For the discovery of those ‘too massive galaxies’ you can look at the following paper: A population of red candidate massive galaxies ~600 Myr after the Big Ba

For the discovery of those ‘too massive galaxies’ you can look at the following paper: A population of red candidate massive galaxies ~600 Myr after the Big Bang https://www.nature.com/articles/s41586-023-05786-2 https://www.nature.com/articles/s41586-023-05786-2