Figure 1: Asteroid belts are thought to exist throughout the Universe; as an example,
here is an artist’s depiction of an asteroid belt around the star Vega.
Image credit: NASA/JPL-Caltech

A Universal Clock Skewed by … Asteroids?

BY SUSANNA KOHLER
FEBRUARY 1, 2013

Title: An Asteroid Belt Interpretation for the Timing Variations of the Millisecond Pulsar B1937+21
Authors: R. M. Shannon et al.
First Author’s Institution: Cornell University; CSIRO Astronomy and Space Science, Australia

Background

As we’ve discussed before, pulsars (rapidly rotating and highly magnetized neutron stars) are incredibly accurate clocks. Every time the hot spot on the surface of a pulsar rotates past the Earth (see this animation), we observe a spike in the signal that corresponds to the beam of radiation from the pulsar passing over the Earth. The periods of pulsars — in particular pulsars with periods in the millisecond-range — are usually extremely regular and can therefore be very accurately measured: as Chris points out in his astrobite, the period of the pulsar PSR B1937+21 is measured to be 1.5578064688197945 +/- 0.0000000000000004 milliseconds!

The regularity of these periods make pulsars an ideal means of timing things in the Universe. In fact, using arrays of pulsars as highly accurate clocks has been proposed as a means of detecting gravitational waves (see Chris’s astrobite). The uniformity of pulsar signals also make them a means for discovering exoplanets: any irregularities in the observed pulsar period can indicate there’s something else going on in the system — such as a planet orbiting the pulsar — that causes the difference in timing.

In the curious case of PSR B1937+21, something even more subtle than this might be happening. The authors of this paper suggest that the slight irregularity in its observed period indicates that it is surrounded by an asteroid belt!

Read more: A Universal Clock Skewed by … Asteroids? | astrobites.

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