Friday, 19 June 2009

Herschel’s daring test: a glimpse of things to come

19 June 2009
Herschel opened its 'eyes' on 14 June and the Photoconductor Array Camera and Spectrometer obtained images of M51, ‘the whirlpool galaxy’ for a first test observation. Scientists obtained images in three colours which clearly demonstrate the superiority of Herschel, the largest infrared space telescope ever flown.

This image shows the famous ‘whirlpool galaxy’, first observed by Charles Messier in 1773, who provided the designation Messier 51 (M51). This spiral galaxy lies relatively nearby, about 35 million light-years away, in the constellation Canes Venatici. M51 was the first galaxy discovered to harbour a spiral structure.

The image is a composite of three observations taken at 70, 100 and 160 microns, taken by Herschel’s Photoconductor Array Camera and Spectrometer (PACS) on 14 and 15 June, immediately after the satellite’s cryocover was opened on 14 June.

Herschel, launched only a month ago, is still being commissioned and the first images from its instruments were planned to arrive only in a few weeks. But engineers and scientists were challenged to try to plan and execute daring test observations as part of a ‘sneak preview’ immediately after the cryocover was opened. The objective was to produce a very early image that gives a glimpse of things to come.

To the left is the best image of M51, taken by NASA’s Spitzer Space Telescope, with the Multiband Imaging Photometer for Spitzer (MIPS), juxtaposed with the Herschel observation on 14 and 15 June at 160 microns. The obvious advantage of the larger size of the telescope is clearly reflected in the much higher resolution of the image: Herschel reveals structures that cannot be discerned in the Spitzer image.

Herschel’s glimpse of M51 at 70, 100, 160 microns.

These images clearly demonstrate that the shorter the wavelength, the sharper the image — this is a very important message about the quality of Herschel’s optics, since PACS observes at Herschel’s shortest wavelengths.

Produced from the very first test observation, these images lead scientists to conclude that the optical performance of Herschel and its large telescope is so far meeting their high expectations.

Within our Galaxy, the mission’s main science objectives are:

* To study Solar System objects such as asteroids, Kuiper belt objects, and comets.
Comets are the best-preserved fossils of the early Solar System, and hold clues to the raw ingredients that formed the planets, including Earth.

* To study the process of star and planet formation.
Herschel is unique in its coverage of a wide range of infrared wavelengths, with which it will look into star-forming regions in our Galaxy, to reveal different stages of early star formation and the youngest stars in our Galaxy for the first time. The telescope will also study circumstellar material around young stars, where astronomers believe that planets are being formed, and debris discs around more mature stars.

* To study the vast reservoirs of dust and gas in our Galaxy and in other nearby galaxies.
Herschel will study in detail the physics and kinematics at work in giant clouds of gas and dust that give rise to new stars and associated planetary bodies. Herschel is also well-suited to study astrochemistry providing fundamental new insight into the complex chemistry of these molecular clouds, the wombs of future stars.

Outside our Galaxy, the mission’s main science objectives are:

* To explore the influence the galactic environment has on interstellar medium physics and star formation. Most of what we have learned about the physics and chemistry of the interstellar medium, and of the processes there such as star formation, has been gained by studies in our own Galaxy. With Herschel, we can carry out similar studies in relatively nearby galaxies as well. For example, studies of nearby low- metallicity galaxies can open the door to the understanding of these processes in the early Universe.

* To chart the rate of star formation over cosmic time. We know that star and galaxy formation commenced relatively early after the Big Bang. We also know that when the Universe was about half its current age, star formation was much more intense than it is today. Herschel is ideal to study infrared-dominated galaxies at the peak of star formation.

* To resolve the infrared cosmic background and characterise the sources. About half the energy produced and emitted throughout cosmic history now appears as a diffuse infrared cosmic background. With its large telescope, Herschel will be able to resolve the far-infrared background and characterise its constituent sources to a degree never achieved before.