Distant black hole mass measurement demonstrates the potential of GRAVITY+

Astronomers have, for the first time, made a direct measurement of the mass of a distant black hole, one so far away that light from its surroundings took 11 billion years to reach us. The team, led by Taro Shimizu at the Max Planck Institute for Extraterrestrial Physics in Germany, involving scientists from IPAG, found the black hole, called J0920, to have a mass of about 320 million times that of the Sun. This achievement, described in a paper published today in Nature, has been made possible thanks to GRAVITY+ [1].

To directly measure the mass of a black hole, astronomers use telescopes to track the movement of gas and stars around it. The faster these move, the more mass is encased within the material’s orbit. This technique has been used to measure the mass of nearby black holes, including the one at the centre of the Milky Way. At very remote distances, however, this motion is extremely hard to observe. This means similar direct measurements of the mass of distant black holes, which provide a window into a period in the history of the Universe when galaxies and black holes were rapidly growing, have not been possible until now.

The direct measurement of J0920’s mass was only possible with the first set of GRAVITY+ improvements. These upgrades have allowed astronomers to observe the faint, distant gas around the black hole with greater accuracy than ever before by using a technique called wide-field, off-axis fringe tracking. Measuring the mass of J0920 accurately is a first step to help astronomers understand how black holes and galaxies grew together at a time when the Universe was only a couple of billion years old and galaxies were still forming. For J0920, the new mass measurement reveals the black hole is about four times less massive than expected given the mass of its host galaxy; this indicates a delay in the growth of the black hole compared to the surrounding galaxy.

GRAVITY+ uses interferometry to combine the light arriving at the four 8-metre Unit Telescopes (UTs) that are part of VLTI. Once completed, it will include upgraded adaptive optics technology that will enable better correction of the blur caused by the Earth’s atmosphere and improve the contrast of observations. GRAVITY+ will also implement one new laser guide star on each of UT1-3, and will make use of one of the lasers currently installed on UT4, to observe fainter and more distant objects than currently possible.

The upgrades to GRAVITY+ are being implemented incrementally, to ensure that there are limited disruptions to the scientific operations of the VLTI. This also allows for astronomers to continually test the performance of GRAVITY+ as it comes online. The full set of upgrades is anticipated to be completed in 2025. The new features will benefit all present and future VLTI instruments and the scientists who use them.

References

• Abuter, R., Allouche, F., Amorim, A. et al. A dynamical measure of the black hole mass in a quasar 11 billion years ago. Nature (2024). DOI : https://doi.org/10.1038/s41586-024-07053-4

Local scientific contact

• Jean-Baptiste Lebouquin - Researcher-Professor | IPAG

This article was initially published by ESO.