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  • [♪ INTRO]

  • Together, the Northern and Southern lights could be considered

  • one of the most beautiful sites in nature.

  • But these giant curtains streaking across the sky

  • aren't the only type of aurora out there.

  • There's also the much more common, but less brilliant pulsating auroras.

  • These can happen at any time, but we haven't

  • been able to actually observe what causes them.

  • Until now.

  • Thanks to research published in Nature last week,

  • we think we finally know how the process works.

  • Active auroras, like the dazzling shows you see at the poles,

  • have one continuous arc of light.

  • But pulsating auroras get their name because they, pulse.

  • Distinct patches of sky vary in brightness over several seconds,

  • and they're generally less striking than the active auroras.

  • These different appearances are caused by the auroras' related, but different origin stories.

  • They're both caused by charged particles, usually electrons,

  • traveling down into the atmosphere and colliding with molecules there.

  • The molecules' electrons gain energy from those collisions, and then release light as

  • they relax back to their usual state.

  • Now, the electrons that spawn active auroras come from

  • dense waves of solar material colliding with the Earth's magnetic field.

  • Ones that create pulsating auroras are a bit more complex,

  • but according to this new paper, we might have figured it out.

  • Basically, when the Earth's magnetic field rearranges itself, which happens all the time,

  • it releases a bunch of stored up energy.

  • That energy triggers the creation of plasma waves, or waves of charged particles.

  • Specifically, these ones called chorus waves.

  • They form high in the Earth's atmosphere near the equator,

  • then move north and south to more extreme latitudes.

  • As they go, they scatter electrons that would otherwise just

  • bounce around in the magnetic field.

  • Some of those electrons get jostled around, and ultimately

  • rain down in batches into the upper atmosphere.

  • And that, finally, creates pulsating auroras.

  • This hypothesis has actually been around for over half a century,

  • but it's only just been proven.

  • We had to wait until we had sensitive enough equipment to observe a clear interaction between

  • chorus wave plasma and the electrons causing the auroras.

  • Still, thanks to the Japanese ERG satellite and some aurora measurements from last March,

  • scientists pulled it off.

  • The authors still acknowledge that there could be holes in their findings, like that these

  • results may not be the same across different distances from Earth and geomagnetic activity.

  • But this new research will help scientists better understand

  • how these interactions affect planets' atmospheres.

  • This applies to any planet with a magnetic field, too, including Jupiter and Saturn,

  • where we've already detected chorus waves.

  • So this is only the beginning.

  • In more wide-reaching news, literally, a group of astronomers have calculated that the neighboring

  • Andromeda Galaxy might be a lot less massive than we thought.

  • Our galactic big sister seems more like a twin.

  • There are a lot of ways to calculate a galaxy's mass,

  • and they all yield slightly different results.

  • Most astronomers have treated our galactic neighbor as 2 to 3 times more massive than

  • the Milky Way, because that's what pops up in a lot of studies.

  • But its mass is still far from certain.

  • It's hard to measure the mass of a whole galaxy, okay?

  • But new research, published last week in the Monthly Notices of the Royal Astronomical

  • Society, attempts to better pin down that mass by using a completely different technique.

  • It requires measuring how fast an object needs to travel to escape a galaxy's gravity;

  • basically, its escape velocity.

  • Galaxies with more mass will have more gravity,

  • so you need to travel faster to get away from them.

  • You'll also need to have a higher escape velocity if you're near the galaxy's center

  • of mass, as opposed to at its edge.

  • Scientists can use all this data to work backwards.

  • By calculating escape velocities at different locations,

  • they can do some math to figure out a galaxy's mass.

  • In this study, the team of astronomers used velocities of 86 speedy planetary nebulas,

  • or the remnants of certain stars, in the Andromeda Galaxy.

  • By doing some math and making some estimates, they were able to use these nebulas to calculate

  • the escape velocity of Andromeda from different locations.

  • For example, at about 49,000 light-years from the galaxy's center, that escape velocity

  • is around 470 kilometers per second.

  • Then, from those escape velocity values,

  • they were able to derive the mass of the galaxy itself.

  • And it came out to be around 800 billion times the mass of our Sun, which is roughly the

  • same mass as the Milky Way, not twice as massive or larger, like we used to suspect.

  • Still, the authors did note that they had to make certain educated assumptions in their

  • calculations, so this mass value isn't 100% certain,

  • just like all the ones that came before.

  • There's also a chance that, although they were moving really quickly, none of the

  • planetary nebulas they studied were going anywhere close to the real escape velocity.

  • That would have also affected the mass estimate.

  • So we'll have to run a few more models before we're totally certain.

  • One way or another, pinning down the deets on Andromeda is crucial for our understanding

  • of galactic evolution, and the ultimate fate of the Milky Way.

  • After all, our galaxy and Andromeda

  • are on their way to a collision in several billion years.

  • But when that happens and how it'll look depend on,surprise, how massive they are.

  • Luckily, we have, you know, some time before we need to get those measurements done precisely.

  • Thanks for watching this episode of SciShow Space!

  • If you would like to keep learning about the universe with us,

  • you can do that at youtube.com/scishowspace,

  • where we have hundreds of episodes that are all very good,

  • and also, we just keep uploading new ones every week.

  • [♪ OUTRO]

[♪ INTRO]

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