James Webb Space Telescope Spots Massive Black Hole With Half the Mass of Its Surrounding Galaxy

A team of astronomers has made an important discovery by identifying an unusually large black hole within one of the universe’s most distant quasars. This black hole, at the heart of the quasar ULAS J1120+0641 in the constellation Leo, is 1.4 billion times the mass of the Sun. In a surprising twist, it is almost half the mass of all the stars in its galaxy combined—an unusually high ratio that far exceeds typical black hole-to-stellar mass ratios.

Breakthrough Observations with James Webb Telescope

Previous attempts to observe this quasar’s host galaxy using the Hubble Space Telescope were unsuccessful due to the quasar’s overwhelming brightness. However, scientists led by MIT astronomer Minghao Yue turned to the James Webb Space Telescope (JWST), which specialises in infrared observations, to capture detailed images of this distant quasar and its host galaxy.

Yue explains that the quasar’s immense brightness—100 times that of its host galaxy—makes it challenging to measure light from surrounding stars. Nevertheless, because the quasar’s light has traveled for approximately 13 billion years to reach Earth, the expansion of the universe has stretched this light into infrared wavelengths, enabling clearer observations with JWST.

An Unprecedented Ratio of Black Hole Mass to Galaxy Mass

The black hole’s mass is not unexpected; earlier estimates were in a similar range. What stands out is the mass ratio: while in typical galaxies, central black holes comprise only about 0.1 percent of the galaxy’s stellar mass, ULAS J1120+0641’s black hole accounts for an astonishing 54 percent. According to Yue, this finding suggests a unique evolutionary relationship between early black holes and their host galaxies, which differs significantly from the way black holes and galaxies evolve in the present-day universe.

Harvard University astronomer Avi Loeb, who was not involved in the study, posits that the black hole’s intense radiation could be suppressing star formation in its galaxy. For stars to form, interstellar gas must cool to collapse effectively; however, the quasar’s energy likely heats the gas, preventing it from forming new stars. Loeb suggests that when the quasar eventually “shuts off,” the galaxy’s gas will cool, leading to an increase in stellar mass and potentially lowering the black hole’s proportionate mass over time.

A Glimpse Into the Early Universe’s Mysteries

While the study does not fully explain why some black holes grew so quickly in the early universe, the observations reveal an interesting detail—a second galaxy is merging with the quasar’s host. This galactic collision likely feeds additional gas into the black hole, increasing its mass and fuelling the quasar’s luminosity, which makes it visible across such a vast cosmic distance.