A new cosmological probe using super-massive black hole shadows

We study the prospects of using the low-redshift and high-redshift black hole shadows as new cosmological standard rulers for measuring cosmological parameters. We show that, using the low-redshift observation of the black hole shadow of \begin{document}${\rm M87}^\star$\end{document} , the Hubble constant can be independently determined with a precision of about 13% as \begin{document}$H_0=70\pm 9$\end{document} km \begin{document}${\rm s}^{-1}$\end{document} \begin{document}${\rm Mpc}^{-1}$\end{document} . The high-redshift observations of super-massive black hole shadows may accurately determine a combination of parameters \begin{document}$H_0$\end{document} and \begin{document}${\Omega_{m}}$\end{document} , and we show by a simple simulation that combining them with the type Ia supernovae observations would give precise measurements of the cosmological parameters.