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  • An exoplanet orbiting a star that entered our Milky Way from another galaxy

  • has been detected by a European team of astronomers.

  • The Jupiter-like planet is particularly unusual,

  • as it is orbiting a star nearing the end of its life

  • and could be about to be engulfed by it,

  • giving tantalising clues about the fate of our own planetary system

  • in the distant future.

  • This is the ESOcast!

  • Cutting-edge science and life behind the scenes at ESO

  • the European Southern Observatory.

  • Exploring the ultimate frontier with our host Dr J, a.k.a. Dr Joe Liske.

  • Hello and welcome to the ESOcast.

  • In this episode we are going to find out how an act of galactic cannibalism

  • has brought a planet from another galaxy within astronomersreach.

  • Astronomers have detected nearly 500 planets

  • orbiting stars in our cosmic neighbourhood,

  • but none outside our Milky Way has been confirmed.

  • Now, however, a planet weighing at least 1.25 times as much as Jupiter

  • has been discovered orbiting a star of extragalactic origin,

  • even though the star now finds itself within our own galaxy.

  • The star, which is known as HIP13044

  • lies about 2000 light-years from Earth and is part of the so-called Helmi stream.

  • This stream of stars originally belonged to a dwarf galaxy,

  • which was devoured by our Milky Way

  • in an act of galactic cannibalism six to nine billion years ago.

  • Astronomers detected the planet by looking for tiny telltale wobbles of the star

  • caused by the gravitational tug of an orbiting companion.

  • For these precise observations,

  • the team used a high resolution spectrograph called FEROS,

  • attached to the 2.2-metre telescope at ESO’s La Silla Observatory in Chile.

  • The planet, HIP 13044 b, is also one of the few exoplanets known

  • to have survived its host star massively growing in size

  • after exhausting the hydrogen fuel supply in its core

  • i.e. the Red Giant phase of stellar evolution.

  • HIP 13044 b is near to its host star.

  • At the closest point in its elliptical orbit,

  • it is less than one stellar diameter from the surface of the star

  • (or only about 0.055 times the Sun-Earth distance),

  • and it completes an orbit in only about 16 days.

  • The astronomers hypothesise

  • that the planet's orbit might initially have been much larger,

  • but that it moved inwards during the Red Giant phase.

  • Any closer-in planets may not have been so lucky.

  • Astronomers suggest that some inner planets

  • may have been swallowed by the star during its Red Giant phase.

  • Although the Jupiter-like exoplanet

  • has escaped the fate of these inner planets so far,

  • the star will expand again in the next stage of its evolution.

  • When this happens, the star may engulf the planet,

  • meaning it may be doomed after all.

  • The astronomers are now searching for more planets

  • around stars near the end of their lives.

  • Their work may tell us about the distant fate of the planets in our own Solar System,

  • as the Sun is also expected to become a Red Giant

  • in about five billion years.

  • This is Dr J signing off for the ESOcast.

  • Join me again next time for another cosmic adventure.

  • ESOcast is produced by ESO, the European Southern Observatory.

  • ESO, the European Southern Observatory, is the pre-eminent intergovernmental science and technology organisation in astronomy,

  • designing, constructing and operating the world’s most advanced ground-based telescopes.

  • Transcription by ESO ; translation by

  • Now that you've caught up with ESO,

  • head 'out of this world' with Hubble.

  • The Hubblecast highlights the latest discoveries of the world´s most recognized and prized space observatory,

  • the NASA/ESA Hubble Space Telescope

An exoplanet orbiting a star that entered our Milky Way from another galaxy


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ESOcast 24: 銀河系外起源の最初の惑星 (ESOcast 24: First planet of extragalactic origin)

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    Wonderful に公開 2021 年 01 月 14 日