Last go-round, M82's gravity likely raised density waves rippling around M81, resulting in the richness of M81's spiral arms.
最近一个周期中，M82的重力增强了M81周围密度波的脉动，导致M81的旋臂更浓密。
It is not speed, but variations in speed that cause density waves.
并不是速度高低引起了拥堵波，而是速度的不一致性。
Gravity, however, causes density waves to move out through the galaxy which in turn triggers the formation of hot, bright young stars, producing the ring that we see in this picture.
引力会使密度波穿透星系，继而形成炽热、耀眼的年轻恒星，产生我们在图片中看到的光环。
Alternatively the shells may be like ripples in a pond, where the ongoing collision with the spiral galaxy just above NGC 474 is causing density waves to ripple though the galactic giant.
另一种说法是，壳状结构如同是池塘中的波纹，是NGC 474与位在其上的螺旋星系正在进行的碰撞所产生的密度波搅动而激起的。
Alternatively the shells may be like ripples in a pond, where the ongoing collision with the spiral galaxy just above NGC 474 is causing density waves to ripple though the galactic giant.
另一种说法是，壳状结构如同是池塘中的波纹，是NGC 474与位在其上的螺旋星系正在进行的碰撞所产生的密度波搅动而激起的。
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