compact object did form at the star's core. Since the supernova first became visible, astronomers have been searching for the collapsed core. The Hubble Space Telescope has taken images of the supernova regularly since August 1990 without a clear detection of a neutron star. A number of possibilities for the "missing" neutron star are being considered. The first is that the neutron star is enshrouded in dense dust clouds so that it cannot be seen. Another is that a pulsar was formed, but with either an unusually large or small magnetic field. It is also possible that large amounts of material fell back on the neutron star, so that it further collapsed into a black hole. Neutron stars and black holes often give off light as material falls onto them. If there is a compact object in the supernova remnant, but no material to fall onto it, it would be very dim and could therefore avoid detection. Other scenarios have also been considered, such as whether the collapsed core became a quark star. In 2019, evidence was presented that a neutron star was inside one of the brightest dust clumps close to the expected position of the supernova remnant. In 2021, further evidence was presented that the hard X-ray emission from SN 1987A originates in the pulsar wind nebula. The latter result is supported by a three-dimensional magnetohydrodynamic model, which describes the evolution of SN 1987A from the SN event to the current age, and reconstructs the ambient environment around the neutron star at various epochs, thus allowing to derive the absorbing power of the dense stellar material around the pulsar. Light curve Much of the light curve, or graph of luminosity as a function of time, after the explosion of a type II supernova such as SN 1987A is produced by the energy from radioactive decay. Although the luminous emission consists of optical photons, it is the radioactive power absorbed that keeps the remnant hot enough to radiate light. Without the radioactive heat, it would quickly dim. The radioactive decay of 56Ni through its daughters 56Co to 56Fe produces gamma-ray photons that are absorbed and dominate the heating and thus the luminosity of the ejecta at intermediate times (several weeks) to late times (several months). Energy for the peak of the light curve of SN1987A was provided by the decay of 56Ni to 56Co (half life of 6 days)