François Levrier
@francoislevrier.bsky.social
Professeur d’astrophysique - ENS Paris - Responsable du Master AADC - Coordinateur de l’action thématique PCMI (Physique et Chimie du Milieu Interstellaire)
(Photo ©A. Vergallo)
flevrier.github.io
(Photo ©A. Vergallo)
flevrier.github.io
Pinned
Je donne depuis quelques années un cours de M2 consacré au milieu interstellaire et à la formation des étoiles. Hier matin avait lieu la première des sept séances pour 2025-2026, et je me suis dit que c'était l'occasion de faire un peu de vulgarisation sur ces thématiques.
Otto Frisch died #OTD in 1979. An Austrian-born British physicist, he and his aunt Lise Meitner explained the process of nuclear fission observed by Hahn and Strassmann. He outlined the process for producing an atomic bomb.
en.wikipedia.org/wiki/Otto_Ro...
en.wikipedia.org/wiki/Otto_Ro...
September 22, 2026 at 6:00 AM
Otto Frisch died #OTD in 1979. An Austrian-born British physicist, he and his aunt Lise Meitner explained the process of nuclear fission observed by Hahn and Strassmann. He outlined the process for producing an atomic bomb.
en.wikipedia.org/wiki/Otto_Ro...
en.wikipedia.org/wiki/Otto_Ro...
Frederick Soddy died #OTD in 1956. With Rutherford, he showed that radioactivity is associated with the transmutation of chemical elements. He received the 1921 Nobel Prize in Chemistry for his work on isotopes.
en.wikipedia.org/wiki/Frederi...
en.wikipedia.org/wiki/Frederi...
September 22, 2026 at 5:59 AM
Frederick Soddy died #OTD in 1956. With Rutherford, he showed that radioactivity is associated with the transmutation of chemical elements. He received the 1921 Nobel Prize in Chemistry for his work on isotopes.
en.wikipedia.org/wiki/Frederi...
en.wikipedia.org/wiki/Frederi...
Michael Faraday was born #OTD in 1791. Arguably one of the most brilliant experimental physicists in history, his work on the relationship between magnetism, electricity, and light laid the path for Maxwell’s electromagnetic theory.
en.wikipedia.org/wiki/Michael...
en.wikipedia.org/wiki/Michael...
September 22, 2026 at 5:59 AM
Michael Faraday was born #OTD in 1791. Arguably one of the most brilliant experimental physicists in history, his work on the relationship between magnetism, electricity, and light laid the path for Maxwell’s electromagnetic theory.
en.wikipedia.org/wiki/Michael...
en.wikipedia.org/wiki/Michael...
Heike Kamerlingh Onnes was born #OTD in 1853. He received the 1913 Nobel Prize for his investigations of matter at very low temperatures, leading to the first liquefaction of helium and the discovery of superconductivity.
en.wikipedia.org/wiki/Heike_K...
en.wikipedia.org/wiki/Heike_K...
September 21, 2026 at 6:43 AM
Heike Kamerlingh Onnes was born #OTD in 1853. He received the 1913 Nobel Prize for his investigations of matter at very low temperatures, leading to the first liquefaction of helium and the discovery of superconductivity.
en.wikipedia.org/wiki/Heike_K...
en.wikipedia.org/wiki/Heike_K...
Pierre Méchain died #OTD in 1804. A surveyor and astronomer, he measured the Dunkirk-Barcelona meridian arc leading to the definition of the metre, and discovered several nebulæ that ended up in Messier's catalogue.
en.wikipedia.org/wiki/Pierre_...
en.wikipedia.org/wiki/Pierre_...
September 20, 2026 at 6:44 AM
Pierre Méchain died #OTD in 1804. A surveyor and astronomer, he measured the Dunkirk-Barcelona meridian arc leading to the definition of the metre, and discovered several nebulæ that ended up in Messier's catalogue.
en.wikipedia.org/wiki/Pierre_...
en.wikipedia.org/wiki/Pierre_...
James Dewar was born #OTD in 1842. A British physicist and chemist, he invented a vacuum flask with which he was able to produce large quantities of liquid oxygen, that he then showed to be attracted by magnets.
en.wikipedia.org/wiki/James_D...
en.wikipedia.org/wiki/James_D...
