Thanks to the Hubble Space Telescope, we all have a vivid image of the Crab Nebula emblazoned in our mind\u2019s eyes. It\u2019s the remnant of a supernova explosion Chinese astronomers recorded in 1056. However, the Crab Nebula is more than just a nebula; it\u2019s also a pulsar.<\/p>\n
The Crab Pulsar pulsates in an unusual \u2018zebra\u2019 pattern, and an astrophysicist at the University of Kansas thinks he\u2019s figured out why.<\/p>\n
<\/p>\n When massive stars explode as supernovae, they leave behind remnants: either a stellar-mass black hole or a neutron star. SN 1054 left behind the latter. The neutron star is highly magnetized and spins rapidly, emitting beams of electromagnetic radiation from its poles. As it spins, the radiation is intermittently directed towards Earth, making it visible to us. In this case, it\u2019s called a pulsar.<\/p>\n Pulsars are complex objects. They\u2019re extremely dense and can pack up to three solar masses of material into a sphere as small as 30 km in diameter. Their magnetic fields are millions of times stronger than Earth\u2019s, they can rotate hundreds of times per second, and their immense gravity warps space-time. And their cores are basically huge atomic nuclei. <\/p>\n One result of their complexity is their radio emissions, and this is especially true of the Crab Pulsar. <\/p>\n Pulsars are known for their main pulse (MP), but they also emit other pulses that are more difficult to detect. In 2007, radio astronomers Hankins and Eilek discovered a strange pattern in the Crab Pulsar\u2019s high-frequency radio emissions. This is the only pulsar known to produce these patterns between the pulsar\u2019s main pulse (MP) and its intermittent pulse (IP). <\/p>\n \u201cThe mean profile of this star is dominated by a main pulse (MP) and an interpulse (IP),\u201d Eilek and Hankins wrote in their paper. However, there are two additional pulses called HFC1 and HFC2 that create the zebra pattern. <\/p>\n Nobody has succeeded in explaining this unusual pattern. However, new research published in Physical Review Letters may finally explain it. The author is Mikhail Medvedev, who specializes in Theoretical Astrophysics at the University of Kansas. His research is \u201cOrigin of Spectral Bands in the Crab Pulsar Radio Emission.\u201d<\/p>\n Medvedev says that the Crab Pulsar\u2019s plasma-filled magnetosphere acts as a diffraction screen to produce the zebra pattern. This can explain the band spacing, the high polarization, the constant position angle, and other characteristics of the emissions. <\/p>\n A typical pulsar emits radio emissions from its poles, as shown in the figure below. They sometimes emit two signals per rotation period, one radio and one high frequency. They appear in a different phase of the rotation, with the higher frequency emission produced outside the light cylinder, the region where linear speed approaches the speed of light.<\/p>\n But the Crab Pulsar is different. <\/p>\n \u201cThe Crab pulsar is, in contrast, very special. Its radio main pulse and interpulse are coincident in phase with high-energy emission, indicating the same emission region,\u201d Medvedev explains. <\/p>\n Medvedev explains that the High-Frequency Interpulse (HFIP) produced by the diffraction effect creates the zebra pattern. \u201cThe spectral pattern of the high-frequency interpulse (HFIP), observed between about Medvedev\u2019s proposed model has an additional benefit. He says it can be used to perform tomography on pulsars to uncover more details about their powerful magnetospheres. <\/p>\n \u201cThe model allows one to perform \u201ctomography\u201d of the pulsar magnetosphere,\u201d he writes. <\/p>\n \u201cWe predict that this HFIP properties can also be observed in other pulsars if their radio and high energy emission are in phase. This would happen if the radio emission is produced in the outer magnetosphere as opposed to the \u201cnormal\u201d emission from the polar region,\u201d Medvedev explains. <\/p>\n Medvedev says his model can also explain the HFC1 and HFC2 in the Crab Pulsar\u2019s emissions spectrum. They\u2019re also artifacts of his proposed diffraction model. \u201cWe propose that these high-frequency components are the reflections off the magnetosphere of the same source producing the diffracted HFIP,\u201d he explains. <\/p>\n \u201cTo conclude, we propose a model, which explains the peculiar spectral band structure (the zebra pattern) of the high-frequency interpulse of the Crab pulsar radio emission,\u201d Medvedev writes. <\/p>\n![\"This](\"https:\/\/www.universetoday.com\/wp-content\/uploads\/2024\/11\/crab-pulsar-overall-geometry.png\")
![\"This](\"https:\/\/www.universetoday.com\/wp-content\/uploads\/2024\/11\/standard-pulsar-emissions.png\")
?~5 and ?~30 GHz is remarkably different and represents a sequence of emission bands resembling the
\u201czebra\u201d pattern,\u201d he writes. <\/p>\n![\"This](\"https:\/\/www.universetoday.com\/wp-content\/uploads\/2024\/11\/pulsar-diffraction-schematic.png\")
![\"This](\"https:\/\/www.universetoday.com\/wp-content\/uploads\/2021\/05\/Crab-nebula-Pulsar-Chandra-X-Ray-Observatory.jpg\")
Like this:<\/h3>\n