{"id":25174,"date":"2024-09-05T10:55:32","date_gmt":"2024-09-05T05:10:32","guid":{"rendered":"https:\/\/www.revoscience.com\/en\/?p=25174"},"modified":"2024-09-05T10:55:39","modified_gmt":"2024-09-05T05:10:39","slug":"alma-detects-hallmark-wiggle-of-gravitational-instability-in-planet-forming-disk","status":"publish","type":"post","link":"https:\/\/www.revoscience.com\/en\/alma-detects-hallmark-wiggle-of-gravitational-instability-in-planet-forming-disk\/","title":{"rendered":"ALMA Detects Hallmark \u201cWiggle\u201d of Gravitational Instability in Planet-Forming Disk"},"content":{"rendered":"\n
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IMAGE- ALMA (ESO\/NAOJ\/NSF NRAO), VLT\/SPHERE (ESO), Speedie et al.<\/em><\/figcaption><\/figure>\n\n\n\n

Interferometry of stunning spiral arms around young star reveals gravity\u2019s hand in planet formation.<\/p>\n\n\n\n

Traditionally, planet formation has been described as a \u201cbottom-up\u201d process, as dust grains gradually collect into bigger conglomerations over tens of millions of years, from microns to centimeters to meters to kilometers. Alternatively, another theory proposes that planets can form rapidly by a \u201ctop-down\u201d process, where circumstellar disk material in spiral arms fragments due to gravitational instability.<\/p>\n\n\n\n

In a powerful match-up of technique, instrumentation, and target, an international team of astronomers led by Jessica Speedie, Department of Physics & Astronomy PhD candidate at the University of Victoria (Canada), observed the well-characterized protoplanetary disk around AB Aurigae and found observational evidence that matches the alternative \u201ctop-down\u201d theoretical sequence of planet formation.<\/p>\n\n\n\n

The Atacama Large Millimeter\/submillimeter Array (ALMA), was crucial to the team\u2019s success. \u201cALMA\u2019s sensitivity and high-velocity resolution enabled us to probe the gas deep within the disk and measure its motion precisely. It was the only tool for the job,\u201d Speedie says.<\/p>\n\n\n\n

Astronomers have already spotted several developing protoplanets currently forming in AB Aurigae\u2019s disk region, including one that is nine times more massive than Jupiter. They appear as clumps nestled within a clear structure of spiral arms rotating counterclockwise around the star. The star itself, AB Aurigae, has a mass of approximately 2.4 times that of our Sun and is roughly 4 million years old. The star\u2019s age implies a conundrum: if the \u201cbottom-up\u201d process has not had time to take place, then by what mechanism are the protoplanets forming?<\/p>\n\n\n\n

Speedie, her PhD advisor Ruobing Dong, and their team set out to use ALMA to study how the gas in the system\u2019s vast spiral arms is moving. \u201cDisks that are gravitationally unstable should have distinctive \u2018wiggles\u2019 in their velocity field, unlike disks that are stable,\u2019\u2019 says Dr. Cassandra Hall, Assistant Professor of Computational Astrophysics at the University of Georgia and co-author of the research.\u00a0<\/p>\n\n\n\n

\u201cBack in 2020, we performed some of the most advanced simulations in the world to predict the existence of this hallmark signature of gravitational instability,\u201d Hall said of\u00a0the research\u00a0she led four years ago. \u201cIt was clear, it was testable, and it was a bit scary \u2013 if we didn\u2019t find it, then something had to be very, very wrong with our understanding of these disks.\u201d<\/p>\n\n\n\n

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IMAGE: ALMA (ESO\/NAOJ\/NSF NRAO), VLT\/SPHERE (ESO), Speedie et al.<\/em><\/figcaption><\/figure>\n\n\n\n

Using the ALMA radio interferometer (12-meter array), Speedie mapped the velocity of 13CO and C18O gases within these vast spiral arms around AB Aurigae and found clear evidence of the predicted \u201cwiggles.\u201d Cristiano Longarini, postdoctoral associate at the University of Cambridge and co-author of the research, explains, \u201cSpiral arms form in the disk when the disk-to-star mass ratio is sufficiently high. <\/p>\n\n\n\n

