{"id":325314,"date":"2025-08-07T13:42:17","date_gmt":"2025-08-07T13:42:17","guid":{"rendered":"https:\/\/www.europesays.com\/uk\/325314\/"},"modified":"2025-08-07T13:42:17","modified_gmt":"2025-08-07T13:42:17","slug":"hubble-finds-remnant-of-white-dwarf-merger-130-light-years-away","status":"publish","type":"post","link":"https:\/\/www.europesays.com\/uk\/325314\/","title":{"rendered":"Hubble Finds Remnant of White Dwarf Merger 130 Light-Years Away"},"content":{"rendered":"

White dwarfs are the dense cores left behind when stars exhaust their fuel and collapse. They are Earth-sized stellar embers weighing typically half as much as the Sun, made up of carbon-oxygen cores with surface layers of helium and hydrogen. Using far-ultraviolet data from the NASA\/ESA Hubble Space Telescope<\/a>, astronomers have discovered atmospheric carbon in the long-known ultramassive white dwarf WD\u20090525+526<\/a>, and also found that the total masses of hydrogen and helium in the star\u2019s atmosphere are substantially lower than those expected from single-star evolution, implying that WD\u20090525+526 is a merger remnant.<\/strong><\/p>\n

\"Illustration<\/a><\/p>\n

Illustration of a merger of a white dwarf with sub-giant star (size not to scale) that would have occurred in past. Image credit: Snehalata Sahu \/ University of Warwick.<\/p>\n

WD 0525+526 is located approximately 130 light-years away in the constellation of Auriga.<\/p>\n

With a mass 20% larger than our Sun, this white dwarf is considered ultramassive, and how this star came to be is not fully understood.<\/p>\n

Such a white dwarf could form from the collapse of a massive star. However, ultraviolet data from Hubble revealed WD 0525+526 to have small amounts of carbon rising from its core into its hydrogen-rich atmosphere \u2014 suggesting this white dwarf did not originate from a single massive star.<\/p>\n

\u201cIn optical light, WD 0525+526 looks like a heavy but otherwise ordinary white dwarf,\u201d said University of Warwick astronomer Snehalata Sahu.<\/p>\n

\u201cHowever, through ultraviolet observations obtained with Hubble, we were able to detect faint carbon signatures that were not visible to optical telescopes.\u201d<\/p>\n

\u201cFinding small amounts of carbon in the atmosphere is a telltale sign that this massive white dwarf is likely to be a remnant of a merger between two stars.\u201d<\/p>\n

\u201cIt also tells us there may be many more merger remnants like this masquerading as common pure-hydrogen atmosphere white dwarfs.\u201d<\/p>\n

\u201cOnly ultraviolet observations would be able to reveal them to us.\u201d<\/p>\n

Normally, hydrogen and helium form a thick barrier-like envelope around a white dwarf core, keeping elements like carbon hidden.<\/p>\n

In a merger of two stars, the hydrogen and helium layers can burn off almost completely as the stars combine.<\/p>\n

The resulting single star has a very thin envelope that no longer prevents carbon from reaching the surface \u2014 this is exactly what is found on WD 0525+526.<\/p>\n

\u201cWe measured the hydrogen and helium layers to be ten-billion times thinner than in typical white dwarfs,\u201d said University of Warwick astronomer Antoine B\u00e9dard.<\/p>\n

\u201cWe think these layers were stripped away in the merger, and this is what now allows carbon to appear on the surface.\u201d<\/p>\n

\u201cBut this remnant is also unusual: it has about 100,000 times less carbon on its surface compared to other merger remnants.\u201d<\/p>\n

\u201cThe low carbon level, together with the star\u2019s high temperature (nearly four times hotter than the Sun), tells us WD 0525+526 is much earlier in its post-merger evolution than those previously found.\u201d<\/p>\n

\u201cThis discovery helps us build a better understand the fate of binary star systems, which is critical for related phenomena like supernova explosions.\u201d<\/p>\n

Adding to the mystery is how carbon reaches the surface at all in this much hotter star.<\/p>\n

The other merger remnants are later in their evolution and cool enough for convection to bring carbon to the surface. But WD 0525+526 is far too hot for that process.<\/p>\n

Instead, the authors identified a subtler form of mixing called semi-convection, seen here for the first time in a white dwarf.<\/p>\n

This process allows small amounts of carbon to slowly rise into the star\u2019s hydrogen-rich atmosphere.<\/p>\n

\u201cFinding clear evidence of mergers in individual white dwarfs is rare,\u201d said University of Warwick\u2019s Professor Boris G\u00e4nsicke.<\/p>\n

\u201cBut ultraviolet spectroscopy gives us the ability to detect these signs early, when the carbon is still invisible at optical wavelengths.\u201d<\/p>\n

\u201cBecause the Earth\u2019s atmosphere blocks ultraviolet light, these observations must be carried out from space, and currently only Hubble can do this job.\u201d<\/p>\n

\u201cAs WD 0525+526 continues to evolve and cool, it is expected that more carbon will emerge at its surface over time.\u201d<\/p>\n

\u201cFor now, its ultraviolet glow offers a rare glimpse into the earliest stage of a stellar merger\u2019s aftermath \u2014 and a new benchmark for how binary stars end their lives.\u201d<\/p>\n

The findings<\/a> appear today in the journal Nature Astronomy.<\/p>\n

_____<\/p>\n

S. Sahu et al. A hot white dwarf merger remnant revealed by an ultraviolet detection of carbon. Nat Astron, published online August 6, 2025; doi: 10.1038\/s41550-025-02590-y<\/p>\n","protected":false},"excerpt":{"rendered":"White dwarfs are the dense cores left behind when stars exhaust their fuel and collapse. They are Earth-sized…\n","protected":false},"author":2,"featured_media":325315,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[3844],"tags":[52969,117397,2813,1159,117398,26969,1309,25380,874,70,413,6682,117399,39468,16,117400,15,117401,117402,45441],"class_list":{"0":"post-325314","1":"post","2":"type-post","3":"status-publish","4":"format-standard","5":"has-post-thumbnail","7":"category-space","8":"tag-atmosphere","9":"tag-binary-star","10":"tag-carbon","11":"tag-esa","12":"tag-helium","13":"tag-hubble","14":"tag-hydrogen","15":"tag-merger","16":"tag-nasa","17":"tag-science","18":"tag-space","19":"tag-star","20":"tag-subgiant-star","21":"tag-temperature","22":"tag-uk","23":"tag-ultramassive-white-dwarf","24":"tag-united-kingdom","25":"tag-uv","26":"tag-wd-0525526","27":"tag-white-dwarf"},"share_on_mastodon":{"url":"https:\/\/pubeurope.com\/@uk\/114987778208259697","error":""},"_links":{"self":[{"href":"https:\/\/www.europesays.com\/uk\/wp-json\/wp\/v2\/posts\/325314","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.europesays.com\/uk\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.europesays.com\/uk\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.europesays.com\/uk\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.europesays.com\/uk\/wp-json\/wp\/v2\/comments?post=325314"}],"version-history":[{"count":0,"href":"https:\/\/www.europesays.com\/uk\/wp-json\/wp\/v2\/posts\/325314\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.europesays.com\/uk\/wp-json\/wp\/v2\/media\/325315"}],"wp:attachment":[{"href":"https:\/\/www.europesays.com\/uk\/wp-json\/wp\/v2\/media?parent=325314"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.europesays.com\/uk\/wp-json\/wp\/v2\/categories?post=325314"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.europesays.com\/uk\/wp-json\/wp\/v2\/tags?post=325314"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}