Chapter 13: Star Birth and Death

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Chapter 1
How Science Works

  • The Scientific Method
  • Evidence
  • Measurements
  • Units and the Metric System
  • Measurement Errors
  • Estimation
  • Dimensions
  • Mass, Length, and Time
  • Observations and Uncertainty
  • Precision and Significant Figures
  • Errors and Statistics
  • Scientific Notation
  • Ways of Representing Data
  • Logic
  • Mathematics
  • Geometry
  • Algebra
  • Logarithms
  • Testing a Hypothesis
  • Case Study of Life on Mars
  • Theories
  • Systems of Knowledge
  • The Culture of Science
  • Computer Simulations
  • Modern Scientific Research
  • The Scope of Astronomy
  • Astronomy as a Science
  • A Scale Model of Space
  • A Scale Model of Time
  • Questions

Chapter 2
Early Astronomy

  • The Night Sky
  • Motions in the Sky
  • Navigation
  • Constellations and Seasons
  • Cause of the Seasons
  • The Magnitude System
  • Angular Size and Linear Size
  • Phases of the Moon
  • Eclipses
  • Auroras
  • Dividing Time
  • Solar and Lunar Calendars
  • History of Astronomy
  • Stonehenge
  • Ancient Observatories
  • Counting and Measurement
  • Astrology
  • Greek Astronomy
  • Aristotle and Geocentric Cosmology
  • Aristarchus and Heliocentric Cosmology
  • The Dark Ages
  • Arab Astronomy
  • Indian Astronomy
  • Chinese Astronomy
  • Mayan Astronomy
  • Questions

Chapter 3
The Copernican Revolution

  • Ptolemy and the Geocentric Model
  • The Renaissance
  • Copernicus and the Heliocentric Model
  • Tycho Brahe
  • Johannes Kepler
  • Elliptical Orbits
  • Kepler's Laws
  • Galileo Galilei
  • The Trial of Galileo
  • Isaac Newton
  • Newton's Law of Gravity
  • The Plurality of Worlds
  • The Birth of Modern Science
  • Layout of the Solar System
  • Scale of the Solar System
  • The Idea of Space Exploration
  • Orbits
  • History of Space Exploration
  • Moon Landings
  • International Space Station
  • Manned versus Robotic Missions
  • Commercial Space Flight
  • Future of Space Exploration
  • Living in Space
  • Moon, Mars, and Beyond
  • Societies in Space
  • Questions

Chapter 4
Matter and Energy in the Universe

  • Matter and Energy
  • Rutherford and Atomic Structure
  • Early Greek Physics
  • Dalton and Atoms
  • The Periodic Table
  • Structure of the Atom
  • Energy
  • Heat and Temperature
  • Potential and Kinetic Energy
  • Conservation of Energy
  • Velocity of Gas Particles
  • States of Matter
  • Thermodynamics
  • Entropy
  • Laws of Thermodynamics
  • Heat Transfer
  • Thermal Radiation
  • Wien's Law
  • Radiation from Planets and Stars
  • Internal Heat in Planets and Stars
  • Periodic Processes
  • Random Processes
  • Questions

Chapter 5
The Earth-Moon System

  • Earth and Moon
  • Early Estimates of Earth's Age
  • How the Earth Cooled
  • Ages Using Radioactivity
  • Radioactive Half-Life
  • Ages of the Earth and Moon
  • Geological Activity
  • Internal Structure of the Earth and Moon
  • Basic Rock Types
  • Layers of the Earth and Moon
  • Origin of Water on Earth
  • The Evolving Earth
  • Plate Tectonics
  • Volcanoes
  • Geological Processes
  • Impact Craters
  • The Geological Timescale
  • Mass Extinctions
  • Evolution and the Cosmic Environment
  • Earth's Atmosphere and Oceans
  • Weather Circulation
  • Environmental Change on Earth
  • The Earth-Moon System
  • Geological History of the Moon
  • Tidal Forces
  • Effects of Tidal Forces
  • Historical Studies of the Moon
  • Lunar Surface
  • Ice on the Moon
  • Origin of the Moon
  • Humans on the Moon
  • Questions

