Studying pulsars, a window on our galaxy

Galaxies are complex ecosystems that still raise many questions for scientists. The GAMALO project aims to study a phenomenon that could provide a better understanding of how they behave: pulsars.

Milky Way seen from the Sechura Desert, near the Pacific Ocean in the far north of Peru. This photograph was taken as part of the “Sechura Desert” program, which aims to understand the interactions between human societies and the environment, particularly the desert, by studying how people and animals have adapted to Peru’s Pacific coast.

“In the galaxy, we observe the acceleration of particles such as protons, electrons and nuclei. This process is similar to what we might imagine in our man-made particle accelerators like the one at CERN. But, as with many things, nature does it more efficiently than we do”, explains Pierrick Martin, researcher at the Institut de recherche en astrophysique et planétologie (1) and leader of the GAMALO project (Révéler l’étendue des halos gamma). These accelerated particles, also known as cosmic rays, are still poorly understood, but play a structuring role in galaxies.

Pierrick Martin is a high-energy astrophysicist who studies the most energetic and violent cosmic phenomena, such as stellar explosions and black hole accretion. His work also concerns cosmic rays, which are a particularly high source of radiation. Understanding them will enable us to better understand our galaxy and galaxies in general. Indeed, it is essential to better understand the interactions of the objects that make them up and their interconnections.

However, these highly energetic particles are difficult to observe because they are few in number and very costly to produce energetically. The discovery of pulsars has revolutionized the field and opened up new research possibilities.

The discovery of pulsars opens up a new field of study

In 2017, thanks to the HAWC ground-based telescope, a research team discovered pulsars, compact objects that accelerate particles entering their field.

Surrounded by a halo of gamma rays, extremely powerful electromagnetic radiation, these pulsars produce light.

The High Altitude Water Cherenkov Experiment is a high-energy gamma-ray and cosmic-ray observatory in Mexico. © The HAWC Collaboration.

Pulsars with gamma-ray halos are windows, magnifying glasses, on cosmic rays, offering an opportunity to observe them in a confined space rather than freely in the galaxy. The GAMALO project focuses on pulsars and how they work. Usually, it’s difficult to link high-energy particles to their sources by observation, so this is an advantageous condition. Beyond pulsars, this study will help us understand the role of cosmic rays in galaxies, and therefore the very structure of galaxies.

“The study of cosmic rays is a century-long quest, which is relatively young compared with other celestial objects”, Pierrick Martin points out. As a result, research teams are still asking fundamental questions.

GAMALO project research areas

The GAMALO project aims to answer an essential question: how does the pulsar phenomenon work? This main question leads to a multitude of sub-questions concerning the frequency of this phenomenon, its reproducibility, and possible undetected past observations. The project can be broken down into three main areas, divided between four laboratories (2).

  • Observation. Scientists are looking to observe the same phenomenon elsewhere, under different conditions. “Compared with biology, for example, astrophysicists can’t experiment. So we have to observe to find similar phenomena and then compare them,” explains Pierrick Martin. Observation in astrophysics means “looking at a region of the sky and making sense of what you see. For example, seeing a source of light and discovering that it’s actually a cloud of gas.
  • Theorizing. Scientists seek to gain a physical understanding of the process by reproducing it in simulations. Starting from the first principles of physics, which are immutable, they look for a result that would show our sky.
  • Tooling. Scientists take an anticipatory interest in the capacity of future sky observation tools. They reflect on the next discoveries in astrophysics to design tomorrow’s observation tools, which will be more efficient and better able to meet scientists’ future needs.

Results and issues

Thanks to the GAMALO project, a number of energy sources have been identified, providing a better understanding of the sky. In terms of modeling, scientists have concentrated on modeling plasmas, ionized cosmic gases, and the subtle interactions between particles and plasma. However, there are still limits to theoretical extrapolation. Finally, the questions raised on the instrumental side are still relevant, and help us to imagine how tomorrow’s astrophysicists will process the data coming from the sky.

Half a dozen publications have emerged from the project. All this research has led to a better overall understanding of the sky.

Pierrick Martin believes that it is now time to turn to another hypothesis. According to him, the study of pulsars is indeed “a window on a much larger phenomenon, which is interconnected with many areas of astrophysics. There’s no doubt that pulsars play an essential role in the evolution of galaxies and star formation on a cosmic scale”. Clarifying the nature of this role will be one of the next questions that Pierrick Martin and his colleagues are already tackling…

Notes

  1. CNRS Unit, CNES, Université Toulouse Paul Sabatier
  2. Institut de recherche en astrophysique et planétologie -Toulouse (IRAP), Laboratoire Univers et Particules de Montpellier (LUPM), Centre d’études nucléaires de Bordeaux Gradignan (CENBG) and Institut de recherche sur les lois fondamentales de l’Univers -Saclay (IRFU)
  3. This research and this article were funded at least in part by the Agence Nationale de la Recherche (ANR). This paper is produced and funded as part of the Science Avec et Pour la Société – Culture Scientifique Technique et Industrielle call for projects for the GAMALO project of the 2018-2019 generic calls for projects.

IRAP Contact

  • Pierrick Marin, pierrick.martin@irap.omp.eu

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