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      In the (convection) zone: Astronomers eavesdrop on stars’ innate “twinkle”

      news.movim.eu / ArsTechnica · Tuesday, 22 August, 2023 - 20:46 · 1 minute

    Visualization of "Twinkle, Twinkle, Little Star" played through three sizes of massive stars. Credit: Northwestern University.

    Science 101 tells us that the twinkling appearance of stars from our vantage point on Earth is due to atmospheric effects: winds and varying temperatures and densities in the air bend and distort the light. But stars have another sort of "twinkle" produced by how gases ripple in waves across their surface, an effect that could provide astronomers with a handy means of exploring the interior of massive stars to learn more about how they form and evolve. But the effect is much too small to be readily detected by telescopes.

    So scientists have now developed the first 3D simulations of that innate twinkle, according to a recent paper published in the journal Nature Astronomy. As a bonus, the researchers converted the data from those rippling waves of gas into an audible sound, so now we can all take a moment to listen to "Twinkle, Twinkle, Little Star" (see video above) and Gustav Holst's "Jupiter" (see video below) in the "language" of the stars.

    “Motions in the cores of stars launch waves like those on the ocean,” said co-author Evan Anders of Northwestern University. “When the waves arrive at the star’s surface, they make it twinkle in a way that astronomers may be able to observe. For the first time, we have developed computer models which allow us to determine how much a star should twinkle as a result of these waves. This work allows future space telescopes to probe the central regions where stars forge the elements we depend upon to live and breathe.”

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      Betelgeuse is bouncing back after blowing its top in 2019

      news.movim.eu / ArsTechnica · Friday, 12 August, 2022 - 17:28 · 1 minute

    Artist’s conception in 2021 provided a close-up of Betelgeuse’s irregular surface and its giant, dynamic gas bubbles, with distant stars dotting the background.

    Enlarge / Artist’s conception in 2021 provided a close-up of Betelgeuse’s irregular surface and its giant, dynamic gas bubbles, with distant stars dotting the background. (credit: European Southern Observatory)

    Astronomers are still making new discoveries about the red supergiant star Betelgeuse, which experienced a mysterious "dimming" a few years ago. That dimming was eventually attributed to a cold spot and a stellar "burp" that shrouded the star in interstellar dust. Now, new observations from the Hubble Space Telescope and other observatories have revealed more about the event that preceded the dimming.

    It seems Betelgeuse suffered a massive surface mass injection (SME) event in 2019, blasting off 400 times as much mass as our Sun does during coronal mass ejections (CMEs). The sheer scale of the event is unprecedented and suggests that CMEs and SMEs are distinctly different types of events, according to a new paper posted to the physics arXiv last week. (It has been accepted for publication in The Astrophysical Journal.)

    Betelgeuse is a bright red star in the Orion constellation— one of the closest massive stars to Earth, about 700 light-years away. It's an old star that has reached the stage where it glows a dull red and expands, with the hot core only having a tenuous gravitational grip on its outer layers. The star has something akin to a heartbeat, albeit an extremely slow and irregular one. Over time, the star cycles through periods when its surface expands and then contracts.

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      When the Sun expands, it will trash all the asteroids

      John Timmer · news.movim.eu / ArsTechnica · Tuesday, 18 February, 2020 - 17:01 · 1 minute

    Cartoon of the Sun, Earth, and Jupiter, with a diffuse collection of asteroids.

    Despite its distance from the Sun, the asteroid belt will disintegrate as it expands. (credit: NASA/ESA/STScI )

    We tend to view the bodies of the Solar System as creations of gravity, which pulled their parts together and hold them in place as they orbit. But as we saw with ideas about the formation of Arrokoth , there are lots of situations where gravity is essentially a constant for long periods of time. And given enough of that time, relatively small forces like friction from sparse gas clouds or pressure from the light of the Sun can add up and create dramatic changes. In fact, a remarkable number of these potential influences have been identified and simulated.

    One of these has been named the YORP effect, for its developers, Yarkovsky, O'Keefe, Radzievskii, and Paddack. It describes how light can alter the rotational properties of orbiting bodies. In a recent edition of the Monthly Notices of the Royal Astronomical Society, Dimitri Veras and Daniel Scheeres decided to calculate what happens as the Sun ages, the intensity of its light increases dramatically, and the entire asteroid belt gets YORPed.

    A (perhaps too) bright future

    It's pretty widely understood that, as the Sun ages, it will expand until its outer edges come close to the Earth's orbit. What's less widely recognized is that it will get quite a lot brighter than it is at present. Other stars with masses similar to the Sun can get thousands of times brighter than the Sun in the last stages of their fusion-driven lives, allowing effects that might otherwise be a bit weak to become dominant.

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