Astronomers are Becoming Highly Skilled at Measuring the Mass of Infant Supermassive Black Holes

In the 1970s, astronomers determined that a persistent radio source emanating from the center of our galaxy was, in fact, a supermassive black hole (SMBH) known as Sagittarius A*. This SMBH, which has a mass equivalent to over 4 million suns, emits radiation in multiple wavelengths, making it detectable. Since this discovery, it has been established that most massive galaxies have a SMBH at their center. Furthermore, a relationship between the properties of galaxies and the mass of their resident SMBH has been observed, suggesting a co-evolution.

A team from the Max Planck Institute for Extraterrestrial Physics (MPE) has recently measured the mass of an SMBH in the galaxy SDSS J092034.17+065718.0, located approximately 11 billion light-years from our Solar System, using the GRAVITY+ instrument at the Very Large Telescope Interferometer (VLTI). This galaxy existed when the Universe was around two billion years old. Surprisingly, the team found that the SMBH has a mass of only 320 million solar masses, significantly lower than the mass of its host galaxy. This discovery could revolutionize the current understanding of the relationship between galaxies and their resident black holes.

The relationship between the properties of a galaxy and its SMBH has been extensively studied in the local Universe, and astronomers have been keen to explore whether this has always been the case. However, measuring black hole masses in far-off galaxies from the early universe using traditional direct methods has proven to be a challenging task.

The GRAVITY interferometric instrument aboard the VLTI, which combines light from four 8-meter telescopes to create a single virtual telescope with a diameter of 130 meters, has provided the opportunity to observe these early galaxies. Recent upgrades to the instrument, known as GRAVITY+, have allowed astronomers to study the growth of black holes during a critical period known as “Cosmic Noon,” a time when both galaxies and black holes were rapidly expanding.

The team used GRAVITY+ to observe the central black hole of SDSS J092034.17+065718.0. The instrument’s superior performance enabled them to resolve the motion of the gas and dust making up the accretion disk around the black hole, leading to a direct measurement of its mass.

The results showed that the black hole, at 320 million solar masses, is underweight compared to its host galaxy, which weighs about 60 billion solar masses. This suggests that the galaxy grew faster than its central SMBH, indicating a possible delay between the growth of some galaxies and their black holes.

The team plans to conduct further observations of other galaxies at Cosmic Noon to confirm if this mass imbalance is a common characteristic of early galaxies and their SMBHs. This will provide valuable insights into the co-evolution of galaxies and their resident black holes.

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