Turn Right At Orion (32 page)

My editors—Amanda Cook, Sean Abbott, and Connie Day—helped to improve the book immeasurably, and I also thank Jeffrey Robbins for his early enthusiasm and support of the project. Dr. Ka Chun Yu found time to complete his ingenious illustration of
Rocinante's
path the very week he was preparing to defend his Ph.D. thesis on the Orion Nebula. And my wife, Claire Hay, provided encouragement, sound advice, and thought-provoking discussion throughout.

Finally, I cannot overemphasize the role that public funding plays in making progress in astrophysics possible. Without research support from organizations like the National Science Foundation and the National Aeronautics and Space Administration, there would have been little to write about.

accretion disk:
disk of gas orbiting in the gravitational field of a body. Internal friction in the gas causes it to spiral toward the body, resulting in accretion.

 

atomic hydrogen:
gas in which hydrogen exists in the form of individual atoms, neither ionized nor paired off into molecules. Much of the interstellar matter in the
Milky Way's
disk takes this form.

 

Betelgeuse:
a red supergiant located in the constellation Orion, about 500 light-years from Earth.

 

black hole:
body whose gravitational field is so strong that northing that falls in, not even light, can escape. Two populations exist: Stellar-mass black holes are formed by the collapse of massive stars; supermassive black holes are of uncertain origin and exist at the centers of most, if not all, galaxies.

 

bulge:
central stellar component of a
spiral galaxy,
consisting of stars on chaotic orbits.

 

Copernican Principle:
guiding principle of astrophysics, according to which no special advantage is accorded to our viewpoint on the Universe. Thus any phenomena we observe are assumed to be commonplace.

 

Crab Nebula:
remnant of a
supernova
explosion observed in A.D. 1054. A
pulsar
that spins 30 times a second powers this compact nebula in Taurus. By the time the narrator reaches it, the nebula has dispersed into interstellar space. M1 in
Messier's
catalogue.

 

Crab II:
an imaginary
supernova
remnant, similar to today's Crab, visited by the narrator 90,000 years after his departure from Earth.

 

Cygnus X-1:
massive X-ray–emitting object in a binary system. Believed to be a
black hole
accreting matter from a disk.

 

degeneracy pressure:
resistance to compression exhibited by dense gases consisting of elementary particles, such as electrons or neutrons, regardless of temperature. Arises from random motions of tightly packed particles predicted by
quantum mechanics.
Prevents
white dwarfs
and
neutron
stars from collapsing.

 

Dumbbell Nebula:
prominent
planetary nebula
located in the constellation Vulpecula. Its shape, resembling two luminous masses connected by a bar, gave rise to its name. M27 in Messier's catalogue.

 

Einstein, Albert (1879–1955):
German born, Swiss-American physicist who formulated the
special and general theories of relativity
. Also demonstrated the particulate nature of light, a key step in the development of
quantum mechanics.

 

elliptical galaxy:
roughly spherical galaxy consisting of stars moving on chaotic orbits under their mutual gravitational attractions.

 

general theory of relativity:
theory of gravitation propounded by
Albert Einstein
in 1915, according to which gravity is a manifestation of the curvature of spacetime. Builds on the foundation laid 10 years earlier by Einstein's special
theory of relativity.

 

globular cluster:
compact, spherical cluster of 100,000 to a few million stars, a few light-years across, orbiting a galaxy. Several hundred globular clusters orbit the
Milky Way;
huge galaxies like
M87
contain thousands.

 

halo: extended region of stars and gas enveloping a galaxy.

 

Herschel, William (1738–1822):
English astronomer who (among other discoveries) deduced the shape of the
Milky Way
through star counts, catalogued and classified numerous binary stars, star clusters and
nebulae
(including
planetary nebulae),
and discovered the planet Uranus.

 

horizon:
surface surrounding a
black hole
from within which nothing can escape.

 

hot star:
star with a high surface temperature and blue-white color. Any star that is a few times more massive than the Sun and is still burning hydrogen in its core. Also, an evolved (non-hydrogen burning) star with a surface temperature considerably higher than that of the Sun.

 

interstellar cloud:
region of interstellar space where the density of gas is relatively high and the temperature is relatively low, compared to the surroundings.

 

interstellar dust:
extremely fine granular material that coexists with gas in most regions of interstellar space.

 

ion:
an atom stripped of one or more of its electrons.

 

jet:
fast-moving, narrow stream of
plasma
that shoots out of the center of an
accretion disk
or other rotating system. Associated especially with
black holes
and
protostars.

 

Kepler, Johannes (1571–1630):
German mathematician and astronomer who deduced three fundamental laws of planetary motion. His
Somnium, sive Astronomia lunaris
(“Dream, or Lunar Astronomy”) was written in 1611 and published posthumously in 1634.

 

light, speed of:
a universal constant, 300,000 kilometers per second. A light-year, the distance light travels in a year, equals 9.5 trillion kilometers.

 

Local Group:
a loose grouping of several dozen galaxies that includes the
Milky Way.

 

M87:
an enormous
elliptical galaxy
in the
Virgo Cluster—
notable for its X-ray–emitting atmosphere, its rich cloud of
globular clusters,
and the high-speed
jets
shooting out of its center—that contains a three-billion-Solar-mass
black hole.
Catalogued by Messier.

