Astronomers are really good at weighing baby supermassive black holes

In the 1970s, astronomers detected what was in fact a supermassive black hole (SMBH) via continuous radio from the center of our galaxy. The black hole, today known as Sagittarius A*, has 4 million solar masses and is detectable by the radiation it emits at many wavelengths. Since then, astronomers have discovered that SMBHs reside at the centers of very large galaxies, some of which are much larger than our own! Over time, astronomers have observed relationships between the properties of galaxies and the masses of their SMBHs, suggesting that the two formed together.

Using Gravity + Tool in Very Large Telescope Interferometer (VLTI), a team Max Planck Institute for Extraterrestrial Physics (MPE) recently measured the mass of the SMBH in SDSS J092034.17+065718.0. About 11 billion light-years from our solar system, this galaxy existed when the universe was just two billion years old. To their surprise, they found that the SMBH weighs in at a modest 320 million solar masses, which is significantly less compared to the mass of its host galaxy. These findings could revolutionize our understanding of the relationship between galaxies and the black holes that reside at their centers.

A correlation between the properties of a galaxy and its SMBH has been observed many times in the local Universe. To determine if this has always been the norm, astronomers are looking forward to looking at galaxies during the Cosmic Dawn, shortly after the first galaxies formed after the Big Bang. However, measuring black hole masses for these distant galaxies is extremely difficult (or impossible) using traditional direct methods, even when quasars („quasi-stars”) are involved.

The gravity of quasars in the early universe + interpretation of observations. © D. Shimizu; Background image: NASA/WMAP; Quasar chart: ESO/M. Kornmesser; VLT sequence: ESO/G. Hudebol

This particularly bright class of galaxies is a subset of galaxies with very active galactic nuclei (AGNs), where the centers temporarily outshine all the stars in the disc. Fortunately, the next generation of telescopes and instruments are allowing astronomers to see these early galaxies for the first time. This includes the GRAVITY interferometric instrument on the VLTI, which combines light from all four 8-meter (26.25 ft) telescopes of the ESO Large Telescope to form a single virtual telescope 130 meters (426.5 ft) in diameter.

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Thanks to recent upgrades, the GRAVITY instrument's successor (GRAVITY+) allows astronomers to precisely study black hole growth during another critical epoch called the „cosmic noon,” when both black holes and galaxies grow rapidly. „In 2018, we made the first breakthrough measurements of a quasar's black hole mass with gravity. However, this quasar was very close. said Taro Shimizu, staff scientist at the Max Planck Institute for Extraterrestrial Physics. MPE press release: „Now, we've pushed all the way to a redshift of 2.3, corresponding to a view time of 11 billion years.”

Thanks to improved performance with GRAVITY+, astronomers can push the envelope and take images of even black holes in the early universe 40 times sharper than otherwise possible. The James Webb Space Telescope (JWST). With the help of GRAVITY+, the team was able to build on their previous observations and spatially resolve the motion of the gas and dust that make up the accretion disk around the central black hole of SDSS J092034.17+065718.0. This allowed them to directly measure the mass of the central black hole.

This artist's rendering depicts a supermassive black hole spinning at high speeds surrounded by an accretion disk. Credit: ESO, ESA/Hubble, M. Kornmesser

At 320 million solar masses, the black hole actually weighs less than its host galaxy, about 60 billion solar masses. This suggests that the host galaxy grew faster than the SMBH at its core, which means that for some galaxies there is a delay between the evolution of the galaxy and the black hole. said Jinyi Shangguan, an MPE scientist with the research team:

„A possible scenario for the evolution of this galaxy appears to be strong supernova feedback, where these starbursts eject gas from the central regions before reaching the black hole at the center of the galaxy. The black hole begins to grow rapidly—and to catch up with the overall growth of the galaxy—so that the galaxy maintains a gas reservoir in its core regions against supernova feedback. turned out to be huge.”

Moving forward, the team plans to conduct follow-up observations of other galaxies in the Cosmic Noon and make high-precision measurements of their central black holes. These observations will determine whether this mass imbalance is the dominant mode of co-evolution for early galaxies and their SMBHs.

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read more: Max Planck Institute for Extraterrestrial Physics

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