3 days ago
This is from August 2000!
Since them, much more detailed magnetic fields maps have been made of the Milk Way: https://www.forbes.com/sites/startswithabang/2019/09/23/this...
Also for other galaxies: https://www3.mpifr-bonn.mpg.de/staff/rbeck/PSSS18.pdf
3 hours ago
“This is from August 2000!
Since them, much more detailed magnetic fields maps have been made of the Milk Way: “
I was surprised to see that followed up with link from 2019?
3 days ago
My undergraduate advisor (David Chuss) at Villanova and some of his students recently put together a really nice visualization of the magnetic fields at the center of our galaxy.
Last I talked to him about it, he said that the results were surprising. I think he said no one really knew yet how to explain the vertical yellow streaks representing hot plasma.
http://www62.homepage.villanova.edu/david.chuss/FIREPLACE_Po...
3 days ago
A galaxy is so large (e.g. the milky way is ~ 1 billion billions km in diameter!), and bodies are so far from each other that it is far from intuitive that there should even be a magnetic field, and it's even neatly aligned along the arms!
2 days ago
It's that 'spooky action at a distance' thing. It's still never been clear to me but what's the speed of Electromagnetism (i.e. if you drop a highly magnetic object into an area - how quickly is the force impacting the distant surroundings)?
2 days ago
The propagation of the change in the magnetic field travels at the speed of light.
The act of moving a magnet and thus changing the magnetic field at one point also induces a change in the electric field and vice versa, that's why you'll always hear talking about "electromagnetic" waves (which light, radio waves, etc are an instance of).
To make things even more interesting there is also this phenomenon: the magnetic field is created by moving electric changes, relative to the observer. If an observer moves at the same velocity as the electric charge it will not observe a magnetic field. It turns out that when you apply special relativity to the effects of electrical charges (coulomb 's law) you get a theory of electro-magnetism (Maxwell's equations). Magnetism this "follows" from the behavior of electrical fields and special relativity. That doesn't make magnetism less "real" but it hints at the intimate connection that the two forces have and what we now talk about them as "electromagnetism"
2 days ago
The speed limit of any information in the universe is the same, as far as we know.
There are effects like quantum entanglement that seemingly bypasses this, but there is no way to extract useful information out of it.
2 days ago
there is no way to extract useful information out of it
2 days ago
Electromagnetic waves travel at the speed of light
2 days ago
Because they literally are light.
2 days ago
No, light is EM radiation. Not all EM is light.
a day ago
Isn’t that distinction more philosophical than not?
Like the Feynman diagram is in any case that a photon is transmitted between two charged objects, whether that photon is “real” or “virtual”.
I know there are physicists who interpret this as there being two distinct things, either particle-like excitations (photons) and more general excitations (not photons). These usually don’t think of Feynman diagrams as representing anything real.
But I also know there are some physicists who consider virtual photons “real”. And in that picture of reality, all EM interaction is “light”.
2 days ago
To add to other comments here: think about what happens when a heavy object (e.g. a planet or a moon) moves, how quickly does the change to the gravitational field propagate to affect the distant surroundings?
Answer; at the speed of light.
3 days ago
Kind of puts into perspective a trillion dollars...
2 days ago
Why is that unintuitive? Shrink down to an atomic level and you'll find similar behavior.
2 days ago
That's pretty unintuitive! Behavior at galactic vs atomic scales are very different!
2 days ago
Still wishing for a space. ycombinator .com (or spacetime. )
Could link to a custom, cached search?
Tried playing with the algolia search and the API but it doesn't seem to properly support multi-keyword searches and OR logic.
Easy to build a list of keywords to search titles and first-posts
2 days ago
This might be a dumb question, but how does this interact with dark matter observations? Do magnetic fields in any way help explain higher than expected galactic orbital rates?
2 days ago
Could we use this magnetic field for propulsion?
2 days ago
Sure. Can we use it to accelerate a smaller object faster than the whole solar system? Maybe. Will the difference in acceleration be at all noteworthy? Unlikely.
3 days ago
Does it have an electric field?
3 days ago
doesn't every moving magnetic field produce an electric field?
given that the galaxy is moving, i'd say yes.
3 days ago
Galaxies with no black hole at the heart have the same arms?
2 days ago
I would be surprised if there would be literally nothing in their centres, ie like some ultra complex version of binary / more complex set of stars circling around each other, with center of rotation being just empty space.
2 days ago
I think almost all evolved galaxies have a central black holes, so my bet would be that no spiral galaxy lack a central black hole.
2 days ago
While SMBH at the center are common, it is believed that there are plenty of galaxies that don't have such a black hole including spiral galaxies. For example, M33 [1].
The upper limit on its central black hole is ~1500x of Sol and it's widely believed right now to just not have one. By comparison, the Milky Way’s black hole is 4 million Sol masses and our galaxies SMBH is quite tiny by comparison to many galaxies.
[1] https://www.science.org/cms/asset/7c8770b5-a357-40f5-a491-19...