Free Astronomy Magazine January-February 2024

50 JANUARY-FEBRUARY 2024 ASTRO PUBLISHING A side-by-side comparison of the Crab Nebula as seen by the Hubble Space Telescope in optical light (left) and the James Webb Space Telescope in in- frared light (right). The Hubble image was released in 2005, while astronomers have recently used Webb’s NIRCam (Near-Infrared Camera) and MIRI (Mid-In- frared Instrument) to reveal new details of the Crab Nebula. In the Hubble image, orange filaments consisting mostly of hydrogen form a crisp, cage-like exterior shell. Blue mottled filaments toward the outer part of the Crab contain neutral oxygen, while singly-ionized sulfur and doubly-ionized sulfur form fluffy red and green material. The bright glow in the interior’s center highlights the nebula’s pulsar, a rapidly rotating neutron star. Similar to the Hubble optical image, Webb’s infrared capabilities show the super- nova remnant’s crisp, cage-like structure of fluffy red-orange filaments of gas that trace doubly ionized sulfur. Among the remnant’s interior, yellow-white and green fluffy ridges form large-scale loop-like structures, which represent areas where dust particles reside. The central area within is comprised of translu- cent, milky material. This white material is synchrotron radiation, which is emit- ted across the electromagnetic spectrum but becomes particularly vibrant thanks to Webb’s sensitivity and spatial resolution. It is generated by particles acceler- ated to extremely high speeds as they wind around magnetic field lines. In the center of this ring-like structure is a bright white dot: the nebula’s pulsar. Note how certain gas filaments are bluer in color. These areas contain singly ionized iron. By studying Webb data and consulting previous observations of the rem- nant taken by other telescopes, like Hubble, astronomers can improve their un- derstanding of the Crab Nebula as well as broaden their knowledge on the life and death of stars. [NASA, ESA, CSA, STScI, Jeff Hester (ASU), Allison Loll (ASU), Tea Temim (Princeton University)] spectrum, the synchrotron radiation is seen in unprecedented detail with Webb’s NIRCam instrument. To locate the Crab Nebula’s pulsar heart, trace the wisps that follow a circular ripple-like pattern in the middle to the bright white dot in the center. Farther out from the core, follow the thin white ribbons of the radiation. The curvy wisps are closely grouped together, outlining the structure of the pulsar’s mag- netic field, which sculpts and shapes the nebula. At center left and right, the white material curves sharply inward from the filamentary dust cage’s edges and goes toward the neutron star’s location, as if the waist of the neb- ula is pinched. This abrupt slimming may be caused by the confinement of the supernova wind’s expansion by a belt of dense gas. The wind produced by the pulsar heart continues to push the shell of gas and dust outward at a rapid pace. Among the remnant’s interior, yellow-white and green mottled fil- aments form large-scale loop-like structures, which represent areas where dust grains reside. The search for answers about the Crab Nebula’s past continues as as- tronomers further analyze the Webb data and consult previous observa- tions of the remnant taken by other telescopes. Scientists will have newer Hubble data to review within the next year or so from the telescope’s reimaging of the supernova rem- nant. This will mark Hubble’s first look at emission lines from the Crab Nebula in over 20 years, and will enable as- tronomers to more accurately com- pare Webb and Hubble’s findings. !