Massive galaxies at the beginning of cosmic time with James Webb: do they break our cosmological model?

Already in the first six months of observations, the James Webb Space Telescope has made many surprising discoveries. One of these is the existence of six candidate very massive galaxies just 500–800 million years after the Big Bang. These candidate galaxies are so massive at such early cosmic times that according to our lambda-CDM cosmological model, there should not be enough baryons available to form them. I will discuss these remarkable objects and their implications for our understanding of how the universe began.