Albert Einstein might not have imagined that, just over a hundred years after his theory of general relativity, it would be possible to contemplate one of his most dazzling predictions: black holes, as shown in the image of Sagittarius A*, located at the center of the Milky Way. According to Elisa Ferreira, a cosmologist at the University of São Paulo and a researcher at the Kavli Institute for the Physics and Mathematics of the Universe, in Japan, “we are living in a moment in which a new observation window for the universe has opened up” – let them say so, by the way. , images from the James Webb telescope presented by NASA this week.
Brazil has been gaining prominence in space investigations. In addition to integrating scientifically relevant telescope projects such as the Dark Energy Survey — a collaboration of research institutes and universities from six countries — the scientific community will soon inaugurate the first telescope with state-of-the-art Brazilian technology. “We have an important role in many projects, but for the first time Brazil is the leader of a telescope, Bingo, located in the hinterland of ParaÃba”, says Ferreira.
The oldest unsolved mystery in physics, dark matter, is among the subjects investigated by cosmology. The numbers are impressive: everything we see is only 4% of the universe. The other 96% correspond to the dark part of the cosmos, a junction of energy and matter that cannot be detected by light and remains unknown to science. But how do we know, then, that dark matter is there?
“In the universe, everything that has mass influences the gravity of the system. So, in order to measure the speed of each star that revolves around the center of our galaxy, we must take into account the total mass of this galaxy. But when the calculation is done, the data do not match”, explains the researcher. Putting just the visible mass into the equation, the result for the speed of stars is very different from what we observe in space. “To arrive at a correct result, the calculation must take into account a much larger amount of mass. Today we know that this mass represents 85% of the matter that exists and that we cannot see, the dark matter.”
There are hundreds of models to explain this mass that does not emit light. “It’s beautiful to see how creative science is: it can postulate from a new fundamental particle to primordial black holes”, says Ferreira. That is, in theory, dark matter can be composed of primordial black holes with a mass equivalent to that of the Sun, or of an elementary particle of very small mass.
That’s where new telescopes come in. Astrophysicists and cosmologists from all over the world have dedicated themselves to testing the different models in order to discover the most appropriate to explain dark matter. “Our predecessors measured the properties of the universe very well, but cutting-edge technologies allow us to find new evidence, deviations in old properties that can indicate new paths or debunk theories about what this matter could be”, explains the scientist.
For some years now, the most popular model for understanding dark matter has been the Weakly Interacting Massive Particle Wimp. According to this theory, dark matter would be a new fundamental particle that interacts very weakly or almost not at all with other standard particles, the ones we see. Along these lines, billions of dollars were spent on experiments that did not generate conclusive results. This made the new generation decide to invest efforts in other models.
The researcher chose to investigate ultralight dark matter models. A prime example is the axion, a hypothetical particle that scientists have proposed to account for incompatibilities in the elementary particle model. It is a theoretical particle that, if it existed in nature, could behave like dark matter.
Ferreira examines a specific behavior of ultralight particles that may give us clues about the properties of dark matter: particle-wave duality. Every particle can be described as a wave, depending on its mass and velocity, the size of the wave being inversely proportional to the size of the mass. In other words, when the particle’s mass is very small, it behaves like a wave. In cases where the mass is smaller than an electron, for example, the wave behavior is very evident. This model is a strong candidate to explain dark matter, as it behaves in the galaxy more like a wave than a particle.
But this behavior is not enough evidence to claim that dark matter is made up of ultralight particles. “Even if I detect a property consistent with the wave, I still need to show that no other model has this property”, explains the scientist. “It’s a lot of work to find this evidence and simulate this scenario as close to the universe as possible to say that’s exactly what I’m looking for.” But this is the way. Currently, the scientist’s team has arrived at one of the closest results of what the mass of this particle could be.
The new generation of cosmologists is eager to put different models to the test. “In the next few years, with the material being collected by the telescopes, we will have data to corroborate models or exclude them.” It is these data that will make the difference in Ferreira’s research. His work, at the interface between theory and observation, involves predictions and simulations that will be compared to the information already available.
“Science is a collective effort to discover the mysteries of our universe. I was never told that. That image of the lonely, mad scientist – always a white man – has nothing to do with the science we do daily: a whole world connection for the greater good”, he concludes.
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Pedro Lira is a journalist at the Serrapilheira Institute.
This article was written for the #scienceinelections campaign, which celebrates Science Month. In July, the texts of the Ciência Fundamental blog will reflect on the role of science in the reconstruction of Brazil and its relationship with other topics of public interest. Today’s is about science and technological development.
