A new study led by Alexander Russell at the University of St Andrews<\/a> offers a clean, intuitive answer: during key phases of a flare, the ions are far hotter than the electrons. <\/p>\n Not just a little hotter \u2013 about 6.5 times hotter, with ion temperatures likely exceeding 60 million degrees Kelvin.<\/p>\n The team argues that this simple shift in perspective neatly explains why many flare emission lines appear broader than expected, without needing to invoke large, persistent turbulence.<\/p>\n Significance of hotter ions<\/p>\n Solar plasma is a soup of charged particles \u2013 lightweight, negatively charged electrons and much heavier, positively charged ions (think iron, calcium, and other elements stripped of electrons).<\/p>\n Historically, many solar models assumed that electrons and ions quickly share energy and settle to a common temperature. That assumption made the math tidy, but it may not reflect reality during a flare\u2019s most dynamic moments.<\/p>\n Russell\u2019s team revisited basic heating physics in flares and drew on a growing body of evidence from space plasmas closer to home.\u00a0<\/p>\n Hot ions and solar flares<\/p>\n Across the solar wind and near-Earth space, a process called magnetic reconnection \u2013 where stressed magnetic field lines snap and rapidly rejoin \u2013 has been observed to heat ions far more than electrons, following a surprisingly consistent ratio.\u00a0<\/p>\n \u201cWe were excited by recent discoveries that a process called magnetic reconnection heats ions 6.5 times as much as electrons,\u201d Russell explained.<\/p>\n \u201cThis appears to be a universal law, and it has been confirmed in near-Earth space, the solar wind and computer simulations. However, nobody had previously connected work in those fields to solar flares<\/a>.<\/p>\n Carry that rule of thumb to the Sun and you get a dramatic, testable prediction: early in a flare and high above the bright loop of hot plasma it creates, the ion temperature can soar past 60 million K, remaining much higher than the electron temperature for tens of minutes.\u00a0<\/p>\n That temperature split matters because it changes how we interpret what telescopes see. Spectral lines \u2013 bright features at specific ultraviolet and X-ray wavelengths \u2013 get wider when the particles emitting them are hotter and moving faster. <\/p>\n For nearly 50 years, those \u201ctoo-wide\u201d lines were usually blamed on unresolved turbulent motions. The new work suggests super-hot ions could be responsible for a big share of that extra width.<\/p>\n Solving an astrophysics mystery<\/p>\n If ions are smoking-hot, they jiggle more rapidly, and the light they emit spreads over a wider range of wavelengths. <\/p>\n That broadening can look exactly like turbulence, which led to decades of debate about what, physically, was stirring flare plasma so vigorously.\u00a0<\/p>\n Russell\u2019s team lays out why ion-heavy heating at the onset of flares \u2013 and in the above-the-loop-top region where reconnection outflows crash into denser plasma \u2013 naturally produces the observed line widths.\u00a0<\/p>\n \u201cWhat\u2019s more, the new ion temperature fits well with the width of flare spectral lines, potentially solving an astrophysics mystery that has stood for nearly half a century,\u201d noted Russell. <\/p>\n A key enabler of this explanation is timescale. In the dense, cooling loops that form after a flare brightens, ions and electrons<\/a> collide often enough to share energy and equalize temperatures relatively quickly.\u00a0<\/p>\n But higher up, where densities are lower, collisions are rarer. That means the ion-electron temperature gap can persist long enough to leave a clear imprint on the flare\u2019s spectrum.\u00a0<\/p>\n The paper argues that past estimates of equilibration were often based on the dense loop conditions \u2013 not the more rarefied, earlier or higher regions where reconnection does its fiercest work.<\/p>\n Past and future observations<\/p>\n The elegance of the proposal is that it doesn\u2019t require radical new physics. It borrows a well-supported heating ratio from reconnection studies in the solar wind<\/a> and Earth\u2019s magnetosphere and simply applies it where reconnection is strongest on the Sun.\u00a0<\/p>\n The result is a unified picture: reconnection preferentially energizes ions; low densities up high let that temperature advantage survive; and hot ions inflate spectral lines that have long looked \u201cnon-thermal.\u201d<\/p>\n If correct, the idea reshapes how researchers interpret past observations and plan future ones. Instruments that separate lines from different ions (and compare them with electron-sensitive diagnostics) could directly test whether line widths track the higher ion temperature rather than turbulence.<\/p>\n This new concept also encourages modelers to let ions and electrons evolve separately in the crucial early minutes of a flare, instead of forcing them to share a single temperature from the start.<\/p>\n Space weather, made a bit clearer<\/p>\n This is more than a bookkeeping fix. Space weather<\/a> forecasts depend on how quickly and how hot flare plasmas get, because the resulting radiation and particle storms determine how much they can disturb Earth\u2019s ionosphere and threaten spacecraft.<\/p>\n If ions get the lion\u2019s share of heat at first, that affects energy transport, shock formation, and particle acceleration \u2013 the seeds of the most disruptive events.<\/p>\n The study also suggests new observational sweet spots. Look early, when the flare is just switching on. Look above the bright loop tops, where reconnection outflows crash and churn. <\/p>\n Furthermore, look at line widths from multiple ions, comparing them with electron-temperature diagnostics. If the widths line up with a ~6.5:1 ion-to-electron temperature split, that\u2019s a powerful fingerprint.<\/p>\n A new look at solar flares<\/p>\n Solar physics has long assumed that ions and electrons quickly come to the same temperature in flares. <\/p>\n Russell and colleagues show that dropping that assumption \u2013 especially during the flare onset and in the high, thin plasma above the loops \u2013 solves a stubborn spectral riddle with one straightforward, physically motivated change: ions are simply much hotter.\u00a0<\/p>\n It\u2019s a tidy answer that ties the Sun\u2019s fiercest moments to a \u201cuniversal\u201d reconnection rule measured throughout near-Earth space, and it gives observers and modelers a clear roadmap for cracking open one of heliophysics\u2019 longest-running mysteries.<\/p>\n The study is published in The Astrophysical Journal Letters<\/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":"Solar flares are the Sun at full volume \u2013 sudden bursts of magnetic energy that can supercharge Earth\u2019s…\n","protected":false},"author":2,"featured_media":399188,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[3844],"tags":[70,413,16,15],"class_list":{"0":"post-399187","1":"post","2":"type-post","3":"status-publish","4":"format-standard","5":"has-post-thumbnail","7":"category-space","8":"tag-science","9":"tag-space","10":"tag-uk","11":"tag-united-kingdom"},"share_on_mastodon":{"url":"https:\/\/pubeurope.com\/@uk\/115150105374386068","error":""},"_links":{"self":[{"href":"https:\/\/www.europesays.com\/uk\/wp-json\/wp\/v2\/posts\/399187","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=399187"}],"version-history":[{"count":0,"href":"https:\/\/www.europesays.com\/uk\/wp-json\/wp\/v2\/posts\/399187\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.europesays.com\/uk\/wp-json\/wp\/v2\/media\/399188"}],"wp:attachment":[{"href":"https:\/\/www.europesays.com\/uk\/wp-json\/wp\/v2\/media?parent=399187"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.europesays.com\/uk\/wp-json\/wp\/v2\/categories?post=399187"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.europesays.com\/uk\/wp-json\/wp\/v2\/tags?post=399187"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
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