 

Magellanic Clouds:
two prominent satellite galaxies of the
Milky Way.

 

Messier, Charles (1730–1817):
French astronomer who compiled an early catalogue of astronomical objects, including many prominent
nebulae,
star clusters, and galaxies. Objects in his catalogue are denoted by the prefix M.

 

Milky Way:
large spiral galaxy that contains the Solar System and most destinations described in this book. When capitalized, the word Galaxy refers specifically to the Milky Way.

 

molecular cloud:
relatively cool, dense region of interstellar space in which a large proportion of the atoms have combined to form molecules.

 

nebula:
illuminated patch of interstellar gas.

 

neutron star:
superdense body with a mass similar to that of the Sun but a size of only 10–20 kilometers. Believed to form from the collapsing core of a massive star. Neutron stars have the strongest gravitational fields of all known objects except for
black holes.

 

Orion:
region of vigorous star formation located about 1500 light-years from Earth. Its appearance from Earth is dominated by the Orion Nebula (M42 in
Messier's
catalogue), which is illuminated by the
Trapezium.
The Orion star-forming region is located in the constellation Orion.

 

planetary nebula:
expanding envelope of gas released by a dying, low-mass star and illuminated by the still-hot stellar core.

 

plasma:
an ionized gas—that is, one in which electrons have been stripped from their atomic nuclei. The hot gases that make up stars,
accretion disks,
and most other systems discussed in
this book are plasmas. They are extremely good electrical conductors, which enables them to trap magnetic fields.

 

protostar:
star in the process of formation, consisting of a central core, an
accretion disk,
and, often,
jets.

 

pulsar:
magnetized, spinning
neutron star
producing beams of radiation that rotate with the star.

 

quantum mechanics:
laws of physics, formulated during the first third of the twentieth century, that describe atoms, molecules, and other small-scale phenomena. This system posits that all forms of energy and matter exhibit characteristics of both particles and waves.

 

red giant:
star that has exhausted the hydrogen in its core and is burning hydrogen in a shell surrounding the core. Characterized by an enormous, cool envelope.

 

red supergiant:
star with an inert core that is burning fuels heavier than hydrogen in shells surrounding the core. Larger and more luminous than a
red giant.

 

Shangri-La effect:
factor by which time is slowed down for the narrator, relative to other objects in the Galaxy, as a result of the narrator's extremely high speed.

 

special theory of relativity:
Einstein's 1905 theory describing the relationships among space, time, and motion, but neglecting gravity. Gravitational effects are treated in Einstein's
general theory of relativity (1915).

 

spiral arms:
curved patterns superimposed on the disk of a
spiral galaxy,
corresponding to “traffic jams” in the orbital flow of stars and gas. Associated with the accumulation of large
molecular clouds
and regions of star formation.

 

spiral galaxy:
galaxy containing a prominent disk of stars and gas embedded in an extended
halo.
Gravitational disturbances within the disk give rise to
spiral arms.

 

SS 433:
binary system notable for producing a pair of
jets
that precess about a fixed axis, like a wobbling top. The jets are believed to arise near the center of an
accretion disk,
but it is not known whether the accreting body is a
neutron star
or
a black hole.

 

superbubble:
large region of hot interstellar gas created by the combined action of stellar winds and
supernovae
from many
hot stars.

 

supernova:
enormous explosion of a stellar envelope that occurs when a massive star's core collapses to form a
neutron star.
This term also refers to explosions of
white dwarfs
that have grown too heavy to support themselves.

 

synchrotron radiation:
radiation produced when electrons moving at close to the speed of light gyrate in a magnetic field.

 

Tarantula Nebula:
huge star-forming region in the
Large Magellanic Cloud.
Thousands of times more luminous than Orion. Site of the fictional
supernova
explosion (based on the real Supernova 1987A) witnessed by the narrator.

 

Texas Symposium:
biennial series of conferences, first held in Dallas in 1963, focusing on the latest results in relativistic astrophysics. The meeting site now rotates among international destinations, returning to Texas only occasionally.

 

tidal force:
differential gravitational force that can stretch or squeeze objects.

 

Trapezium:
quartet of young, massive stars responsible for illuminating the Orion Nebula.

 

Virgo Cluster:
cluster of more than a thousand galaxies located about 60 million light-years from the
Milky Way.

 

white dwarf:
body with a mass similar to that of the Sun but a size similar to that of Earth. Supported against gravity by electron
degeneracy pressure.

Accretion disks; definition; jets and; plasma and; protostars and; of SS 433;
See
also Disks

Accretion streams

Aging

Alcohol in molecular clouds

Ammonia in dust disks

Andromeda (spiral galaxy)

Angular momentum; black holes and; Milky Way halo and

Antares

Asteroid impact with sheperd planets

Atomic hydrogen

Atoms; the aurora borealis and; electron clouds and; filaments of Crab II and; in gap between molecular clouds and Trapezium stars; hydrogen; hydrogen in interstellar clouds; hydrogen in molecular clouds; jets of SS 433 and; neutron stars and; in Orion Nebula molecular clouds; planetary nebulae; the Sun and; Trapezium stars and;
See also
Molecules; Particles

Aurora borealis, the

Barnard's Loop

Betelgeuse (red supergiant); in comparison to the Sun; core of; distance from Earth; helium and; surface of; winds of

Binary systems: Cygnus X–1; planets and; SS 433