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  • Einstein's theory of General Relativity completely changed the way we think about

  • space, time, and gravity when it dropped, pun intended, over one hundred years ago.

  • General relativity says that objects warp space and time, and this warping is experienced

  • as gravity.

  • This idea has some pretty mind-bending implications that ripple down from it, and now scientists

  • have strong evidence that spinning objects put space-time in a twist.

  • The analogy most of you have probably seen is that space-time is like a sheet, or a trampoline.

  • Put a bowling ball on the trampoline and it warps the taut surface.

  • While that's a helpful image to have in your head in most cases, it doesn't cover

  • all the effects a massive object can have on spacetime, like when it's rotating.

  • Three years after Einstein published his theory, he and two Austrian mathematicians, Josef

  • Lense and Hans Thirring, realized that a spinning object should also drag spacetime around with it.

  • So if I may, I'd like to substitute the trampoline analogy with something I'm always

  • thinking about: noodles.

  • Picture spacetime as a plate of pasta, and a spinning object as a twisting fork stuck

  • into it.

  • Dragging the noodles of spacetime around is known as the Lense-Thirring effect, or frame

  • dragging, since it's literally dragging the local frame of reference around with it.

  • Of course, like most things with general relativity, you don't notice them on a small scale.

  • When I spin around as fast as I can nothing swirls around me in a vortex, even though

  • it kinda feels like that when I stop.

  • Even an object as large as the earth produces miniscule frame dragging, though we have observed

  • it in the past.

  • NASA's Gravity Probe B was launched in 2004 and orbited in a polar orbit, so, perpendicular

  • to the rotation of the Earth.

  • The satellite was equipped with a set of gyroscopes that measured precession, or wobble, due to

  • frame dragging.

  • It isolated the effects of frame dragging by compensating for other sources of drag

  • like Earth's gravity, solar radiation, and the atmosphere.

  • Gravity Probe B then observed a star for a year and measured how much the churning spacetime

  • threw off its gaze.

  • In the end, the change was tiny: just 39 milliarcseconds, or 0.00001 degrees.

  • That's next to nothing, but in extreme and rare cases, frame dragging can be hugely noticeable.

  • In January of 2020, scientists published their observations of just such a special case.

  • The scientists watched a binary star system with some unusual qualities.

  • One star is a white dwarf about the size of the Earth but much chunkier, about 300,000

  • times the density.

  • This white dwarf is spinning so fast it completes a rotation in a matter of minutes.

  • That mass and speed means it drags space-time around it much more strongly than Earth does.

  • Of course the question is, how do you observe the space time around it actually twisting?

  • And that's where the white dwarf's companion comes in.

  • Whipping around it like an excited chihuahua is a neutron star just 20 kilometers across,

  • but 100 billion times the density of Earth.

  • This neutron star is also spinning rapidly, causing it to shoot off powerful beams of

  • electromagnetic radiation.

  • These types of stars are known as pulsars, because their spinning beams look like regular

  • pulses to distant observers, kind of like a cosmic lighthouse.

  • The pulsar in this system is orbiting the white dwarf in a different plane than the

  • white dwarf's rotation, so the entire orbit tumbles around.

  • By measuring how the timing of the neutron star's pulses varied, they could figure

  • out how much frame dragging was caused by the white dwarf.

  • Simple, right?

  • Well, it took them almost 20 years to untangle exactly what was going on, but in the end

  • they concluded the white dwarf exhibited frame dragging 100 million times stronger than Gravity

  • Probe B observed around Earth.

  • The scientists are extremely happy with the results of their research, which confirms,

  • once again, Einstein's notion of how the universe works...

  • and makes me hungry for spaghetti.

  • Frame dragging can also account for the precession in the jets of matter shot out by black holes.

  • Oh, you didn't know black holes shot out jets of matter?

  • Well, it just so happens that I made a video about that, tooand you can watch it here!

  • If you like what we're doing, go ahead and leave us a comment, and don't forget to subscribe.

  • I'll see you next time on Seeker!

Einstein's theory of General Relativity completely changed the way we think about


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この死んだ星は時空を捻じ曲げている (This Dead Star Is Twisting Spacetime)

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    林宜悉 に公開 2021 年 01 月 14 日