Vlad Tarko writes on Softpedia:
According to Einstein’s theory of general relativity, a moving mass should create another field, called gravitomagnetic field, besides its static gravitational field. This field has now been measured for the first time and to the scientists’ astonishment, it proved to be no less than one hundred million trillion times larger than Einstein’s General Relativity predicts.
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This gravitomagnetic field is similar to the magnetic field produced by a moving electric charge (hence the name “gravitomagnetic” analogous to “electromagnetic”). For example, the electric charges moving in a coil produce a magnetic field — such a coil behaves like a magnet. Similarly, the gravitomagnetic field can be produced to be a mass moving in a circle. What the electric charge is for electromagnetism, mass is for gravitation theory (the general theory of relativity).
A spinning top weights more than the same top standing still. However, according to Einstein’s theory, the difference is negligible.