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The researchers found that two of the Milky Way\u2019s outer spiral arms lie farther from Earth than long-standing maps suggest.<\/p>\n
The study provides the most precise measurements yet of the galaxy\u2019s distant edge.<\/p>\n
Echoes from powerful explosions <\/p>\n
The Milky Way is hard to study from the inside. Earth sits deep within one of its arms, and thick clouds of cosmic dust block the view across the disk, leaving the galaxy\u2019s outer edges poorly charted.<\/p>\n
The new approach leans on gamma-ray bursts<\/a>, the brightest explosions known. Each burst releases more energy in seconds than the Sun will over its entire life. <\/p>\n The three gamma-ray bursts studied here went off in galaxies far beyond our own. <\/p>\n When a burst fires, its X-rays stream across space and pass through the Milky Way on the way to our telescopes.<\/p>\n Some strike grains of dust in the galaxy\u2019s spiral arms<\/a> and scatter, veering slightly off their straight path.<\/p>\n Scattered X-rays travel a longer route, arriving a little late and appearing offset from the burst. Over time, that offset traces a bright ring that swells outward around the explosion\u2019s position.<\/p>\n A geometric solution<\/p>\n How quickly each ring expands depends only on how far away the scattering dust sits, which turns a distance measurement into a problem of pure geometry.<\/p>\n That appealed to Dr. Beatrice Vaia, an astrophysicist at Italy\u2019s Istituto Nazionale di Astrofisica (INAF<\/a>).<\/p>\n \u201cThis is a very direct way, relying only on geometry, to precisely measure distances to the Milky Way\u2019s spiral arms,\u201d said Dr. Vaia.<\/p>\n Older techniques, she noted, lean on assumptions about the galaxy\u2019s spin that grow shakier toward its edges.<\/p>\n Reaching the edge<\/p>\n The team drew on archived data from the European Space Agency\u2019s XMM-Newton and NASA\u2019s Chandra, two X-ray observatories that watched three bursts near the plane of our galaxy.<\/p>\n An image of the brightest burst ever recorded, from 2022, held a nest of rings cast by dust clouds<\/a> spread across tens of thousands of light-years.<\/p>\n Reading those rings let the team place the galaxy\u2019s outermost known arm, the Outer Scutum-Centaurus Arm, at about 62,000 light-years from Earth<\/a>.<\/p>\n The measurement is good to within roughly one percent, a sharpness that earlier methods could not touch at such distances.<\/p>\n The only previous direct distance to that arm came from a single measurement<\/a> of a star-forming region, which put it near 66,000 light-years but carried an uncertainty about ten times larger.<\/p>\n Redrawing the map<\/p>\n The new figure shrinks that uncertainty roughly tenfold and pulls the arm inward.<\/p>\n In the same analysis, the researchers confirmed the distance to the Perseus Arm, a nearer structure whose position was already well known.<\/p>\n That agreement showed the ring method was working. Two other arms, however, did not sit where the maps<\/a> said they should.<\/p>\n The Outer Arm and the outermost arm both lay farther out than the galaxy\u2019s rotation-based charts predicted, by as much as ten percent.<\/p>\n Moving beyond rotation models <\/p>\n Most distances to the far reaches of the Milky Way come from measuring how clouds of gas move. <\/p>\n Astronomers calculate a cloud\u2019s distance by measuring its speed and comparing it with models of how the Milky Way rotates.<\/p>\n That model has a weak spot. In the outer galaxy, where dark matter dominates and few landmarks exist, it grows unreliable. The ring method skips that step. <\/p>\n Because it measures distance directly from the geometry of scattered light, the method does not depend on models of how the Milky Way rotates. <\/p>\n It also remains accurate out to the galaxy\u2019s outer edge, where traditional approaches become less reliable.<\/p>\n The elusive outer arms<\/p>\n The outer arms have long resisted mapping. The outermost was only identified in 2011, in a survey<\/a> of carbon monoxide gas, because it tilts well above the flat plane where surveys look.<\/p>\n Even the galaxy\u2019s arm count stayed unsettled until star-mapping data recently pointed the way to four.<\/p>\n That tilt shows up in the data. The dust producing the most distant ring lies some 4,600 light-years above the galaxy\u2019s flat plane. <\/p>\n This is part of why the bright 2022 burst, the subject of the team\u2019s earlier work<\/a> on its scattered X-rays, could reach it at all.<\/p>\n A sharper view of our galaxy<\/p>\n The payoff is a sharper map of where the galaxy\u2019s outer arms lie. The study swaps a rough estimate for a distance nailed down to a few hundred light-years.<\/p>\n The rotation-based models placed the outer arms too close. The X-ray rings showed they are actually farther away.<\/p>\n That gap hints at something off in the assumed motion of the outer disk, where dark matter dominates the galaxy\u2019s gravitational pull.<\/p>\n Correcting those distances will help astronomers better estimate the Milky Way\u2019s mass and map the shape of its faint outer regions. <\/p>\n A gamma-ray burst as bright as the one seen in 2022 may not occur again for years.<\/p>\n However, next-generation X-ray observatories should be able to detect fainter echoes from many more directions, extending the method deeper into the galaxy\u2019s outer reaches.<\/p>\n The study is published in the journal Astronomy & Astrophysics<\/a>.<\/p>\n \u2014\u2013<\/p>\n Like what you read? Subscribe to our newsletter<\/a> for engaging articles, exclusive content, and the latest updates.<\/p>\n Check us out on EarthSnap<\/a>, a free app brought to you by Eric Ralls<\/a> and Earth.com.<\/p>\n \u2014\u2013<\/p>\n","protected":false},"excerpt":{"rendered":"Astronomers have spent decades mapping the Milky Way, but the galaxy is too vast for anyone to see…\n","protected":false},"author":2,"featured_media":511214,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[23],"tags":[111,139,69,147,392],"class_list":["post-511213","post","type-post","status-publish","format-standard","has-post-thumbnail","category-space","tag-new-zealand","tag-newzealand","tag-nz","tag-science","tag-space"],"_links":{"self":[{"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/posts\/511213","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/comments?post=511213"}],"version-history":[{"count":0,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/posts\/511213\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/media\/511214"}],"wp:attachment":[{"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/media?parent=511213"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/categories?post=511213"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/tags?post=511213"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}