Meet LEDA 1205871 and LEDA 29228, two of the hundreds of thousands of galaxies captured in NSF–DOE Rubin Observatory’s deep COSMOS image...

Meet LEDA 1205871 and LEDA 29228, two of the hundreds of thousands of galaxies captured in NSF–DOE Rubin Observatory’s deep COSMOS image.

In particular, these two are "shell" galaxies surrounded by arcs that form when a large galaxy absorbs a smaller one.

Shell galaxies are tough to spot, but NSF–DOE Rubin Observatory's deep imaging will uncover more! Scientists will be able to trace the collision history of galaxies and study how they grow over time🌌🌊

What is a Shell Galaxy?
A shell galaxy is a rare type of galaxy surrounded by faint, concentric arcs or "shells" of stars. like, LEDA 1205871 and LEDA 29228, captured in deep imaging data from the NSF–DOE Vera C. Rubin Observatory's COSMOS field survey. These delicate stellar ripples are notoriously difficult to detect because they are extremely faint compared to the galaxy's bright central core.

These intricate structures are cosmic fingerprints of past gravitational encounters, typically created through a minor merger or galactic cannibalism,
 A massive galaxy gravitationally captures and absorbs a smaller companion galaxy.
 As the smaller galaxy plunges through the core of the larger one, its stars are pulled out into elongated, overlapping orbits.
  These stars bunch up at the turning points of their orbits to form visible, rippling arcs—much like ripples spreading across water when a stone is dropped.
The Power of the NSF–DOE Rubin Observatory
Traditionally, catching these faint tidal features required exceptionally long exposures on specialized telescopes. The Vera C. Rubin Observatory changes the game through its unprecedented sensitivity and deep sky surveys.
   Its 8.4-meter telescope and gigantic 3.2-gigapixel camera can scan vast swaths of the sky with extreme depth.
   Deep imaging fields allow astronomers to peer past the intense glare of the main galaxy to resolve ultra-faint structures.
   Rubin is expected to uncover thousands of new shell galaxies, transforming what were once rare anomalies into a rich dataset.

Why This Matters for Astronomy
Studying shell galaxies offers a window into galactic archaeology. By mapping these stellar shells, scientists can reconstruct the collision history of galaxies, measure how rapidly galaxies grow by consuming neighbors, and even help map the distribution of invisible dark matter that shapes these cosmic structures.

📷: NSF–DOE RubinObs/NOIRLab/SLAC/AURA

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