Sky and Telescope - December 2015 - 21

Next Step 1: The Event Horizon Telescope
One of the speakers at that ﬁrst Texas Symposium was
John Archibald Wheeler. In his inimitable style he covered the blackboard with elaborate colored drawings of
spacetime, the insides of neutron stars, and aphorisms
such as "the issue of the ﬁnal state." He was obsessed
with Oppenheimer's discovery that overloaded neutron
stars must collapse to a mathematical point with zero

S&T: LEAH TISCIONE, SOURCE: EHT PROJECT

size, the mass of a star, and inﬁnite density. Could that
possibly be true? No inﬁnite value ever exists for any
physical quantity in nature . . . supposedly. Wheeler's
philosophy, he later recalled, was that "by pushing a
theory to its extremes, we also ﬁnd out where the cracks
in its structure might be hiding."
As I look around at astronomy today, I see this viewpoint guiding some of the great astronomical endeavors
of the 21st century. For a start, black holes remain one of
the bugbears of physics even as astronomers ﬁ nd them
in abundance. It's not just that they should have a central
point of inﬁnite curvature and density. Black holes
that form by real-world processes should also surround
themselves with an event horizon, a "surface" out of
which nothing can escape, that gives ﬁts to the theory of
quantum mechanics.
In the 1960s, X-ray, radio, and optical measurements
made a compelling case that the X-ray source known as
Cygnus X-1, a something orbiting a giant, 9th-magnitude

IRAM
30-meter
telescope

SMT
SMA,
JCMT

PARADOX PIONEER John Archibald Wheeler, who
named black holes, played a central role in bringing general relativity deep into astronomy in the 1960s. He's seen
here in 1986 with one of his memorable aphorisms.

LMT

APEX,
ALMA

SPT

EMILIO SEGRE / VISUAL ARCHIVES / AMERICAN INST. OF PHYSICS / SCIENCE PHOTO LIBRARY

Roy Kerr, one of Alfred Schild's postdoctoral students, stood up and presented a new solution to the
equations of general relativity. That summer he had
found that black holes could be more complicated
than physicists had thought: they could spin, dragging
spacetime around with them. Kerr's solution would play
a huge role in explaining the quasars as rotating black
holes shredding material around them and funneling
some of it into radio-emitting jets. But at the meeting his
radical new result was too mathematical, too dry, and it
seemed to fall on deaf ears among the astronomers. Yet,
they were intrigued by what the relativists were saying.
From now on the astronomers would need to pay closer
attention to Einstein's theory if they were going to understand their own data.
Astronomer Thomas Gold gave the after-dinner
speech. He celebrated the beginning of a new era. About
the quasars, he said, "Here we have a case that allowed
one to suggest that the relativists with their sophisticated
work were not only magniﬁcent cultural ornaments but
might actually be useful to science!"
The Texas relativists' gamble had paid oﬀ. The "Texas
Symposium" became a biannual event (the 28th happens this December 13-18 in Geneva, still under the
same name). Over the next half decade, the exotic lore of
general relativity - black holes, cosmology, gravitational
waves - became part and parcel of astrophysics. Today
they are inextricable. And new frontiers are opening.

APEX,
ALMA

SPT

IRAM Plateau
de Bure
interferometer

WORLD'S SHARPEST
TELESCOPE Millimeterwave observatories around the
globe are linking up to form
the Event Horizon Telescope,
a giant interferometer with
baselines nearly as wide as the
planet. Its team plans to incorporate at least nine dishes
and arrays. The ﬁnal network,
with its very long baselines
and very short operating
wavelengths, should resolve
features as tiny as 15 microarcseconds, sharp enough
to reveal geometrical eﬀects
right around the black hole at
the center of the Milky Way.

Sk yandTelescope.com December 2015

http://www.SkyandTelescope.com

Sky and Telescope - December 2015

Table of Contents for the Digital Edition of Sky and Telescope - December 2015