USA: Planet found from another galaxy

[Ann]

http://content.usatoday.com/communities ... r-galaxy/1

USA Today, Science Fair wrote:

Exoplanet detected orbiting star from another galaxy
02:12 PM

Astronomers report Thursday the discovery of a planet orbiting a star that originated in another galaxy.

The finding suggests that stars in galaxies besides our own Milky Way, where more than 400 exoplanets have been detected in the last two decades, likely have solar systems as well.

In the journal Science, a team led by Johny Setiawan of Germany's Max-Planck-Institut für Astronomie, reports the star HIP 13044, a dying red giant, harbors a planet 1.25 times as big as Jupiter. The planet has a 16-day orbit of the star, the team suggests, which is puzzling because the star should have engulfed the world when it expanded millions of years ago as part of the death process of elderly stars.

HIP 13044 belongs to the "Helmi Stream" of stars, which circle the center of the Milky Way galaxy on an inclined orbit, traveling up to 42,380 light years above and below the central disk of the galaxy. That indicates the stars once belonged to a dwarf galaxy, ripped apart by our Milky Way galaxy's gravity at least six billion years ago.

"... as a member of the Helmi stream, HIP 13044 most probably has an extragalactic origin. This implies that its history is likely different from those of the majority of known planet-hosting stars. HIP 13044 was probably attracted to the Milky Way several Ga ago. Before that, it could have had belonged to a satellite galaxy of the Milky Way similar to Fornax or the Sagittarius dwarf spheroidal galaxy. Because of the long galactic relaxation timescale, it is extremely unlikely that HIP 13044 b joined its host star through exchange with some Milky Way star, after the former had been tidally stripped. The planet HIP 13044 b could thus have a non-Galactic origin."

Alan Boss, a planetary theorist at the Carnegie Institute of Washington, calls the finding, "Big news if it is correct," by email.

"As the host star is not from the normal population of stars in our galaxy, and has very little of the elements associated with forming rock/ice planets and the cores of gas giant planets (i.e., low metallicity). Hence this object with a mass of a gas giant planet is unlikely to have formed by the conventional mechanism of first building a massive core of rock and ice and then pulling on enough gas to form a true gas giant planet. That leaves, of course, my hobby horse: disk gravitational instability. The fact that the star is also likely to have come from somewhere other than the disk of our galaxy makes it even more remarkable, and supports the suspicion that planetary systems are rife in the universe, i.e., we live in a crowded universe."

By Dan Vergano

Ann

[bystander]

Planet from another galaxy discovered
European Southern Observatory | eso1045 | 18 Nov 2010

Galactic cannibalism brings an exoplanet of extragalactic origin within astronomers' reach

Visible light wide-field image of the region around HIP 13044 b. Created from photographs forming part of the Digitized Sky Survey 2 (DSS2). At the image center, HIP 13044 is visible as an unremarkable, moderate brightness star. Planet HIP 13044 b is much too faint to be seen in this image. [i](Credit: ESO/DSS2. Acknowledgment: Davide De Martin)[/i]

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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 using the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory in Chile. 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.

Over the last 15 years, 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 with a minimum mass 1.25 times that of Jupiter has been discovered orbiting a star of extragalactic origin, even though the star now finds itself within our own galaxy. It is part of the so-called Helmi stream — a group of stars that originally belonged to a dwarf galaxy that was devoured by our galaxy, the Milky Way, in an act of galactic cannibalism about six to nine billion years ago. The results are published today in Science Express.
...
The star is known as HIP 13044, and it lies about 2000 light-years from Earth in the southern constellation of Fornax (the Furnace). The astronomers detected the planet, called HIP 13044 b, by looking for the tiny telltale wobbles of the star caused by the gravitational tug of an orbiting companion. For these precise observations, the team used the high-resolution spectrograph FEROS attached to the 2.2-metre MPG/ESO telescope [4] at ESO’s La Silla Observatory in Chile.

Adding to its claim to fame, HIP 13044 b is also one of the few exoplanets known to have survived the period when its host star expanded massively after exhausting the hydrogen fuel supply in its core — the red giant phase of stellar evolution. The star has now contracted again and is burning helium in its core. Until now, these so-called horizontal branch stars have remained largely uncharted territory for planet-hunters.
...
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 0.055 times the Sun-Earth distance). It completes an orbit in only 16.2 days. Setiawan and his colleagues hypothesise that the planet's orbit might initially have been much larger, but that it moved inwards during the red giant phase.

A Giant Planet Around a Metal-Poor Star of Extragalactic Origin - J Setiawan et al

• Science Express (online 18 Nov 2010) DOI: 10.1126/science.1193342

Exoplanet of Extragalactic Origin Could Foretell Our Solar System’s Future
Universe Today | Nancy Atkinson | 18 Nov 2010

While astronomers have detected over 500 extrasolar planets during the past 15 years, this latest one might have the most storied and unusual past. But its future is also of great interest, as it could mirror the way our own solar system might meet its demise. This Jupiter-like planet, called HIP 13044 b, is orbiting a star that used to be in another galaxy but that galaxy was swallowed by the Milky Way. While astronomers have never directly detected an exoplanet in another galaxy, this offers evidence that other galaxies host stars with planets, too. The star is nearing the end of its life and as it expands, could engulf the planet, just as our Sun will likely snuff out our own world. And somehow, this exoplanet has survived the first death throes of the star.

Planet Found Around Wrong Kind Of Star
Scientific American | Christopher Intagliata | 18 Nov 2010

An exoplanet has been discovered orbiting a star of extragalactic origin that contains far less metal than models predict for stars with planets.

[Ann]

Thanks for editing my post, bystander. I haven't quite figured out how to quote other publications and make the posts look good.

Ann