The hyperactive sunspot region responsible for May’s incredible aurora has done it again, firing not one but two X-class solar flares in less than 12 hours.

The first X-class solar flare peaked at 6:03 PM ET (2203GMT) on Friday, May 31, and the second peaked at 4:48 AM ET (0848 GMT) today (June 1).

Solar flares are powerful bursts of electromagnetic radiation from the surface of the Sun. They are divided into letter groups according to their strength; Class X is the strongest. In each class, numbers 1 through 10 (and more for Class X flashes) describe the relative power of the flash. Friday’s and today’s major flares were X1.18 and X1.43 respectively.

The complex magnetic core of the collapsing sunspot AR3664 provides ideal conditions for creating powerful explosions. This is because two magnetic poles of opposite signs are tightly squeezed together at the very center of the AR3664. This can be seen in the image below from NASA’s Solar Dynamics Observatory magnetogram; where white indicates north magnetic polarity and black indicates south magnetic polarity.

When oppositely directed magnetic field lines in the solar plasma break and reconnect (a process known as magnetic reconnection), the energy of the magnetic field is converted into the plasma’s kinetic and thermal energy, which can lead to powerful flares on its surface. The sun—in this case, two recent X-class solar flares.

During both solar flares, radio blackouts were observed on the sunny side of the Earth; the first was in the western United States and the Pacific Ocean, and the second was in Europe, Africa, and Asia.