![]() ![]() Learn more by listening to the "Ask a Spaceman" podcast, available on iTunes (opens in new tab) and. But every year, the techniques get better, and the hope is that soon, these arrays will unlock a huge part of the gravitational wave universe. So far, they've had limited success, finding shifts in timings from various pulsars but no hints of correlations. Many collaborations across the world have used radio telescopes to study pulsar timing arrays for decades. ![]() The "array" part of "pulsar timing array" comes from studying many pulsars at once and looking for correlated movements: If a gravitational wave passes over one region of space, then all the timings from the pulsars in that direction will shift in unison. Astronomer Jocelyn Bell Burnell recounts her discovery of pulsars How a future gravitational wave detector in space will reveal more about the universe But the measurements of the millisecond pulsars are sensitive enough that those changes can be detected - at least in principle. For a typical gravitational wave, the shift in the timings is incredibly tiny - a change of just 10 or 20 nanoseconds every few months. One flash from the pulsar may arrive a bit too soon then another may arrive a little too late. That change in distance will appear to us as changes in the rotational period. As the wave moves, the pulsar will appear slightly closer, then slightly farther, then slightly closer, and so on until the wave has moved on. If a gravitational wave passes over Earth, over a pulsar or even between us, then as it passes, it will change the distance between Earth and the pulsar. First, astronomers observe the rotational periods of as many millisecond pulsars as possible. That's the same level of precision as our best atomic clocks.Īnd those millisecond pulsars are perfect gravitational wave detectors. Astronomers think millisecond pulsars are "revived" pulsars, spun up to incredible speeds after infalling material from a companion star accelerates them like a grown-up pushing a kid on a schoolyard merry-go-round.īecause of their ludicrous speed, millisecond pulsars can maintain fantastic precision over very long timescales. So instead, timing arrays rely on a subset of pulsars known as millisecond pulsars, which, as the name suggests, have rotational periods of a few milliseconds. That means most pulsars aren't good for studying gravitational waves. But most pulsars are susceptible to random starquakes (when the star's contents shift around, disturbing the pulsar's rotation), glitches and slowdowns that change their regularity. They are so heavy, and spin so quickly, that we can use their flashes as extremely precise clocks. Related: Gravitational waves play with fast spinning stars, study suggests When those beams cross over Earth, we see them as periodic flashes of radio emission, putting the "pulse" in "pulsar." ![]() This forces the beams of radiation to sweep out circles in the sky. ![]() Those magnetic poles don't always line up with the rotational axis of the pulsar, in much the same way Earth's North and South magnetic poles don't line up with our planet's rotational axis. Together, they power beams of radiation (if you're getting Death Star vibes here, you're not far off) that blast out from the magnetic poles in each direction. Those intense magnetic fields also whip up strong electric fields. Those spinning charges power up incredibly strong magnetic fields - in some cases, the most powerful magnetic fields in the universe. They are ultradense balls made almost purely of neutrons, with some electrons and protons thrown in for good measure. Pulsars are the leftover cores of giant stars and are among the most exotic objects ever known to inhabit the cosmos. Pulsars are already fantastic objects, and that's especially true for the kinds of pulsars used as gravitational wave detectors. This is the idea behind so-called pulsar timing arrays. So, instead of using instruments on the ground, we can use distant pulsars to help us measure gravitational waves. For that, we need a much, much larger detector. Our detectors simply don't have the sensitivity to measure those small differences over such long time spans. Those kinds of low-frequency waves come from mergers of giant black holes, which take a lot longer to merge than their smaller cousins do. But ground-based detectors have a much harder time finding low-frequency gravitational waves, since those take weeks, months or even years to pass through Earth. ![]()
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