Quasar 3C 279 Shown in Unprecedented Sharpness

Quasar 3C 279 Artist’s Impression

This is an artist’s impression of the quasar 3C 279. Astronomers connected the Atacama Pathfinder Experiment (APEX), in Chile, to the Submillimeter Array (SMA) in Hawaii and the Submillimeter Telescope (SMT) in Arizona for the first time, 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 that are powered by supermassive black holes. This quasar contains a 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 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. Credit: ESO/M. Kornmesser

Using three telescopes (Atacama Pathfinder Experiment (APEX) in Chile, Submillimeter Array (SMA) in Hawaii, and the Submillimeter Telescope (SMT) in Arizona) to create an interferometer, scientists were able to observe the heart of a distant quasar 3C 279 with unprecedented sharpness.

An international team led by scientists from the Max Planck Institute for Radio Astronomy has succeeded in observing the heart of a distant quasar with unprecedented sharpness, or angular resolution. The observations, made by connecting radio telescopes on different continents, are a crucial step towards a dramatic scientific goal: to depict the supermassive black hole at the center of our own galaxy and also the central black holes in other nearby galaxies.

On May 7, 2012, astronomers connected radio telescopes in Chile, Hawaii, and Arizona for the first time using the technique of Very Long Baseline Interferometry (VLBI). They were able to make the sharpest observation ever of the center of a distant galaxy, the bright quasar 3C 279, which contains a supermassive black hole with a mass of as much as a billion times the mass of the sun.

The observations show that the quasar’s radio signals come from within a region only 28 micro-arc seconds in diameter, corresponding to just 1 light-year within the nucleus of this quasar. It is quite remarkable to reach a resolution of only half a light-year when the quasar is situated at a distance of more than 5 billion light-years from Earth.

The observations were made with radio waves with a wavelength of 1.3 mm (corresponding to a frequency of 230 GHz), using three telescopes which had never before been connected together in this way. The Atacama Pathfinder Experiment (APEX), a radio telescope of 12-meter (39-foot) diameter at 5100 m (16,700 ft) altitude in the Chilean Atacama desert, was combined in interferometry mode with the Submillimeter Telescope (SMT) at 3100 m (10,200 ft) atop Mount Graham in Arizona (USA) and the Submillimeter Array (SMA), located at 4100 m (13,500 ft) altitude on Mauna Kea, Hawaii (USA).

Astronomers connected the Atacama Pathfinder Experiment (APEX), in Chile, to the Submillimeter Array (SMA) in Hawaii, USA, and the Submillimeter Telescope (SMT) in Arizona for the first time, to make the sharpest observation ever of the center of a distant galaxy, the bright quasar 3C 279. Credit: ESO/L. Calçada

The observations represent a new milestone in depicting supermassive black holes and the regions around them. In the future, it is planned to go further and connect more telescopes in this way to create the so-called ‘Event Horizon Telescope’ (EHT). The Event Horizon Telescope will be able to depict the shadow of the super-massive black hole in the center of our Milky Way, as well as others in nearby galaxies.

The shadow is the result of gravitation redshift around the outer horizon of a black hole. In theory, it should be possible to directly observe this dark area. However, the size of the shadow on the sky is in the region of micro-arc seconds, i.e. one-millionth of an arc-second, an angle which cannot be observed with the detail resolution of a regular telescope. (As a reference: the apparent diameter of the full moon is about 1800 micro-arc seconds on the sky).

Using VLBI, the sharpest images 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 9,447 km (5,870 mi) from Chile to Hawaii, 7,174 km (4,458 mi) from Chile to Arizona, and 4,627 km (2,875 mi) from Arizona to Hawaii.

To synchronize the measurements, each telescope was equipped with an atomic clock. After observations, 4 terabytes of data recorded on large hard disks at each station were shipped to Germany and processed at the Max Planck Institute for Radio Astronomy in Bonn.

The bright jet from the quasar could be detected on all three baselines, with an angular resolution that corresponds to a telescope magnification of about 2.1 million. That is the equivalent of being able to resolve a tennis ball on the surface of the Moon. On Earth this would allow one to read a Newspaper in Los Angeles from Frankfurt.

Connecting APEX in Chile to the network was crucial in achieving such sharp observations at millimeter wavelengths, marking an important step towards realizing an interferometer stretching across the globe.

The experiment is the culmination of three years of hard work at high altitude making APEX ready for VLBI observations. Scientists from Germany and Sweden installed new digital data acquisition systems, a precise atomic clock, and pressurized data recorders capable of recording 4 gigabits per second for many hours.

The addition of APEX is also important for another reason. It shares its location and technology with the new telescope ALMA (Atacama Large Millimeter/submillimeter Array) which will finally consist of 66 antennas, each similar to APEX. With ALMA connected to the network, the observations could achieve 10 times better sensitivity than today. That puts the shadow of the Milky Way’s supermassive black hole within reach for future observations.

2 Comments on "Quasar 3C 279 Shown in Unprecedented Sharpness"

  1. Okaaay….so where is the photo? All they have is an artists impression.

  2. You have an error above: the Moon is 1800 arcsec across, thus 1800e6 micro-arcsec.

    Otherwise, nice article!

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