 1 light-year and a mass of gas of around 0.3 solid mass. These are the remains of stars that once looked like the sun. Planetary nebulas spend their lives in the universe turning hydrogen into helium. These massive fusion reactions happen in the core of the planetary nebula.
When the hydrogen runs out during the fusion reaction, the star uses helium as a replacement fuel source. However, the helium source burns heavier than a combination of carbon, nitrogen, and oxygen. Eventually, the helium source is exhausted, and the star dies. When the star dies, it puffs off its outer gaseous layer and leaves behind a tiny, hot, dense core called the white dwarf. It is the size of planet earth but has a mass that is close to an original star.
The glow from planetary nebulae is intriguing as it spreads across the broad swath of the spectrum. It goes from ultraviolet to infrared. Some examples of the planetary nebula are Helix nebula, butterfly nebula, engraved hourglass nebula, Saturn nebula, dumbbell nebula, and stingray nebula.
Forms and Structures of Planetary Nebulae
There are around three thousand planetary nebulae in our galaxy. Most of these nebulae are found suitable in the centre of our galaxy, the Milky Way. Here are some of the planetary nebulae seen in our universe:
Helix Nebula
Among these three thousand is the Helix Nebula, which is one of the largest-known planetary nebulae. The Helix Nebula is also referred to as the NGC 7293 and is found in the Aquarius constellation. It subtends at an angle of about twenty minutes of arc and is the two-thirds angular size of the Moon.
It was discovered in the 18th century and named Helix because it resembled gas-giant planets. The Helix Nebula lies six hundred and fifty light-years away from world Earth.
Butterfly Nebula
The butterfly nebula is another form of a planetary nebula. The bright clusters of nebulae in the Earth’s night sky are named after flowers and insects. Hence, the NGC 6302 is a planetary nebula which is called the Butterfly Nebula. It is named so because of its wingspan, which covers over three light-years.
It has a surface temperature of about 2,500,000 degrees Celsius. It is a dying central star that is extremely hot and shines brightly in ultraviolet light. However, it is hidden from the dense amount of dust.
Saturn Nebula
Saturn Nebula is a planetary nebula that Sir William Herschel in1783 discovered. It is referred to as NGC 7009. It was named Saturn because of the resemblance it had to the planet Saturn with its rings.
It is a bright star with a dark cavity that is bounded by an oval shape rim. This oval shape rim contains dense red and blue gases.
They are trapped in a green material that is shaped like a barrel. This barrel forms the outer layer of the Saturn Nebula. These stars become cooler and redder as they grow old. Along with these two changes, the star starts increasing its size and energy outputs. Eventually, they are referred to as red giants.
Dumbbell Nebula
The dumbbell nebula is referred to as Messier 27 after Charles Messier, who discovered the planetary nebula. The Hubble shows three different colours around the nebula when you look at the Dumbbell Nebula or Messier 27’s images. The three colours represent elements of the nebula.
The blue is the oxygen, green is the hydrogen, and red is the sulfur and nitrogen. M27 is a host of gases and dust. Their size ranges from seventeen billion and fifty-six billion kilometres. It is much greater than the distance from the sun to Pluto. The mass of a Dumbbell Nebula has as many as three Earths. Dumbbell Nebula is the brightest planetary nebula in the sky. It is found near the constellation Fox (Vulpecula) and can be seen with binoculars.