Press Release

Remote Observations with the ESO NTT from Trieste

How to Stay in Italy, Look Through a Telescope in Chile and Observe a Cosmic Mirage 5000 Million Light-years Away

13 August 1992

Italian astronomers, working from the Astronomical Observatory in Trieste, have performed remote observations with the ESO 3.5 metre New Technology Telescope (NTT) at La Silla, Chile. This is the first time ever that such observations have been made directly from an astronomical institute in one of the ESO member countries. Quite unexpectedly, a "cosmic mirage", that is a gravitational lens in a distant cluster of galaxies, was found during these observations.

Extending remote observing to Trieste

During three nights in June 1992, very successful remote observations were carried out with the ESO New Technology Telescope from Trieste, Italy, via a complex data link. The experimental system was so reliable that eight astronomers in Trieste were able to observe during almost 30 hours and to obtain many valuable data.

The Italian astronomers had complete control of the telescope, without any intervention by ESO staff at La Silla. They received back the complete observational data via the link, immediately after each exposure.

The successful test of this new system, also referred to as "second level remote observing", implies that, sometime in the future, scientists at astronomical institutes in the ESO member states will have the possibility to remain at their home institute while observing with ESO telescopes in Chile. The present experiment was carried out with a new remote control system which was developed in a close collaboration between ESO and the Trieste Observatory. It involved control computers in Trieste, a leased data line from Trieste to the ESO Headquarters in Garching and from there the permanent satellite link which connects ESO-Europe with the ESO Observatory at La Silla in Chile, more than 12,000 km away.

Since 1987, remote observations are regularly made from Garching with two other telescopes at La Silla [1]. The NTT can also be remotely controlled from Garching by means of a new system, which from the users' point of view is identical to that now tested from Trieste.

ESO now plans to perform tests like the one done in Trieste with other European institutes. Further into the future, second-level remote observing from individual European astronomical institutes will allow very efficient use of the ESO 16-metre Very Large Telescope (VLT) [2], now under construction. When ready on the Paranal mountain in Chile in 1999, it will be the largest and most powerful optical telescope in the world.

A cosmic mirage

Although the observations with the NTT from Trieste primarily served to test the technical reliability of the remote control system, everything went so well that many "real" observations were also made by a team of Italian astronomers there.

Among the highlights were the observations of a distant cluster of galaxies, known as EMSS 2137-23 and situated in the southern constellation of Capricornus. This cluster emits rather strong X-ray radiation, and spectroscopic observations have shown that it moves away from us with a velocity of about 80,000 km/sec. This velocity reflects the expansion of the Universe and corresponds to a distance of about 5,000 million light-years. In other words, the light recorded by the NTT was emitted by the galaxies in this cluster about 5,000 million years ago, that is at about the same time as our solar system was born.

Massimo Ramella and Mario Nonino from the Trieste Observatory, together with Dan Fabricant of the Center for Astrophysics in Cambridge, Mass., U.S.A. had earlier observed the spectra of about 50 galaxies in EMSS 2137-23 and mea¬sured their individual velocities. Using the opportunity to work with the NTT, by many considered the best optical telescope in the world, the two Italian astronomers decided to have another look at this cluster of galaxies from the control room in Trieste. They sent the commands which made the NTT point in this direction and made several exposures which were immediately sent back to Trieste In digital form.

To their great surprise, the astronomers noted a strange, curved structure, an "arc", just north of the central region of the cluster. A reproduction of the NTT image accompanies this Press Release.

This feature could be readily identified as a so-called "gravitational lens", i.e. the image of a very distant galaxy, distorted and magnified into a "cosmic mirage" by the strong gravitational field in the EMSS 2137-23 cluster [3].

A closer inspection revealed that the arc consists of two sections and that several other possible "arclets" are present in this field. Together with the available, detailed optical and X-ray observations, the exact geometrical arrangement of the arcs yields the gravitational field and therefore the distribution of visible and invisible ("dark") matter in the EMSS 2137-23 cluster.

The main arc is bright enough (magnitude R = 21.5) that spectroscopic observations will be possible. They are now being planned and will allow to determine the distance and nature of the very distant galaxy, so faint that it would have been completely impossible to observe it without the present amplification effect.

When the Trieste astronomers informed other astronomers about the new gravitational lens, they learned that it had already been observed with the NTT in 1991 by another group of scientists, led by French astronomer Bernard Fort! The 1991 observations were made from the NTT control room at La Silla and have recently been submitted for publication.

It bodes well for the future that the first ever "second-level" remote observations went so well and were able to produce astronomical observations of superior quality!


[1] See eso8714

[2] The most recent ESO Press Releases about the VLT are eso9108, eso9201, and eso9204.

[3] See also eso8715 and eso9109.

More information

A full report about the technical and scientific aspects of this experience will appear in the September issue of ESO's house journal The Messenger.


Richard West
Garching, Germany

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About the Release

Release No.:eso9211
Legacy ID:PR 06/92
Name:EMSS 2137–23, Gravitational Microlensing
Type:Unspecified : Technology
Facility:New Technology Telescope


Gravitational lens in EMSS 2137–23
Gravitational lens in EMSS 2137–23