Within those arms, changes in density lead to changes in gravity, which in turn lead to variations in the velocities of gas in the local area around and within the arms. We see these variations in the velocity as wiggles.\u201d The magnitude of these velocity wiggles, Longarini confirmed, can be used to infer the mass ratio between the host star and its surrounding disk material.<\/p>\n\n\n\n

\u201cOur detection of gravitational instability in the disk around AB Aurigae is a direct observational confirmation of this \u2018top-down\u2019 pathway to planet formation,\u201d Speedie summarizes.<\/p>\n\n\n\n

Similar to how an MRI generates images of the brain in \u201cslices,\u201d ALMA interferometry measurements yielded a three-dimensional rectangular \u201cdata cube\u201d that mapped gas velocity and position along the line of sight within the protoplanetary disk. By parsing strategically oriented cuts through the data cube, Speedie and her team were able to conclusively identify the telltale velocity wiggle indicating gravitational instability.<\/p>\n\n\n\n

\u201cWe worked with one of the deepest ALMA observations taken with such high-velocity resolution toward a single protoplanetary disk to date,\u201d Speedie says. \u201cThe ALMA data provides a clear diagnosis of gravitational instability in action. There is no other mechanism we know of that can create the global architecture of spiral structure and velocity patterns that we observe.\u201d Adds Speedie in reference to Hall\u2019s predictions, \u201cThis is a classic science story of, \u2018we predicted it, and then we found it\u2019. <\/p>\n\n\n\n

The Hall-mark of gravitational instability.\u201d Her use of ALMA won\u2019t end with this research. As part of the\u00a0NSF-NRAO-ALMA ambassador program,<\/a>\u00a0she is training alongside other postdocs and early career astronomers to share ALMA\u2019s resources and capabilities with the wider astronomy community.<\/p>\n","protected":false},"excerpt":{"rendered":"

Interferometry of stunning spiral arms around young star reveals gravity\u2019s hand in planet formation.<\/p>\n","protected":false},"author":2,"featured_media":25177,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[20],"tags":[],"class_list":["post-25174","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-space-news"],"featured_image_urls":{"full":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2024\/09\/alma.jpg",1366,768,false],"thumbnail":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2024\/09\/alma-200x200.jpg",200,200,true],"medium":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2024\/09\/alma-675x380.jpg",675,380,true],"medium_large":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2024\/09\/alma-768x432.jpg",750,422,true],"large":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2024\/09\/alma-675x380.jpg",675,380,true],"1536x1536":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2024\/09\/alma.jpg",1366,768,false],"2048x2048":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2024\/09\/alma.jpg",1366,768,false],"ultp_layout_landscape_large":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2024\/09\/alma-1200x768.jpg",1200,768,true],"ultp_layout_landscape":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2024\/09\/alma-870x570.jpg",870,570,true],"ultp_layout_portrait":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2024\/09\/alma-600x768.jpg",600,768,true],"ultp_layout_square":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2024\/09\/alma-600x600.jpg",600,600,true],"newspaper-x-single-post":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2024\/09\/alma-760x490.jpg",760,490,true],"newspaper-x-recent-post-big":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2024\/09\/alma-550x360.jpg",550,360,true],"newspaper-x-recent-post-list-image":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2024\/09\/alma-95x65.jpg",95,65,true],"web-stories-poster-portrait":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2024\/09\/alma.jpg",640,360,false],"web-stories-publisher-logo":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2024\/09\/alma.jpg",96,54,false],"web-stories-thumbnail":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2024\/09\/alma.jpg",150,84,false]},"author_info":{"info":["RevoScience"]},"category_info":"Space\/ AstroPhysics<\/a>","tag_info":"Space\/ AstroPhysics","comment_count":"0","_links":{"self":[{"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/posts\/25174","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/comments?post=25174"}],"version-history":[{"count":1,"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/posts\/25174\/revisions"}],"predecessor-version":[{"id":25178,"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/posts\/25174\/revisions\/25178"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/media\/25177"}],"wp:attachment":[{"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/media?parent=25174"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/categories?post=25174"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/tags?post=25174"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}