THE NEXT BIG STEPS FOR SCIENCE
NASA/CHANDRACygnus X-1 (location outlined in red). In
this image, the blue supergiant companion
star can be clearly seen to its rightGerman army. Somehow, perhaps
as a distraction from the devastation
a round him, he found time to t hink
about Einstein’s elegant equations
and his brand-new theory of General
Relativity. Einstein’s equations are
too complex to provide a universal
solution, but Schwarzschild solved
them for the special case of a spherical
body that was not spinning.
It emerged from the mathematics
that, if all the mass of that body wascrammed into a sphere of a size now
called the Schwarzschild radius, the
distortion in space-time would be so
great that light from the object would
never escape. Anything closer than a
sphere around the body of that radius
would travel through a surface of no
return – the black hole’s event horizon.
The most obvious source of such a
body would be a collapsing star. In
nor mal operation, a sta r’s nuclea r
reactions fluff it up against the pull of5 based on an incorrect assumption
- that light was made up of normal
particles that could be slowed down
like any other projectile by gravity.
But the idea of these mysterious ‘dark
stars’ faded into history.
Fast-for wa rd to t he 20t h centu r y
and Karl Schwarzschild revived the
theories in the heat and horror of
World War One. It was 1915 and the
41-year-old German physicist had
volunteered to join up wit h t he
Black holes are tricky to study as even the closest one lies many light-years away,
but scientists can identify candidates by observing their X-ray emissionsPerforming experiments on black holes
is a non-starter, as the nearest candidate
so far detected is around 3,000 light-
years away.
Official confirmation of Cygnus X-1,
the first significant candidate found,
took a number of years as no single
observation was capable of establishing
such a remarkable find.
In 1964, a rocket launched from the
White Sands Range in New Mexico
discovered a strong X-ray source in the
constellation of Cygnus. Also in 1964, two
sub-orbital rockets mapped out X-ray
sources, pinning down the location of
Cygnus X-1. In 1971, observations by the
Uhuru X-ray satellite telescope showed
that the Cygnus X-1 source underwent
rapid oscillations, suggesting it was a
compact object that was smaller than
the Sun. That same year, radio telescope
observations linked the X-ray source to
the star HDE226868. This blue supergiant
would not itself produce X-ray emissions,
implying that it had a companion. Also in
1971, astronomers at the Royal Greenwich
Observatory and Toronto’s David Dunlap
Observatory made further observations
of HDE226868. They confirmed that it was
in a binary with a massive but compact
object. And, in 1972, Charles Bolton at
Toronto was the first to state definitively
that this object was a black hole. This
view was generally accepted by 1973.THE KEY EXPERIMENT
“When matter is dragged into a spinning
hole, it should produce a glowing ‘accretion
disc’ and distinctive ‘jets’ from the poles”