# A new cosmological probe using super-massive black hole shadows

## TL;DR

This paper explores the potential of using super-massive black hole shadows at various redshifts as new standard rulers for cosmology, providing a novel method to measure key parameters like the Hubble constant.

## Contribution

It introduces a new cosmological probe based on black hole shadows and demonstrates its potential for precise parameter estimation when combined with existing observations.

## Key findings

- Low-redshift black hole shadow of M87* can determine H_0 with 13% precision.
- High-redshift black hole shadows can constrain a combination of H_0 and Ω_m.
- Combining black hole shadow data with supernovae improves cosmological parameter accuracy.

## Abstract

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