{"page":"<link rel=\"stylesheet\" href=\"https://lessonplanet.com/assets/packs/css/resources-572d6a42.css\" />\n<link rel=\"stylesheet\" href=\"https://lessonplanet.com/assets/packs/css/lp_boclips_stylesheets-f4d0de30.css\" media=\"all\" />\n<div data-title='How Is the Mass of an Unseen Black Hole in a Binary System Calculated?' data-url='/boclips/videos/68bddc524064c243911f05b5' data-video-url='/boclips/videos/68bddc524064c243911f05b5' id='bo_player_modal'>\n<div class='boclips-resource-page modal-dialog panel-container'>\n<div class='react-notifications-root'></div>\n<div class='rp-header'>\n<div class='rp-type'>\n<i aria-hidden='true' class='fai fa-regular fa-circle-play'></i>\nVideo\n</div>\n<h1 class='rp-title' id='video-title'>\nHow Is the Mass of an Unseen Black Hole in a Binary System Calculated?\n</h1>\n<div class='rp-actions'>\n<div class='mr-1'>\n<a class=\"btn btn-success\" data-posthog-event=\"Signup: LP Signup Activity\" data-posthog-location=\"body_link_boclips\" 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of a visible star—its speed and period—to infer the mass of its invisible companion, often a black hole, in a binary system.</span>\n<span class='full-description hide'>Learn how astrophysicists use the orbital motion of a visible star—its speed and period—to infer the mass of its invisible companion, often a black hole, in a binary system.</span>\n</div>\n<div class='rp-report'>\n</div>\n<div aria-labelledby='resource-details-heading' class='rp-info-section'>\n<h2 class='title' id='resource-details-heading'>Resource Details</h2>\n<div class='rp-resource-details clearfix'>\n<div class='detail'>\n<dl>\n<dt>Curator Rating</dt>\n<dd><span class=\"star-rating\" aria-label=\"4.0 out of 5 stars\" role=\"img\"><i class=\"fa-solid fa-star text-action\" aria-hidden=\"true\"></i><i class=\"fa-solid fa-star text-action\" aria-hidden=\"true\"></i><i class=\"fa-solid fa-star text-action\" aria-hidden=\"true\"></i><i class=\"fa-solid fa-star text-action\" aria-hidden=\"true\"></i><i 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