In the summer of 1957, astronomers Braulio Iriarte and Enrique Chavira logged 817 faint blue stars recorded on photographic plates at the Tonantzintla Observatory in Mexico, cataloging entry number 618 as a routine stellar object. 1 The concept of a quasar had not yet been conceived. Today, that object is known as TON 618—a hyperluminous quasar whose light has traveled 10.8 billion years to reach Earth, powered by gas falling into a central black hole so intensely radiant that it completely outshines its host galaxy.

In 2004, researchers calculated the mass of this cosmic behemoth at 66 billion times the mass of the Sun, inferred from an era when the universe was barely three billion years old. 2

How do astronomers weigh a distant black hole?

Astronomers measure a distant black hole by observing the orbital velocities of gas clouds swirling around its event horizon, utilizing spectral line broadening to calculate gravitational force. Because the black hole itself emits no light, high velocities correspond to wider emission lines due to Doppler shifting—where gas moving toward Earth shifts to the blue spectrum and receding gas shifts to the red. The physical distance between the gas clouds and the black hole is estimated using the quasar's total luminosity, relying on a empirical calibration derived from a small sample of closely monitored local quasars.

Using near-infrared spectroscopy at Tel Aviv University in 2004, Ohad Shemmer and his team analyzed TON 618's hydrogen emission line, recording gas velocity widths of 10,527 kilometers per second—the broadest among 29 observed quasars. 2 The resulting equation yielded the iconic figure of 66 billion solar masses, though the authors explicitly cautioned that relying on single spectral line broad-line regions could introduce significant calibration errors.

By 2019, an updated catalog compiled by Xue Ge and colleagues standardized measurement techniques across 130 distant quasars, revising TON 618's estimated mass downward to approximately 41 billion solar masses. 3 The black hole had not lost physical matter; rather, refined observational calibration reduced the estimated baseline by 38 percent.

Notes and Sources

  1. Iriarte, B., Chavira, E. (1957). Estrellas azules en el casquete galáctico norte. Boletín de los Observatorios de Tonantzintla y Tacubaya, 2(16), 3-36. 1957BOTT....2p...3I ↩
  2. Shemmer, O., Netzer, H., Maiolino, R., Oliva, E., Croom, S., Corbett, E., di Fabrizio, L. (2004). Near-infrared spectroscopy of high-redshift active galactic nuclei. I. A metallicity-accretion rate relationship. The Astrophysical Journal, 614(2), 547-557. doi:10.1086/423607 ↩
  3. Ge, X., Zhao, B.-X., Bian, W.-H., Frederick, G. R. (2019). The blueshift of the C IV broad emission line in QSOs. The Astronomical Journal, 157(4), 148. doi:10.3847/1538-4357/ab0956 ↩