Stellar mass vs. effective radius distribution of 36 157 galaxies within the pure sample. The magenta dash-dotted line represents the initial Damjanov et al. (2015) cut for massive compact sources, the blue solid line indicates one of the most restrictive criteria proposed by Trujillo et al. (2009), and the orange dashed line visualises the cut adopted in this work to select 6961 UCMG candidates. The red points with error bars represent our final sample of 77 VIPERS red nuggets. The black dashed line shows the stellar mass completeness in the VIPERS catalogue. With other lines different compactness criteria are indicated: blue dot-dashed line – ultracompact Cassata et al. (2011); orange dotted line – Barro et al. (2013); green dashed line – ultracompact van der Wel et al. (2014); red solid line – Charbonnier et al. (2017); brown solid line – Buitrago et al. (2018); violet solid line – Spiniello et al. (2021).