Penrose, Ghez, Genzel and their Nobel Prize
Every year, thousands of people wait for the Nobel Prize award event.
The Nobel prize is an award of worldwide value awarded annually to living personalities who
have distinguished themselves in the various fields of human knowledge, bringing "The greatest
benefits to humanity" or their research, discoveries and inventions, for their literary work, for
their commitment to world peace.
The Royal Swedish Academy of sciences has decided to award the Nobel Prize in Physics
2020 with one half to Roger Penrose “for the discovery that black hole formation is
a robust prediction of the general theory of relativity” and the other half jointly
to Reinhard Genzel and Andrea Ghez “for the discovery of a supermassive compact object
at the centre of our galaxy”.
It is crystal clear that we are living in the black-hole-era.
But how did we get to this point? How did we prove that they existed? And what
did it take to have the first observation of them?
Why did some scientists' way of thinking become so important in our understanding of the universe?
Follow me on this journey to know the answer to all of these questions, and to take part
in the black-hole-era.
(roll intro)
In classical physics, based on the principles of dynamics, it was theorized in the eighteenth
century the possibility that a body has such a large mass as not to allow, even light,
to exceed the escape velocity, that is, the minimum speed needed for a free, non propelled
object to escape from the gravitational influence of a massive body.
That's why these bodies would have been invisible. Physics referred to these objects as “dark
stars”.
So, why do we call them Black Holes?
We call them Black holes after physicist John Archibald Wheeler: the adjective “black”
comes from the fact that it cannot emit light. The fact that no particles that were captured
there can re-emerge (not even photons) is the reason for the term “hole”.
After Einstein's theory of relativity, a concept of a black hole was theorized by scientist
Karl Schwarzchild in 1916: exploring some solutions to the equations of the theory,
Schwarzchild calculated that a body hypothetically endowed with very high density would produce
such deformation of spacetime in its vicinity that the light moving away from it would tend
to undergo a gravitational redshift to infinity.
Einstein didn't actually believe that black holes existed in physical reality because
his theory showed that they were a perfect spherical-symmetry solution to his equations,
and he thought that such a spherical object could not exist and give birth to a black
hole: nature would have found a way to avoid that creation.
But then, in 1965, sir Roger Penrose, entered the game.
Roger Penrose was born in Colchester (Great Britain) in 1931. He studied at the University
College School in London and the St. John's College di Cambridge.
In 1965 he came out with an article that showed that black holes existed as a natural consequence
of the general theory of relativity. According to him, he started thinking about it on his
own and thinking about the problem more geometrically, not really solving equations because it was
too complicated, and not making simple assumptions about symmetry because that was the point,
you mustn’t have that, so he produced arguments. Penrose made a huge effort to demonstrate
mathematically that even chaotic geometries could have given birth to black holes. Ladies
and gentlemen, his paper was awarded the 2020 Nobel Prize.
He told the Nobel Prize interviewer Adam Smith this story:
“At that time I was at Birkbeck College, and a friend of mine, Ivor Robinson, who’s
an Englishman but he was working in Dallas, Texas at the time, and he was talking to me
… I forget what it was … he was a very … he had a wonderful way with words and
so he was talking to me, and we got to this crossroad and as we crossed the road he stopped
talking as we were watching out for traffic. We got to the other side and then he started
talking again. And then when he left I had this strange feeling of elation and I couldn’t
quite work out why I was feeling like that. So I went through all the things that had
happened to me during the day – you know, what I had for breakfast and goodness knows
what – and finally, it came to this point when I was crossing the street, and I realised
that I had a certain idea, and this idea what the crucial characterisation of when a collapse
had reached a point of no return, without assuming any symmetry or anything like that.
So this is what I called a trapped surface. And this was the key thing, so I went back
to my office and I sketched out a proof of the collapse theorem. The paper I wrote was
not that long afterwards, which went to Physical Review Letters, and it was published in 1965
I think.”
