The ngEHT's Role in Measuring Supermassive Black Hole Spins

TL;DR

The paper discusses how the next-generation Event Horizon Telescope (ngEHT) will enhance measurements of supermassive black hole spins, providing new insights into black hole growth and cosmic evolution.

Contribution

It outlines the potential of ngEHT to measure black hole spins with improved techniques, expanding the sample to include low-accretion-rate objects.

Findings

ngEHT can measure spins of tens of supermassive black holes

It will provide a less biased sample of black hole spins

Enhanced imaging techniques will improve spin constraints

Abstract

While supermassive black hole masses have been cataloged across cosmic time, only a few dozen of them have robust spin measurements. By extending and improving the existing Event Horizon Telescope (EHT) array, the next-generation Event Horizon Telescope (ngEHT) will enable multifrequency, polarimetric movies on event horizon scales, which will place new constraints on the space-time and accretion flow. By combining this information, it is anticipated that the ngEHT may be able to measure tens of supermassive black hole masses and spins. In this white paper, we discuss existing spin measurements and many proposed techniques with which the ngEHT could potentially measure spins of target supermassive black holes. Spins measured by the ngEHT would represent a completely new sample of sources that, unlike pre-existing samples, would not be biased towards objects with high accretion rates. Such a sample would provide new insights into the accretion, feedback, and cosmic assembly of supermassive black holes.