|PRI (MPIfR) 07/2012 (3)||Press Release||July 18, 2012|
An international team of astronomers led by scientists from Max-Planck-Institut für Radioastronomie, Bonn, Germany, has observed the heart of a distant quasar with unprecedented sharpness, or angular resolution. The observations, made by connecting radio telescopes on different continents, is a crucial step towards a dramatic scientific goal: to image the supermassive black hole at the centre of our own galaxy and also the central black holes in other nearby galaxies.
Artist's impression of the central region of the quasar 3C 279.
Positions of the Telescopes in the 1.3 mm VLBI experiment: The baseline length from Chile (APEX) to Hawaii (SMA) is 9447 km, from Chile to Arizona (SMT) 7174 km, and from Arizona to Hawaii 4627 km.
Credit: ESO/M. Kornmesser (Fig. 1a); ESO/L. Calçada (Fig. 1b). (Click images for higher resolution).
On 7 May 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 centre of a distant galaxy, the bright quasar 3C 279, which contains a supermassive black hole with the 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-arcseconds in diameter, corresponding to just 0.5 light year within the nucleus of this quasar. It is quite remarkable, to reach less than a light year resolution in the quasar's 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 m diameter at 5100 m altitude in the Chilean Atacama desert, was combined in interferometric mode with the Submillimeter Telescope (SMT) at 3100 m atop Mount Graham in Arizona (USA) and the Submillimeter Array (SMA), located at 4100 m altitude on Mauna Kea, Hawaii (USA).
The observations represent a new milestone towards imaging supermassive black holes and the regions around them. In 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 image the shadow of the super-massive black hole in the center of our Milky Way, as well as others in nearby galaxies.
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 intercontinental baseline lengths of 9447 km from Chile to Hawaii, 7174 km from Chile to Arizona and 4627 km 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 millimetre wavelengths, and marks an important step towards realizing an interferometer stretching across the globe.
The experiment is the culmination of three years hard work at high altitude making APEX ready for VLBI observations. Scientists from Germany and Sweden have installed new digital data acquisition systems, a very 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.
Radio Telescopes participating in the 1.3 mm VLBI experiment: 10 m Submillimeter Telescope (SMT, upper left), 12 m APEX telescope (upper right), Submillimeter Array (SMA, bottom).
Credit: University of Arizona/David Harvey (Fig. 2a), ESO/B. Tafreshi (twanight.org) (Fig. 2b), SMA/Jonathan Weintraub (Fig. 2c). (Click images for higher resolution).
The Atacama Pathfinder Experiment (APEX) is a collaboration between Max-Planck-Institut für Radioastronomie (MPIfR), Onsala Space Observatory (OSO), and the European Southern Observatory (ESO) to construct and operate a modified ALMA prototype antenna as a single dish on the high altitude site of Llano Chajnantor. The telescope was manufactured by VERTEX Antennentechnik in Duisburg, Germany. Operation of APEX at Chajnantor is entrusted to ESO.
The Submillimeter Telescope (SMT, the former "Heinrich-Hertz-Teleskop") of 10 m diameter on top of Mt. Graham, Arizona, is operated by the Arizona Radio Observatory (ARO) in Tucson, Arizona (USA).
The Submillimeter Array (SMA) on top of Mauna Kea, Hawaii, consisting of 8 dishes of 6 m diameter each, is operated by the Smithsonian Astrophysical Observatory (USA) and the Academia Sinica Institute of Astronomy and Astrophysics (Taiwan).
The Event Horizon Telescope project (EHT) is coordinated by the MIT Haystack Observatory (USA).
Very Long Baseline Interferometry (VLBI): For terrestrial arrays the diameter of the earth sets an upper limit to the station separation measured in kilometers. However it is the separation between stations measured in radio wavelengths which is material, so by pushing VLBI towards shorter wavelengths the resolution on terrestrial baselines improves. This is technically difficult for many reasons, including that at about 1 mm wavelength the humidity in the lower atmosphere attenuates the already very faint cosmic radio signals. Therefore one must use a new generation of radio telescopes which are located at very high elevations where atmospheric humidity and thus absorption is small.
To equip APEX for VLBI operation, the new acquisition systems at APEX allow wide bandwidth recording (up to 4 Gbit/s) of faint millimeter-wave signals. These systems were developed in parallel in the USA (MIT-Haystack observatory) and in Europe (MPIfR, INAF/Noto and HAT-Lab). A hydrogen maser time standard (T4Science) was installed as the very precise atomic clock. The SMT and SMA had already been equipped similarly for VLBI.
Zwei Millionen mal schärfer als das menschliche Auge: APEX beteiligt sich an Quasarbeobachtungen , eso1229de - Organisatorische Pressemitteilung, 18. Juli 2012 (in German).
APEX takes part in sharpest observation ever , eso1229 - Organisation Release, July 18, 2012 (in English).
Ein Teleskop mit zweimillionenfacher Vergrößerung , MPG Pressemitteilung, 18. Juli 2012 (in German).
A magnification of two million , MPG Press Release, July 18, 2012 (in English).
APEX deltar i skarpaste observationerna någonsin , Chalmers Onsala Pressemitteilung, 23. Juli 2012 (in Swedish).
APEX takes part in sharpest observation ever
, Chalmers Onsala Pressemitteilung, 23. Juli 2012 (in English).
Max-Planck-Institute für Radioastronomie (MPIfR), Bonn, Germany
Atacama Pathfinder EXperiment (APEX)
Onsala Space Observatory (OSO), Sweden
Submillimeter Telescope (SMT), Arizona Radio Obserevatory (ARO)
Submillimeter Array (SMA), Smithsonian Astrophysical Observatory, USA
Haystack Observatory, Massachussetts Inmstitute of Technology (MIT), USA
Digital BaseBand Converter Project, INAF, Noto, Italy
European Southern Observatory (ESO), Atacama Large Millimeter/submillimeter Array (ALMA)
Event Horizon Telescope (EHT)
Michael Lindquist, Onsala Space Observatory (OSO): E-mail: michael.lindqvist (at) chalmers.se
Lucy Ziurys, Arizona Radio Observatory (ARO): E-mail: lziurys (at) as.arizona.edu
Jonathan Weintraub, Submillimeter Array (SMA): E-mail: jweintroub (at) cfa.harvard.edu
Shep Doeleman, Haystack Observatory, Event Horizon Telescope (EHT): E-mail: dole (at) haystack.mit.edu
Douglas Pierce-Price, European Southern Observatory (ESO):
E-mail: dpiercep (at) eso.org
Dr. Alan Roy,
APEX VLBI Project Lead,
Max-Planck-Institut für Radioastronomie.
E-mail: aroy (at) mpifr-bonn.mpg.de
Dr. Thomas Krichbaum,
APEX VLBI Project Scientist,
Max-Planck-Institut für Radioastronomie.
E-mail: tkrichbaum (at) mpifr-bonn.mpg.de
Prof. Dr. Anton Zensus,
Director and Head of Research Group "Radio Astronomy / VLBI",
Max-Planck-Institut für Radioastronomie, Bonn.
E-mail: azensus (at) mpifr-bonn.mpg.de
Dr. Norbert Junkes,
Press and Public Outreach,
Max-Planck-Institut für Radioastronomie.
E-mail: njunkes (at) mpifr-bonn.mpg.de