THE EXISTENCE OF BLACK HOLESAL
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JOHN MICHELL
(1724-1793)
Michell was born in
Nottinghamshire and
spent his academic
life in Cambridge
working on geology,
gravity, magnetism
and astronomy. After
his marriage in 1764,
he spent the rest of
his life as a clergyman,
most notably at
Thornhill in Yorkshire.
Here he continued
with his scientific
work from 1767 until
his death in 1793.KARL
SCHWARZSCHILD
(1873-1916)
Schwarzschild was a
German physicist and
astronomer who was
born in Frankfurt. He
worked as a professor
for several years in
Göttingen, before
moving on in 1909 to
become director of the
town’s observatory.
He subsequently
headed up the
Potsdam Astrophysical
Observatory. He
volunteered for the
German army in 1914
and died of a skin
disease in 1916.STEPHEN HAWKING
(1942-2018)
Cambridge-based
Hawking is among
the most famous
physicists thanks to
his bestselling book
A Brief History of
Time and for defying
the onset of motor
neurone disease to
continue working
into his 70s. His work
has largely involved
the General Theory
of Relativity and
cosmology.KIP THORNE
(1940-) Thorne
is an American
astrophysicist whose
studies of General
Relativity have
resulted in a wide
range of predictions
on black holes,
wormholes and
time travel. Thorne
was consultant to
the best cinematic
representation of a
black hole to date, the
2014 film Interstellar.ALBERT EINSTEIN
(1879-1955)
German-born Einstein
is best known for his
theories of Special
Relativity and General
Relativity, laying
the foundations of
quantum theory. Via
Belgium and the UK,
he moved to the US
in 1933 to escape Nazi
Germany and took
up a position at the
Institute of Advanced
Study in Princeton.gravity. But once those reactions start
to fade, matter in the star can collapse.
The expectation is that this collapse
would be halted by a quantum effect
called the Pauli exclusion principle,
forming an intensely dense neutron
star. If the star were massive enough,
though, exceeding about three times
the mass of the Sun, the exclusion
principle should be overcome and the
collapse would be unstoppable. In
principle, the material in the black
hole would continue to collapse all
the way to a dimensionless point – a
‘singularity’ with infinite density and
a force of gravity that headed off to
infinity as it was approached. In
reality, we don’t know what would
actually happen, because the
singularity is an admission that our
physics has broken down. For a good
time after Schwarzschild, black holes
were purely theoretical.
Or at least collapsed stars were, as
they were yet to receive their more
intriguing moniker.Down the hole
The term ‘Black hole’ is often ascribed
to the American physicist John
Wheeler, but its origins are shrouded
in mystery. The term was first reported
at an American Association for the
Advancement of Science meeting in
January 1964. It’s not certain who used
it, but Wheeler soon popularised it. It
might seem that searching for black
holes would be a waste of time. How
do you see something that doesn’t give
off light? But, as the physics of black
holes developed, scientists realised
that indirect routes were available.
As astronomers can’t see the hole
itself, they need to look for its side
effects. When matter is dragged into
a spinning hole, it should produce an
‘accretion disc’, glowing brightly as a
result of f riction produced by t he
spinning matter – and would also
generate distinctive ‘jets’ from the
poles. Then there are the gravitational
effects. We might see nearby bodies
influenced by the black hole. This is
a venerable technique and was used
in the past to infer the existence of
Neptune. Astronomers studied the
way the orbits of the other planets 5Five giants of physics who made invaluable
contributions to our understanding of black holesCAST OF CHARACTERS