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 ${\rm M87}^\star$ , the Hubble constant can be independently determined with a precision of about 13% as $H_0=70\pm 9$ km ${\rm s}^{-1}$ ${\rm Mpc}^{-1}$ . The high-redshift observations of super-massive black hole shadows may accurately determine a combination of parameters $H_0$ and ${\Omega_{m}}$ , and we show by a simple simulation that combining them with the type Ia supernovae observations would give precise measurements of the cosmological parameters. * Supported by the National Natural Science Foundation of China (11975072, 11835009, 11690021), the National Program for Support of Top-Notch Young Professionals, the Liaoning Revitalization Talents Program (XLYC1905011), and the Fundamental Research Funds for the Central Universities (N180503014)