June 14, 2009
Possible Planet Found Outside Our Galaxy
Astronomers have reason to believe that they have witnessed signs of the first planet to be spotted outside of our galaxy.
The planet is located in the Andromeda galaxy and is estimated to have a mass six times that of Jupiter.
The method of viewing this newly discovered planet is through gravitational lensing, where the light from a very distant, bright source is "bent" around a massive object between the source object and the observer.
The team that utilized a type of gravitational lensing known as microlensing is comprised of researchers from the National Institute of Nuclear Physics in Italy and collaborators in Switzerland, Spain, and Russia.
The advantage of gravitational microlensing is that it is most effective in witnessing more distant objects, which makes it ideal for searching for planets in other galaxies. In theory, it might even be possible to see Earth-size objects in this way.
Large, massive objects situated between an observer and a distant planet or star are often distorted by the gravity of the intermediary object bending the light. Microlensing is when the less massive object is found in the middle.
A substantial increase in the observed intensity of light is seen coming from the aligned pair as the middle object focuses the light of the distant object.
Since the effect relies on smaller objects that move quickly in relation to each other, microlensing events are quickly passing and happen within minutes or hours, making observation of such an event exceptionally rare.
In order to detect such an exceptional event, dense groups containing millions of stars like those of the Andromeda galaxy are carefully watched.
A computer model was developed by Francesco De Paolis of the INFN along with his colleagues in order to determine the likelihood of finding an exoplanet (what astronomers call planets around a star other than the Sun) within the Andromeda galaxy through a microlensing event.
They modeled the variation in light, known as the "light curve", that a microlensed star would display if it were orbited by another star or a planet.
After determining what signs an Andromeda planet would show, they referred to a survey conducted in 2004 by the Point-Agape collaboration of astronomers that revealed an unusual light curve.
The group says that the event served to confirm its theory and can be attributed to an object with a mass approximately six times that of Jupiter. That's heading into brown-dwarf territory, but it's also well within planetary territory too.
This means that this may have well been our first-ever witnessed extra-galactic planet.
The disadvantage of microlensing is that it is a relatively rapid, single occurrence, making observations unfortunately difficult for astronomers to reevaluate and verify their findings.
However, De Paolis remains encouraged by the mere possibility of finding planets at such outrageous distances.
"The interesting thing is that the technology is in place to truly see planets of Jupiter's mass and even less in other galaxies...it's an exceptional thing," he said in an interview with BBC.
Now that the authors of the work are equipped with this new theory, they are seeking to secure time on a larger telescope to further their observations hopes of finding more planet candidates.
Dr. De Paolis said that with about 350 extra-solar planets already found in our galactic neighborhood, it is likely that they will find such candidates to be plentiful. The difficulty is in finding one through a gravitational lens.
"It's not easy, obviously," he said. "The problem is that we don't know when a gravitational microlensing event is going to happen."
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