available on the pre-print site arXiv<\/a>.<\/p>\n\u201cLight doesn\u2019t travel in a straight line in a gravitational field because space itself is curved,\u201d he said. \u201cWhat would be straight in flat spacetime becomes curved in the presence of strong gravity. In that sense, gravity acts as a lens in curved spacetime.\u201d<\/p>\n
According to Medvedev, while gravitational lensing has been discussed extensively in the context of black holes, this is the only case where astronomers see a \u201ctug-of-war\u201d between plasma and gravity shaping the observed signal.<\/p>\n
\u201cIn black hole images, gravity alone shapes the structure,\u201d he said. \u201cIn the Crab Pulsar, both gravity and plasma act together. This represents the first real-world application of this combined effect.\u201d<\/p>\n
Relatively close in astronomical terms, the Crab Pulsar is centered within the Crab Nebula, located in the Perseus Arm of the Milky Way galaxy \u2014 only about 6,500 light-years away from Earth with a good line-of-sight. Because it\u2019s nearby and easily observed, study of the Crab Nebula and Crab Pulsar gives astronomers insight into nebulae, supernovae and neutron stars in general.<\/p>\n
\u201cThere\u2019s a remarkable pattern in Pulsar\u2019s spectrum,\u201d Medvedev said. \u201cUnlike ordinary broad spectra \u2014 such as sunlight, which contains a continuous range of colors \u2014 the Crab\u2019s high-frequency inter-pulse shows discrete spectral bands. If it were a rainbow, it\u2019s as if only specific \u2018colors\u2019 appear, with nothing in between.\u201d<\/p>\n
Most pulsar radio emissions are spectrally broader and noisy, not banded so cleanly like the Crab Pulsar.<\/p>\n
\u201cThe stripes are absolutely distinct with complete darkness between them,\u201d Medvedev said. \u201cThere\u2019s a bright band, then nothing, bright band, nothing. No other pulsar shows this kind of striation. That uniqueness made the Crab Pulsar especially interesting \u2014 and challenging \u2014 to understand.\u201d<\/p>\n
While earlier Medvedev\u2019s model could reproduce stripes, the high contrast of the bands actually observed in the Crab Pulsar couldn\u2019t be accounted for. Indeed, his research recently determined the Crab Pulsar\u2019s plasma matter causes diffraction in the electromagnetic pulses largely responsible for the neutron star\u2019s singular zebra pattern.<\/p>\n
But now Medvedev has factored in Einstein\u2019s theory of gravity into the mix, finding it plays a pivotal role in the Crab Pulsar\u2019s zebra pattern.<\/p>\n
\u201cThe previous theoretical model could reproduce stripes, but not with the observed contrast. The inclusion of gravity provides the missing piece,\u201d Medvedev said. \u201cThe plasma in the pulsar\u2019s magnetosphere can be thought of as a lens \u2014 but a defocusing lens. Gravity, by contrast, acts as a focusing lens. Plasma tends to spread light rays apart; gravity pulls them inward. When these two effects are superimposed, there are specific paths where they compensate each other.\u201d<\/p>\n
The KU researcher said the combination of a defocusing magnetospheric plasma and a focusing gravity create in-phase and out-of-phase interference bands of radio-wave intensity that appear as the Crab Pulsar\u2019s zebra stripes.<\/p>\n
\u201cBy symmetry, there are at least two such paths for the light,\u201d he said. \u201cWhen two nearly identical paths bring light to the observer, they form an interferometer. The signals combine. At some frequencies, they reinforce each other (in phase), producing bright bands. At others, they cancel (out of phase), producing darkness. That is the essence of the interference pattern.\u201d<\/p>\n
The KU researcher said he\u2019s satisfied the mechanism for the observed zebra pattern now has been almost fully explained.<\/p>\n
\u201cThere appears to be little additional physics required to explain the stripes qualitatively,\u201d Medvedev said. \u201cQuantitatively, there may be refinements. For example, the current treatment includes gravity in a static, lowest-order approximation. The pulsar is rotating, and including rotational effects could introduce quantitative changes, though not qualitative ones.\u201d<\/p>\n
The KU researcher said the work may allow scientists to probe rotating gravitational objects more directly. Further, the new understanding could lead to a new grasp of pulsars in general, which are small and difficult to represent visually. It also presents a unique test ground for the pulsar theory and simulations. The model can also be a sensitive tool for the matter distribution around neutron stars and possibly even probe their interiors via its gravitational effects. \u00a0<\/p>\n","protected":false},"excerpt":{"rendered":"LAWRENCE \u2014 For the past two decades, scientists have wondered about a bright, distinct striped pattern seen in…\n","protected":false},"author":2,"featured_media":364050,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":"","_share_on_mastodon":"0"},"categories":[77],"tags":[18,19,17,169350,7037,165042,56580,133,169349],"class_list":["post-364049","post","type-post","status-publish","format-standard","has-post-thumbnail","category-science","tag-eire","tag-ie","tag-ireland","tag-jayhawks","tag-kansas","tag-ku","tag-lawrence","tag-science","tag-university-of-kansas"],"share_on_mastodon":{"url":"https:\/\/pubeurope.com\/@ie\/116160198333569349","error":""},"_links":{"self":[{"href":"https:\/\/www.europesays.com\/ie\/wp-json\/wp\/v2\/posts\/364049","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.europesays.com\/ie\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.europesays.com\/ie\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.europesays.com\/ie\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.europesays.com\/ie\/wp-json\/wp\/v2\/comments?post=364049"}],"version-history":[{"count":0,"href":"https:\/\/www.europesays.com\/ie\/wp-json\/wp\/v2\/posts\/364049\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.europesays.com\/ie\/wp-json\/wp\/v2\/media\/364050"}],"wp:attachment":[{"href":"https:\/\/www.europesays.com\/ie\/wp-json\/wp\/v2\/media?parent=364049"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.europesays.com\/ie\/wp-json\/wp\/v2\/categories?post=364049"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.europesays.com\/ie\/wp-json\/wp\/v2\/tags?post=364049"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}