The NIRSpec instrument is the workhorse near-infrared spectrograph on board the James Webb Space Telescope and is provided by ESA.

NIRSpec can make spectroscopic observations of complex targets in space, such as galaxies, nebulae, or crowded fields of stars or galaxies, in one single shot.

One technology it uses is that of ‘integral field units’ (IFUs). Here, an image-slicing technique is used to reorganise the signal from a two-dimensional image of the sky into a set of slices.

These slices are fed to a spectrograph that generates a spectrum for each pixel, where the light is split into its different wavelengths. The slices are then arranged into a data cube. This cube is a stack of many images of the same target object in space, each at a different wavelength, and provides a comprehensive overview of the whole object under study.

This animation shows the path followed by light from an astronomical object as it travels through the NIRSpec components and onto the detector.

~ 0:24 min: The light from the telescope enters NIRSpec via the Pick-off Mirror

~ 0.29 min: The second flat mirror directs the beam towards the FORE optics that form an image of the sky onto the Micro Shutter Assembly (MSA).

~ 0:38 min: The light passes through a Filter Wheel Assembly (FWA) for selecting specific wavelength bands and through the refocusing mechanism (RMA).

~ 0:44 min: A sharp image of the sky is formed onto the MSA.

~ 0:51 min: With MSA shutters all closed a small portion of light passes through the now open IFU entrance aperture.

~ 0:54 min: Two small flat mirrors and two powered mirrors form a magnified image of the IFU field of view onto the “slicer” mirror.

~ 1.03 min: The slicer mirror creates 30 new beams, each for a specific fraction of the IFU field of view.

~ 1:07 min: 30 individual beams exit the IFU and enter the NIRSpec spectrometer optics.

~ 1:14 min: The collimator optics brings the beam to the Grating Wheel Assembly (GWA).

~ 1:18 min: The Grating or Prism unravels the incoming beam in all its wavelengths by dispersing it vertically.

~ 1:20 min: The Camera optical system forms 30 spectra (one for each individual IFU beam) onto the detector.

NIRSpec will allow scientists to study objects embedded in shrouds of gas and dust, to find out more about how galaxies formed and evolved, and to characterise the atmospheres of extrasolar planets to determine if water is present.

NIRSpec is built by European industry to ESA’s specifications and managed by the ESA Webb Project at ESTEC, the Netherlands. The prime contractor is Airbus Defence and Space in Ottobrunn, Germany. The NIRSpec detector and Micro-Shutter Array subsystems are provided by NASA’s Goddard Space Flight Center (GSFC).

Learn more about spectroscopy with the Webb telescope here.