A magnetar is a dead star about the size of a city, spinning in space and wrapped in an almost unimaginable magnetic field. Get close enough and atoms would stop behaving as they do on Earth. Their electron clouds would be squeezed into elongated shapes, their binding energies would change and the familiar chemistry sustaining a human body would fail.
These distances are rough thought experiments rather than precise boundaries. Nobody has tested what happens to a person beside a magnetar, and any real encounter would also involve lethal gravity, X-rays and gamma rays.
Still, the calculations reveal just how extreme these objects are.
A rare kind of neutron star
When a massive star exhausts the fuel in its core, the core can collapse during a supernova and leave behind a neutron star. NASA describes neutron stars as about 20 kilometres across, roughly the width of a city, while typically containing more mass than the Sun.
Their density is almost impossible to picture. A teaspoon of neutron-star material would weigh about a billion tons under Earth’s gravity.
A magnetar is a rare neutron star whose behaviour is dominated by an exceptionally powerful and often complicated magnetic field. Only about 30 are known in the Milky Way, although the number varies depending on whether uncertain candidates are included.
Fields at the limits of nature
Earth’s surface magnetic field measures roughly 0.25 to 0.65 gauss. Magnetar fields commonly reach between 1014 and 1015 gauss. At the upper end, that is between one and several quadrillion times stronger than Earth’s field, depending on where Earth’s field is measured.
Astrophysicist Kenzie Nimmo described neutron-star fields as being “at the limits of what the universe can produce.” Magnetars are therefore not merely powerful magnets by terrestrial standards. They occupy a region of physics no human laboratory can reproduce.
What an extreme field does to atoms
It is often said that a magnetar would simply tear atoms apart, but the reality is more complicated. Calculations show that atoms can remain bound in enormous magnetic fields, although they no longer resemble the roughly spherical atoms familiar on Earth.
The field confines electrons tightly across its direction, producing narrow, elongated electron clouds and changing the energy required to bind electrons to nuclei. Under some conditions, atoms may even join into molecular chains or condensed forms of strongly magnetised matter.
Christopher Bochenek, an astrophysicist at Caltech, described the effect by saying magnetar fields can “squish atoms into pencil-like shapes.” That is more accurate than imagining every atom being stripped instantly into a bare nucleus. The atoms may remain bound, but their structure and chemistry become radically different.
What it might do to a person
NASA has used the striking example that a person within roughly 600 miles, or about 1,000 kilometres, of a magnetar would have the atoms in their body ripped apart. Of course, that wording is best understood as dramatic outreach language rather than a precise physical threshold.
NASA has also said that a magnetar placed halfway to the Moon could erase credit cards on Earth!
The variation shows that this is an illustration of scale, not a universal erasure distance. Magnetars differ in strength, while magnetic stripes vary in how strongly they resist demagnetisation. Orientation and shielding would matter as well.
Why magnetars matter
The same conditions that make magnetars terrifying also make them scientifically valuable. ESA observations of SGR 0418+5729 indicated local regions where the field may reach 1015 gauss across areas only a few hundred metres wide.
Magnetars may also produce at least some fast radio bursts. In 2020, an FRB-like flash was detected from a known magnetar in the Milky Way, proving that these stars can generate brief but extraordinarily powerful radio explosions.
Up close, a magnetar would make survival impossible through a combination of radiation, gravity and magnetic distortion. From a safe distance, however, it becomes a natural laboratory for studying matter and energy under conditions found nowhere on Earth.
