You know when you’re having a bad day when you get hit by a billion ton asteroid. But for a pulsar 37,000 light-years away, it’s just a another day at the office. And besides, PSR J0738-4042 has an uber-powerful X-ray blaster to deal with errant space rocks.
Astronomers of Australia’s Commonwealth Scientific and Industrial Research Organisation (CSIRO) made the pulsar-pounding, asteroid-zapping discovery while using the Parkes Telescope to study the dusty, high-radiation environment surrounding the tiny spinning husk of the dead star. Pulsars are spinning compact stellar objects known as neutron stars that generate powerful beams of radiation from their intensely magnetized poles that, if aligned correctly with Earth, can be observed as ultra-precise radio pulses.
Pulsars are considered the most precise ‘clocks’ in the universe, but if a pulsar’s pulse timings abruptly change, a cataclysmic event likely occurred.
In the case of PSR J0738-4042, the CSIRO astronomers noticed weird changes in the pulsar’s timing and its characteristic pulse, signals that the researchers have attributed to multiple asteroid hits.
“One of these rocks seems to have had a mass of about a billion tons,” said CSIRO astronomer Ryan Shannon in a press release.
In 2008, Shannon theorized that should a large rocky object, like an asteroid or even a small planet, collide with a pulsar, the pulsar will react in a very precise way; now it seems PSR J0738-4042 has become the prime candidate as observational evidence for this theory. The time of the pulse has lengthened and the radio signal received by Parkes has changed.
“We think the pulsar’s radio beam zaps the asteroid, vaporizing it. But the vaporized particles are electrically charged and they slightly alter the process that creates the pulsar’s beam,” said Shannon. The electrically charged particles interact with the pulsar’s magnetic field, like a magnetic blender, generating energy, sapping some of the pulsar’s angular momentum. This has a drag effect, slowing the spin rate. However, once all the ionized material has been converted to energy, the pulsar is expected to return to its pre-asteroid strike spin rate.
It is thought that the surrounding asteroids originated from the star that exploded to form the pulsar. The pulsar is a byproduct of a supernova, but before the star went supernova, it formed a system of rocky bodies, such as the billion ton asteroid and, possibly, planets.
This asteroid-vaporizing event is exciting in that it proves that rocky debris that formed before the star went supernova persisted after the star’s death, forming a debris disk around PSR J0738-4042. It’s possible that the surviving debris disk could be rejuvenated, spawning the agglomeration of larger and larger objects, potentially forming new planets.
The discovery of asteroid vaporization events close to PSR J0738-4042 is an interesting development in the study of disks surrounding pulsars. For example, another pulsar, J0146+61, has been found to be sporting a dusty debris disk and, in 1992, two planet-sized objects were discovered orbiting pulsar PSR 1257+12.
“This sort of dust disk could provide the ‘seeds’ that grow into larger asteroids,” said Ph.D. student Paul Brook, of the University of Oxford and CSIRO who led the PSR J0738-4042 study.
This research has been published in The Astrophysical Journal Letters.
Publication: Evidence of an asteroid encountering a pulsar, Brook et al., ApJL, 2014. doi:10.1088/2041-8205/780/2/L31