Could all supermassive objects in the center of galaxies be SGR's post mortem?

Short lifetime

In the outer layers of a magnetar, which consist of a plasma of heavy elements (mostly iron), tensions can arise that lead to 'starquakes'. These seismic vibrations are extremely energetic, and result in a burst of X-ray and gamma ray radiation. To astronomers, such an object is known as a soft gamma repeater.

The life of a magnetar as a soft gamma repeater is short: Starquakes cause large ejections of energy, and matter. The matter is held in the strong magnetic field, and evaporates in minutes. Radial ejection of matter carries away angular momentum which slows the rotation. Magnetars lose rotational speed at a higher rate than other neutron stars, attributed to their high magnetic field. Slowdown weakens the magnetic field, and after only about 10,000 years the starquakes cease. After this, the star still radiates X-rays, and astronomers conjecture it forms an anomalous X-ray pulsar. After another 10,000 years, it becomes completely quiet. Starquakes are blockbuster detonations and some have been directly recorded, such as that at SGR 1806-20 on December 27, 2004, and more are expected to be recorded as telescopes increase in fidelity.