James Webb Space Telescope (JWST) is next generation. The long wait for new images is over! Let’s look at some of these new and improved JWST images from NIRCam and MIRI. Here we look at planetary nebula NGC 3132, which contains a visual binary of a low mass star and a white dwarf.
Dr. MMM of AstroPicionary has taught astronomy to 10,000+ students over 15+ years at a USA Carnegie Level R1 University. Dr. MMM continues to teach astronomy and physics. She authors textbooks in astronomy that are in use worldwide. Here, Dr. MMM discusses a JWST image in comparison with an HST image to see what science is apparent with the newer and finer detailed JWST images.
James Webb Space Telescope (JWST)
On December 25, 2021, JWST launched into space from Earth. The image at left shows JWST in 2016 fully expanded at NASA Goddard Space Flight Center. As the image shows, the size of the telescope is very large. Compare its size to that of a nearby yellow ladder, people dressed in white, clean room suits, and a door with an exit sign above in the background. At 20 m x 14 m (about 66 ft x 46.5 ft), JWST is indeed a large space telescope.
JWST First Image – NGC 3132
After carefully prepping the telescope in early 2022, first full color images are available for public release in July 2022. One of these images is NGC 3132, which is a planetary nebula. Planetary nebula is a stage in stellar evolution of a low mass star like the Sun. Definition and explanation of a planetary nebula is below, which is from the YouTube AstroPictionary channel.
NGC 3132 has several other names. One is Eight-Burst due to a figure eight shape the nebula makes in smaller, ground-based amateur telescopes. Another name is Southern Ring nebula: This planetary nebula is in constellation Vela, which is in the southern hemisphere sky, hence the name.
Near Infrared (NIR) Image of NGC 3132
The images below show NGC 3132 using Hubble Space Telescope (HST) on left and using JWST NIRCam on right. NIRCam is a near-infrared (NIR) camera (Cam) that is not observing in V band; it is observing in the infrared band of the electromagnetic spectrum (EM spectrum).
The below, left image is from the Hubble Space Telescope. It shows what appears to be a dying low mass star near center. Zooming in, though, reveals two stars in a visual binary: the fainter is a white dwarf and the apparently brighter is a dying low mass star. The white oval is gas pushing out in this two-dimensional image.
The upper right image has been newly released in July 2022. It is much more crisp and shows much more detail compared to the HST image on left. Whereas HST observes mostly in V band of the EM spectrum, NIRCam observes in infrared, which is different wavelengths in the EM spectrum. Since both telescopes observe in different wavelength bands, JWST is not exactly a next generation telescope of HST. Nonetheless, instruments improvements do show crisper images due to high resolution.
Diffraction Spikes in JWST Images
In the JWST NIRCam image, we see six large and two small diffraction spikes around the low mass dying star. These diffraction spikes mostly block the white dwarf, which is just to upper right of the low mass star. The image does not show diffraction spikes around all stars; only stars nearby to this telescope show these diffraction spikes.
Nearby is relative, as the distance to NGC 3132 is around 2500 light years. Although this number is large, this object is within our Milky Way Galaxy. Stars in the image not showing diffraction spikes are much further from Earth than 2500 ly. Many of these non-diffracting stellar objects should be outside our Milky Way Galaxy.
A source to diffraction spikes in these JWST images is diffraction: Significant amounts of light from nearby stars bend around edges of the outer JWST hexagonal mirror segments and around the JWST secondary support. The image of JWST at Goddard Space Flight Center (see top image above) shows these gold color hexagonal mirror segments that make up the primary mirror.
Diffraction spikes appear in images other than NIR. Below we look at NGC 3132 in mid infrared (MIR) wavelengths. Diffraction spikes are present around the low mass star in the MIR below, but you have to zoom in to see them.
Mid Infrared (MIR) of NGC 3132 Image
Another instrument on JWST is MIRI, which stands for Mid-Infrared instrument (MIRI). The MIRI image clearly shows the visual binary near center: The low mass star is at upper right, and the white dwarf is at lower left. Of the two, the brighter one is the low mass star. Besides being dimmer, the white dwarf is redder in comparison.
Let’s compare the white dwarf in the NIR image to that in the MIR image. The white dwarf in the MIR image above is larger, brighter, and redder than in the NIR image. Being in further wavelengths than NIR, MIR images show locations of dust. Hence, the reason why the white dwarf appears larger in the MIR image is due to dust around the white dwarf. The white dwarf is emitting copious amounts of dust that is seen by MIRI, but not by NIRCam.
NGC 3132 Low Mass Star and White Dwarf
Not seen in a comparison of the NIR and MIR images is an apparently larger low mass star in the NIRCam image. The low mass star has not yet reached a stage in its evolution where much dust is emitting.
The dust in the MIR image is from the white dwarf. This dust has been emitting ever since this star began its dying stages. As dying stages with dust emission are not continuous, shells of dust are often not circular around the dying star. The low mass star in the visual binary helps to push out the dust, generating the shape we see of this planetary nebula.
Let’s compare the NIR and MIR images again, but this time looking at gas emissions. The gas emissions in the MIR image appear blue and in an eye shape that is well away from the visual binary at the center. The NIR image shows this blue region as orange. These gasses are emitting heat, and hence the reason why they are seen in these infrared images. The gases absorb UV and V light energy from the white dwarf and re-emit this light in infrared. Notice that the gasses extend very far from the visual binary. More of these gasses are seen in the NIR image at the edges than MIR. The further these gasses travel away from the visual binary, the cooler these gasses become.
Bottom Line
JWST has given us finer detail in images, from which we can learn more information about systems and processes. In this example, we compare NGC 3132 in NIR and MIR as seen by JWST cameras to an HST V band image. New science shows dust emissions from the white dwarf in the visual binary within NGC 3132. These dust emissions are new science! We have JWST to thank for this new science. JWST science is proving to be quite lucrative, and we look forward to new images and new spectra.
