Theoretical assumptionson black holes date back to the 18th century. The first part of the Mini Lecture series presents the most important physical models and assumptions that were initially used to describe black holes.
Black Holes
Chapter 1
They Really Do Exist
When we think of black holes,
we think of science fiction and Hollywood movies.
Massive monsters that suck in the
surrounding universe and break the laws of physics.
They are incredibly fascinating.
People have been theorising
about black holes since the 18th century.
For a long time, however,
their existence could only be described
or predicted mathematically.
Black holes were considered
difficult to study
because they don’t have a surface
like other objects.
Their gravitational pull is so strong
that they swallow light itself,
meaning that black holes are invisible.
In his general theory of relativity,
formulated in 1915,
Albert Einstein hinted at how
they might still be detected.
Essentially, he said:
All bodies with mass or energy
interact with four-dimensional spacetime.
This spacetime is curved
by the acceleration of mass,
creating oscillations.
It is therefore plausible that,
in addition to swallowing everything,
black holes also have measurable
effects on their surroundings.
In 1969,
mathematician Roger Penrose
suggested that
the rotational energy
of a black hole might
also be found outside of it.
He has since been proven right.
The first empirical evidence
for the real physical existence of black holes
came from radio astronomers
in the 1960s.
They discovered star-like centres,
quasi-stellar radio sources
that shine very brightly,
which they named quasars.
At their heart are powerful centres of energy,
that we now know are black holes.
These various hypotheses
and observations eventually culminated
in our ability
to physically detect black holes.
We now understand
that there is a radius around the black hole
called the event horizon.
At this edge,
the motion of passing stars or gas clouds
is accelerated to such an extent
that they heat up
and can, for example,
be seen in infrared light.
This effect can be observed
using space telescopes,
which capture non-optical light,
in combination with
optical telescopes and computers.
There are thought to be
hundreds of millions of black holes
in the Milky Way alone.
One of them,
the Sagittarius A* region,
is located in the constellation Sagittarius,
right at the centre of our galaxy.
Its mass is 4.3 million times greater
than the mass of the sun.
German astrophysicist Reinhard Genzel
and American astronomer Andrea Ghez
German astrophysicist Reinhard Genzel
and American astronomer Andrea Ghez
used long-term observations
of stellar motions
used long-term observations
of stellar motions
to prove its existence,
providing the most
convincing evidence so far
that black holes really do exist.
Together with the aforementioned
mathematician Roger Penrose,
they received the