Roger Penrose tried to explain what is happening inside a black hole, going as deep as he could,
reaching the so-called “singularity”. To understand more of this, let's do a small
step back. We know that spacetime is curved and that
the Einstein curve equation describes how the deformation of spacetime is due to the
mass existing at a certain point in space. The thing is, that light itself gets curved
by gravity. All of this has his consequences: if gravity
can deflect light, the cause and effect bound between two events are influenced by gravity.
And there is the possibility to have, in some points, a so curved spacetime that we couldn't
have any effect on the outside. This is exactly what happens in black holes!
Penrose studied the collapse of a star and how the system would evolve until reaching
the singularity. We can't say what happens after that: despite
we know collapses happen we won't be able to observe one of them until the end, that
is, we won't ever be able to observe the formation of a black hole!
That's because as the black hole is forming, time slows more and more.
In the end, the observer sees the black hole freezing one moment before his formation.
For the observer, the formation of the black hole would take an infinite time.
Furthermore, Penrose supposed the so-called “Penrose Process”, a theory that tried
to explain how a black hole could lose mass. In fact, he was trying to explain the formation
of quasars in terms of supermassive black holes.
Historically, the term quasar originated as a contraction of quasi-stellar radio source
because quasars were first identified during the 1950s as sources of radio-wave emission
of unknown physical origin.
We know today that a quasar is an extremely luminous active galactic nucleus (AGN), in
which a supermassive black hole with mass ranging from millions to billions the mass
of the Sun is surrounded by a gaseous accretion disk.
But...did we find them?
"Before finding out the answer to this question, be sure to like or dislike the video so that
we can continue to improve and make these videos better for you the viewer. Plus, be
sure to subscribe to the channel clicking the bell so that you don't miss ANY of our
weekly videos."
Observations over time lead to confirm Penrose demonstrations.
In the '60s, experimental scientists started to look around and search some traces of black
holes. For example, they found that a black hole
can “eat” a star, making it wind round inwards inside the black hole. This contributes
to the creation of a so-called Accretion Disk, that releases very hot X radiation. That's
how they found the Cygnus X-1 object.
But the most important one was the case of Andrea Ghez and Reinhard Genzel. They wanted
to study the region of our Galactic Center, where they detected a huge radio source (maybe
a Quasar), called Sagittarius A*.
They carried their work for decades, trying to find a method to lead better observations
of the galactic centre. Developing new telescope technologies (adaptive optics), it was possible
to make observations of our Galactic Center in which we can see many stars orbiting around
something, even if we can't tell what that “something” is.
But what is adaptive optics?
According to Wikipedia:
“Adaptive optics (AO) is a technology used to improve the performance of optical systems
by reducing the effect of incoming wavefront distortions by deforming a mirror in order
to compensate for the distortion. When light from a star or another astronomical
object enters the Earth's atmosphere, atmospheric turbulence (introduced, for example, by different temperature
layers and different wind speeds interacting) can distort and move the image in various
ways. Visual images produced by any telescope larger than approximately 20 centimetres are
blurred by these distortions. An adaptive optics system tries to correct
these distortions, using a wavefront sensor which takes some of the astronomical light,
a deformable mirror that lies in the optical path, and a computer that receives input from
the detector. The computer calculates the optimal mirror
shape to correct the distortions and the surface of the deformable mirror is reshaped accordingly.
“ Anyway, by studying those stars' velocity
(for example, the so-called S2 star, that completes his orbit in 16 years around that
object), we can tell how heavy that “something” should be.
Its weight was estimated in 4.5 million solar masses.
That huge object occupied the same point of Sagittarius A * radio source, and with the
work done by Penrose that connected Quasars and Black Holes, they concluded that they
were facing a supermassive black hole! Ghez and Genzel discovery was awarded the
2020 Nobel Prize, that they shared with Roger Penrose.
Their discovery led to a lot of questions: for example, why does the vast majority of
the galaxies seem to have a black hole in his very centre?
But we still have a long way to go before we find the answers.
"This video ends here! Thanks for watching everyone! Are you happy with the choice of
the Nobel Prize winners? What would you ask them? Which discoveries do you think should
be awarded the Nobel Prize in the future? Let us know in the comments below!
See you on the channel!
Credits: Wikipedia, NASA, NobelPrize.org