VLT stares into the eyes
by Louisa Connolly
for ASTRONOMY NOW
Posted: 24 August 2011
The peculiar pair of galaxies nicknamed The Eyes in the constellation of Virgo have been captured by the European Southern Observatory’s (ESO) ground-based Very Large Telescope (VLT). It is the first image to be produced by ESO’s Cosmic Gems outreach programme.
The image shows clear details of the galaxy NGC 4435, found in the lower right of the image, and the disturbed spiral galaxy NGC 4438 located in the upper left. The smaller of the two, NGC 4435, appears to be lacking gas and dust and is compact, highly contrasting with NGC 4438, which shows an obscuring dust lane passing just below its nucleus, with gas extending to the upper left of the image. Young stars are also clearly visible to the left of the galaxy.
The Eyes in Virgo, a remarkable image of this peculiar pair of galaxies in Virgo, taken by the ESO’s VLT FORS2 instrument. The Galaxy shown in the top left, NGC 4438, is a distorted spiral galaxy, deformed after a number of collisions with other galaxies in the Virgo cluster. Two filters were used to compose the image: red (1800 seconds exposure), and green-yellow (1900 second exposure). Image: ESO/Gems project.
The nickname The Eyes derives from the noticeable similarity of the luminous white oval shaped cores both galaxies have, which appear to resemble two glistening eyes against the dark back-drop. This beautiful pair of galaxies is situated in the constellation Virgo, 50 million light years away, and with around 100,000 light years of space between them, it is believed by some astronomers that a collision may have occurred between them. It has been suggested that the galaxies came within 16,000 light years of each other approximately 100 million years ago, resulting in strong gravitational tides stripping away the contents and distorting the shape of NGC 4438 and significantly reducing the mass of gas and dust from NGC 4435. The distortion of the large spiral galaxy could be replicated in three to four billion years time in our own Galaxy when the Milky Way and its neighbouring galaxy Andromeda collide.
Virgo is well known for containing a mixture of elliptical and spiral galaxies. One giant elliptical galaxy in particular – Messier 86 – has also become a possible culprit responsible for the deformation of NGC 4438. Messier 86 is not visible in this particular image and lies further away from The Eyes. However, recent observations using H-alpha imaging with the Mayall four-metre telescope on Kitt Peak, together with spectroscopic measurements with the WIYN telescope, found a significant amount of filaments of ionized hydrogen gas, linking the two galaxies thus strongly suggesting a previous collision between them.
Mark Westmoquette, an astronomer at ESO says: "It is likely that all three galaxies are in the process of interacting, although the timescales and order of interaction will be different and are as yet unknown. The only way to determine which scenario has been dominant in shaping NGC 4438 is through detailed computer modelling of the interaction of the galaxies."
The ESO Cosmic Gems Programme makes use of small amounts of observing time when sky conditions are unsuitable to take accurate images of the ESO’s main science targets, but is still able to take some images. The main objective is to produce astronomical images for educational and public outreach purposes as well as providing data for professional astronomers through ESO’s science archive.
This first image has proved a success and Westmoquette's opinion is widely shared: "I am really pleased by the quality of this first image. It is exceptionally sharp, despite being taken on a partly cloudy night. We already have some other spectacular images that we will publish over the next few months and are hoping for more in the future."Find out more about ESO’s Cosmic Gems Programme here.