wp-plugin-hostgator domain was triggered too early. This is usually an indicator for some code in the plugin or theme running too early. Translations should be loaded at the init action or later. Please see Debugging in WordPress for more information. (This message was added in version 6.7.0.) in /home4/scienrds/scienceandnerds/wp-includes/functions.php on line 6114ol-scrapes domain was triggered too early. This is usually an indicator for some code in the plugin or theme running too early. Translations should be loaded at the init action or later. Please see Debugging in WordPress for more information. (This message was added in version 6.7.0.) in /home4/scienrds/scienceandnerds/wp-includes/functions.php on line 6114Source:https:\/\/www.quantamagazine.org\/quaking-giants-might-solve-the-mysteries-of-stellar-magnetism-20230821\/#comments<\/a><\/br> Our planet is doomed. In a few billion years, the sun will exhaust its hydrogen fuel and swell into a red giant\u00a0\u2014\u00a0a star so big it will scorch, blacken and swallow up the inner planets.<\/p>\n While red giants are bad news for planets, they\u2019re good news for astrophysicists. Their hearts hold the keys to understanding a range of stellar bodies, from fledgling protostars to zombie white dwarfs, because deep within them lies an invisible force that can shape a star\u2019s destiny: the magnetic field.<\/p>\n Magnetic fields near the surfaces of stars are often well characterized, but what\u2019s happening in their cores is mostly unknown. That\u2019s changing, because red giants are uniquely suited for studying magnetism deep within a star. Scientists do this by using starquakes \u2014 subtle oscillations at a star\u2019s surface \u2014 as a portal to stellar interiors.<\/p>\n \u201cRed giants have these oscillations that allow you to probe the core very sensitively,\u201d said Tim Bedding<\/a>, an asteroseismologist at the University of Sydney who studies red giant stars.<\/p>\n Last year, a team at the University of Toulouse decoded those oscillations and measured the magnetic fields within a trio of red giants<\/a>. Earlier this year, the same team detected magnetic fields<\/a> inside a further 11 red giants. Together, the observations showed that the hearts of giants are more mysterious than expected.<\/p>\n Close to a star\u2019s heart, magnetic fields play crucial roles in chemical mixing in the star\u2019s interior, which in turn affects how a star evolves. By refining stellar models and including internal magnetism, scientists will be able to calculate stellar ages more accurately. Such measurements could help determine the ages of potentially habitable faraway planets and pin down the timelines of galaxy formation.<\/p>\n \u201cWe don\u2019t include magnetism in stellar modeling,\u201d said Lisa Bugnet<\/a>, an astrophysicist at the Institute of Science and Technology Austria who developed methods for studying magnetic fields inside red giants. \u201cIt\u2019s crazy, but it\u2019s just not there because we have no idea how it looks [or] how strong it is.\u201d<\/p>\n The only way to probe the heart of a star is with asteroseismology, the study of stellar oscillations.<\/p>\n In the same way that seismic waves rippling through Earth\u2019s interior can be used to map the planet\u2019s subterranean landscape, stellar oscillations open a window into a star\u2019s innards. Stars oscillate as their plasma churns, producing waves that carry information about a star\u2019s internal composition and rotation. Bugnet compares the process to a ringing bell \u2014\u00a0the shape and size of a bell produces a specific sound that reveals the properties of the bell itself.<\/p>\n To study quaking giants, scientists use data from NASA\u2019s planet-hunting Kepler telescope<\/a>, which monitored the brightness of over 180,000 stars for years. Its sensitivity allowed astrophysicists to detect minute changes in starlight linked to stellar oscillations, which affect both the radius and the brightness of the star.<\/p>\n But decoding stellar oscillations is tricky. They come in two basic flavors: acoustic pressure modes (p-modes), which are sound waves that move through the outer regions of a star, and gravity modes (g-modes), which are lower in frequency and mostly confined to the core. For stars like our sun, p-modes dominate their observable oscillations; their g-modes, which are affected by internal magnetic fields, are too weak to detect and can\u2019t reach the star\u2019s surface.