What is a planetary nebula?
If you know what a planet is, you might know what a planetary nebula is.
The first step in defining a new market is to pinpoint the universe of things you are looking at and to answer the questions:
• What are the things I’m looking at? Are there more than just planets out there? Will that list expands in time?
• How can I use this data to make better decisions about products?
If you have answers to these questions, then it’s time to start thinking about a different set of questions and look at those things again.
How are planetary nebulae formed?
Everybody knows that the Sun is a star. But what makes it a star? What makes a star look like the Sun? Kepler’s laws tell us that every star must have a planetary system. So, what are planets? The Solar System is made up of:
• The sun (a star)
• 9 planets (planets)
• 6 moons (moons)
• 1 asteroid belt (asteroids)
• 1 Kuiper belt (Kuiper Belt objects which are not planets but which could be, based on the mass and orbit of their orbits)
So, I propose we call this set of objects “planetary nebulae” instead. You can be sure that some people will hate this idea, but I know it will make sense to them someday. And if you disagree with me — well, at least you’ll know why I think it’s a good idea.
What does planetary nebula look like?
We are really glad to announce that the second volume of our book “The Planetary Nebulae” is now available. This new one, entitled “Planetary Nebulae: From Dust to Stardust” deals with shooting stars, comets, and meteors, and includes a chapter on the Sun’s planetary nebula that we did not have time for in the first volume (it was too involved).
And picking up where volume 1 left off, we discuss comet and meteor showers in more detail than we did in volume 1 and even include a chapter on the elusive supernova called SN 2011gv.
We hope you enjoy this book as much as we enjoyed putting it together!
Where are planetary nebulae located?
The most famous and best-known example of a planetary nebula is found in the constellation Lyra. It is known as the Bubble Nebula, and it is named after its shape.
Lyra is a fairly large constellation (it has more than 60 stars in it) and seems to have an endless supply of gas to host massive stellar explosions. The outer part of Lyra’s star cluster forms a huge bubble, which is what gives it its name. When this happens, the gas gets pushed outwards at high speed by strong wind particles streaming out of the central star (it’s called ‘stellar winds’).
The space between the star and the bubble gets filled with hydrogen atoms and then starts losing hydrogen atoms to space, which results in a red glow in the sky (the color is determined by the ratio of hydrogen to helium).
The next few paragraphs are going to be based on information from NASA’s Hubble Space Telescope, as well as information from several papers on dusty disks published in 2011; these were obtained from Wikipedia.
A planetary nebula can be seen with the naked eye under dark skies, but if you want to see one you need a telescope. In fact, if you want to see star clusters like our own Milky Way galaxy you need a telescope: they are too small for your eye lens to focus on them without magnification, so you need a telescope.
The Hubble Space Telescope can see some planetary nebulas in detail thanks to its Wide Field Planetary Camera 2 (WFPC2), but it isn’t very good at seeing objects like those found in Lyra:
I think that WFPC2 is only really good at seeing low-mass stars that are not big enough for planets (which is why we only spot them when looking at very young stars). This means that any planet around one of those would have been destroyed long ago by stellar winds or other factors before it could form.
When are planetary nebulae created?
If you’re going to be space rock, you have a few options: to land on another planet (and become part of the planet), or to explode. The latter is much easier, but it comes with its own problems. Astronomers have been looking at solar-system-scale nebulae from sunsets for decades, and we’re just starting to get our first glimpses of them in other parts of the sky. They’re so beautiful that we’ll probably never see them in person, but when we do — and they are amazing — there are lots of questions.
What is a planetary nebula? What kind of explosion is this? Is it like an explosion on Earth? What happens after it explodes?
Dr. John Mathers had one idea: find a new way to extend the life of our telescopes by looking at these objects in other places. He wanted to look at them not as they had been seen before, but as they would be seen in the future. His idea was that he could look at them when they were just starting out — even though we’d only see them as blips on our monitors now — and then follow their evolution over time.
Mathers did his research and worked out that there are five kinds of planetary nebulae: Type I (called Wolf-Rayet); Type II (called Cepheids); Type III (called Mira); Type IV (called Supernovae); and Type V (called Wolfram).
Type I are called Wolf-Rayet because their gas cloud is filled with hot gas from the supernova explosion itself rather than from an earlier generation star or another nebula . . . . this type is rare because its mass is so high; typically only twenty million tons or so, but occasionally up to two hundred million tons could form in a single supernova event (which would create something like three light-years worth of material). Type II is named after the type of star used by the nebula’s progenitor system…the more massive stars within its collapse produce heavier elements than typical; creating more massive gas clouds than normal…
These clouds age through gravitational processes over billions of years before exploding; producing pure white dwarf stars that are hot enough to ignite hydrogen atoms into helium-burning bursts which result in what we see as supernovas… Type III occur after a supernova…the hydrogen-burning processes may last for millions or
How long do planetary nebulae live for?
You probably have a read or two of science fiction and wonder…what are those? Most people know them as stars that suddenly go supernova.
But, there’s a whole other story to tell about them, where they become planetary nebulae.
A planetary nebula is when the outer layers of a star (the envelope) become so hot and dense that it ignites into a white dwarf. This is the ultimate end for stars. As the star ages, its envelope will cool down and expand outwards towards space; eventually, it will explode as a supernova.
When the inner part of a star becomes too dense to support itself, it begins to collapse inward on itself (in this case, the core), forming an implosion called an accretion disk. As it spins up and heats up, gas in the disk pushes outward against the spin-down center – this is called “accretion” – causing the further gravitational collapse of an increasingly massive star. This is when we see that outer part of our sun as a planetary nebula (a very faint one).
In fact, there are actually two types of planetary nebulae: those that are visible because they have dust around them (known as stellar-class nebulae) and those that are invisible because they don’t have dust around them (known as galactic-class nebulae). Stellar-class nebulae contain very large amounts of hydrogen gas which emits light from ultraviolet light at this wavelength; galactic-class nebulae contain hydrogen gas which has been ionized into heavier atoms at longer wavelengths (this means everything except light can be seen by us). We can track both types in telescopes at night time with great detail:
I’m sure you can see where I am going with this…and why it can be such fun for us non-astronomers!