September 20, 2026 at 6:43 AM
James Dewar was born #OTD in 1842. A British physicist and chemist, he invented a vacuum flask with which he was able to produce large quantities of liquid oxygen, that he then showed to be attracted by magnets.
en.wikipedia.org/wiki/James_D...
en.wikipedia.org/wiki/James_D...
Ole Rømer died #OTD in 1710. He timed Io’s eclipses in Jupiter’s shadow from different points on the Earth’s orbit, allowing Huygens and others to determine a value of approximately 212000 km/s for the speed of light.
en.wikipedia.org/wiki/Ole_R%C...
en.wikipedia.org/wiki/Ole_R%C...
September 19, 2026 at 5:55 AM
Ole Rømer died #OTD in 1710. He timed Io’s eclipses in Jupiter’s shadow from different points on the Earth’s orbit, allowing Huygens and others to determine a value of approximately 212000 km/s for the speed of light.
en.wikipedia.org/wiki/Ole_R%C...
en.wikipedia.org/wiki/Ole_R%C...
Masatoshi Koshiba was born #OTD in 1926. He received the 2002 Nobel prize in Physics for pioneering work in neutrino astronomy, solving the solar neutrino problem by detecting evidence of neutrino oscillation with S-Kamiokande.
en.wikipedia.org/wiki/Masatos...
en.wikipedia.org/wiki/Masatos...
September 19, 2026 at 5:55 AM
Masatoshi Koshiba was born #OTD in 1926. He received the 2002 Nobel prize in Physics for pioneering work in neutrino astronomy, solving the solar neutrino problem by detecting evidence of neutrino oscillation with S-Kamiokande.
en.wikipedia.org/wiki/Masatos...
en.wikipedia.org/wiki/Masatos...
Hippolyte Fizeau died #OTD in 1896. Working together with L. Foucault, and then as his rival, he determined the speed of light in air to within five percent, improving on Rømer’s much earlier determination.
en.wikipedia.org/wiki/Hippoly...
en.wikipedia.org/wiki/Hippoly...
September 18, 2026 at 5:07 AM
Hippolyte Fizeau died #OTD in 1896. Working together with L. Foucault, and then as his rival, he determined the speed of light in air to within five percent, improving on Rømer’s much earlier determination.
en.wikipedia.org/wiki/Hippoly...
en.wikipedia.org/wiki/Hippoly...
John Douglas Cockroft died #OTD in 1967. With E. Walton, he designed the « charge pump » that was used to perform the first artificial nuclear fission. After WWII, he went on to develop several civil nuclear power projects.
en.wikipedia.org/wiki/John_Co...
en.wikipedia.org/wiki/John_Co...
September 18, 2026 at 5:07 AM
John Douglas Cockroft died #OTD in 1967. With E. Walton, he designed the « charge pump » that was used to perform the first artificial nuclear fission. After WWII, he went on to develop several civil nuclear power projects.
en.wikipedia.org/wiki/John_Co...
en.wikipedia.org/wiki/John_Co...
Leonhard Euler died #OTD in 1783. One of the greatest mathematicians of all time, he developed analysis, number theory, and graph theory. In physics, he made contributions in optics, elasticity, and fluid mechanics.
en.wikipedia.org/wiki/Leonhar...
en.wikipedia.org/wiki/Leonhar...
September 18, 2026 at 5:06 AM
Leonhard Euler died #OTD in 1783. One of the greatest mathematicians of all time, he developed analysis, number theory, and graph theory. In physics, he made contributions in optics, elasticity, and fluid mechanics.
en.wikipedia.org/wiki/Leonhar...
en.wikipedia.org/wiki/Leonhar...
Léon Foucault was born #OTD in 1819. The Foucault pendulum’s oscillation plane appears to rotate due to Earth’s own rotation. Foucault’s currents occur when a conducting material is subjected to a varying magnetic field.
en.wikipedia.org/wiki/L%C3%A9...
en.wikipedia.org/wiki/L%C3%A9...
September 18, 2026 at 5:05 AM
Léon Foucault was born #OTD in 1819. The Foucault pendulum’s oscillation plane appears to rotate due to Earth’s own rotation. Foucault’s currents occur when a conducting material is subjected to a varying magnetic field.
en.wikipedia.org/wiki/L%C3%A9...
en.wikipedia.org/wiki/L%C3%A9...
