that ancient rock strata in the southern highlands
were weakly magnetized, strongly suggesting that
the young Mars had a global magnetic field and a
molten iron core.
Telescopes on the Earth’s surface must look up
through a turbulent ocean of air. Because that turbu-
lence causes stars to twinkle and blurs the finer de-
tails of planets and stars, astronomers place tele-
scopes on mountain tops in an effort to rise above as
much of that ocean as possible. Launched on April
24, 1990, the Hubble Space Telescope fulfilled the
long-held dream of placing a telescope completely
above the atmosphere. Hubble photographed a
dusty disk swirling around the nucleus of galaxy
M87. The rotational speed of the disk implied that it
circled an otherwise invisible object that was around
three billion times the mass of the Sun—the first di-
rect evidence for the existence of such a supermas-
sive black hole candidate.
Black holes are predicted by Einstein’s general
theory of relativity. Perhaps the two most bizarre pre-
dicted properties of a black hole are first, that if
enough mass is concentrated within a given volume
bounded by the event horizon, gravity will become
so strong that light itself cannot escape; second, if
the mass collapses forever, it will eventually form a
vanishingly small ball of infinite density called a sin-
gularity. The Achilles heel of general relativity is that
it does not incorporate quantum mechanics, the
theory that governs the behavior of atoms. Quan-
tum mechanics predicts that the singularity will
never form; instead, before a solar mass object could
collapse to a ball a few centimeters across, the energy
of the gravitational field would go into the creation
of matter in the form of electron-positron pairs, halt-
ing the collapse.
The event horizon is so named because since light
cannot escape from it, the outside universe can
never know of events that occur within it. In 1997,
Harvard astrophysicist Ramesh Narayan and his col-
leagues studied X rays from neutron stars and from
black hole candidates. They interpreted their data
to mean that they could observe X rays from a neu-
tron star’s surface, but not from the surface of a
black hole candidate—presumably because it lies
within the event horizon. This was heralded as proof
of the existence of the event horizon, and hence of
black holes. Dr. Stanley Robertson of Southwestern
Oklahoma State University soon challenged this
conclusion. Robertson has shown that with the in-
clusion of more data points, and accounting for the
deeper gravity wells of the black hole candidates,
there was no evidence for event horizons. However,
astronomers are in the habit of calling any collapsed
object over three solar masses a black hole, regard-
less of the lack of evidence for event horizons.
Impact Computer chips with their digital electron-
ics have seeped into the very fabric of American soci-
ety. They direct electric power generation and subway
trains. They are embedded in pets for identification,
in artificial limbs for better control and operation of
the limb, and in automobile braking systems ever-
vigilant for wheel slippage. If computer chips magi-
cally disappeared, modern civilization would stag-
ger, and perhaps even fall in some places. The past
few decades have been called the “information age,”
“digital age,” and “computer age.” All three titles are
intertwined. For example, information can be digi-
tized by a computer, assembled into packets, and
sent across the world in such a small fraction of a sec-
ond that it is not worth billing. This makes any com-
puter connected to the Web a cornucopia of infor-
mation about the world past and present. While the
Web is used for many other purposes, the free flow of
news strengthens the currents of democracy. It is
thought that the spreading influence of the Web
played an important role in the breakup of the So-
viet Union.
Subsequent Events The astrophysicist Abhas Mitra
calculated that a true black hole could not actually
form because it would take an infinitely long time to
release the energy of its collapse. He called such pre-
black holes eternally collapsing objects (ECOs). In
2001, Robertson, with the American astrophysicist
Darryl Leiter, wrote a paper showing that ECOs
would have both a surface and a magnetic field, but
no event horizon. They proposed such objects be
called magnetospheric eternally collapsing objects,
or MECOs. In 2004, Robertson and Leiter demon-
strated that the MECO model could explain a hith-
erto unexplained universal correlation between ra-
dio and X-ray luminosities of black hole candidates.
In 2005, American astronomer Rudy Schild joined
Robertson and Leiter in showing that the detailed
structure of quasar Q0957+561 was convincingly ex-
plained by the MECO model, but not by the black
hole model. If (and only if) new experimental data
continue to support the MECO model, astronomy is
on the verge of an important paradigm shift.The Nineties in America Science and technology 757