Chapter 6
The Terrestrial Planets

  • Studying Other Planets
  • The Planets
  • The Terrestrial Planets
  • Mercury
  • Mercury's Orbit
  • Mercury's Surface
  • Venus
  • Volcanism on Venus
  • Venus and the Greenhouse Effect
  • Tectonics on Venus
  • Exploring Venus
  • Mars in Myth and Legend
  • Early Studies of Mars
  • Mars Close-Up
  • Modern Views of Mars
  • Missions to Mars
  • Geology of Mars
  • Water on Mars
  • Polar Caps of Mars
  • Climate Change on Mars
  • Terraforming Mars
  • Life on Mars
  • The Moons of Mars
  • Martian Meteorites
  • Comparative Planetology
  • Incidence of Craters
  • Counting Craters
  • Counting Statistics
  • Internal Heat and Geological Activity
  • Magnetic Fields of the Terrestrial Planets
  • Mountains and Rifts
  • Radar Studies of Planetary Surfaces
  • Laser Ranging and Altimetry
  • Gravity and Atmospheres
  • Normal Atmospheric Composition
  • The Significance of Oxygen
  • Questions

Chapter 7
The Giant Planets and Their Moons

  • The Gas Giant Planets
  • Atmospheres of the Gas Giant Planets
  • Clouds and Weather on Gas Giant Planets
  • Internal Structure of the Gas Giant Planets
  • Thermal Radiation from Gas Giant Planets
  • Life on Gas Giant Planets?
  • Why Giant Planets are Giant
  • Gas Laws
  • Ring Systems of the Giant Planets
  • Structure Within Ring Systems
  • The Origin of Ring Particles
  • The Roche Limit
  • Resonance and Harmonics
  • Tidal Forces in the Solar System
  • Moons of Gas Giant Planets
  • Geology of Large Moons
  • The Voyager Missions
  • Jupiter
  • Jupiter's Galilean Moons
  • Jupiter's Ganymede
  • Jupiter's Europa
  • Jupiter's Callisto
  • Jupiter's Io
  • Volcanoes on Io
  • Saturn
  • Cassini Mission to Saturn
  • Saturn's Titan
  • Saturn's Enceladus
  • Discovery of Uranus and Neptune
  • Uranus
  • Uranus' Miranda
  • Neptune
  • Neptune's Triton
  • Pluto
  • The Discovery of Pluto
  • Pluto as a Dwarf Planet
  • Dwarf Planets
  • Questions

Chapter 8
Interplanetary Bodies

  • Interplanetary Bodies
  • Comets
  • Early Observations of Comets
  • Structure of the Comet Nucleus
  • Comet Chemistry
  • Oort Cloud and Kuiper Belt
  • Kuiper Belt
  • Comet Orbits
  • Life Story of Comets
  • The Largest Kuiper Belt Objects
  • Meteors and Meteor Showers
  • Gravitational Perturbations
  • Asteroids
  • Surveys for Earth Crossing Asteroids
  • Asteroid Shapes
  • Composition of Asteroids
  • Introduction to Meteorites
  • Origin of Meteorites
  • Types of Meteorites
  • The Tunguska Event
  • The Threat from Space
  • Probability and Impacts
  • Impact on Jupiter
  • Interplanetary Opportunity
  • Questions

Chapter 9
Planet Formation and Exoplanets

  • Formation of the Solar System
  • Early History of the Solar System
  • Conservation of Angular Momentum
  • Angular Momentum in a Collapsing Cloud
  • Helmholtz Contraction
  • Safronov and Planet Formation
  • Collapse of the Solar Nebula
  • Why the Solar System Collapsed
  • From Planetesimals to Planets
  • Accretion and Solar System Bodies
  • Differentiation
  • Planetary Magnetic Fields
  • The Origin of Satellites
  • Solar System Debris and Formation
  • Gradual Evolution and a Few Catastrophies
  • Chaos and Determinism
  • Extrasolar Planets
  • Discoveries of Exoplanets
  • Doppler Detection of Exoplanets
  • Transit Detection of Exoplanets
  • The Kepler Mission
  • Direct Detection of Exoplanets
  • Properties of Exoplanets
  • Implications of Exoplanet Surveys
  • Future Detection of Exoplanets
  • Questions

