Plasma

All About Electromagnetic Radiation

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Anyone who took elementary science in grade school recalls the lesson about the three states of matter, right? That was the one where we were told that matter comes in three basic forms: liquid, solid and gas. This works for the periodic table of elements and can be extended to include just about any compound. Except perhaps for whipped cream (that damnable compound continues to defy attempts as classification!) But what if there were a fourth state for matter? It occurs when a state of matter similar to gas contains a large portion of ionized particles and generates its own magnetic field. It’s called Plasma, and it just happens to be the most common type of matter, comprising more than ninety-nine percent of matter in the visible universe and which permeates the solar system, interstellar and intergalactic environments.

The basic premise behind plasma is that heating a gas dissociates its molecular bonds, rendering it into its constituent atoms. Further heating leads to ionization (a loss of electrons), which turns it into a plasma. This plasma is therefore defined by the existence of charged particles, both positive ions and negative electrons.The presence of a large number of charged particles makes the plasma electrically conductive so that it responds strongly to electromagnetic fields. Plasma, therefore, has properties quite unlike those of solids, liquids, or gases and is considered a distinct state of matter. Like a gas, plasma does not have a definite shape or a definite volume unless enclosed in a container. But unlike gas, under the influence of a magnetic field, it may form structures such as filaments, beams and double layers. It is precisely for this reason that plasma is used in the construction of electronics, such as plasma TVs and neon signs.

The existence of plasma was first discovered by Sir William Crookes in 1879 using an assembly that is today known as a “Crookes tube”, an experimental electrical discharge tube in which air is ionized by the application of a high voltage through a voltage coil. At the time, he labeled it “radiant matter” because of its luminous quality. Sir J.J. Thomson, a British physicist, identified the nature of the matter in 1897, thanks to his discovery of electrons and numerous experiments using cathode ray tubes. However, it was not until 1928 that the term “plasma” was coined by Irving Langmuir, an American chemist and physicist, who was apparently reminded of blood plasma.

As already mentioned, plasmas are by far the most common phase of matter in the universe. All the stars are made of plasma, and even the space between the stars is filled with a plasma, albeit a very sparse one.

We have written many articles about plasma for Universe Today. Here’s an article about the plasma engine, and here’s an article about the states of matter.

If you’d like more info on plasma, check out these articles from Chem4Kids and NASA Science.

We’ve also recorded an episode of Astronomy Cast all about the Sun. Listen here, Episode 30: The Sun, Spots and All.

Sources:
http://en.wikipedia.org/wiki/Plasma_%28physics%29
http://en.wikipedia.org/wiki/Crookes_tube
http://en.wikipedia.org/wiki/Charge_carrier
http://en.wikipedia.org/wiki/J._J._Thomson
http://en.wikipedia.org/wiki/Irving_Langmuir
http://www.plasmas.org/basics.htm
http://www.plasmas.org/what-are-plasmas.htm

States of Matter

Solid, liquid, gas … those are the states of matter we’re thoroughly familiar with, but what makes for a state of matter? And are there other states of matter?

Since people first made distinctions between them, the states of matter were defined by how the matter behaved, in bulk; so a solid had a fixed shape (and volume), a liquid a fixed volume (but changed shape to fit the container it was in), and a gas expanded to fill its container. Once we realized that matter is made up of atoms (and molecules), the states of matter were distinguished by how the molecules (or atoms, in an element) behaved: in solids they are both close by and in a fixed arrangement (e.g. in crystals), in liquids close by but the arrangement is not fixed, and in gases not close by (so no particular arrangement).

But what about plasma? Sorta like a gas – so as it fills any container it’s in, it’s a gas – but not (the ions and electrons interact in completely different ways, in a plasma, than molecules (or atoms) do in a solid, liquid, or gas). Hence, plasma is the fourth state of matter.

Things got a bit more complicated as scientists studied matter more carefully.

For example, if you heat water in a strong, but transparent, container, above a certain temperature (and pressure) – called the critical temperature (critical pressure) – the liquid and gas states become one … the water is now a supercritical fluid (you may have seen this demonstrated, in a chemistry class perhaps, though likely not with water!).

Then there’s the distinction between crystals (crystalline state) and glasses (glassy state); both seem very solid, but the arrangement of molecules in a glass is more like that of molecules in a liquid than those in a crystal … and glasses can flow, just like liquids, if left for a long enough time.

Is there a ‘fifth state of matter’? Yes! A Bose-Einstein condensate (BEC) … which is like a gas, except that the constituent atoms are all (or mostly) in the lowest possible quantum state … so a BEC has bulk properties quite unlike those of any other state of matter (quantum behavior become macroscopic).

In astrophysics, there are quite a few exotic states of matter; for example, in white dwarf stars matter is prevented from further (gravitational) collapse by electron degeneracy pressure; the same sort of thing happens in neutron stars, except that its neutron degeneracy pressure (there may also be an even more extreme state of matter, held up by quark degeneracy pressure!). There’s also a counterpart to ordinary plasmas: quark-gluon plasma (in an ordinary plasma made of hydrogen the atoms are broken into electrons and protons; in a quark-gluon plasma protons and neutrons ‘melt’ into their constituent quarks and gluons).

Are there related Universe Today stories? Sure! For example: Forget Neutron Stars, Quark Stars May Be the Densest Bodies in the Universe, Schwarzschild Radius, and Next Generation Magnetoplasma Rocket Could be Tested on Space Station.

States of matter, including some exotic ones, is something you’ll find discussed in Astronomy Cast; for example this Questions Show.

Sources:
Wikipedia
Purdue University
New York University
Wikipedia: Bose-Einstein Condensate