THE NEXT BIG STEPS FOR SCIENCE
5 were influenced by Neptune’s
gravitational pull.
Finally, there is ‘Hawking radiation’.
Stephen Hawking surprised himself
when, in 1974, he realised that black
holes couldn’t truly be black. The
idea ca me f rom his understa nding
of quantum physics – the science
governing very small things – and in
particular the ‘uncertainty principle’.
This said t hat localised energy ca n
fluctuate significantly over small
periods of time, allowing pairs of
quantum particles to emerge and
then disappear again before they are
observed. If this happens near a black
hole’s event horizon, one of these
‘virtual’ particles could be pulled in
while the other flies off. These stray
particles make up Hawking radiation.
This is unlikely to be detectable at a ny
great distance.
After Schwarzschild’s solution,
black holes seemed the natural end for
the right kind of stars with masses at
least three times that of the Sun. But
this particular scale is not a limitation
of the black hole itself, merely the
formation mechanism. In principle,
black holes could exist on any scale
from the microscopic all the way
through to millions of times the mass
of the Sun. There are broadly four
categories, two of which have probably
been detected.
At the tiny, totally hypothetical end
of the scale are micro black holes and
quantum black holes. A micro black
hole would form, for instance, if Earth
collapsed, forming an event horizon
about 9mm across, though thankfullythere is no known mechanism for this
to occur. Quantum black holes are
even smaller, from a scale of around
5,000 protons up. In principle, they
could be produced in a particle
accelerator and would almost
immediately decay. Current
accelerators don’t have the energy
to produce one unaided, but if the
Universe has extra dimensions, this1783
John Michell’s ‘dark stars’
paper is read at the Royal
Society. He hoped to deduce
the mass of stars from their
effect on light and thought a
massive-enough star would
be able to stop light entirely.1915
Albert Einstein
publishes his field
equations. This set
of 10 equations at
the heart of General
Relativity describe
gravity as a curvature
of space and time.1916
Karl Schwarzschild comes
up with his theory, the
Schwarzschild radius,
which states that if all a
body’s mass is crammed
into a sphere, space-time
distortion would be so great
that light from the object
would never escape.1995
Star S2 (Source 2) is
observed by the Max
Planck Institute and UCLA.
It orbits an apparent
supermassive black hole,
Sagittarius A*, at the heart
of the Milky Way.1971
The first candidate black
hole is found. Cygnus X-1
is an X-ray source that was
first detected in 1964 and is
thought to be a binary star,
where material from one
star is accelerated into a
black hole.On 10 April 2019, astronomers using
the Event Horizon Telescope
unveiled the first image of the
silhouette of a black hole, spotted
at the centre of the galaxy M87TIMELINE