Telescopes Team to Make Sharpest Observation Ever

Three telescopes spaced thousands of miles apart were linked together to capture the sharpest direct observation of the center of a distant galaxy: the bright quasar 3C 279, which has a supermassive black hole at its core. The observation represents a milestone toward imaging supermassive black holes and the regions around them.

Astronomers connected Atacama Pathfinder Experiment (APEX) in Chile to the Submillimeter Array (SMA) in Hawaii and the Submillimeter Telescope (SMT) in Arizona using a technique known as very long baseline interferometry (VLBI). Larger telescopes can make sharper observations, and interferometry allows multiple telescopes to function as a single telescope as large as the separation — or baseline — between them. Using VLBI, the sharpest observations can be achieved by positioning the telescopes as far apart as possible.

For their quasar observations, the team members 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 to the network was crucial because it contributed the longest baselines. The scientists were able to make the sharpest direct observation ever of the center of quasar 3C 279, which has a black hole with a mass about 1 billion times that of the sun; the quasar is so far from Earth that its light takes more than 5 billion years to reach us.

This is an artist’s impression of the quasar 3C 279. For the first time, astronomers connected the Atacama Pathfinder Experiment (APEX) in Chile to the Submillimeter Array (SMA) in Hawaii and the Submillimeter Telescope (SMT) in Arizona to make the sharpest observations ever of the center of a distant galaxy: the bright quasar 3C 279. Quasars are the very bright centers of distant galaxies and are powered by supermassive black holes. This quasar’s black hole has a mass about 1 billion times that of the sun, and it is so far from Earth that its light takes more than 5 billion years to reach us. The team was able to probe scales of less than a light-year across the quasar — a remarkable achievement for a target that is billions of light-years away. (Image: ESO/M. Kornmesser)

The observations were made in radio waves with a wavelength of 1.3 mm. This is the first time that observations at a wavelength this short have been achieved 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 2 million times sharper than human vision. This represents the capacity to probe scales of less than a light-year across the quasar — a remarkable achievement for a target that is billions of light-years away.

In the future, the astronomers plan to connect even more telescopes to create a so-called Event Horizon Telescope, which should be able to image the shadow of the supermassive black hole in the center of our Milky Way galaxy, as well as black holes in surrounding 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.

This experiment marks the first time that APEX has taken part in VLBI observations. It is the culmination of three years of work at its high-altitude site on the 5000-m plateau of Chajnantor in the Chilean Andes. Scientists from Germany and Sweden installed new digital data acquisition systems, a very precise atomic clock and pressurized data recorders capable of recording 4 Gb/s for many hours under challenging environmental conditions. The data was shipped to Germany on hard drives and processed at the Max Planck Institute for Radio Astronomy in Bonn.

APEX shares its location with the new Atacama Large Millimeter/Submillimeter Array (ALMA) telescope, which will consist of 54 dishes with the same 12-m diameter as APEX, plus 12 smaller dishes with a 7-m diameter. The new telescope is currently under construction, but the possibility of connecting it to the network is being studied. With ALMA’s large dishes, the observations could reach 10 times better sensitivity than these initial tests. This would put the shadow of the Milky Way's supermassive black hole within reach for future observations.

APEX is a collaboration between the Max Planck Institute for Radio Astronomy, the Onsala Space Observatory and the European Southern Observatory (ESO). It is operated by ESO.

For more information, visit: www.eso.org