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24 August 2011
VLT looks 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 programme, an initiative in which ESO has granted dedicated observing time for outreach purposes.
The Eyes are about 50 million light-years away in the constellation of Virgo (The Virgin) and are some 100 000 light-years apart. The nickname comes from the apparent similarity between the cores of this pair of galaxies — two white ovals that resemble a pair of eyes glowing in the dark when seen in a moderate-sized telescope.
But although the centres 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 centre, and gas extends at least up to the edges of the image.
The Eyes in the constellation of Virgo
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 neighbouring 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 ionised 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 programme. This is a new initiative to produce astronomical images for educational and public outreach purposes. The programme 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.
Zooming in on The Eyes
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 [1] instrument. Light passing through two different filters was used: red (coloured red) and green-yellow (coloured blue), and the exposure times were 1800 seconds and 1980 seconds, respectively.
Notes:
[1] 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.
More information:
ESO, the European Southern Observatory, is the foremost intergovernmental astronomy organisation 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 programme 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 organising 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-metre-class European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.
Links:
ESO’s Cosmic Gems Programme: http://www.eso.org/public/outreach/gems.html
Photos of the VLT: http://www.eso.org/public/images/archive/category/paranal/
Images, Text, Credits: ESO / Gems project / IAU and Sky & Telescope / Richard Hook / Olivier R. Hainaut / Lars Lindberg Christensen / Video: ESO / A. Fujii and Digitized Sky Survey 2. Music: John Dyson (from the album Moonwind).
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