Where do magnetar babies come from? Mysterious “fast radio bursts” can provide clues.

New research suggests a completely different route: A star corpse called a white dwarf crashes into a neutron star, producing an extremely powerful explosion and leaving behind a magnetar.

Related: Mysterious “fast radio bursts” from deep space repeat every 16 days

The mystery of the FRB

In recent decades, astronomers have seen incredibly bright, brief, and strange bursts of radio energy, known as fast radio bursts, or FRBs. To date, just over 100 FRBs have been detected in the sky. Whatever they are, they almost certainly come from outside our galaxy, the Milky Way; otherwise, scientists would have seen them concentrated throughout the band of our galaxy, rather than across the entire sky.

With some notable exceptions, FRBs are not repeated. They are one and they are made, representing a ridiculous amount of energy poured into the cosmos in less than a second. To make things even more mysterious, the FRBs for which astronomers have managed to identify an origin (not an easy task, because the phenomenon is so brief) are not associated with any particular type of galaxy or another.

The diversity of sources suggests that different types of processes in the universe, all of them violent, lead to the formation of rapid radio bursts. Whatever the processes, they require enormous amounts of energy and occur fairly quickly.

Mergers between stars are an interesting candidate. When one star crashes into another, there is obviously a lot of energy flying. And while it may take eons for the stars to get close enough to merge, the act itself is a brief moment of intense fury.

But the merging regular stars just aren’t enough to power a full FRB. To obtain the required energies, you must fuse more exotic objects, such as neutron stars and white dwarfs. Only then will you have the necessary masses and densities to organize a party.

Making a magnetar

One fusion scenario to potentially generate a FRB is the fusion of a white dwarf with a neutron star. Both neutron stars and white dwarfs are exotic types of dead star debris that were once normal.

A white dwarf is the planet-sized leftover nucleus of a star like our sun, a mass of carbon and oxygen that cools slowly as the cosmic age progresses. A neutron star is like a white dwarf but more: it is the leftover nucleus of a much more massive star, made up almost entirely of neutrons compressed into a ball no larger than a city.

Since stars are often born in pairs, it’s not crazy to think that after enough time, both stars in a system could die, leaving behind their particular type of dead cores, and that slowly, slowly, slowly, those dead bundles They could circulate closer, eventually reaching a critical point where their gravitational interaction overwhelms everything, sending the stellar corpses spiraling toward each other (and their fate).

Right on the cusp of their final collision, one of the two scenarios could unfold. In one case, the white dwarf can swell, allowing the external tendrils of its atmosphere to escape and channel to the neutron star. In the other, the neutron star’s extreme gravity completely destroys the white dwarf, and its tattered star body falls on its heavier and denser brother.

In any case, a large amount of mass is transferred to the white dwarf and neutron star, and that’s when the fun really begins, according to new research.

Igniting the monster

The scientists behind the new research want to know if a merger between a white dwarf and a neutron star might be just right to cause an extreme magnetic field to escalate. At first, the falling material (either stripped from the white dwarf or made from the torn white dwarf) spirals over the neutron star.

As it falls, it speeds up the neutron star’s rotation, like an adult pushing the carousel in the playground, to the delight and horror of the children in it. Soon, the neutron star spins faster than the kitchen blender blades.

This spiral takes the surrounding magnetic field and spins it around itself, coiling like a snake ready to attack. But the flow of matter over the neutron star is not smooth at all; It is incredibly turbulent and chaotic. Small twists and strains in the magnetic field stretch, twist, and grow, causing the magnetic field to feed itself into a dynamo mechanism, harnessing the powerful energies unleashed in the collision of the white dwarf and the neutron star to ignite a stronger magnetic field than anything else in the universe.

Finally the magnetar is born. (At least, according to this theory).

Like a newborn baby, the magnetar enters the world screaming and crying. It is unstable; Due to all the chaotic forces of fusion, it has not yet established itself at a regular rate of rotation. And because that rotation is so fast, any small glitch or snag will release a powerful burst of energy in the form of electromagnetic radiation, scientists suggest.

And radio waves, like massive FRB bursts, are electromagnetic radiation.

The new research suggests that at least some of the FRBs we observe in the sky are the screams of newborn magnetars, created from the cosmic collision of neutron stars with white dwarfs. If the premise is correct, it is almost poetic: the collision of two exotic stellar remnants, creating another strange inhabitant of the cosmos, giving rise to one of the most extreme bursts of energy known to astronomers, an explosion of radiation so intense that it can be witness from all over the universe.

It is perhaps the most difficult birth in the cosmos.

The research is described in an article published April 8 in the Astrophysical Journal.