The universe is extremely big, and this makes it hard to measure. One way to measure an object in space is to check its known intrinsic brightness. However, it has a limit as intrinsic brightness is linked to the timing of their pulses. So, astronomers have demonstrated the viability of the most valid tool in the universe for the supermassive black holes, at least for the echoes.

First of all, why are black holes used in research? Black holes give out no discernible radiation, and we can use them effectively. There are billion stellar-mass black holes in the Milky Way though we cannot see them all. Measuring the distance of the stars and planets by black holes with developed scientific techniques can be used to make them massive echoes at all. Astronomer Yue Shen of the University of Illinois at Urbana-Champaign said that measuring cosmic distances is a fundamental challenge in astronomy, so the possibility of having an extra trick up one's sleeve is very exciting.

Then, how can black holes help? Is it by being the stations in space? Outside the accretion disc of the black hole is a large cloud and a doughnut-shaped ring of dust is called the torus. Moreover, it is the key to a technique known as echo mapping. According to the article, "Science Alert", in the regions they surveyed, scientists can calculate the distance between the inner edge of the accretion disc and the torus.
To sum up, astronomers have researched black holes for the effective tool of echoes to measure the cosmos distance in the universe. The ongoing surveys with better technology will continue to provide us higher quality observations for future universe development.