The Royal Swedish Academy awarded the Nobel Prize in Physics this Tuesday, 6th October, to Roger Penrose, Reinhard Genzel and Andrea Ghez, for discoveries related to the “darkest secrets in the Universe”.

“The discoveries of this year’s Laureates have broken new ground in the study of compact and supermassive objects”, said David Haviland, Chair of the Nobel Committee for Physics. “These exotic objects still pose many questions that beg for answers and motivate future research. Not only questions about their inner structure, but also questions about how to test our theory of gravity under the extreme conditions in the immediate vicinity of a black hole,” he added.

Professor José Sande Lemos, president of CENTRA/IST, started to become interested in astrophysics and gravitation while he was a physics student and, since then, he has dedicated a large part of his studies and works to black holes, “in particular to the quantum and thermodynamic processes that occur around and within these objects”. So, he was “very pleased” to know that the Nobel Prize in Physics 2020 had been awarded to this research area.

CENTRA researchers Paulo Garcia, António Amorim and Vítor Cardoso participate in the international project “Gravity Collaboration”, which is coordinated by professor Reinhard Genzel and developed by the European Southern Observatory (ESO). “CENTRA is involved not only in the instrument performance but also in the results of its observations”, says professor José Sande Lemos.

“Gravity Collaboration”

About 20 years ago, when professor Vítor Cardoso started to work on black hole physics and gravitational waves, this area was flourishing. “I believe that the general thought was: black holes must exist, but in reality they are not relevant to anything”, recalls the professor. Nowadays, professor Vítor Cardoso is one of the most renowned names in this area.

“This Nobel Prize rewards an entire community that showed that black holes exist, they are fundamental to understand the universe, the evolution of galaxies and perhaps the origin of life”, says the Técnico professor. “But it also highlights the scientific and rigorous aspect of this type of research, a complex part of mathematics, and complex astronomy and astrophysics”, he adds.

Professor Vítor Cardoso emailed Reinhard Genzel saying “congratulations on the prize, but above all for the work behind the prize”. The professor shared with us that the relationship between both “have been purely theoretical involving scientific discussion, namely on data from both LIGO and Gravity”. “The impression that I get is that bright minds like these want to know everything, as much as possible. It doesn’t matter that it doesn’t directly concern their work, they always want to know more”, says the CENTRA researcher.

The “Gravity Collaboration” aims to develop a second generation instrument to make more accurate observations of stars – or what is left of them – that gravitate towards the black hole at the center of the Milky Way. “The center of the Milky Way still has many mysteries, for example, in terms of Sun-like stars, or neutron stars, or stellar-mass black holes. But perhaps even more important is to study in depth the precise behaviour of the massive, dark and compact object that is there”, explains professor Vítor Cardoso.

“We think it is a black hole, but we have to know more precisely how it behaves”, stresses the professor. “Why?” – we asked. “Because humans are innately curious creatures, and in this specific case, we have reasons to go deeper. The general theory of relativity fails to be consistent on black holes, and we haven’t been able to unify quantum mechanics and gravity. Perhaps we will find the answers to these questions when we know in depth the behaviour of these objects”, says the CENTRA researcher.

The Gravity instrument is already on ESO’s Very Large Telescope in Chile, but the research team continues to improve it. According to professor Vítor Cardoso, much can still be done: “One of the things that can be done is to improve the technology, allowing us to see better and closer the centre of the Milky Way. Another very important thing is time and luck”. “We are looking in the dark, and we have to wait. With some luck, a luminous star will pass near the black hole. Only then we can list the stars that inhabit there and the behaviour of this massive object”, explains the Técnico professor.

Black Hole, one of the most mysterious phenomena in the Universe

But what are black holes anyway? Professor José Sande Lemos helps us to understand: “Black holes are extreme spacetime deformations where even light is imprisoned. Mathematically, black holes are described as solutions to the field equations in Albert Einstein’s theory of general relativity. Inside the event horizon lies the heart of the black hole – the singularity”. “Based on observations, there is total astrophysical evidence for the real and abundant existence of these prisons of matter and light”, adds the president of CENTRA.

In 1915, Einstein described how everything, from the tiniest atom to the largest supernova, is held in the grip of gravity. If gravity is proportional to mass, an extremely massive body could, in theory, modify space and could slow clocks down.

Roger Penrose’s mathematical and theoretical developments were crucial to understand black hole physics and astrophysics. He discovered that black formation is a robust prediction of the general theory of relativity. “Penrose was able to see singularities, closed trapped surfaces, black holes and cosmic censorships”, says professor Vítor Cardoso. “He discovered that it is possible to extract energy from the vacuum and that perhaps this energy was the cause of some cosmic explosions. He discovered this in the 1960s”, he adds.

Professor José Sande Lemos sent his congratulations to professor Roger Penrose. “We exchanged emails two years ago about white holes, which are the opposite of black holes and are purely speculative”, he shares.

Super Massive Black Holes

Sagittarius A* is probably the most famous supermassive black hole, of around 4 million solar masses, located at the centre of the Milky Way. In the early 1990s, Reinhard Genzel and Andrea Ghez began to develop new technology to explore the centre of the galaxy and, after observing 30 brightest stars close to the Milky Way, ended up discovering “Sagittarius A”. “Genzel and Ghez were brilliant when they realised that they were able to see what lies at the centre of the galaxy, and that they would be rewarded by doing that”, says professor Vítor Cardoso.

According to professor José Sande Lemos “the work developed by Genzel and Ghez and their collaborations require skills in several unusual scientific and technological areas”. “It is certainly a work that is worth a Nobel Prize”, underlines, the Técnico professor.

“I like to think that this award is just a start: now comes the interesting part, let’s find out what are the failures of Einstein’s Theory, and let’s see how black holes really rule galaxies”, says professor Vítor Cardoso. “This is an incentive to all brilliant minds out there”, he adds.