Astronomers using three telescopes – APEX in Chile, SMA in Hawaii, and the Submillimeter Telescope in Arizona – have observed the heart of a distant quasar with unprecedented sharpness, two million times finer than human vision.
The team was able to make the sharpest direct observation ever, of the center of a distant galaxy, the bright quasar 3C 279, which contains a supermassive black hole with a mass about one billion times that of the Sun, and is so far from Earth that its light has taken more than 5 billion years to reach us.
The telescopes were linked using a technique known as Very Long Baseline Interferometry (VLBI). Larger telescopes can make sharper observations, and interferometry allows multiple telescopes to act like a single telescope as large as the separation – or “baseline” – between them. Using VLBI, the sharpest observations can be achieved by making the separation between telescopes as large as possible.
For their quasar observations, the team used the three telescopes to create an interferometer with transcontinental baseline lengths of 9447 km from Chile to Hawaii, 7174 km from Chile to Arizona and 4627 km from Arizona to Hawaii. Connecting APEX in Chile to the network was crucial, as it contributed the longest baselines.
The observations were made in radio waves with a wavelength of 1.3 mm. This is the first time observations at a wavelength as short as this have been made using such long baselines. The observations achieved a sharpness, or angular resolution, of just 28 microarcseconds – about 8 billionths of a degree. This represents the ability to distinguish details an amazing two million times sharper than human vision. Observations this sharp can probe scales of less than a light-year across the quasar – a remarkable achievement for a target that is billions of light-years away.
The observations represent a new milestone towards imaging supermassive black holes and the regions around them. In future it is planned to connect even more telescopes in this way to create the so-called Event Horizon Telescope.
The Event Horizon Telescope will be able to image the shadow of the supermassive black hole in the center of our Milky Way galaxy, as well as others in nearby galaxies. The shadow – a dark region seen against a brighter background – is caused by the bending of light by the black hole, and would be the first direct observational evidence for the existence of a black hole’s event horizon, the boundary from within which not even light can escape.