Joseph Petzval died #OTD in 1891. A Hungarian mathematician and physicist, he made important contributions to geometrical optics. The Petzval lens design, which allowed snapshot photography for the first time, is still in use.
en.wikipedia.org/wiki/Joseph_...
en.wikipedia.org/wiki/Joseph_...
September 17, 2026 at 5:52 AM
Joseph Petzval died #OTD in 1891. A Hungarian mathematician and physicist, he made important contributions to geometrical optics. The Petzval lens design, which allowed snapshot photography for the first time, is still in use.
en.wikipedia.org/wiki/Joseph_...
en.wikipedia.org/wiki/Joseph_...
James Jeans died #OTD in 1946. Jeans’ criterion gives the maximum mass for a gas cloud to be stable under the effects of self-gravity and thermal pressure. It is a fundamental tool to approach problems in star formation.
en.wikipedia.org/wiki/James_J...
en.wikipedia.org/wiki/James_J...
September 16, 2026 at 6:33 AM
James Jeans died #OTD in 1946. Jeans’ criterion gives the maximum mass for a gas cloud to be stable under the effects of self-gravity and thermal pressure. It is a fundamental tool to approach problems in star formation.
en.wikipedia.org/wiki/James_J...
en.wikipedia.org/wiki/James_J...
Alexander Friedmann died #OTD in 1925. The Friedmann equations describe the expansion of an isotropic and homogeneous universe with positive, null, or negative curvature, based on Einstein’s field equations of gravitation.
en.wikipedia.org/wiki/Alexand...
en.wikipedia.org/wiki/Alexand...
September 16, 2026 at 6:32 AM
Alexander Friedmann died #OTD in 1925. The Friedmann equations describe the expansion of an isotropic and homogeneous universe with positive, null, or negative curvature, based on Einstein’s field equations of gravitation.
en.wikipedia.org/wiki/Alexand...
en.wikipedia.org/wiki/Alexand...
Daniel Gabriel Fahrenheit died #OTD in 1736. He was a pioneer of thermometry, inventing the mercury-in-glass thermometer and devising the first standardized temperature scale, mostly still in use in the USA.
en.wikipedia.org/wiki/Daniel_...
en.wikipedia.org/wiki/Daniel_...
September 16, 2026 at 6:32 AM
Daniel Gabriel Fahrenheit died #OTD in 1736. He was a pioneer of thermometry, inventing the mercury-in-glass thermometer and devising the first standardized temperature scale, mostly still in use in the USA.
en.wikipedia.org/wiki/Daniel_...
en.wikipedia.org/wiki/Daniel_...
Joseph Plateau died #OTD in 1883. A Belgian physicist and mathematician, he worked in optics, inventing an early stroboscopic device, and surface tension problems. Plateau’s laws describe the structure of soap films.
en.wikipedia.org/wiki/Joseph_...
en.wikipedia.org/wiki/Joseph_...
September 15, 2026 at 5:58 AM
Joseph Plateau died #OTD in 1883. A Belgian physicist and mathematician, he worked in optics, inventing an early stroboscopic device, and surface tension problems. Plateau’s laws describe the structure of soap films.
en.wikipedia.org/wiki/Joseph_...
en.wikipedia.org/wiki/Joseph_...
Oskar Klein was born #OTD in 1894. He proposed that the fifth dimension introduced by Kaluza to generalize Einstein’s GR theory may be « curled up » and microscopic, an idea central to the development of string theory.
en.wikipedia.org/wiki/Oskar_K...
en.wikipedia.org/wiki/Oskar_K...
September 15, 2026 at 5:57 AM
Oskar Klein was born #OTD in 1894. He proposed that the fifth dimension introduced by Kaluza to generalize Einstein’s GR theory may be « curled up » and microscopic, an idea central to the development of string theory.
en.wikipedia.org/wiki/Oskar_K...
en.wikipedia.org/wiki/Oskar_K...
Pierre Duhem died #OTD in 1916. A French theoretical physicist, philosopher and historian of science, he is best remembered for his works on chemical thermodynamics, including the Gibbs-Duhem and Duhem-Margules relations.
en.wikipedia.org/wiki/Pierre_...
en.wikipedia.org/wiki/Pierre_...
