{"id":25076,"date":"2021-10-21T00:00:00","date_gmt":"2021-10-21T00:00:00","guid":{"rendered":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/?post_type=purple_issue&#038;p=25076"},"modified":"2021-10-21T12:28:59","modified_gmt":"2021-10-21T12:28:59","slug":"white-dwarfs-slow-down-their-ageing","status":"publish","type":"post","link":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/2021\/10\/21\/white-dwarfs-slow-down-their-ageing\/","title":{"rendered":"White dwarfs slow down their ageing"},"content":{"rendered":"\n<p class=\"has-text-align-center intro\">The stars could still be burning hydrogen in their outer layers<\/p>\n\n<div class=\"no-tts wp-block-image article-in-image photo\"><figure class=\"no-tts aligncenter\"><img loading=\"lazy\" width=\"2048\" height=\"1166\" src=\"https:\/\/dj9jqhxgw9833.cloudfront.net\/uploads\/sites\/77\/2021\/10\/0938d7ec-a263-41bf-b0ce-836d0ed1559e.jpg\" alt=\"\" class=\"no-tts wp-image-25075\" srcset=\"https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2021\/10\/0938d7ec-a263-41bf-b0ce-836d0ed1559e.jpg 2048w, https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2021\/10\/0938d7ec-a263-41bf-b0ce-836d0ed1559e-300x171.jpg 300w, https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2021\/10\/0938d7ec-a263-41bf-b0ce-836d0ed1559e-1024x583.jpg 1024w, https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2021\/10\/0938d7ec-a263-41bf-b0ce-836d0ed1559e-768x437.jpg 768w, https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2021\/10\/0938d7ec-a263-41bf-b0ce-836d0ed1559e-1536x875.jpg 1536w\" sizes=\"(max-width: 2048px) 100vw, 2048px\" \/><figcaption>White dwarf stars in two globular clusters were still undergoing thermonuclear activity, casting doubt on the way stars are dated <\/figcaption><\/figure><\/div>\n\n<p class=\"article-full-body sans-serif\">White dwarfs<strong> <\/strong>could be lying about their age by hiding behind a youthful veil of hydrogen, a new study has found.<\/p>\n\n<p class=\"article-full-body sans-serif\">These small, dense stars represent the final stage in the life cycle of most stars, when they have thrown off their outer layers of hydrogen, leaving only the core behind. The current understanding of white dwarfs is that all fusion within them has stopped and that they are cooling down over time. This creates a strong link between a star\u2019s temperature and its age, which astronomers make use of to date how old stars are. However, a new set of observations made with the Hubble Space Telescope has thrown this relationship into doubt.<\/p>\n\n<p class=\"article-full-body sans-serif\">\u201cWe have found the first observational evidence that white dwarfs can still<span> undergo stable thermonuclear activity,\u201d says Jianxing Chen from Alma Mater Studiorum Universit\u00e0 (AMSU), who led the study. \u201cThis was quite a surprise as it\u2019s at odds with what is commonly believed.\u201d<\/span><\/p>\n\n<p class=\"article-full-body sans-serif\">The study compared the white dwarfs in two globular clusters, M13 and M3. The clusters are similar in age and metallicity (how many elements they have other than hydrogen and helium), but have differences in the stellar populations that are expected to go on to become white dwarfs. That makes them the perfect testing grounds to see how these stars cool over time.<\/p>\n\n<p class=\"article-full-body sans-serif\">\u201cThe superb quality of our Hubble observations provided us with a full view of stellar populations in the two globular clusters,\u201d says Chen. \u201cThis<span>&nbsp;allowed us to really contrast how stars evolve in M3 and M13.\u201d<\/span><\/p>\n\n<p class=\"article-full-body sans-serif\">Chen and his team were able to see that M13 contained a population of stars that were still burning hydrogen in their outer layers, which slowed their cooling, making them appear more youthful than they actually are.<\/p>\n\n<p class=\"article-full-body sans-serif\">\u201cOur discovery challenges the definition of white dwarfs as we consider a new perspective on the way in which stars get old,\u201d added Francesco Ferraro, also from AMSU, who coordinated the study. \u201cWe\u2019re now investigating other clusters that are similar to M13 to further constrain the conditions that drive stars to maintain the thin hydrogen envelope which allows them to age slowly.\u201d <a href=\"http:\/\/www.hubblesite.org\">www.hubblesite.org<\/a><\/p>\n\n<p>IMAGES: ESA\/HUBBLE\/NASA AND G PIOTTO ET AL<\/p>\n","protected":false},"excerpt":{"rendered":"<p>The stars could still be burning hydrogen in their outer layers<\/p>\n","protected":false},"author":24,"featured_media":25075,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"ub_ctt_via":"","purple_page_number":"12","purple_custom_meta_purple_page_number":"12","purple_seq_number":"1","purple_custom_meta_purple_seq_number":"1","purple_source_article":"article_12-1.xml","purple_custom_meta_purple_source_article":"article_12-1.xml","purple_source_issue":"November-2021","purple_custom_meta_purple_source_issue":"November-2021","purple_external_id":"November-2021-12-1","purple_custom_meta_purple_external_id":"November-2021-12-1","purple_issue_code":"|0000086546||","purple_custom_meta_purple_issue_code":"|0000086546||","purple_android_product":"com.im.skyatnight.198","purple_custom_meta_purple_android_product":"com.im.skyatnight.198","purple_ios_product":"com.im.skyatnight.198","purple_custom_meta_purple_ios_product":"com.im.skyatnight.198","purple_web_product":"","purple_custom_meta_purple_web_product":"","purple_publication_id":"075fab74-0a21-4201-866a-899d6c41c40c","purple_migrated":"","kt_blocks_editor_width":""},"categories":[19],"tags":[14],"featured_image_src":"https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2021\/10\/0938d7ec-a263-41bf-b0ce-836d0ed1559e.jpg","author_info":{"display_name":"importmanagerhub@sprylab.com","author_link":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/author\/importmanagerhubsprylab-com\/"},"acf":{"readingTimeMinutes":"2","apple_news_title":""},"uagb_featured_image_src":{"full":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2021\/10\/0938d7ec-a263-41bf-b0ce-836d0ed1559e.jpg",2048,1166,false],"thumbnail":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2021\/10\/0938d7ec-a263-41bf-b0ce-836d0ed1559e-150x150.jpg",150,150,true],"medium":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2021\/10\/0938d7ec-a263-41bf-b0ce-836d0ed1559e-300x171.jpg",300,171,true],"medium_large":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2021\/10\/0938d7ec-a263-41bf-b0ce-836d0ed1559e-768x437.jpg",768,437,true],"large":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2021\/10\/0938d7ec-a263-41bf-b0ce-836d0ed1559e-1024x583.jpg",800,455,true],"1536x1536":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2021\/10\/0938d7ec-a263-41bf-b0ce-836d0ed1559e-1536x875.jpg",1536,875,true],"2048x2048":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2021\/10\/0938d7ec-a263-41bf-b0ce-836d0ed1559e.jpg",2048,1166,false]},"uagb_author_info":{"display_name":"importmanagerhub@sprylab.com","author_link":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/author\/importmanagerhubsprylab-com\/"},"uagb_comment_info":0,"uagb_excerpt":"The stars could still be burning hydrogen in their outer 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