Starship Asterisk*

Case wrote: ↑Wed Jun 17, 2020 10:17 am Can't resist comparing the magnetic streamlines of the Milky Way with the post-impressionist swirly painting style of Van Gogh.

La Nuit étoilée (1889) by Vincent van Gogh

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APOD Robot wrote: ↑Wed Jun 17, 2020 4:08 am Magnetic Streamlines of the Milky Way

Explanation: What role do magnetic fields play in interstellar physics? Analyses of observations by ESA's Planck satellite of emission by small magnetically-aligned dust grains reveal previously unknown magnetic field structures in our Milky Way Galaxy -- as shown by the curvy lines in the featured full-sky image. The dark red shows the plane of the Milky Way, where the concentration of dust is the highest. The huge arches above the plane are likely remnants of past explosive events from our Galaxy's core, conceptually similar to magnetic loop-like structures seen in our Sun's atmosphere. The curvy streamlines align with interstellar filaments of neutral hydrogen gas and provide tantalizing evidence that magnetic fields may supplement gravity in not only in shaping the interstellar medium, but in forming stars. How magnetism affected our Galaxy's evolution will likely remain a topic of research for years to come.

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Ann wrote: ↑Wed Jun 17, 2020 7:24 am
And by any chance, does magnetism play any sort of global role in the Universe? Particularly if the Universe actually happens to be spinning?

Ann

johnnydeep wrote: ↑Wed Jun 17, 2020 1:59 pm

APOD Robot wrote: ↑Wed Jun 17, 2020 4:08 am Magnetic Streamlines of the Milky Way

Explanation: What role do magnetic fields play in interstellar physics? Analyses of observations by ESA's Planck satellite of emission by small magnetically-aligned dust grains reveal previously unknown magnetic field structures in our Milky Way Galaxy -- as shown by the curvy lines in the featured full-sky image. The dark red shows the plane of the Milky Way, where the concentration of dust is the highest. The huge arches above the plane are likely remnants of past explosive events from our Galaxy's core, conceptually similar to magnetic loop-like structures seen in our Sun's atmosphere. The curvy streamlines align with interstellar filaments of neutral hydrogen gas and provide tantalizing evidence that magnetic fields may supplement gravity in not only in shaping the interstellar medium, but in forming stars. How magnetism affected our Galaxy's evolution will likely remain a topic of research for years to come.

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So the text says the image is of dust that is aligning with magnetic field lines in the milky way. The obvious question is what's causing the field lines in the first place? Is it "just" ionized interstellar gas that is in motion? And since electromagnetism is so much stronger than gravity, could it be that gravity is actually the less dominant force governing the evolution of galaxies and stars?!

Case wrote: ↑Wed Jun 17, 2020 10:17 am Can't resist comparing the magnetic streamlines of the Milky Way with the post-impressionist swirly painting style of Van Gogh.

La Nuit étoilée (1889) by Vincent van Gogh

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johnnydeep wrote: ↑Wed Jun 17, 2020 2:06 pm

Ann wrote: ↑Wed Jun 17, 2020 7:24 am
And by any chance, does magnetism play any sort of global role in the Universe? Particularly if the Universe actually happens to be spinning?

Ann

That youtuber sure produces a lot of videos! I watch him occasionally. In this video he talks about a 1% preference for galaxies spinning either clockwise or counterclockwise depending on direction. But as for the entire universe spinning, I'm not sure what that means. If we use the 2-D universe on the surface of a 3-D balloon analogy, how would the spinning be done? You could pick a 3-D spin axis through the center of the balloon, but that would mean that two places in the 2-D surface would be the "poles". Is that really what's being considered?

johnnydeep wrote: ↑Wed Jun 17, 2020 1:52 pm

Case wrote: ↑Wed Jun 17, 2020 10:17 am Can't resist comparing the magnetic streamlines of the Milky Way with the post-impressionist swirly painting style of Van Gogh.

La Nuit étoilée (1889) by Vincent van Gogh

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Yup. When I first opened this APOD, I thought oh no, another "artist's interpretation". Imagine my surprise when I read that it was a real image!

Chris Peterson wrote: ↑Wed Jun 17, 2020 2:07 pm There is no evidence that magnetic fields like this play any role in the formation of stars. But they may form paths that over long periods influence the movement of dust and gas, and therefore affect where stars form and a degree of large scale structure. At the scale of stellar systems, gravity exerts much larger forces than electromagnetism. The fields we see in this image are incredibly weak.

Avalon wrote: ↑Wed Jun 17, 2020 4:34 pm

johnnydeep wrote: ↑Wed Jun 17, 2020 2:06 pm That youtuber sure produces a lot of videos! I watch him occasionally. In this video he talks about a 1% preference for galaxies spinning either clockwise or counterclockwise depending on direction. But as for the entire universe spinning, I'm not sure what that means. If we use the 2-D universe on the surface of a 3-D balloon analogy, how would the spinning be done? You could pick a 3-D spin axis through the center of the balloon, but that would mean that two places in the 2-D surface would be the "poles". Is that really what's being considered?

Wouldn't all spinning objects be spinning "clockwise" or "counterclockwise" depending on whether you're viewing it from "above" or "below"?

Second question, is there a way to see in which direction these magnetic streamlines are flowing?

johnnydeep wrote: ↑Wed Jun 17, 2020 6:46 pm

Chris Peterson wrote: ↑Wed Jun 17, 2020 2:07 pm There is no evidence that magnetic fields like this play any role in the formation of stars. But they may form paths that over long periods influence the movement of dust and gas, and therefore affect where stars form and a degree of large scale structure. At the scale of stellar systems, gravity exerts much larger forces than electromagnetism. The fields we see in this image are incredibly weak.