Chapter 10
Detecting Radiation from Space

  • Observing the Universe
  • Radiation and the Universe
  • The Nature of Light
  • The Electromagnetic Spectrum
  • Properties of Waves
  • Waves and Particles
  • How Radiation Travels
  • Properties of Electromagnetic Radiation
  • The Doppler Effect
  • Invisible Radiation
  • Thermal Spectra
  • The Quantum Theory
  • The Uncertainty Principle
  • Spectral Lines
  • Emission Lines and Bands
  • Absorption and Emission Spectra
  • Kirchoff's Laws
  • Astronomical Detection of Radiation
  • The Telescope
  • Optical Telescopes
  • Optical Detectors
  • Adaptive Optics
  • Image Processing
  • Digital Information
  • Radio Telescopes
  • Telescopes in Space
  • Hubble Space Telescope
  • Interferometry
  • Collecting Area and Resolution
  • Frontier Observatories
  • Questions

Chapter 11
Our Sun: The Nearest Star

  • The Sun
  • The Nearest Star
  • Properties of the Sun
  • Kelvin and the Sun's Age
  • The Sun's Composition
  • Energy From Atomic Nuclei
  • Mass-Energy Conversion
  • Examples of Mass-Energy Conversion
  • Energy From Nuclear Fission
  • Energy From Nuclear Fusion
  • Nuclear Reactions in the Sun
  • The Sun's Interior
  • Energy Flow in the Sun
  • Collisions and Opacity
  • Solar Neutrinos
  • Solar Oscillations
  • The Sun's Atmosphere
  • Solar Chromosphere and Corona
  • Sunspots
  • The Solar Cycle
  • The Solar Wind
  • Effects of the Sun on the Earth
  • Cosmic Energy Sources
  • Questions

Chapter 12
Properties of Stars

  • Stars
  • Star Names
  • Star Properties
  • The Distance to Stars
  • Apparent Brightness
  • Absolute Brightness
  • Measuring Star Distances
  • Stellar Parallax
  • Spectra of Stars
  • Spectral Classification
  • Temperature and Spectral Class
  • Stellar Composition
  • Stellar Motion
  • Stellar Luminosity
  • The Size of Stars
  • Stefan-Boltzmann Law
  • Stellar Mass
  • Hydrostatic Equilibrium
  • Stellar Classification
  • The Hertzsprung-Russell Diagram
  • Volume and Brightness Selected Samples
  • Stars of Different Sizes
  • Understanding the Main Sequence
  • Stellar Structure
  • Stellar Evolution
  • Questions

Chapter 13
Star Birth and Death

  • Star Birth and Death
  • Understanding Star Birth and Death
  • Cosmic Abundance of Elements
  • Star Formation
  • Molecular Clouds
  • Young Stars
  • T Tauri Stars
  • Mass Limits for Stars
  • Brown Dwarfs
  • Young Star Clusters
  • Cauldron of the Elements
  • Main Sequence Stars
  • Nuclear Reactions in Main Sequence Stars
  • Main Sequence Lifetimes
  • Evolved Stars
  • Cycles of Star Life and Death
  • The Creation of Heavy Elements
  • Red Giants
  • Horizontal Branch and Asymptotic Giant Branch Stars
  • Variable Stars
  • Magnetic Stars
  • Stellar Mass Loss
  • White Dwarfs
  • Supernovae
  • Seeing the Death of a Star
  • Supernova 1987A
  • Neutron Stars and Pulsars
  • Special Theory of Relativity
  • General Theory of Relativity
  • Black Holes
  • Properties of Black Holes
  • Questions

Chapter 14
The Milky Way

  • The Distribution of Stars in Space
  • Stellar Companions
  • Binary Star Systems
  • Binary and Multiple Stars
  • Mass Transfer in Binaries
  • Binaries and Stellar Mass
  • Nova and Supernova
  • Exotic Binary Systems
  • Gamma Ray Bursts
  • How Multiple Stars Form
  • Environments of Stars
  • The Interstellar Medium
  • Effects of Interstellar Material on Starlight
  • Structure of the Interstellar Medium
  • Dust Extinction and Reddening
  • Groups of Stars
  • Open Star Clusters
  • Globular Star Clusters
  • Distances to Groups of Stars
  • Ages of Groups of Stars
  • Layout of the Milky Way
  • William Herschel
  • Isotropy and Anisotropy
  • Mapping the Milky Way
  • Questions

