Right, magnetars. Perhaps one of the most ferocious beasts to inhabit the cosmos. Loud, unruly, and temperamental, they blast their host galaxies with wave after wave of electromagnetic radiation, running the gamut from soft radio waves to hard X-rays. They are rare and poorly understood.
Some of these magnetars spit out a lot of radio waves, and frequently. The perfect way to observe them would be to have a network of high-quality radio dishes across the world, all continuously observing to capture every bleep and bloop. Some sort of network of deep-space dishes.
Like NASA’s Deep Space Network.
Magnetars are almost too unreal to believe. The description you’re about to read might seem too fantastical and violent to possibly exist in our universe. But oh, my sweet summer child, never underestimate the intensity of mother nature.
Imagine an object several times the mass of the sun, squeezed into a space no bigger than a small midwestern town. And that already-exotic object is spinning, rapidly, in some cases faster than a kitchen blender. Like I said, almost too unreal to be believable.
These particular objects are a kind of pulsar, and pulsars themselves are exotic dead remnants of giant stars. In the final moments of a massive star’s death, the entire weight of the star crushes inwards with nothing to resist it – with no nuclear fire burning in its core, there’s nothing left to keep the precious equilibrium that maintains a star for eons. Over the span of just a few minutes, the intense pressures squeeze the core smaller and smaller and smaller, converting all the protons into neutrons and forging a pulsar in the process.
This stellar cinder isn’t supported by the usual physics like heat and radiation, but instead by quantum degeneracy pressure – the simple refusal of neutrons to occupy the same state and same position.
But why “magnetars”? Their name is important here. Magnetars, as far as we can tell, appear to be young freshly-forged pulsars. While all pulsars are almost entirely made of neutrons, some stray charged particles like protons and electrons survive the crucible. These embedded charges spin around and around along with the rest of the stellar body, and charges moving around rapidly make magnetic fields. In this case, strong ones.
How strong? Thank you for asking.
How about a trillion to a quadrillion times stronger than the magnetic field of the Earth? How about the strongest magnetic fields known in existence?
I told you, almost unbelievable.
So you’ve got this weirdo star with its giant magnetic field spinning around like a demonic oversize top. This situation won’t last forever, though, because interactions between the magnetic field and the pulsar itself cause it to emit electromagnetic radiation, and in some cases especially radio waves. This radiation saps energy from the pulsar, slowing it down and eventually shutting off the awesome magnetic field altogether.
Of the over two thousand known pulsars, just a couple dozen are magnetars, and just four of them emit exceptionally strong radio signals. Astronomers aren’t exactly sure why these magnetars are so special. Perhaps their local environment is so rich in charged particles that their natural radio emission gets enhanced, but that’s only a guess.
The radio emission from these magnetars can change rapidly, as quickly as a day. Sometimes starquakes rock the surfaces of the pulsars as their shell-like exteriors crack and reassemble, causing so-called “glitches” that ripple like hiccups in the radio emission. What’s more, each pulse from a radio magnetar contains a lot of bright sub-pulses that each need to be tracked and analyzed.
It’s only through these detailed observations can we get a hint as to the extreme astrophysics of the magnetars themselves.
Enter NASA’s Deep Space Network, consisting of three telescopes at specifically-chosen locations across the globe: Madrid, Spain, Canberra, Australia, and Goldstone, California. These sites are primarily used for tracking and communicating with NASA’s various interplanetary (and in one notable case, interstellar) spacecraft. The locations were chosen to provide continuous, round-the-clock and round-the-sky coverage.
But it’s not used all the time. It takes a long time to communicate with robotic probes flung throughout the solar system, and there’s a lot of downtime. And in that time the telescopes and antennae are just sitting there, listening to the cosmos above them, capable of picking up a variety of radio signals.
Including the signals from exotic magnetars.
In a recent paper, a team of astronomers used NASA’s Deep Space Network to make detailed observations of three radio magnetars, and an additional magnetar that appears to be winding down and ending its life. As expected, these objects varied rapidly during the course of the weeks and months of the observations, with strange and (currently) unexplained changes to the radio emission.
This work was the most detailed observations yet of these radio magnetars. This is usually the part where I would close with some comments about the astrophysical processes that led to the observations, but alas, when it comes to these exotic beasts of the cosmos, we still have a lot more listening to do.
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