The most finicky readers will know that the Earth is not exactly spherical because, due to its rotation, the material at the equator experiences a greater centrifugal force than the one closest to the poles. This difference “flattens” our planet, so that the diameter between the two poles is almost 40 kilometers less than its equatorial diameter. So if you want to be repellent, correct anyone who claims that the Earth is round by saying that the Earth is actually a geoid . If you want to be more repellent than the repellent, point out that geoid only means that “the Earth has the shape of the Earth” and that in reality its shape is that of an “oblate spheroid”.
The fact is that, although the Earth is “flattened”, the difference between its diameters is so minimal that it cannot be seen in a photo. But there are objects that experience greater differences in force throughout their volume and that present a visible flattening .
The most extreme case is that of the star Achernar, which completes a rotation on itself every two days. It may seem little, of course, but it must be taken into account that this star has a diameter that, on average, is 9 times greater than that of the Sun. Note that I say on average because, in reality, this star is so flattened that its diameter at the equator it is 11.4 times that of the Sun, but between its poles it is only 7.3 times the diameter of the Sun.
But there are other objects that rotate even faster … Although they do not deform as much because their size is much smaller and, therefore, the forces generated by acceleration are not so extreme.
For example, when a very massive star is killed by exploding in the form of a supernova, one of the possible results of the explosion is a neutron star, an extremely dense object barely measuring a few tens of kilometers in diameter. But, of course, the angular momentum of the star must be conserved after the explosion so, to compensate for the compression of the mass, they begin to rotate at extremely high speeds. So high that the fastest known pulsar rotates at a dizzying 700 revolutions per second.
The figure is difficult to imagine, but humans have approached that mark in 2013, when a group of researchers managed to make a microscopic sphere of calcium carbonate rotate at 600 million revolutions per minute inside a chamber of vacuum using lasers … which implies, nothing more and nothing less, that the sphere rotated 10 million times every second … amazing!
