Scientists have observed M31-2014-DS1, a hydrogen-depleted supermassive star in the Andromeda galaxy.[1] In 2014, its brightness increased in the mid-infrared spectrum.[1] From 2017 to 2022, it dimmed more than 10,000 times in optical light and more than 10 times in total light until it became undetectable.[1] They interpret these changes as evidence of a failed supernova in which the core collapsed to form a stellar-mass black hole.[1] The star had an initial mass of about 13 solar masses and in the final stage of nuclear burning about 6.7 solar masses.[1][2][3] Most of its mass, about 98% including more than 5 solar masses, collapsed into the core to form a black hole with a mass of about 6.5 solar masses.[2][3] The similar case of NGC 6946-BH1 confirms that hydrogen-depleted massive stars can end up like this without exploding.[1] Observations rule out a significant optical burst and show the presence of an ejected dust shell.[1][2][3]