James Webb Space Telescope Feed Post

The difference between MIRI and NIRCam in the James Webb Space Telescope's last NGC 6822 images

This image shows the irregular galaxy NGC 6822, which was observed by the Near-InfraRed Camera (NIRCam) and Mid-InfraRed Instrument (MIRI) mounted on the NASA/ESA/CSA James Webb Space Telescope. As their names suggest, NIRCam and MIRI probe different parts of the electromagnetic spectrum. This allows the instruments to observe different components of the same galaxy, with MIRI especially sensitive to its gas-rich regions and NIRCam suitable for observing its densely packed field of stars. On the left, Webb’s near-infrared NIRCam image shows the galaxy’s countless stars in incredible detail. Here, the dust and gas that pervade the galaxy are reduced to translucent red wisps, laying the stars bare for astronomical study. The power of Webb’s ice-cold infrared instruments and the incredible resolution of its primary mirror is necessary to examine stars hidden in dusty environments, and the results as shown here are spectacular. The brightest stars appear in pale blue and cyan colours in this image, colours which are assigned to the shortest wavelengths of light that NIRCam can detect: red and near infrared. The amount of light emitted by any star decreases at longer and longer wavelengths, towards the mid-infrared, so the stars that are more faint to NIRCam also appear more warmly coloured here. A bright blue orb to the lower left of the gas is particularly prominent: this is a globular cluster, packed with stars. On the right, mid-infrared wavelengths are probed in Webb’s MIRI image. The emission of the galactic dust is much more prominent here, once again obscuring the stars, which themselves are more faint at these longer infrared wavelengths. Brilliant blue gas indicates light emitted by organic compounds called polycyclic aromatic hydrocarbons, which play a critical role in the formation of stars and planets. Cyan marks cooler patches of dust, while warmer dust is more orange. Distant galaxies far beyond NGC 6822 are displayed in orange. The few galaxies that are relatively closer, meanwhile, are marked in green by their own light-emitting dust, which MIRI can pick out. Bright red and magenta colours indicate active areas of star formation in the galaxy. With so many stars, supernova explosions are routine, and an amazing example of a supernova remnant is visible in this image: a red ring just below the centre.