Complex sentence: The primary component of the binary star system AX Persei is another star in an advanced phase of stellar evolution, in this case a red giant, which is transferring material onto an accretion disc around a smaller star.
Split into simpler sentences: The primary component of the binary star system AX Persei is another star in an advanced phase of stellar evolution, in this case a red giant. The red giant is transferring material onto an accretion disc around a smaller star.