How big is the Eagle Nebula

Germ cells of star formation in the Eagle Nebula

Messier 16 (or M16 for short), also known as the Eagle Nebula, is located in the constellation Serpens (the serpent). With the infrared instrument ISAAC on the 8.2-meter Antu telescope at the VLT, European astronomers were able to study the Eagle Nebula at near-infrared wavelengths. The ISAAC infrared images cover a field of view of 9.1 x 9.1 arc minutes in three broadband filters - this corresponds to 17 x 17 light years at a distance of about 6500 light years from the Eagle Nebula - and are sensitive enough to detect young stars of all masses with an accuracy of up to 0.35 arcseconds.

The large field image of M16 shows that a lot is happening in this region of the sky. The first impression you get is that of an incredible number of stars. Stars that are shown in blue b in the infrared image are either members of the young star cluster NGC 6611, whose massive stars are concentrated in the upper right of the image (in the northwest), or foreground stars that happen to be in the line of sight towards M16.

Most of the stars are fainter and appear yellowish. These are normal stars that stand behind M16 in the direction of the galactic center and that shine through the molecular clouds from which NGC 6611 was formed. You can also see some reddish stars: They are either very young and still embedded in clouds of dust and gas or bright background stars that shine through these clouds.

The image is a false color representation of a mosaic of the Eagle Nebula (Messier 16), based on 144 individual images with 1024 x 1024 pixels, which were taken with the infrared instrument ISAAC on ESO's Very Large Telescope (VLT) at the Paranal Observatory. In the center of the picture are the so-called "pillars of creation". The large-field infrared image shows not only the central three pillars, but also other similar pillars in the same star formation region. The bright and hot blue stars in NGC 6611 illuminate these pillars.

Technical details: The data for the image was taken between April 8, 2001 and May 8, 2001. The image is a 4x4 mosaic, for which a series of images in the near-infrared bands Js - (centered on a wavelength of 1.24 µm), H (1.65 µm) and Ks (2.16 µm) were made at each position. North is up and east is left. The total exposure times were 1200, 300 and 300 seconds respectively within the central 4.5 x 4.5 arc minutes and 200, 50 and 50 seconds in the outer areas. The FWHM (full width at half maximum), a measure of the quality of the image, was excellent, at 0.38, 0.36 and 0.33 arc seconds. In the center of the image, point sources up to a limit size of 22.6, 21.3 and 20.4 magnitudes can be detected at the 3-sigma level. According to this, a one million year old object with 0.075 solar masses at the border between stars and brown dwarfs in M16 can also be detected with an attenuation of 15, 20, and 30 magnitudes.

After removing instrumental effects and the bright infrared background, all recordings from the same filter band were carefully rectified and seamlessly arranged in a mosaic. The three monochromatic mosaics were then scaled according to the cubes of their intensities in order to reduce the enormous dynamic range and to reinforce the weaker nebula structures. The mosaics were then combined into the false color image in such a way that Js is shown in blue, H in green and Ks in red.

Proof of origin:

ESO / M.McCaughrean & M.Andersen (AIP)