zapatos Posted yesterday at 04:10 AM Posted yesterday at 04:10 AM Quote NASA’s James Webb Space Telescope (JWST) launched into orbit around the sun in December 2021. Since then, it has been studying the history of our universe. Now, images of deep space from JWST’s Advanced Deep Extragalactic Survey (JADES) have revealed something puzzling: most galaxies rotate in the same direction. About two-thirds of the 263 galaxies studied in a paper published February 17 in the Monthly Notices of the Royal Astronomical Society rotate clockwise, while the other one-third rotate counterclockwise. https://www.smithsonianmag.com/smart-news/james-webb-space-telescope-reveals-that-most-galaxies-rotate-clockwise-180986224/?utm_source=smithsoniandaily&utm_medium=email&utm_campaign=editorial&lctg=92132029
exchemist Posted 22 hours ago Posted 22 hours ago (edited) 5 hours ago, zapatos said: https://www.smithsonianmag.com/smart-news/james-webb-space-telescope-reveals-that-most-galaxies-rotate-clockwise-180986224/?utm_source=smithsoniandaily&utm_medium=email&utm_campaign=editorial&lctg=92132029 Why would galaxies rotating in the opposite direction to ours seem brighter? I can see the Doppler effect would make one side red-shifted and the other blue-shifted. But I'd have thought our own motion, either towards or away from the galaxy, would simply make the galaxy look a bit more blue or red shifted overall and the rotation of the galaxy would not affect overall brightness. Edited 22 hours ago by exchemist
swansont Posted 17 hours ago Posted 17 hours ago 4 hours ago, exchemist said: Why would galaxies rotating in the opposite direction to ours seem brighter? I can see the Doppler effect would make one side red-shifted and the other blue-shifted. But I'd have thought our own motion, either towards or away from the galaxy, would simply make the galaxy look a bit more blue or red shifted overall and the rotation of the galaxy would not affect overall brightness. There’s relativistic aberration (relativistic beaming) which means light is preferentially emitted in the direction of motion, but at speeds of less than 10^3 km/sec (our speed is ~230 km/s) it shouldn’t be that big
exchemist Posted 16 hours ago Posted 16 hours ago (edited) 1 hour ago, swansont said: There’s relativistic aberration (relativistic beaming) which means light is preferentially emitted in the direction of motion, but at speeds of less than 10^3 km/sec (our speed is ~230 km/s) it shouldn’t be that big They refer to the Doppler effect, which is what has thrown me. How can that brighten anything? And how would it be affected by the direction of rotation of the observed galaxy, as opposed to relative motion of the whole thing towards or away from us? Here's the paper: https://academic.oup.com/mnras/article/538/1/76/8019798?login=false. I've only skimmed it as yet, admittedly, but could not immediately see an explanation. Edited 16 hours ago by exchemist
swansont Posted 16 hours ago Posted 16 hours ago 2 hours ago, exchemist said: They refer to the Doppler effect, which is what has thrown me. How can that brighten anything? And how would it be affected by the direction of rotation of the observed galaxy, as opposed to relative motion of the whole thing towards or away from us? Here's the paper: https://academic.oup.com/mnras/article/538/1/76/8019798?login=false. I've only skimmed it as yet, admittedly, but could not immediately see an explanation. Relativistic beaming is from the relativistic doppler effect https://en.m.wikipedia.org/wiki/Relativistic_beaming “In physics, relativistic beaming (also known as Doppler beaming, Doppler boosting, or the headlight effect) is the process by which relativistic effects modify the apparent luminosity of emitting matter that is moving at speeds close to the speed of light. … How all of these effects modify the brightness, or apparent luminosity, of a moving object is determined by the equation describing the relativistic Doppler effect (which is why relativistic beaming is also known as Doppler beaming).” edit: Here’s one of the cited references, by the same author https://www.degruyter.com/document/doi/10.1515/astro-2020-0001/html They mention a Doppler shift of the bolometric flux; this means the “brightness” they are measuring is related to total energy, and blue-shifting does increase that. It’s not simply number of photons. more: https://en.m.wikipedia.org/wiki/Luminosity edit 2: In that reference I gave they note that observers in the southern hemisphere see rotations in the opposite direction, but I assume they accounted for this, and also for any anisotropy in the viewing field (e.g. we don’t see what’s on the other side of the galactic core)
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