Chandra’s Cosmos: Dark Matter, Black Holes, and Other Wonders Revealed by NASA’s Premier X-Ray Observatory

313 Pages·2017·50.13 MB·English

by  Wallace H. Tucker

© 2017 by Wallace H. Tucker All rights reserved. No part of this publication may be reproduced or
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Library of Congress Cataloging-in-Publication Data Names: Tucker, Wallace H.
Title: Chandra’s cosmos : dark matter, black holes, and other wonders revealed by NASA’s premier X-
ray observatory / Wallace H. Tucker.
Description: Washington, DC : Smithsonian Books, [2017] | Includes bibliographical references and
index.
Identifiers: LCCN 2016016560 | ISBN 9781588345875
Subjects: LCSH: Chandra X-ray Observatory (U.S.) | X-ray astronomy.
Classification: LCC QB472.T8114 2017 | DDC 523.1—dc23
LC record available at https://lccn.loc.gov/2016016560
Ebook ISBN 978-1-58834588-2
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Title pages: 30 Doradus, a.k.a. the Tarantula Nebula. See here.
Endsheets: Cygnus A (colorized). See here.
v4.1
CONTENTS
Cover
Title Page
Copyright
Introduction. Cool Stories from the Hot Universe
THE BIG
part I
1 Galaxy Clusters
2 The Evidence for Dark Matter
3 Cold Dark Matter
4 Dark Matter Going Bananas
5 The Wonderful—and Fearful—Dark Side
6 What Is Dark Energy?
7 The Cosmic Web
THE BAD
part II
8 Taking Pleasure in the Dimness of Stars
9 Cygnus X-1, Microquasars, and the Galactic Jet Set
10 Downtown Milky Way
11 The Secret in the Middle
12 Ducks Unlimited
13 The Origin and Growth of Supermassive Black Holes
14 Green Black Holes
15 Black Hole Feedback
THE BEAUTIFUL
part III
16 Going Not Gentle into That Good Night
17 Core Collapse
18 The Crab and Other Pulsar Wind Nebulas
19 A Thin Cosmic Rain: Particles from Outer Space
20 Elemental Change
21 Cosmic Renewal
References
Acknowledgments
Index
Photography and Illustration Credits
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1
IC 443 SUPERNOVA REMNANT
A wide-field view of a supernova remnant (SNR) made with X-ray (blue; from Chandra
and ROSAT, the Roentgensatellite), radio (green; from the Jansky Very Large Array),
and optical (red; from the Sloan Digitized Sky Survey) observations. Embedded near
IC 443’s lower edge is neutron star J0617, spewing out a cometlike wake of high-
energy particles as it races through the SNR’s multimillion-degree Celsius gas.
INTRODUCTION
You will behold through the telescope a host of
other stars, which escape the unassisted sight, so
numerous as to be almost beyond belief.
Galileo, The Starry Messenger, 1610
COOL STORIES FROM THE HOT
UNIVERSE
In Florence, Italy, in the year 1609, the world changed. Using a small
telescope, Galileo Galilei proved that Earth is not distinct from the universe
but part of it, and that there is much more to the universe than we see with
the naked eye. In the twentieth century, astronomers made another
revolutionary discovery: Optical telescopes reveal only a portion of the
universe. Telescopes sensitive to invisible wavelengths of light have detected
microwave radiation from the Big Bang, infrared radiation from
protoplanetary disks around stars, and X-rays from matter swirling into black
holes.
On July 23, 1999, NASA launched the Chandra X-Ray Observatory aboard
the space shuttle Columbia. A telescope designed to detect X-ray emissions
from extraordinarily hot regions of the universe—exploded stars, galaxy
clusters, and matter around black holes—Chandra now orbits above Earth’s
X-ray-absorbing atmosphere at an altitude of up to 86,500 miles. The
Smithsonian’s Astrophysical Observatory in Cambridge, Massachusetts, is
the site of the Chandra X-Ray Center, which operates the satellite, processes
the data it collects, and distributes it to scientists around the world for
analysis.
Since its launch, Chandra has given us a view of the universe that is largely
hidden from telescopes sensitive only to visible light. It is a universe of
violent and extreme environments, such as intense gravitational and
magnetic fields around black holes, supernova shock waves, and titanic
collisions between clusters of galaxies.
X-ray astronomy is one of the newest fields of astronomy. Earth’s
atmosphere absorbs X-rays so strongly that it is impossible to observe them
with ground-based telescopes. There is another problem: An X-ray photon
has about a thousand times more energy than an optical photon, and because
of this high energy, X-rays are difficult to focus onto a detector. X-ray
telescopes therefore require extremely smooth mirrors, and Chandra’s
mirrors are the smoothest ever made for any telescope.
As an X-ray telescope, Chandra collects and images X-rays that it detects
from cosmic sources. In essence, Chandra is making the first ever high-
resolution X-ray pictures of cosmic X-ray machines, images of a quality
equivalent to those of large optical telescopes. This unique capability has
transformed twenty-first-century astrophysics.
Chandra is part of a larger effort in which, for the first time, it is possible
to make high-resolution images of star clusters, galaxies, and other cosmic
phenomena with powerful telescopes tuned to many wavelengths, from radio
to X-ray, including the infrared and visible bands in between. Chandra’s
