Dormant massive black hole spotted in the Milky Way

Colleagues from the Wide-Field Astronomy Unit involved in Gaia space telescope discovery, which challenges our understanding of how massive stars develop and evolve.

Gaia discovery

Scientists working on data from the European Space Agency’s Gaia space telescope have uncovered a ‘sleeping’ giant: a large black hole, with a mass of nearly 33 times the mass of the Sun, hiding in the constellation Aquila, less than 2000 light-years from Earth. 

This is the first time a black hole of stellar origin this big has been spotted so close to home, which will enable detailed follow up by the astronomical community.

The discovery challenges our understanding of how massive stars develop and evolve. 

Black holes

Matter in a black hole is so densely packed that nothing can escape its immense gravitational pull, not even light. The great majority of stellar-mass black holes that we know of are gobbling up matter from a nearby star companion. The captured material falls onto the collapsed object at high speed, becoming extremely hot and releasing X-rays. These systems belong to a family of celestial objects named X-ray binaries.  

When a black hole does not have a companion close enough to steal matter from, it does not generate any light and is extremely difficult to spot. These black holes are called ‘dormant’.

Wide-Field Astronomy Unit

The Gaia team at the Institute for Astronomy’s Wide-Field Astronomy Unit are excited to have contributed to this discovery of a large black-hole within our Galaxy. The team have been deeply involved in the development and operation of the mission since 2007, with work falling into three main strands, all of which have played a part in this discovery.

Much of their effort is devoted to the detailed characterisation of the spacecraft, telescopes and detectors that is required to achieve the extreme precision and reliability delivered by the mission. For instance, models of the Point Spread Function (the 'prescription' of the telescope optics) are provided by the team. These calibrations are then used to obtain position and brightness measurements for each of the star observations used in Gaia Data Release 4, of which there are around 2 trillion.

The team also work on the Big Data tools required by the wider network of Gaia colleagues and scientific community in order to explore the Milky Way.

This black-hole discovery is based on the Wide-Field Astronomy Unit’s astrometric position measurements; improvements since the previous Data Release 3 have allowed the characteristic wobble to be uncovered.

Future plans

This dormant black hole is the third found with Gaia and was aptly named ‘Gaia BH3’. Its discovery is exciting because of the mass of the object: much remains to be investigated on the origin of black holes as large as Gaia BH3.

It is encouraging to see the efforts from the Wide-Field Astronomy Unit and wider collaboration come to fruition, and more will be learned as the mission continues.