The night sky seems unchanging, but galaxies constantly exchange matter. The Milky Way, like a great river, absorbs smaller streams — dwarf galaxies. Along with their stars, planets may also come to us.
Astronomers studied catalogs of stars with planet candidates from the Kepler, K2, and TESS telescopes. They compared stellar motions from Gaia data and compositions from LAMOST spectra. They found 11 stars that move differently from their neighbors and resemble interlopers from dwarf galaxies in composition. For four of them, the metal content is so low that it cannot be explained by the normal evolution of the Milky Way.
Next, the authors filtered out false alarms: they checked whether a neighboring star might interfere, whether the eclipse depth changes with each planetary transit, and whether there is a second dip in brightness from a companion star. After all checks, two stars remained — EPIC 211407755 and TIC 239541449. If their planets are confirmed, they will be the first known worlds to have survived the absorption of their home galaxy by ours.
Dwarf galaxies are poor in heavy elements because they contain few supernovae, the main “forges” of metals in the universe.
In the series “Stargate Universe,” the ship Destiny travels between galaxies, finding planets formed under conditions quite different from those in the Milky Way.