@article{opher_2001,  title={Dark Matter in the Universe},  volume={31},  ISSN={0103-9733},  url={https://doi.org/10.1590/S0103-97332001000200008},  DOI={10.1590/S0103-97332001000200008},  number={2},  journal={Brazilian Journal of Physics},  publisher={Sociedade Brasileira de Física},  author={Opher, Reuven},  year={2001},  month={Jun},  pages={183–187} }