August 24, 2011
Looking Into The Eyes Of The Virgin
ESO´s Very Large Telescope has taken a striking image of a beautiful yet peculiar pair of galaxies nicknamed The Eyes. The larger of these, NGC 4438, was once a spiral galaxy but has become badly deformed by collisions with other galaxies in the last few hundred million years. This picture is the first to come out of ESO´s Cosmic Gems program, an initiative in which ESO has granted dedicated observing time for outreach purposes.
But although the centers of these two galaxies look similar, their outskirts could not be more different. The galaxy in the lower right, known as NGC 4435, is compact and seems to be almost devoid of gas and dust. In contrast, in the large galaxy in the upper left (NGC 4438) a lane of obscuring dust is visible just below its nucleus, young stars can be seen left of its center, and gas extends at least up to the edges of the image.
The contents of NGC 4438 have been stripped out by a violent process: a collision with another galaxy. This clash has distorted the galaxy´s spiral shape, much as could happen to the Milky Way when it collides with its neighboring galaxy Andromeda in three or four billion years.
NGC 4435 could be the culprit. Some astronomers believe that the damage caused to NGC 4438 resulted from an approach between the two galaxies to within about 16 000 light-years that happened some 100 million years ago. But while the larger galaxy was damaged, the smaller one was significantly more affected by the collision. Gravitational tides from this clash are probably responsible for ripping away the contents of NGC 4438, and for reducing NGC 4435´s mass and removing most of its gas and dust.
Another possibility is that the giant elliptical galaxy Messier 86, further away from The Eyes and not visible in this image, was responsible for the damage caused to NGC 4438. Recent observations have found filaments of ionized hydrogen gas connecting the two large galaxies, indicating that they may have collided in the past.
The elliptical galaxy Messier 86 and The Eyes belong to the Virgo Cluster, a very rich grouping of galaxies. In such close quarters, galaxy collisions are fairly frequent, so perhaps NGC 4438 suffered from encounters with both NGC 4435 and Messier 86.
This picture is the first to be produced as part of the ESO Cosmic Gems program. This is a new initiative to produce astronomical images for educational and public outreach purposes. The program mainly makes use of time when the sky conditions are not suitable for science observations to take pictures of interesting, intriguing or visually attractive objects. The data are also made available to professional astronomers through ESO´s science archive.
In this case, although there were some clouds, the atmosphere was exceptionally stable, which allowed very sharp details to be revealed in this image taken using the VLT´s FORS2  instrument. Light passing through two different filters was used: red (colored red) and green-yellow (colored blue), and the exposure times were 1800 seconds and 1980 seconds, respectively.
 FORS2 is the visual and near ultraviolet FOcal Reducer and low dispersion Spectrograph for the VLT. It is installed on the VLT´s Unit Telescope 1.
ESO, the European Southern Observatory, is the foremost intergovernmental astronomy organization in Europe and the world´s most productive astronomical observatory. It is supported by 15 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious program focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organizing cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world´s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world´s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning a 40-meter-class European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world´s biggest eye on the sky”.
Image Caption: This striking image, taken with the FORS2 instrument on the Very Large Telescope, shows a beautiful yet peculiar pair of galaxies, NGC 4438 and NGC 4435, nicknamed The Eyes. The larger of these, at the top of the picture, NGC 4438, is thought to have once been a spiral galaxy that was strongly deformed by collisions in the relatively recent past. The two galaxies belong to the Virgo Cluster and are about 50 million light-years away. Credit: ESO/Gems project
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