I suppose you must be right, but I'm having a hard time convincing myself. Electromagnetism is something like 10³⁷ times stronger than gravity, and both have infinite range. Why then is gravity seen to be dominant over huge distances? Is it because there are so few charged particles relative to particles with mass?

BDanielMayfield wrote: ↑Thu Jun 18, 2020 3:44 am

johnnydeep wrote: ↑Wed Jun 17, 2020 6:46 pm

Chris Peterson wrote: ↑Wed Jun 17, 2020 2:07 pm There is no evidence that magnetic fields like this play any role in the formation of stars. But they may form paths that over long periods influence the movement of dust and gas, and therefore affect where stars form and a degree of large scale structure. At the scale of stellar systems, gravity exerts much larger forces than electromagnetism. The fields we see in this image are incredibly weak.

I suppose you must be right, but I'm having a hard time convincing myself. Electromagnetism is something like 10³⁷ times stronger than gravity, and both have infinite range. Why then is gravity seen to be dominant over huge distances? Is it because there are so few charged particles relative to particles with mass?

Gravity is dominant at large ranges for several reasons. Gravity is always attractive, so gravitational force grows with all masses, whereas electromagnetic force can be attractive or repulsive. There seems to be a universal balance of positive and negative charges, which attract and tend to cancel each other out, thus rendering bulk objects with little or no difference in charge over time.

Chris Peterson wrote: ↑Wed Jun 17, 2020 2:07 pm
There is no evidence that magnetic fields like this play any role in the formation of stars. But they may form paths that over long periods influence the movement of dust and gas, and therefore affect where stars form and a degree of large scale structure. At the scale of stellar systems, gravity exerts much larger forces than electromagnetism. The fields we see in this image are incredibly weak.

• No star could form without first dissipating a great deal of angular momentum through electromagnetism:

https://en.wikipedia.org/wiki/Herbig%E2%80%93Haro_object wrote:

HH objects are formed when accreted material is ejected by a protostar as ionized gas along the star's axis of rotation, as exemplified by HH 34.

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<<Herbig–Haro (HH) objects are bright patches of nebulosity associated with newborn stars. They are formed when narrow jets of partially ionised gas ejected by stars collide with nearby clouds of gas and dust at several hundred kilometres per second. Herbig–Haro objects are commonly found in star-forming regions, and several are often seen around a single star, aligned with its rotational axis. Most of them lie within about one parsec (3.26 light-years) of the source, although some have been observed several parsecs away. HH objects are transient phenomena that last around a few tens of thousands of years. They can change visibly over timescales of a few years as they move rapidly away from their parent star into the gas clouds of interstellar space (the interstellar medium or ISM). Hubble Space Telescope observations have revealed the complex evolution of HH objects over the period of a few years, as parts of the nebula fade while others brighten as they collide with the clumpy material of the interstellar medium.

https://en.wikipedia.org/wiki/H_II_region wrote:

NGC 604, a giant HII region in the Triangulum Galaxy

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<<An HII region or HII region is a region of interstellar atomic hydrogen that is ionized. It is typically a cloud of partially ionized gas in which star formation has recently taken place, with a size ranging from one to hundreds of light years, and density from a few to about a million particles per cubic cm. The Orion Nebula, now known to be an HII region, was observed in 1610 by Nicolas-Claude Fabri de Peiresc by telescope, the first such object discovered.

The precursor to an HII region is a giant molecular cloud (GMC). A GMC is a cold (10–20 K) and dense cloud consisting mostly of molecular hydrogen. GMCs can exist in a stable state for long periods of time, but shock waves due to supernovae, collisions between clouds, and magnetic interactions can trigger its collapse. When this happens, via a process of collapse and fragmentation of the cloud, stars are born (see stellar evolution for a lengthier description).

As stars are born within a GMC, the most massive will reach temperatures hot enough to ionise the surrounding gas. Soon after the formation of an ionising radiation field, energetic photons create an ionisation front, which sweeps through the surrounding gas at supersonic speeds. At greater and greater distances from the ionising star, the ionisation front slows, while the pressure of the newly ionised gas causes the ionised volume to expand. Eventually, the ionisation front slows to subsonic speeds, and is overtaken by the shock front caused by the expansion of the material ejected from the nebula. The HII region has been born.

The lifetime of an HII region is of the order of a few million years. Radiation pressure from the hot young stars will eventually drive most of the gas away. In fact, the whole process tends to be very inefficient, with less than 10 percent of the gas in the HII region forming into stars before the rest is blown off. Contributing to the loss of gas are the supernova explosions of the most massive stars, which will occur after only 1–2 million years.>>

neufer wrote: ↑Thu Jun 18, 2020 12:53 pm

Chris Peterson wrote: ↑Wed Jun 17, 2020 2:07 pm
There is no evidence that magnetic fields like this play any role in the formation of stars. But they may form paths that over long periods influence the movement of dust and gas, and therefore affect where stars form and a degree of large scale structure. At the scale of stellar systems, gravity exerts much larger forces than electromagnetism. The fields we see in this image are incredibly weak.

• No star could form without first dissipating a great deal of angular momentum through electromagnetism:

Chris Peterson wrote: ↑Thu Jun 18, 2020 1:36 pm Fine. But not really relevant to my comment.