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Star-forming region, the Eagle Nebula, M16
This is a picture of part of the Eagle Nebula. The word
“nebula” refers to
any cloud of interstellar gas and dust. In this picture, taken
by the
Hubble Space Telescope, young stars are forming in the
“fingertips” that stick out of the larger columns of gas and
dust.
Planetary nebula, NGC 2392 (The Eskimo Nebula)
The word “nebula” refers to any
cloud of interstellar gas and dust. Through small telescopes, these
objects looked like the planets Uranus and Neptune, and so early
astronomers called them “planetary” nebulae. Astronomers now
know that they have nothing to do with planets, but the name has
stuck. Our own Sun will eventually, billions of years from now as
it nears the end of its life, will sit at the center of a planetary
nebula of glowing gas, perhaps like this one. This object is known
as the Eskimo Nebula, because it resembles a face enclosed by a
fur parka
Supernova remnant, The Crab Nebula, M 1
Astronomers also see areas in which gigantic stars have literally
blown themselves to pieces. The stellar explosion, called a
supernova, which led to the formation of the Crab Nebula, shown
in this picture, was witnessed by Chinese astronomers in 1054
A.D. One night they noticed that an extremely bright star had
appeared in the sky where before there had seen nothing. It
remained visible for over a year, before slowly fading from view.
Centuries later, when astronomers look where the Chinese saw
the “guest star,” they see this nebula of glowing gas and dust, the
remains of a once massive star.
Black hole candidate, Cygnus X-1
With their telescopes, astronomers have found evidence for black
holes. Black holes are incredibly dense objects with such high
gravity that not even light can escape from them, if it gets too
close. This artist’s drawing shows one possible black hole, called
Cygnus X-1. Gas from the large star at the right is falling onto a
disk around the black hole at the left. As this disk material swirls
around and falls into the black hole, it gives off X-rays, which is
how astronomers were able to “see” the otherwise “black” hole.
Interstellar Cloud, the Trifid Nebula, M20
When they look through their telescopes, astronomers also see
enormous interstellar clouds of gas and dust. Part of this
interstellar cloud, known as the Trifid Nebula, appears blue
because it is reflecting light from nearby stars. The red part of the
cloud is glowing hydrogen gas, lit up by ultraviolet radiation from
a star embedded deep within it.
The Pleiades star cluster, M45
Astronomers also see clusters of hundreds of stars, all
born from
the same giant interstellar cloud. This group is called
the Pleiades
(Plee-a-deez), and can be seen with the unaided eye in
the
constellation Taurus the Bull.
Spiral Galaxy, M 81
Astronomers also see collections of billions of stars
known as
galaxies. This one, known as M 81, has two “arms”
full of stars
that spiral out from its center.
Artist’s drawing of planet orbiting 51 Pegasi
And in recent years, astronomers have begun to see
evidence that
planets orbit around stars other than the Sun. This
artist’s drawing
shows a giant planet orbiting the star 51 Pegasi. It was
the first
planet discovered outside of our solar system.