Chapter 15
Galaxies

  • The Milky Way Galaxy
  • Mapping the Galaxy Disk
  • Spiral Structure in Galaxies
  • Mass of the Milky Way
  • Dark Matter in the Milky Way
  • Galaxy Mass
  • The Galactic Center
  • Black Hole in the Galactic Center
  • Stellar Populations
  • Formation of the Milky Way
  • Galaxies
  • The Shapley-Curtis Debate
  • Edwin Hubble
  • Distances to Galaxies
  • Classifying Galaxies
  • Spiral Galaxies
  • Elliptical Galaxies
  • Lenticular Galaxies
  • Dwarf and Irregular Galaxies
  • Overview of Galaxy Structures
  • The Local Group
  • Light Travel Time
  • Galaxy Size and Luminosity
  • Mass to Light Ratios
  • Dark Matter in Galaxies
  • Gravity of Many Bodies
  • Galaxy Evolution
  • Galaxy Interactions
  • Galaxy Formation
  • Questions

Chapter 16
The Expanding Universe

  • Galaxy Redshifts
  • The Expanding Universe
  • Cosmological Redshifts
  • The Hubble Relation
  • Relating Redshift and Distance
  • Galaxy Distance Indicators
  • Size and Age of the Universe
  • The Hubble Constant
  • Large Scale Structure
  • Galaxy Clustering
  • Clusters of Galaxies
  • Overview of Large Scale Structure
  • Dark Matter on the Largest Scales
  • The Most Distant Galaxies
  • Black Holes in Nearby Galaxies
  • Active Galaxies
  • Radio Galaxies
  • The Discovery of Quasars
  • Quasars
  • Types of Gravitational Lensing
  • Properties of Quasars
  • The Quasar Power Source
  • Quasars as Probes of the Universe
  • Star Formation History of the Universe
  • Expansion History of the Universe
  • Questions

Chapter 17
Cosmology

  • Cosmology
  • Early Cosmologies
  • Relativity and Cosmology
  • The Big Bang Model
  • The Cosmological Principle
  • Universal Expansion
  • Cosmic Nucleosynthesis
  • Cosmic Microwave Background Radiation
  • Discovery of the Microwave Background Radiation
  • Measuring Space Curvature
  • Cosmic Evolution
  • Evolution of Structure
  • Mean Cosmic Density
  • Critical Density
  • Dark Matter and Dark Energy
  • Age of the Universe
  • Precision Cosmology
  • The Future of the Contents of the Universe
  • Fate of the Universe
  • Alternatives to the Big Bang Model
  • Space-Time
  • Particles and Radiation
  • The Very Early Universe
  • Mass and Energy in the Early Universe
  • Matter and Antimatter
  • The Forces of Nature
  • Fine-Tuning in Cosmology
  • The Anthropic Principle in Cosmology
  • String Theory and Cosmology
  • The Multiverse
  • The Limits of Knowledge
  • Questions

Chapter 18
Life On Earth

  • Nature of Life
  • Chemistry of Life
  • Molecules of Life
  • The Origin of Life on Earth
  • Origin of Complex Molecules
  • Miller-Urey Experiment
  • Pre-RNA World
  • RNA World
  • From Molecules to Cells
  • Metabolism
  • Anaerobes
  • Extremophiles
  • Thermophiles
  • Psychrophiles
  • Xerophiles
  • Halophiles
  • Barophiles
  • Acidophiles
  • Alkaliphiles
  • Radiation Resistant Biology
  • Importance of Water for Life
  • Hydrothermal Systems
  • Silicon Versus Carbon
  • DNA and Heredity
  • Life as Digital Information
  • Synthetic Biology
  • Life in a Computer
  • Natural Selection
  • Tree Of Life
  • Evolution and Intelligence
  • Culture and Technology
  • The Gaia Hypothesis
  • Life and the Cosmic Environment

Chapter 19
Life in the Universe

  • Life in the Universe
  • Astrobiology
  • Life Beyond Earth
  • Sites for Life
  • Complex Molecules in Space
  • Life in the Solar System
  • Lowell and Canals on Mars
  • Implications of Life on Mars
  • Extreme Environments in the Solar System
  • Rare Earth Hypothesis
  • Are We Alone?
  • Unidentified Flying Objects or UFOs
  • The Search for Extraterrestrial Intelligence
  • The Drake Equation
  • The History of SETI
  • Recent SETI Projects
  • Recognizing a Message
  • The Best Way to Communicate
  • The Fermi Question
  • The Anthropic Principle
  • Where Are They?