September 14, 2026 at 5:49 AM
Pierre Duhem died #OTD in 1916. A French theoretical physicist, philosopher and historian of science, he is best remembered for his works on chemical thermodynamics, including the Gibbs-Duhem and Duhem-Margules relations.
en.wikipedia.org/wiki/Pierre_...
en.wikipedia.org/wiki/Pierre_...
Jean-Dominique Cassini died #OTD in 1712, the first of a long lineage of astronomers of the Paris Observatory. Among many contributions, he discovered four satellites of Saturn and the ring division that bears his name.
en.wikipedia.org/wiki/Giovann...
en.wikipedia.org/wiki/Giovann...
September 14, 2026 at 5:49 AM
Jean-Dominique Cassini died #OTD in 1712, the first of a long lineage of astronomers of the Paris Observatory. Among many contributions, he discovered four satellites of Saturn and the ring division that bears his name.
en.wikipedia.org/wiki/Giovann...
en.wikipedia.org/wiki/Giovann...
Sarah Frances Whiting died #OTD in 1927. An American physicist and astronomer, she set up one of the first undergraduate physics labs in the USA, at Wellesley College, and was the first director of Whitin Observatory.
en.wikipedia.org/wiki/Sarah_F...
en.wikipedia.org/wiki/Sarah_F...
September 12, 2026 at 6:35 AM
Sarah Frances Whiting died #OTD in 1927. An American physicist and astronomer, she set up one of the first undergraduate physics labs in the USA, at Wellesley College, and was the first director of Whitin Observatory.
en.wikipedia.org/wiki/Sarah_F...
en.wikipedia.org/wiki/Sarah_F...
Irène Joliot-Curie was born #OTD in 1897. She received the 1935 Nobel Prize in Chemistry, together with her husband Frédéric, for their discovery of artificial radioactivity, opening the path to harnessing atomic power.
en.wikipedia.org/wiki/Ir%C3%A...
en.wikipedia.org/wiki/Ir%C3%A...
September 12, 2026 at 6:34 AM
Irène Joliot-Curie was born #OTD in 1897. She received the 1935 Nobel Prize in Chemistry, together with her husband Frédéric, for their discovery of artificial radioactivity, opening the path to harnessing atomic power.
en.wikipedia.org/wiki/Ir%C3%A...
en.wikipedia.org/wiki/Ir%C3%A...
James Jeans was born #OTD in 1877. Jeans’ criterion gives the maximum mass for a gas cloud to be stable under the effects of self-gravity and thermal pressure. It is a fundamental tool to approach problems in star formation.
en.wikipedia.org/wiki/James_J...
en.wikipedia.org/wiki/James_J...
September 11, 2026 at 5:57 AM
James Jeans was born #OTD in 1877. Jeans’ criterion gives the maximum mass for a gas cloud to be stable under the effects of self-gravity and thermal pressure. It is a fundamental tool to approach problems in star formation.
en.wikipedia.org/wiki/James_J...
en.wikipedia.org/wiki/James_J...
Émilie du Châtelet died #OTD in 1749. She translated Newton’s « Principia » in French and contributed to the diffusion of Leibniz’s ideas in France. She is considered the first woman scientist in France.
en.wikipedia.org/wiki/%C3%89m...
en.wikipedia.org/wiki/%C3%89m...
September 10, 2026 at 6:37 AM
Émilie du Châtelet died #OTD in 1749. She translated Newton’s « Principia » in French and contributed to the diffusion of Leibniz’s ideas in France. She is considered the first woman scientist in France.
en.wikipedia.org/wiki/%C3%89m...
en.wikipedia.org/wiki/%C3%89m...
Hermann Bondi died #OTD in 2005. An Austrian-British cosmologist, he defended the steady-sate model with F. Hoyle and T. Gold. He also explained the nature of gravitational waves and worked on accretion onto compact objects.
en.wikipedia.org/wiki/Hermann...
en.wikipedia.org/wiki/Hermann...
September 10, 2026 at 6:36 AM
Hermann Bondi died #OTD in 2005. An Austrian-British cosmologist, he defended the steady-sate model with F. Hoyle and T. Gold. He also explained the nature of gravitational waves and worked on accretion onto compact objects.
en.wikipedia.org/wiki/Hermann...
en.wikipedia.org/wiki/Hermann...