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Hint: It's not your collection of awesome refrigerator magnets!

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Whether you use them to hang pictures on your fridge or they’re inside your hard drive, the world is full of magnets.

And sure, the magnets in MRI machines or particle accelerators are powerful, but the strongest magnetic fields are actually scattered throughout the rest of the universe. They come from a type of star called a magnetar, and they’re so strong that getting within 1000 kilometers of one would tear apart your atoms!

But a magnetar that we’ll just call SGR 0418 for short, is special: it currently holds the title of the strongest magnetic field in the known universe. A magnetar is a special kind of neutron star with an extremely strong magnetic field. Neutron stars form after a big star, somewhere between 8 and 15 times the size of the sun, has burned up all of its fuel and exploded in a supernova.

After the explosion, all that’s left over is the dead, super dense core. Imagine the mass of the sun squeezed into a sphere about 20 kilometers across, and you’ll get a good idea of how dense neutrons stars are. Everything is packed together so tightly that protons and electrons get fused together into neutrons.

The star might have once been made of carbon or hydrogen or iron, but now it’s mostly just neutrons with a few protons scattered around. About one in every ten neutron stars becomes a magnetar, which has a powerful magnetic field that makes it shoot out X-ray bursts every so often. Astrophysicists aren’t positive what causes magnetars to form, but one theory is that it requires just the right combination of spin, temperature, and an existing magnetic field.

Other neutron stars might stay as they are, or they could become pulsars - rotating stars that emit beams of radiation. Even regular neutron stars have incredibly strong magnetic fields: around a trillion Gauss. Compare that to a standard bar magnet, which might be around 100 Gauss, or even the strongest magnets used in an MRI, which are about 30,000 Gauss.

So the magnetic field in a regular neutron star is ridiculously strong. But magnetars are 10 to 1,000 times stronger than that! Now, SGR 0418, our record holder for the strongest magnetic field, is 1000 times more powerful than many magnetars.

But the strange thing is, we used to think it had an especially weak magnetic field. It was discovered in 2009, using the European Space Agency’s XMM-Newton space telescope and NASA’s Chandra X-ray Observatory. Like with any new magnetar discovery, astronomers calculated the magnetic field on the magnetar’s surface by measuring the change in its spin.

They calculated that its magnetic field was 6 trillion Gauss, 100 times lower than a typical magnetar. Because its surface magnetic field seemed so weak, astronomers suspected that there was something up with this magnetar. So in 2013, they developed a new way to measure it.

Instead of measuring the spin on a normal day, they measured it during an X-ray burst instead. And this time they found that SGR 0418 wasn’t a weak magnet at all — it’s actually the strongest magnetar we’ve ever seen, with a magnetic field of over a quadrillion Gauss! It turns out that this magnetar behaves a lot differently than other magnetars we’ve seen.

While most magnetars have a strong surface magnetic field, SGR 0418’s is weak, which is why the normal methods of measurement didn’t work. Instead, its strong magnetic field is mostly below the surface, where it breaks out during X-ray bursts. It’s possible this magnetar is so strange because it’s much older than other magnetars.

Most only last around 10,000 years before their magnetic field is too weak for them to be called a magnetar, but SGR 0418 is over 550,000 years old and, for some reason, still going strong. We don’t know if there are other old magnetars with similar behavior — that is, with strong internal magnetic fields but weak surface ones. But at least now we know how to look for them and how to measure them.

So who knows? Maybe someday we’ll even find a stronger magnetic field. Thanks for watching this episode of SciShow Space, and thanks especially to our patrons on Patreon!

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