From a MCU wiki:

Powers and Abilities

Hybrid Physiology: Due to his heritage, he is part Celestial and part human, giving him superhuman abilities. Even while not having awakened his celestial power, Quill had enough power to briefly survive holding the Power Stone on his own and after awakening his full power, was able to challenge his father, a true Celestial, who had easily subdued the other Guardians. Although he seems to have lost his cosmic powers after Ego died, Quill retained his superhuman physical powers.

Superhuman Durability: Due to his paternal heritage from Ego, Quill holds considerable amounts of supernatural durability and endurance to the point that he even was able to physically withstand the exposure to the energy from an Infinity Stone. He held the Power Stone for a short length of time without dying, and was able to harness its power when sharing the burden with the other Guardians. Quill himself also noted that he was able to survive numerous injuries while working for the Ravagers, though none were implausible enough to raise any suspicion. When he fought Ego, he was able to withstand Ego's attacks and only had minor injuries at the end of the fight. Later, Quill managed to survive a shockwave from Thanos using the Infinity Gauntlet and quickly recovered.