The Pulsar That Munched a Billion Ton Asteroid
An asteroid gets blasted by the powerful X-rays from a pulsar, turning it into energized particles that interact with the pulsar's magnetic field.
NASA's Dawn spacecraft orbited the massive asteroid Vesta in 2011 and 2012, giving us an unprecedented look at the protoplanet's landscape, craters and mineral composition. The probe, which is now on its way to dwarf planet Ceres, not only revealed the evolution of Vesta, it also provided vital clues as to the evolution of our solar system. Now,in new images published by NASA
, an unusually colorful Vesta landscape is on display. Using data from the mission, scientists at Max Planck Institute for Solar System Research in Katlenburg-Lindau, Germany have produced a rather psychedelic view of this otherwise bland landscape. Dawn's camera system is equipped with seven filters, each filter sensitive to a specific wavelength of light. Normally, Vesta would look gray to the naked eye, but when analyzing the ratios of light through Vesta's filters, the landscape pops with color. Shown here, the flow of material inside and outside a crater called Aelia is demonstrated. As different minerals reflect and absorb different wavelengths of light, this composite image is alive with color, each shade representing different kinds of minerals littering Vesta's landscape.
This is Antonia, a crater located inside the huge Rheasilvia basin in the southern hemisphere of Vesta. From this image, planetary scientists have been ableto deduce that
"the light blue material is fine-grain material excavated from the lower crust. The southern edge of the crater was buried by coarser material shortly after the crater formed. The dark blue of the southern crater rim is due to shadowing of the blocky material."
The impact crater Sextilia can be seen in the lower right of this image. The mottled dark patches are likely impact ejecta from a massive impact and the redish regions are thought to be rock that melted during the impact. The diversity of the mineralogy is obvious here. "No artist could paint something like that. Only nature can do this," said Martin Hoffman, a member of the framing camera team at Max Planck Institute.
Earlier images of Vesta have shown an unusual "pitted terrain" on the floors of the craters named Marcia (left) and Cornelia (right). Once again, the varied colors demonstrate the different minerals and processes that cover Vesta's surface.
of Vesta shows the abundance of hydrogen on Vesta's surface. Note that the hydrogen signal is enhanced near the asteroid's equator. The hydrogen is likely from hydroxyl or water bound to minerals in Vesta's surface.
Another, earlier view of Antonia crater, demonstrating the mineral diversity of the region.
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