Cat's Eye Nebula facts for kids
| Emission nebula | |
|---|---|
| Planetary nebula | |
Composite image using optical images from the HST and X-ray data from the Chandra X-ray Observatory.
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| Observation data: J2000 epoch | |
| Right ascension | 17h 58m 33.423s |
| Declination | +66° 37′ 59.52″ |
| Distance | 3.3±0.9 kly (1.0±0.3 kpc) ly |
| Apparent magnitude (V) | 9.8B |
| Apparent dimensions (V) | Core: 20″ |
| Constellation | Draco |
| Physical characteristics | |
| Radius | Core: 0.2 ly ly |
| Absolute magnitude (V) | −0.2+0.8 −0.6B |
| Notable features | complex structure |
| Designations | NGC 6543, Snail Nebula, Sunflower Nebula, (includes IC 4677), Caldwell 6 |
The Cat's Eye Nebula (also known as NGC 6543 and Caldwell 6) is a beautiful planetary nebula found in the northern sky, in the Draco constellation. It was first seen by William Herschel on February 15, 1786.
This nebula was the first of its kind to be studied using a special tool called a spectroscope. An English amateur astronomer, William Huggins, used it to show that planetary nebulae are made of glowing gas, not individual stars. Amazing pictures from the Hubble Space Telescope show the Cat's Eye Nebula has complex shapes like knots, jets, and bubbles. A super hot star in its center makes all this gas glow brightly. Scientists have studied this nebula using all kinds of light, from radio waves to X-rays.
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What is the Cat's Eye Nebula?
The Cat's Eye Nebula, or NGC 6543, is a bright object in the northern sky. It looks quite small from Earth, but it is very bright. The main part of the nebula is about 16 arcseconds wide. That's like looking at a small coin from far away!
However, deeper images show a much larger, faint cloud of gas around it, called a halo. This halo is about 5 arcminutes wide. This outer cloud was pushed out by the central star when it was much older and bigger, in its red giant phase.
The Cat's Eye Nebula is very close to the north ecliptic pole. This means it's a great marker in the sky for the Earth's ecliptic axis, which is the center point around which the celestial North Pole slowly moves. Unlike the pole star, which changes over thousands of years, the Cat's Eye Nebula stays in this special spot for a very long time.
What is the Cat's Eye Nebula Made Of?
Like most things in space, the Cat's Eye Nebula is mostly made of hydrogen and helium. It also has small amounts of heavier elements. Scientists figure out what it's made of by studying its light with spectroscopes.
The bright parts of the nebula are very hot, between 7,000 and 9,000 K. They are also quite dense, with about 5,000 particles in every cubic centimeter. The fainter outer halo is even hotter, around 15,000 K, but it's much less dense.
The central star of the nebula is incredibly hot, about 80,000 K. It shines 10,000 times brighter than our Sun! This star is a type called an O7 + [WR]-type star. It's thought to be more than one solar mass (the mass of our Sun). The Cat's Eye Nebula is about 3,300 light-years away from Earth.
How Do We Observe the Cat's Eye Nebula?
Scientists use different types of telescopes to study the Cat's Eye Nebula. Each type of light tells us something new about it.
Studying Light from the Nebula
The Cat's Eye was the first planetary nebula to be looked at with a spectroscope by William Huggins in 1864. He saw that the nebula's light wasn't a continuous rainbow. Instead, it had a few bright lines. This showed that planetary nebulae are made of thin, glowing gas. Today, we still use this method to learn what elements are in the nebula.
Infrared Light Observations
When we look at the Cat's Eye Nebula with far-infrared telescopes, we can see cool dust. This dust probably formed when the star was in its final stages of life. The dust absorbs light from the central star and then glows in infrared light. This dust is about 85 K cool.
Infrared light also shows us un-ionized materials, like molecular hydrogen (H2). In many nebulae, these molecules are found far from the star. But in the Cat's Eye, they are bright at the inner edge of the outer halo. This might be because fast-moving gas from the star crashes into older gas, creating shock waves that make the H2 glow.
Optical and Ultraviolet Light Observations
The famous Hubble Space Telescope image of the Cat's Eye Nebula uses "false colors." This helps scientists see areas with different levels of ionization (where atoms have lost or gained electrons). The image combines three different views:
- Light from ionized hydrogen (shown as red).
- Light from ionized nitrogen (also shown as red).
- Light from ionized oxygen (shown as blue).
Even though the true colors are red and green, combining them this way helps us see the nebula's amazing details. The image shows two "caps" of less ionized material at the edges of the nebula.
X-ray Light Observations
In 2001, the Chandra X-ray Observatory looked at the Cat's Eye Nebula. It found extremely hot gas inside, reaching temperatures of 1.7 million K! Scientists think this super hot gas comes from a fast stellar wind (gas blowing off the star) crashing into the material the star had already pushed out. This crash created the hollow inner bubble of the nebula.
Chandra also found a bright spot at the center of the nebula, right where the star is. The X-rays from this spot are very strong, which is a bit of a mystery. A single hot star shouldn't emit such strong X-rays. This might mean there's a binary star system (two stars orbiting each other) at the center, with an accretion disk of hot material.
How Far Away and How Old is It?
It's tricky to measure the exact distance to planetary nebulae like the Cat's Eye. But scientists have used the Hubble Space Telescope to watch the nebula expand over several years. By measuring how fast it seems to grow in the sky, and knowing how fast the gas is actually moving, they can estimate its distance.
One estimate suggests the Cat's Eye Nebula is about 3,300 light-years away from Earth. Other studies give slightly different numbers, but it's definitely very far!
We can also use the nebula's expansion to guess its age. If it has been expanding at a steady rate, it might have taken about 1,000 to 2,000 years to reach its current size. This is probably an upper limit, though, because the gas would slow down as it bumps into other material in space.
What Are the Shapes in the Cat's Eye Nebula?
The Cat's Eye Nebula has a very complicated shape, and scientists are still trying to fully understand how it got that way. The bright inner part looks like an elongated bubble filled with hot gas. This bubble is inside two larger, rounder bubbles that are joined together.
The main shape of the bright nebula is caused by the fast stellar wind from the central star. This wind blows at an incredible speed of 1,900 km per second! It has "hollowed out" the inner bubble and seems to have burst through it at both ends.
Scientists also think that the central star might actually be two stars orbiting each other (a binary star system). If so, material moving between these stars could create powerful polar jets. These jets would shoot out from the poles of the system and crash into the gas that was pushed out earlier. Over time, these jets might wobble, causing the complex shapes we see.
Outside the bright inner part, there are many faint, concentric rings. These rings were probably pushed out by the star before the main nebula formed, when the star was in a phase called the asymptotic giant branch. These rings are very evenly spaced, which suggests they were ejected at regular times and similar speeds. The total mass of these rings is about one-tenth the mass of our Sun. These pulsations likely started about 15,000 years ago and stopped about 1,000 years ago, right before the bright central part of the nebula began to form.
Even further out, there's a large, faint halo that extends far from the star. This halo is even older than the main nebula. Its mass is estimated to be between a quarter and almost a whole solar mass.
Images for kids
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An optical image of the nebula's surrounding halo
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X-ray image of Nebula.
See also
In Spanish: Nebulosa Ojo de Gato para niños
- List of largest nebulae
