LIRA, a pioneer in astrophysics and instrumentation, pushes back the frontiers of knowledge
LIRA
Laboratory for Instrumentation and Research in Astrophysics
The Milky Way shaped by galactic collisions
11 May 2026The Milky Way is the result of a long history of collisions and mergers with smaller galaxies. Among these, Gaia-Sausage-Enceladus is thought to have played a major role in the evolution of our Galaxy. This dwarf galaxy, whose mass was between one-tenth and one-quarter that of the early Milky Way, is thought to have collided with it around 11 billion years ago. This event is believed to have triggered an intense episode of star and globular cluster formation, whilst permanently reshaping the structure of the young Milky Way.
This image illustrates a simulation of the evolution of a spiral galaxy similar to the Milky Way over 13.5 billion years. At the centre is a galaxy analogous to what our Galaxy may have been in the past, in continuous interaction with several smaller galaxies that are gradually merging with it. The major collision visible on the left illustrates an event comparable to the merger with Gaia-Sausage-Enceladus. Dark matter is shown in grey, whilst cosmic gas is coloured: the coldest regions appear blue and the hottest red.
Séminaires du pôle Étoiles et Galaxies Asteroseismology, the study of stellar...
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News
The Milky Way was shaped by a galactic collision that occurred earlier than expected
Presentation
LIRA, a CNRS joint research unit at Paris Observatory, is a laboratory of excellence in astrophysics and instrumentation. It studies astrophysical objects, from the Solar System to our Galaxy and beyond, through five thematic areas. Through international collaboration and instrumental innovation, it pushes back the frontiers of science and contributes to the training and dissemination of knowledge.
Our projects
MIRS on the JAXA MMX mission
The Martian Moons eXploration (MMX) mission of JAXA (Japan Aerospace Exploration Agency) is the first sample-return mission from the Phobos satellite. It also includes an exploration of the Martian system. The mission’s primary objective is to decipher the origin of Martian moons, which will provide important information on planet formation and the conditions for the emergence of water on Earth-like planets.
The MIRS (MMX InfraRed Spectrometer) instrument, developed under the leadership of LESIA (now LIRA), is an imaging spectrometer that will characterize the composition of the Martian system and help select candidate sites for sample collection.
GRAVITY+
The GRAVITY instrument, installed on the European Southern Observatory’s Very Large Telescope Interferometer (VLTI/ESO), has produced spectacular and transformative results on the supermassive black hole at the centre of the Milky Way, the active nuclei of other galaxies, proto-planetary disks around young stars and exoplanets. GRAVITY+ aims to modernise both VLTI and GRAVITY to make them ≈ 100 times more sensitive, while increasing sky coverage by a factor of ≈ 100, and contrast in the vicinity of bright objects by a factor of ≈ 10. These gains will benefit all the VLTI’s current and future instruments for the next 20 years, and will perpetuate it as a unique infrastructure in the world.
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Observatoire de Paris
5, place Jules Janssen
92195 Meudon
Phone
01 45 07 77 01
Meudon site
LIRA
Observatoire de Paris
5, place Jules Janssen
92195 MEUDON Cedex
Paris site
LIRA
Observatoire de Paris
77, Avenue Denfert-Rochereau
75014 Paris
Cergy site
LIRA - Site de Neuville II
UFR Sciences et Techniques - Département de physique
5, mail Gay Lussac
95000 Neuville-sur-Oise