Sagittarius A*: the invisible centre

Reading the invisible

What draws me to Sagittarius A* is not only its darkness, but the way we have learned to recognise it. We watch what moves around it. The stars become clues; their paths turn an apparently empty place into a measurable presence.

Stars that reveal the centre

Sagittarius A* lies at our galaxy’s centre. Decades of stellar-orbit measurements reveal an enormous mass packed into a very small region. One particularly useful star, S2, completes an orbit in roughly 16 years. Its motion lets astronomers test gravity close to a supermassive black hole.

Closer to the edge

In 2018, GRAVITY observations tracked infrared flares consistent with hot gas orbiting very close to Sagittarius A*. The interpretation involved speeds around 30% of the speed of light. The smooth close-up in ESO’s zoom film is a simulation of this extreme environment—not a camera travelling beside the gas.

An image, and what it means

In 2022, the Event Horizon Telescope released its first image of Sagittarius A*. The bright structure comes from surrounding gas; the dark centre is its shadow, not a photograph of the interior. This milestone is separate from the earlier ESO visualisation shown here.

For me, this is the beauty of astronomy: not simply collecting light, but learning what light and motion can tell us about the unseen.