Astro Bob: Bones of a Galaxy / Spectacular DART impact photos, video
New Webb images reveal a galaxy's dusty skeleton. DART's target Dimorphos has grown a tail!
Spiral galaxies are some of the most elegantly beautiful structures in the universe. One of them, the Milky Way Galaxy, is our home. And while we may never be able to vault out of the galaxy to admire it from afar, we can "look in the mirror" by examining other galaxies like our own.
Recently, the Webb Space Telescope took this striking image of the spiral galaxy IC 5332 located 29 million light-years away in the constellation of Sculptor. With a diameter of 66,000 light-years it's about two-thirds the size of the Milky Way. Lucky for us we view it almost perfectly face on, the better to admire the symmetrical sweep of its spiral arms. The two similarly composed photos compare views from the Webb, taken in mid-infrared light, and the Hubble Space Telescope in visible and ultraviolet (UV) light.
Webb used its Mid-InfraRed Instrument (MIRI) to capture the galaxy's surprising and unfamiliar form. MIRI operates at a frosty -447° F (-266° C), only 13°F (7°C) warmer than absolute zero, which is the lowest possible temperature. Atoms stop moving at absolute zero. The Webb's sunshade keeps the telescope below -370° F (-223° C), but that's nowhere near frigid enough to operate MIRI. Since the slightest heat would render the instrument useless, it has its own special refrigeration unit.
Mid-infrared light lies well beyond the red end of the rainbow, about midway between visible light and the microwaves we use to heat a cup of tea. Similar to X-rays it provides a unique view of the world around us. Earth's atmosphere absorbs most mid-infrared, the reason we launch infrared telescopes into space.
The Hubble photo shows dark regions that seem to separate the star-packed spiral arms, while the Webb reveals a continual tangle of structures that echo the spiral arms’ shape. The difference is caused by dust, which scatters and absorbs the visible light of stars embedded within the stellar "soot" as well as those located in the distance, creating darker regions. The same dusty regions are no longer dark in the Webb image, as mid-infrared light easily passes through. It's as if Webb reveals the galaxy's hidden "bones" while Hubble highlights its fleshy exterior.
Dimorphos mimics a comet
The latest photos of NASA's DART spacecraft crashing into the tiny asteroid Dimorphos show a big, spidery impact plume. A cubesat, a shoebox-sized satellite that accompanied the mission, took the remarkable image of the crash directly from the site. Numerous telescopes back on Earth did the same. Together they reveal an evolving plume of debris.
Radiation from the sun has pushed back some of the dusty debris into a broad fan and tail behind the asteroid. Comet tails form similarly except the sun first heats and vaporizes dust-laden ice from the comet's nucleus before "blowing" the dust back into a tail.
Still no word on how much the impact changed the orbital period of Dimorphos. Researchers expect it to shorten by about 1% or 10 minutes. We should know soon. NASA will likely hold a news conference when the results are in.
I'm still hoping to see the Didymos-Dimorphos asteroid system myself. It's near the limit of my telescope but slowly rising higher in the morning sky beneath Orion. Although it will show as just a faint star this important historical site will be worth the visit.