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# Summary

## To determine spin of black holes, we focus on X-ray emission, namely Quasi-Periodic-Oscillation (QPO), from accretion disks around black holes.

## While QPO itself is a big puzzle in modern astrophysics, since

## theorized in 60s, black hole’s spin has not been determined.

## We show that QPO is due to resonance of accreting blobs’ dynamics occurred very close to the black hole.

## In explaining this, we determine spin (frequency) of black holes which is a parameter of our model.

## For the best observational fit, we obtain the spin parameter of black holes ranges: 0.6 ≤ a ≤ 0.8: None of them corresponds to an extremally (a~1) rotating black hole.

## This is a test of Einstein’s theory of General Relativity.