‘Fossil galaxy’ found hidden deep inside the Milky Way: study

The Apache Point Observatory Galactic Evolution Experiment (APOGEE) discovered a fossil galaxy named Hercules within the Milky Way. This galaxy collided with the Milky Way 10 billion years ago, contributing significantly to its mass. The collision was hidden by interstellar dust, making it difficult to observe. Using data from over half a million stars, scientists identified stars with unique chemical compositions, indicating their origin from another galaxy. This discovery suggests the Milky Way's unusual history compared to other spiral galaxies.

What challenges did scientists face in observing the galaxy Hercules?

According to the study, how does the mass of Hercules compare to the Milky Way's halo?