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A new paper that borrows old astrological data from the Voyager 2 probe has used brand-new computer simulations to find some new weird data about Uranus’s magnetic field. Another paper has new information about our galaxy’s fastest stars, called hypervelocity stars.

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Hypervelocity stars:


Uranus has always been a bit of an oddball, the planet, I mean.  For one thing, it orbits the Sun tilted over on its side so there are parts of its orbit where its north or south pole points almost directly at the Sun.  There's a lot we don't know about the planet, since we've only visited once, when the Voyager 2 probe passed by back in 1986, but it sent back so much data that we're still learning new things from it.

Just this week, a paper in the Journal of Geophysical Research combined that old data with brand new computer simulations and found that Uranus's magnetic field does something pretty weird.  It acts like a switch, opening and closing every day.  On most planets with magnetic fields, the field is pretty much lined up with the axis that the planet spins around.  That's why compasses work so well on Earth--they point to magnetic North which is pretty close to geographic North.  Our magnetic field also blocks most of the solar wind, the constant stream of particles from the Sun, although sometimes the magnetic field gets sort of overpowered and those particles get sent down toward the surface to cause auroras.

 But Uranus's magnetic field isn't tilted nearly as much as the planet itself, so it's not even close to lining up with the geographic poles, and the center of the magnetic field is shifted pretty far from Uranus's center, which is also super weird.

 Scientists still aren't totally sure why Uranus's magnetic field is so strange, but they think it might be affected by liquid sloshing around inside the planet.  What we do know is that as Uranus turns, its magnetic field sweeps through space like a wobbling top, pushing the solar wind in different directions as the field mixes and merges and clashes with the Sun's own magnetic field, and all this shifting and merging and tilting makes Uranus's magnetic field really complicated, which is why the authors of this new paper decided to use Voyager 2's measurements of the magnetic field to model exactly what that field does as the planet rotates.  

Uranus rotates about once every 17 hours, and according to the team's model, in those 17 hours, the planet's magnetic field makes a switch.  It goes from clashing with the Sun's magnetic field and blocking out all solar wind to being aligned with the Sun's magnetic field and letting just about everything down toward the planet.  Every day, it flips from closed to open to closed again.  

If their model is right, that means Uranus's magnetic field switches and mixes with the Sun's more than pretty much any other planet we know about, and since a lot of the planets we've found around other stars look kind of like Uranus, understanding these complicated exchanges might help us figure out how those other planets act, too.  Not bad for 30 year old data!  

And speaking of other stars, in a paper presented this week at the National Astronomy Meeting in the UK, a group of astronomers found that some of the Milky Way's fastest stars might have come from a nearby galaxy called the Large Magellanic Cloud, or LMC.  Our galaxy's fastest stars, called hypervelocity stars, move about 500km per second relative to our Sun, so fast that the Milky Way's gravity isn't strong enough to keep them in the galaxy forever.

They were first discovered back in 2005 and astronomers think that most of them started out in binaries, where two stars orbit each other.  If something tears a binary apart like a supernova or a close brush with a supermassive black hole at the center of the galaxy, that can send one of these super fast stars zooming off into space.  

The authors of this new study decided to look into where those original binaries were and based on their simulations, hypervelocity stars could have come all the way from the LMC.  The LMC orbits the Milky Way at just under 300 km/sec, which isn't too far from the at least 500km/sec of hypervelocity stars.  

Astronomers already think at least one super fast star comes from the LMC based on its composition, and if other hypervelocity stars come from the LMC, that would solve one of the hardest problems surrounding these stars: we tend to only find them in certain parts of the sky.  That wouldn't make sense if random events like supernovas within the Milky Way produced most hypervelocity stars.  In that case, we should see them in totally random parts of the sky, but it makes perfect sense if a lot of them come from the LMC outside our galaxy, because they would mostly be moving along the same path.

When the team simulated stars being ejected from binaries in the LMC and shooting off toward the Milky Way, they found that the stars tended to look and clump just like most of the hypervelocity stars that we've already found.  That doesn't mean they all came from outside our galaxy, but a lot of them might have.  

The researchers predict that we'll find more hypervelocity stars along the LMC's path with future surveys, which would be more evidence that they come from outside our galaxy and help us learn about them in general, but it looks like at least some of our stellar companions are just on loan from a neighbor.

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