As of 2017, what produces the strongest known magnetic field?

A magnetar’s magnetic field is about a quadrillion (1015) Gauss. In comparison, the Earth’s magnetic field is uneven, ranging from 0.25 to 0.65 Gauss. A 15 Tesla Magnetic Resonance Image (MRI) machine generates a magnetic field of 150,000 Gauss. A standard neodymium magnet’s field is about 12,500 Gauss. One Gauss is defined as one maxwell per square centimeter.

On December 27, 2007, a magnetar designated “SGR 1806-20” released a burst of x-rays more powerful than any ever recorded. SGR 1806-20 is about 50,000 light years away. If it had been only 10,000 light years away, it probably would have destroyed the earth's ozone layer and caused mass extinctions. As it was, the burst was powerful enough to interfere with the planet's atmosphere, as it gave off about 10,000 trillion, trillion, trillion watts of power.

When a star much more massive than our sun explodes in a supernova, it leaves behind a core of incredibly dense matter. This is called a neutron star because it is made up of neutrons. SGR 1806-20 is about 20 kilometers (12 miles) across, spins on its axis once every seven and a half seconds, and has a mass of about two to three times that of the sun.

“SGR” stands for “Soft Gamma Repeater”. SGRs flare up—possibly because of a “starquake”, which is similar to an earthquake—without warning and emit gamma rays, such as x-rays. No known magnetar is closer to Earth than 4,000 or 5,000 light years.