About Deep Space Objects and Cosmic Terms
Raw Materials of Space
Raw Materials of Space
is a great deal of what you might call "raw material" out in space,
and much of it is pretty cold and hard to see. The formation of
the objects we can see in space, including stars, nebulae,
and the objects that are actually collections of other objects (e.g.,
star clusters and galaxies),
started with these raw materials. Gas makes up roughly 99%
of the raw material found in space. The word gas, as used in astronomy,
refers to loose collections of atoms
or molecules, often found
in giant "clouds" among the stars (known as nebulae).
The most common kind of gas found in space is made up of hydrogen
atoms, which glow with a characteristic red color when "excited,"
i.e., energized by heat or radiation. (You can see the red glow
of hydrogen on many of the cards in the Cosmic
Decoders Card Set.) The next most common gas in
space is made up of helium atoms. Other gases are also common, such
as nitrogen and oxygen, although they are much rarer in space than
hydrogen and helium.
common raw material in space is dust. The term dust in astronomy
simply means individual grains of solid material (denser collections
of atoms and molecules).
Dust in space is typically found in the same clouds among the stars
where gas is found. Astronomers believe that the dust in space is
not that different from what you find under your bed when you are
too distracted by your love of astronomy to clean up properly.
is a cloud of gas and dust
in space. A nebula can be "lit up" by the energy of one or more
nearby stars (including stars inside the nebula). In this state,
the cloud of gas and dust becomes visible to us (although most are
only visible with the aid of telescopes).
The plural of nebula is nebulae (pronounced neb' u lee).
Nebulae are found in galaxies.
Some nebulae are small while others are huge. Some can contain thousands
of stars while others surround just a single star. Some nebulae
are "star nurseries," otherwise known as star birth nebulae,
where new stars are formed. Other types of nebulae, called star
death nebulae, are produced when a star loses its raw material
at the end of its life.
birth nebula (or star formation region) is a cloud of gas
and dust in which new stars are being formed from the raw material
of the cloud. In places where the cloud has become compressed (where
the gas and dust are very close together), the gas and dust start
"clumping." At a certain stage, these clumps start heating
up in the center, and when that happens, star formation begins.
After many years of clumping and heating, a star will get so hot
in the middle (over 10 million degrees Centigrade) that it will
begin to make its own energy – it starts to shine. In many
of the star forming regions depicted on the Cosmic
Decoders Cards, new stars have already begun to shine, and
their energy makes the clouds of gas and dust around them glow with
a star nears the end of its existence, astronomers say it begins
to "die." One characteristic of dying stars is that they
lose the raw material that helped form them. A star death nebula
is thus formed from the raw material expelled from a dying star.
The way in which the raw material is expelled determines the type
of resulting star death nebula. There are two types of star death
nebulae: planetary nebulae and supernova remnants.
planetary nebula has nothing to do with planets. Instead,
it is created when a dying star loses material all around it. This
material leaves the star in one or more "last gasps" before the
star dies, and creates a sort of "shell" (made mostly of hot gas)
around the dead star. Sometimes the gas comes off pretty much uniformly,
giving the shell a ball or donut shape (as seen in the Retina
Nebula from the Cosmic
Decoders Card Set). At other
times, old material that is already around the star closes off some
"avenues of escape" for newly lost material (which creates yet its
own shell). Then the shape of the nebula can be complicated, as
you can see in the Saturn
Nebula from the Cosmic
Decoders Card Set.
can see the glowing shells of gas from planetary nebula because
the atoms within are "excited" (energized by heat or radiation)
by the energy of the hot dead star, or star "corpse," in the middle.
The dead star is called a white dwarf because it is now much
smaller and white-hot. Planetary nebulae and white dwarfs form when
relatively smaller stars, like our Sun, die. However, when larger
stars die, another type of star death nebula, called a supernova
remnant, is formed.
supernova remnant consists of the gas and dust left
over from the explosion of a star at the end of its life. Instead
of "quietly" letting off some material (as the smaller stars mostly
do), the really big stars blow up when they die, scattering their
fragments into space at great speed. Years after the explosion,
we see these fragments, or remains, of gas and dust spread out over
a great distance. We can see them because sometimes a star corpse
still survives (known as a pulsar, a rapidly whirling object)
and it provides energy to light up the gas and dust remains (as
in the Crab Nebula).
In other supernova remnants, the exploded material collides with
other material in space, and it is the energy of these collisions
that causes the gas to glow.
cluster is a group of stars that are born together and move
through space together. In general, stars in such a cluster are
closer to each other than other stars' neighbor stars tend to be.
Star clusters can include as few as a dozen stars or as many as
a million stars. Star clusters are found in galaxies.
open star cluster is a relatively small star cluster group
with anywhere from a dozen to a thousand stars. Such star clusters
tend to be much more loose and spread out than the other type of
star cluster — the globular star cluster. A globular star
cluster is a large, tightly bound group of stars, which typically
has a hundred thousand or more stars.
is a collection of many millions or billions of stars, nebulae,
and other cosmic objects. Our Sun and its planets are part of one
such collection, called the Milky Way Galaxy. One of the
great discoveries in astronomy during the 20th century
was that there are billions of other galaxies (or "islands" of stars
and other cosmic objects) throughout the universe.
tend to be "social," in that they come in groups. Our Milky Way
Galaxy, for example, is part of a loose group of several dozen
galaxies that we call The Local Group. Some
large groups can contain thousands and thousands of galaxies. In
a group, collisions among galaxies can occur over time. When
two galaxies collide, their stars are mostly too far apart to suffer
actual collisions. But the nebulae
of raw material (gas and dust)
in them can come together and get compressed (squeezed together).
This compression often leads to the formation of many new stars.
In colliding galaxies, we not only see "bursts" of new star formation,
but we also see the overall shapes of the galaxies get distorted,
sometimes resulting in what are called warped disk galaxies
and polar ring galaxies (http://antwrp.gsfc.nasa.gov/apod/ap990510.html).
Several of the galaxies
depicted on the Cosmic
Decoders Cards show the results
of colliding galaxies.
spiral galaxy is a basically flat galaxy with a disk shape,
something like a Frisbee® with a rounded bulge in
the center. In such galaxies, the stars and other objects that make
up the disk are typically organized into a multiple-armed spiral
structure, like a pinwheel. Spirals generally have quite a bit of
gas and dust in addition to stars. Many spiral galaxies have a bar
of stars and raw material across their centers, and hence are called
elliptical galaxy has an overall curved elongated shape like
a football or a blimp. Some are much more round like a basketball.
Such galaxies typically have very little raw
material (gas and dust) and contain more older stars. Ellipticals
come in a variety of sizes from small, loosely packed dwarf ellipticals,
all the way to giant ellipticals that can contain a thousand billion
stars or more!
irregular galaxy is a galaxy whose appearance is more complicated
than either a spiral or an elliptical. Irregulars come in
a bewildering variety of shapes, which are probably the results
of collisions of two or more galaxies. As galaxies collide (see
above for more), their mutual gravity can distort the stars, gas,
and dust in them into many different shapes.