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News Release
Office of News and Information
Johns Hopkins University
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Phone: (410) 516-7160 / Fax (410) 516-5251
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March 5, 1999
FOR IMMEDIATE RELEASE
MEDIA CONTACT:
Gary Dorsey,
gdd@jhu.edu
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Astronomer Brings Coherence to Study of Active
Galactic
Nuclei
At a critical juncture in astronomy's rapid maturation,
Julian
Krolik has
stepped into the scholarly void to produce the first
comprehensive textbook
for researchers about the great powerhouses of the universe:
active
galactic nuclei.
Although the publication of a textbook is rarely a moment of
startling
significance, Krolik's signals a new moment of coherence in the
field.
The book,
"Active
Galactic Nuclei: From Central Black Hole to the Galactic
Environment," published by
Princeton University Press, is being touted by
one of the world's leading astronomers, Sir Martin Rees, as "an
impressive
book (that) fills a notable gap in the existing literature."
Krolik, a professor of theoretical
astrophysics at The Johns
Hopkins
University, hopes the work will correct misconceptions and
influence the
next generation of astronomers.
For nearly a century, students of the cosmos have created, Krolik
says, "an
entire zoo of
classifications" as they puzzled over the super-bright,
super-massive
enigmas that are now known as active galactic nuclei, or AGN.
Indications of strange activity in the centers of galaxies
accumulated
gradually throughout this century, starting as early as 1918. As
different
examples were found, they were divided into an ever-increasing
number of
categories: Seyfert galaxies (which were further divided into two
distinct
types), radio galaxies, quasi-stellar radio sources,
quasi-stellar objects,
and even the fancifully named "blazars."
This untidy state of affairs could not be fully resolved until
the 1990s,
when scientists began to realize that their observations often
simply
amounted to different signatures of the same kinds of mighty
objects. In
some cases, objects simply looked different when viewed from
different
directions. For example, they would appear to change if viewed
from the
side rather than straight on.
"Astronomers often revel in the marvelous variety of the
universe," Krolik
observes, "and love to divide the objects they find into
ever-finer
classes. But we've now learned that there is a fundamental unity
here, and
much of the historic terminology is holding back progress more
than
promoting it."
In recent years, as the pace of startling discoveries finally
slowed and
long-standing conjectures -- most notably that AGN are powered by
accretion
onto supermassive black holes -- were bolstered by confirming
evidence,
Krolik seized the day. He decided to write the textbook, in part,
to bring
organization to a fragmented, but increasingly critical area of
research.
"I want people to realize that many of the categorical
distinctions we have
made rest somewhere between arbitrary and misleading," he says.
"Particularly for AGN, many astronomers have pretended there's
nobody else
studying the objects -- people have tended to observe them in
their own
favorite parts of the spectrum. Consequently, we have had optical
astronomers and
radio astronomers and X-ray astronomers and so on, each believing
that the
only really interesting action falls within their own bailiwick.
"It's silly--and it's unfortunate. Because what really
distinguishes AGN
is that they emit enormous amounts of power across the spectrum,
all the
way from radio wavelengths to X-rays, and sometimes even
high-energy
gamma-rays. What I have done is to finally write a book that
encompasses
the complete spectrum. We now have a text that can serve as a
standard for
everyone."
As the research has evolved and matured, interest in these exotic
beasts
has attracted the curiosity of increasing numbers of scientists.
It is
estimated today that as many as one in five of all research
astronomers are
making inquiries into AGN or some aspect of their awesome
components.
With such a rising phalanx of support, and with the aid of new
orbiting
telescopes that have been able to detect the extremely broad
range of
wavelengths produced by AGN, it is now possible to produce a
unified
portrait that is easily available to researchers and advanced
graduate
students.
"When you're writing a technical book, you don't do it to get
rich," Krolik
says. "That's just not in the cards. You do it, first, to
organize the
subject in your own mind, and secondly, to influence others,
especially
those who are coming into the discipline fresh. I want to shape
the way
people think. There may be other ways to bend the twig, so to
speak, but
writing a good book can be particularly effective."
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