- 3633- JAMES WEBB - lessons learned, so far? On July, 2022, our understanding of the Universe changed forever as the first science images from the James Webb Space Telescope (JWST) were released to the world.
--------------------- 3633 - JAMES WEBB - lessons learned, so far?
- The very first James Webb image that was unveiled was a deep-field image of galaxy cluster SMACS 0723. Across the variety of filters and instruments that were used to observe it aboard JWST, a total of 12.5 hours of time was spent observing this region of space.
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- Although that might seem like an enormous amount of time, it’s just 2% of the time that was spent observing Hubble’s deepest view of the Universe Hubble’s “eXtreme Deep Field” consisted of a cumulative 23 days of observing time.
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- JWST outperforms Hubble by more than we expected. Hubble has a primary mirror that’s 2.4 meters across, JWST’s segmented mirror spans 6.5 meters.
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- This leads to a resolution that’s 270% as sharp for the same wavelength light and light-gathering power that’s 730% as great as Hubble’s For the same amount of observing time, expect that JWST would collect 730% as much light as Hubble.
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- Hubble time is divided up into “orbits,” as from its position in low-Earth orbit, it completes a revolution around our planet every 96 minutes. A total of 6 orbits, 4 in optical wavelengths and 2 in infrared wavelengths, were used to make the Hubble composite. 6 orbits multiplied by 96 minutes per orbit would equal 9.6 hours (576 minutes) of Hubble time.
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- During the first month after its launch, JWST’s priority was to reach and enter a stable orbit around the L2 Lagrange point. With the Sun, Earth, and Moon always behind it, there’s no chance of any of those sources ever obscuring its view.
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- Because it’s in orbit around Earth, spends more than 50% of its time with the Earth (and the Earth’s atmosphere) in the way of its desired target, and can only acquire useful data when its target is in full, unobstructed view of the telescope.
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- Meanwhile, JWST is some 1.5 million km away at the L2 Lagrange point. It always faces away from the Sun, away from the Earth, and away from the Moon. It never has to contend with these obstacles to pristine observing, and so its observations of targets are 100% time-efficient, as opposed to less than 50% time-efficient like Hubble was.
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- Areas of the sky that appeared to be cosmic voids aren’t always empty, after all. In theory, we knew this should be true, but with its very first deep-field images, JWST gave us the proof we needed. There are large regions of space that appear to have no stars or galaxies in them at all. Scientists have wondered, ever since these “voids” were discovered.
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- Galaxies come in many different morphologies, including spirals, ellipticals, rings, irregulars, and other various types and sub-types. With Hubble, the most distant galaxies were only visible as smudges that could not be resolved. With JWST, instead, their types and abundances can be tracked, measured, and classified across cosmic time and location.
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- Having a 270% increase in resolution actually means a 700% increase in the number of pixels available for each source. A galaxy that’s just 3×3 pixels, to Hubble, will appear as 8×8 pixels to JWST. By seeing how the shapes and configurations of galaxies vary over cosmic time and location, we’ll learn how our Universe grew up throughout its history.
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- Spectroscopy involves breaking up the arriving light into its component wavelengths, and looking for either emission lines (spikes at particular wavelengths) or absorption lines (deficits at particular wavelengths) that correspond to quantum mechanical transitions of particular elements. If you can obtain multiple lines from the same element, you can determine how much that light has been shifted by from its emitted wavelengths due to the expansion of the Universe.
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- The most distant galaxy identified in JWST’s first deep-field image, this object’s light comes to us from 13.1 billion years ago. With its extraordinary sensitivity to wavelengths beyond 2000 nanometers any galaxy that’s a high-redshift candidate will now be subject to true spectroscopic confirmation, something neither one has been subjected to before. JWST can do this for each and every galaxy we want to measure, and will obtain:
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---------------------- oxygen,
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---------------------- hydrogen,
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---------------------- neon lines,
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---------------------- among potential others
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- The individual galaxies seen in this Hubble/JWST composite are much more clearly resolved in the JWST version. If spectroscopy can be performed on individual components of the same galaxy we can measure the rotational properties of the material inside, putting various dark matter models and modified gravity theories to the test.
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- Astronomer are going to be able to rule out all sorts of versions of modified gravity. One of the most beautiful things about the idea of dark matter is that it explains so many observational phenomena on so many different scales with just that one addition. A Universe with dark matter can explain:
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--------------------- how individual galaxies rotate and interact,
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--------------------- how galaxies group and cluster together,
--------------------- how galaxies within a cluster move,
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--------------------- how gravitational lensing distorts and magnifies background objects,
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--------------------- how the large-scale structure of the Universe forms,
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--------------------- how the imperfections imprinted in the Big Bang’s leftover glow should appear and be distributed.
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- Some versions of modified gravity predict that the behavior of rotating galaxies will evolve over cosmic time; other versions predict that young rotating galaxies and old rotating galaxies should have similar rotation curves. As we combine JWST’s resolution and spectroscopic capabilities, and apply them to rotating galaxies seen all across the Universe, we’ll be able to rule one class or the other of modified gravity theories out. We can also test our theories of dark matter as never before; whatever we learn, it will be because the Universe told us how it’s truly behaving.
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- The centers of galaxy clusters will be revealed in more detail than ever.
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--------------------- how much gas is present,
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--------------------- what the stellar populations inside are like,
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--------------------- how many globular clusters are inside of it,
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--------------------- how many faint, satellite galaxies there are surrounding it,
for the closest galaxy clusters of all.
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- JWST, will be able to see what sorts of structures are present around these central galaxies; it will be able to resolve small, faint galaxies that would otherwise simply “smear” together with inferior resolution.
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- We may even be able to use this to explain the distribution of sources that contribute to the intracluster light, and detect and determine the properties of satellite galaxies and globular clusters in the halos of galaxies like never before.
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- We have 20+ years of time with JWST to look forward to, and the new discoveries are only just starting. As Edwin Hubble so eloquently put it: With increasing distance, our knowledge fades, and fades rapidly. Eventually, we reach the dim boundary, the utmost limits of our telescopes. There, we measure shadows, and we search among ghostly errors of measurement for landmarks that are scarcely more substantial.
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- The search will continue. Not until the empirical resources are exhausted, need we pass on to the dreamy realms of speculation.
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- With the new, unprecedented capabilities of JWST, we’re just beginning to see the Universe in, quite literally, a whole new light.
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July 21, 2022 JAMES WEBB - lessons learned, so far? 3633
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--------------------- --- Thursday, July 21, 2022 ---------------------------
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