Found: An Exoplanet From Another Galaxy

By Andrew Moseman | November 18, 2010 2:44 pm

ExtragalacticExoplanetA fascinating discovery from today’s edition of the journal Science: Astronomers from Germany report a new exoplanet with two startling characteristics. First, it closely orbits a star that has already exhausted its hydrogen supply and moved past the red giant stage, so this hot Jupiter has so far survived without being evaporated (despite its proximity—just 0.12 astronomical units).

But second, and most striking: This planet and star came from another galaxy.

From Phil Plait:

OK, first, this planet is in our own Milky Way galaxy. The star, called HIP 13044, is about 2000 light years away, well inside our galaxy. So how do we know it’s from a different galaxy? All the stars in our galaxy orbit the galactic center, like planets orbit around a star. But many years ago, astronomers noticed that many stars in the sky have the same sort of motion as they orbit, as if they all belong to streams of stars, flowing like water in a river. Many such streams exist, and eventually astronomers figured out that these were the leftover remnants of entire small galaxies that had collided with, been torn apart, and basically eaten by our Milky Way.

HIP 13044 is part of one of those streams, called the Helmi Stream. It’s the remains of a dwarf galaxy the Milky Way tore apart probably more than 6 billion years ago. So the star and its planet formed in an actual other galaxy, one that either orbited the Milky Way or had an unfortunately too-close pass to it. Either way, wow!

During a web conference this morning, study coauthor Rainer Klement said we shouldn’t be surprised the star and planet are still together even though our galaxy tore theirs apart. Galaxies are structures of stars, but the stars themselves are still so far away that even during a galactic breakup they don’t pass near enough to one another to gravitationally influence a planet. “The timescale upon which such stars play a role is larger than the age of the universe,” he said.

Read the rest of Phil’s post at Bad Astronomy.

Related Content:
80beats: Astronomers Predict a Bonanza of Earth-Sized Exoplanets
80beats: Um… That “Goldilocks” Exoplanet May Not Exist
Discoblog: So, How Long Would It Take to Travel to That Exciting New Exoplanet?
DISCOVER: How Long Until We Find a Second Earth?

Image: ESO

  • nick

    This was way more exciting when I thought the headlines were “in another galaxy.”

  • Jockaira

    I should think that if one goes back in time far enough, most stars in a galaxy as large as ours would have become a part of the Milky Way Galaxy as their parent galaxies were captured by gravitational attractions. The word “galaxy” only describes a group of stars, gas, and dust orbiting around a common center of gravity and not part of another galaxy, pretty much the same thing on a grander scale as a “cluster” or a “stream” circulating around its own center of gravity and then orbiting a galactic center, and that galaxy likewise orbiting around another center of gravity of a “local group”of galaxies. HP13044 enjoys no particular distinction except for the fact that it is part of a stream identified as having an extra-galactic origin.

    It is even possible for the local group of stars that includes our solar system to have come from somewhere other than the Milky Way Galaxy.

  • Brian Too

    @1. nick,

    +5 your comment.

  • Dan

    Strange Signal Comes From Alien Planet, Scientist Says… Does ET live on Goldilocks planet? How scientists spotted ‘mysterious pulse of light’ from direction of newly-discovered ‘2nd Earth’ two years ago:

  • Victor

    Still pretty cool, but Nick said what I was thinking. You can’t judge a story by its headline these days.

  • Albert Bakker

    #4 – When directed to a site or even worse a private blog featuring the often so violently raped Schopenhauer quote in big fat print, it is like screaming at me to tune out immediately. But I was able to withstand even the pressure put on me by Faux News and the Daily Fail and try to find a word from the source himself:–2

  • VIP

    Rainer Klement, you are only one of many mortals who do not understand that there is no ‘age of the universe’. Only because you and I are mortal doesn’t give any reason for the universe to be mortal. There is no beginning, there is no end. there is no proof that it can be anything else. That’s why it’s called the universe. You and I know that it is impossible to create space or matter, therefore it is also impossible to destroy space or matter.

  • Albert Bakker

    VIP you are probably, hopefully even, one of exceptionally few mortals who would read “age of the universe” especially in context in which it was used as meaning to be anything else than the time passed from the Big Bang event to present day Earth as a frame of reference.

  • Kate

    “The timescale upon which such stars play a role is larger than the age of the universe,” he said.

    Smaller, surely?


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