Milky Way grew by devouring galaxies, leaving ghost stars, Pg II

Key Highlights:

• Astronomers Vasily Belokurov, Amina Helmi, and Rodrigo Ibata received the Kavli Award for their discoveries on the Milky Way's growth through galactic collisions.
• Rodrigo Ibata first identified the Sagittarius dwarf galaxy being absorbed by the Milky Way over three decades ago.
• Amina Helmi utilized data from the European Space Agency's (ESA) Gaia mission to identify Gaia-Enceladus, a galaxy that merged with the Milky Way 10-12 billion years ago.
• Recent research confirmed the Low-energy-Kraken-Heracles (LKH) galaxy collided with the Milky Way around 12 billion years ago, potentially marking its first major merger.
• The Small and Large Magellanic Clouds, two of the closest galaxies, are currently in the process of being absorbed by the Milky Way.

Milky Way Galaxy.jpg

Detailed Insights:

• Galaxies evolve through a "snowball effect" of violent collisions, where larger galaxies gravitationally tear apart smaller ones.
• Remnants of absorbed galaxies are identifiable by streams and clusters of stars with distinct motions and chemical compositions.
• Galactic archaeology is a field that uses precise measurements of stellar age, chemistry, and motion to reconstruct the Milky Way's evolutionary history.
• Dr. Ibata's discovery of the Sagittarius dwarf galaxy provided the first direct evidence of galactic absorption, stimulating further research into the Milky Way's past mergers.
• Dr. Helmi's theoretical models predicted the visible star streams left behind by destroyed galaxies, which were later confirmed by ESA Gaia mission data.
• The collision with Gaia-Enceladus was significant enough to have altered the Milky Way's overall shape.
• Studying very old collisions, such as with LKH, is challenging due to the young state of the merging galaxies and obscuring stardust in the galactic bulge.
• Researchers analyze globular clusters, which are groups of millions of stars born together, to trace the origins of ancient mergers.
• Upcoming instruments like 4MOST and the MOONS telescope are expected to provide more detailed data, further enhancing our understanding of galactic history.

Scientific/Technical Concepts Involved:

• Tidal Forces: Gravitational forces exerted by a larger celestial body that stretch and deform a smaller body.
• Galactic Archaeology: The study of the formation and evolution of galaxies by analyzing the properties and distribution of their stars.
• Globular Clusters: Dense, spherical collections of hundreds of thousands to millions of stars, gravitationally bound together.
• Photometry: The measurement of the intensity of light from celestial objects, used to determine their brightness and color.
• Spectroscopy: The study of light emitted or absorbed by celestial objects to determine their chemical composition, temperature, and velocity.