Searching for smoke after the fire

At the centre of this Picture of the Week shows are the three telescopes of the BlackGEM array, located in ESO’s La Silla Observatory. BlackGEM is looking for the most intense events in the Universe: the origins of gravitational waves.

Different mechanisms can produce these ripples in space-time. For instance, two neutron stars — the collapsed cores of massive stars — can merge in violent spirals, spinning thousands of times per second and emitting powerful signals. In the chaos, precious metals are born into the Universe and colossal magnetic fields cause immense but short bursts of gamma rays.

Back on Earth, the LIGO and Virgo gravitational wave detectors can only roughly estimate where these waves may originate. Enter BlackGEM, which quickly scours the target area of the sky with incredible sensitivity to spot the optical light emitted in these events. This allows astronomers to pinpoint their location and study them in more detail with larger telescopes.

But there is still much to learn about these events. Merging black holes, for example, do not release electromagnetic waves, but would also be visible to BlackGEM when sat in dense regions where they illuminate the matter around them. BlackGEM will therefore be vital to make the first optical observations of these mergers, and establish the environments black holes may form in.