Molecular Clouds


This composite image of Cepheus B combines data from the Chandra X-ray Observatory and the Spitzer Space Telescope. A molecular cloud is a region containing cool interstellar gas and dust left over from the formation of the galaxy and mostly contains molecular hydrogen. The Spitzer data, in red, green and blue show the molecular cloud (in the bottom part of the image) plus young stars in and around Cepheus B, and the Chandra data in violet show the young stars in the field. The Chandra observations allowed the astronomers to pick out young stars within and near Cepheus B, identified by their strong X-ray emission. The Spitzer data showed whether the young stars have a so-called "protoplanetary" disk around them. Such disks only exist in very young systems where planets are still forming, so their presence is an indication of the age of a star system.

Stars form from sparse material between other stars. In most cases, the region between stars is a near vacuum containing very thin, cold gas. Atoms and molecules number only about 106 per cubic meter. The temperature is typically around 10 to 20 K. However, certain regions of space have a density of gas and dust 10,000 times greater. With some 1010 atoms per cubic meter, the atoms are close enough to collide frequently. Moreover, the temperature is low enough that atoms will stick together to form molecules. The most important molecular species is molecular hydrogen (H2), and it forms on dust grains. These regions are called molecular clouds. They are rich in molecular hydrogen, carbon monoxide (CO), water (H2O), and more complex forms such as formaldehyde (H2CO) and ethyl alcohol (C2H5OH). Such complex molecules are virtually absent in most parts of interstellar space. Although a molecular cloud is denser than most interstellar gas, it is still a near-perfect vacuum compared with ordinary room air, where there are about 20 trillion trillion (2 × 1025) molecules per cubic meter.

 

The Swedish ESO Submillimetre Telescope at La Silla Observatory in Chile.

Molecular clouds are important because they are the places where most stars form. In these regions the atoms and molecules and dust grains are crowded close enough to begin to attract each other gravitationally — a key step in forming stars from a gas. Observations taken with a radio telescope can show the dynamic activity of molecules in the clouds. Spectra made at millimeter wavelengths show many spectral features caused by different states of molecular vibration and rotation. The low energy of the transitions explains why the spectral lines are seen at long wavelengths, in the millimeter or sub-millimeter part of the electromagnetic spectrum. Astronomers have found that the chemistry within a molecular cloud can be very complex.

 

Certain dense regions in molecular clouds display particularly spectral lines that are as intense and pure as the light from a laser! Astronomers have observed OH and H2O molecules that generate maser emission. Maser is an acronym for microwave amplification by the stimulated emission of radiation, analogous to the familiar phenomenon in optical light called a laser. Normally, gas in space is at such a low density that most of the atoms or molecules are in their lowest energy states. However, molecules in the dense cores of molecular clouds can be forced to overpopulate the excited energy levels. When this happens, a single photon can trigger a surge of radiation as the molecules drop into their lowest energy states.


Institute of Astronomy, statue of Sir Fred Hoyle Sir Fred Hoyle (1915-2001) cosmologist, founded the Institute of Theoretical Astronomy here in 1967.

Nearly 130 different molecules have been discovered in interstellar space, including ten containing ten or more atoms. Examples include benzene (C6H6), acetone ((CH3) 2CO), and ethanol (CH3CH2OH). One of the most remarkable molecules discovered in interstellar space is the amino acid glycine (NH2CH2COOH), one of the building blocks of life. In the 1950s, British astronomer Sir Fred Hoyle wrote a science fiction novel called The Black Cloud. In it, he speculated that life might form in the dark depths of a molecular cloud. Scientists do not think it likely that replicating molecules could form in the near vacuum of space, but the discovery of complex molecules such as glycine is certainly intriguing.

The Sagittarius B2 molecular cloud contains a substantial amount of ethyl alcohol or ethanol. The American astronomer Ben Zuckerman noted that, if purged of impurities, this cloud would yield approximately 1028 fifths at 200 proof! This exceeds the sum of all human fermentation efforts in recorded history. A few years after this discovery, NASA received a proposal from a Texas businessman to "harvest" this alcohol. Molecular clouds are too diffuse to make this idea practical. It turns out that a spaceship pushing a funnel with a diameter of one kilometer at 10% of the speed of light would take 1000 years to collect enough ethyl alcohol to fill a shot glass.

Author: Chris Impey