<\/p>\n In 2011, the KU Leuven astrophysicist Paul Beck and colleagues used Kepler data<\/a> to show that in red giants, p-modes and g-modes interact and produce what\u2019s known as a mixed mode. The mixed modes are the tool that probes the heart of a star \u2014 they allow astronomers to see the g-mode oscillations \u2014 and they\u2019re only detectable in red giant stars.\u00a0Studying mixed modes revealed that red giant cores rotate much more slowly than the star\u2019s gaseous envelope, contrary to what astrophysicists had predicted.<\/p>\n That was a surprise \u2014 and a possible indication that something crucial was missing in those models: magnetism.<\/p>\n Last year, Gang Li<\/a>, an asteroseismologist now at KU Leuven, went digging through Kepler\u2019s giants.\u00a0He was searching for a mixed-mode signal that recorded the magnetic field in the core of a red giant. \u201cAstonishingly, I actually found a few instances of this phenomenon,\u201d he said.<\/p>\n Typically, mixed-mode oscillations in red giants occur almost rhythmically, producing a symmetric signal. Bugnet and others had predicted<\/a> that magnetic fields would break that symmetry, but no one was able to make that tricky observation \u2014 until Li\u2019s team.<\/p>\n Li and his colleagues found a giant trio that exhibited the predicted asymmetries, and they calculated that each star\u2019s magnetic field was up to<\/a> \u201c2,000 times the strength of a typical fridge magnet\u201d \u2014 strong, but consistent with predictions.<\/p>\n However, one of the three red giants surprised them: Its mixed-mode signal was backward. \u201cWe were a bit puzzled,\u201d said S\u00e9bastien Deheuvels<\/a>, a study author and an astrophysicist at Toulouse. Deheuvels thinks this result suggests that the star\u2019s magnetic field is tipped on its side, meaning that the technique could determine the orientation of magnetic fields, which is crucial for updating models of stellar evolution.<\/p>\n A second study, led by Deheuvels, used mixed-mode asteroseismology to detect magnetic fields in the cores of 11 red giants. Here, the team explored how those fields affected the properties of g-modes \u2014\u00a0which, Deheuvels noted, may provide a way to move beyond red giants and detect magnetic fields in stars that don\u2019t show those rare asymmetries. But first \u201cwe want to find the number of red giants that show this behavior and compare them to different scenarios for the formation of these magnetic fields,\u201d Deheuvels said.<\/p>\n Using starquakes to investigate the interiors of stars kicked off a \u201crenaissance\u201d in stellar evolution, said Conny Aerts<\/a>, an astrophysicist at KU Leuven.<\/p>\n The renaissance has far-reaching implications for our understanding of stars and of our place in the cosmos.\u00a0So far, we know the exact age of just one star \u2014 our sun \u2014 which scientists determined based on the chemical composition of meteorites that formed during the birth of the solar system<\/a>. For every other star in the universe, we only have estimated ages based on rotation and mass. Add internal magnetism, and you have a way to estimate stellar ages with more precision.<\/p>\n And age is not just a number, but a tool that could help answer some of the most profound questions about the cosmos. Take the search for extraterrestrial life. Since 1992, scientists have spotted more than 5,400 exoplanets. The next step is to characterize those worlds and determine if they\u2019re suitable for life. That includes knowing the planet\u2019s age. \u201cAnd the only way you can know its age is by knowing the age of the host star,\u201d Deheuvels said.<\/p>\n Another field that requires precise stellar ages is galactic archaeology, the study of how galaxies are assembled. The Milky Way, for instance, gobbled up smaller galaxies during its evolution; astrophysicists know this because chemical abundances in stars trace their ancestry. But they don\u2019t have a good timeline for when that happened \u2014 the inferred stellar ages aren\u2019t accurate enough.<\/p>\n \u201cThe reality is, sometimes we are a factor [of] 10 wrong in stellar age,\u201d Aerts said.<\/p>\n The study of magnetic fields within stellar hearts is still in its infancy; there are many unknowns when it comes to understanding how stars evolve. And for Aerts, there\u2019s beauty in that.<\/p>\n \u201cNature is more imaginative than we are,\u201d she said.<\/p>\n Jackson Ryan\u2019s travel for this story was partly funded by the ISTA Science Journalist in Residence Program.<\/i><\/p>\n<\/div>\n <\/br><\/br><\/br><\/p>\n
\nQuaking Giants Might Solve the Mysteries of Stellar Magnetism<\/br>
\n2023-08-22 21:58:53<\/br><\/p>\nStare Into the Sun<\/strong><\/h2>\n
Stellar Symmetry<\/strong><\/h2>\n
Not Just a Number<\/strong><\/h2>\n