synergy with the Hubble Space Telescope, which can observe near-infrared,
optical, and ultraviolet radiation, and the Spitzer Space Telescope, which
detects infrared radiation, along with many other telescopes, is providing a
much more complete view of the evolution of stars and galaxies as well as the
extreme physics associated with black holes and cosmic explosions.
Since the launch of Chandra, as science spokesman for the Chandra X-Ray
Center, I have been privileged to enjoy a front-row seat to the observatory’s
exploration of the universe. During this time, I have been profoundly
impressed by the work of a growing community of ingenious scientists who
have used Chandra’s unique and critical capabilities in the quest to
understand our place in the universe and the fundamental laws that govern
our existence.
My role has been primarily to explain or document some of the successes
in this quest, and from time to time I have been asked to put together lists of
“top ten” Chandra stories. On one of these occasions, a colleague suggested
that I should prepare a list of Chandra’s coolest discoveries. Not being an
especially cool person—at least I don’t think I’m cool, and, as I understand it,
if you’re cool, you know it—I was a little perplexed. My reaction confirmed
one of Malcolm Gladwell’s rules of cool: “It can only be observed by those
who are themselves cool” (1997).
As I pondered what might constitute cool discoveries, I came across these
words of wisdom from best-selling author Stephen King: “The meaning of
cool is beyond definition…beyond modification. It just is, man” (2007). Not
much help there. The words of William Gibson, prophet of the cyberpunk
subgenre of noir fiction, seemed more appropriate: “Secrets are the very root
of cool” (2007). This fits in nicely with something an unquestionably cool
scientist, Albert Einstein, once said: “The most beautiful experience we can
have is the mysterious. It is the fundamental emotion that stands at the
cradle of true art and true science” (1949).
Secrets and mysteries. I have selected the interconnected stories presented
here with these criteria of “cool” in mind. They fall into three broad
categories, which we will explore in detail in the pages that follow: the big,
the bad, and the beautiful.
The big stories deal with the big picture: What is the universe made of?
How did it evolve into its present state? What does the future hold? The past
decade has seen revolutionary progress toward finding the answers to these
questions. Based upon a broad suite of astronomical observations made with
microwave, optical, and X-ray observatories, a consensus has emerged: Only
about 5 percent of the matter in the universe is normal matter consisting of
protons, neutrons, and electrons; 25 percent is dark matter; and 70 percent is
thought to be dark energy, a mysterious force that causes the observed
accelerating expansion of the universe. These numbers convey a sobering
message: 95 percent of the universe is “dark,” a label chosen to express our
inability to directly detect or identify it.
We know that dark matter plays a major role in how galaxies form. In the
past decade, astrophysicists have found that another type of darkness—black
holes—may be critical to the evolution of galaxies. Black holes are the
ultimate bad guys of the cosmos. The forces associated with their immense
gravitational fields can tear apart anything that ventures too near, be it stars,
planets, or atoms. A substantial body of evidence shows that a supermassive
black hole with a mass of several million Suns lies at the center of most, if
not all, galaxies. Furthermore, the growth of such supermassive black holes
appears to be closely connected to the growth of galaxies as a whole.
On a stellar scale, black holes are formed by the collapse of extremely
massive stars. This collapse occurs when the nuclear reactions in the center
of a star can no longer support the enormous weight bearing down on them
from the rest of the star. A star less massive than about eight times the mass
of the Sun reaches equilibrium by expelling its outer layers and settling down
to become a dense white dwarf star. Stars with larger masses, however, do
not leave the stage quietly (figure 1 and figure 2). Their weight is too much
for equilibrium to hold; the central regions collapse to form a neutron star or
black hole, and most of the star is blasted away in one of the most violent
events in nature, a supernova. If a supernova occurred within a dozen or so
light-years of our home planet, it would in all probability extinguish most life
on Earth. Whether supernovas have exterminated other civilizations in our
galaxy is unknown, but that is certainly a possibility. What is known is that
supernovas disperse planet-building and life-giving elements manufactured
in their interiors—elements such as carbon, nitrogen, oxygen, silicon,
calcium, and iron—over regions thousands of light-years in diameter.
Their effects don’t end there. If the expanding supernova shock wave
slams into a dormant cloud of dust and gas, the impact can trigger the
collapse of clumps of gas. A million years later, the sky will blaze with
colorful, utterly beautiful lights from a new generation of stars, and possibly
new planets and new civilizations. Cool indeed.