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Fraser
2003-Nov-12, 09:21 PM
SUMMARY: Astronomers from the University of Arizona have used a new technique called "nulling interferometry" to reveal the planetary disk around a newly-forming star. Incredibly, they discovered a gap in the disk, where a Jupiter-like planet is probably forming. This nulling technique works by combining the light from the central star in such a way that it gets canceled out. This allows fainter objects, such as dust and planets to be observed. The planet is likely several times the mass of Jupiter and orbits its star at about 1.5 billion kilometers.


Comments or questions about this story? Feel free to share your thoughts.

VanderL
2003-Nov-12, 09:29 PM
"We realized the disk appeared about the same size at warmer (10 micron) wavelengths and at colder (20 micron) wavelengths. The only way that could be is if there's an inner gap."

The most likely explanation for this gap is that it is created by the gravitational field of a giant protoplanet =AD an object that could be several times more massive than Jupiter. The researchers believe the protoplanet may be orbiting the star at perhaps 10 AU. (An AU, or astronomical unit, is the distance between Earth and the sun. Jupiter is about 5 AU from the sun.)

Can anyone explain to me why the disk's size at different wavelengths means there is an inner gap, and how this would mean that a planet exists there. I suppose that the star "wobble" would be pronounced enough to detect the planet with this method as well, is there any evidence for this?

IonDrive
2003-Nov-16, 01:11 PM
Originally posted by VanderL@Nov 12 2003, 09:29 PM
I suppose that the star "wobble" would be pronounced enough to detect the planet with this method as well, is there any evidence for this?
Actually I too don't understand that thing about disk size, but to answer that other question of yours:

Even if that planet got several Jupiter masses, it's so far from it's star that it would be difficult to detect with the wobble method because the changes it causes in the star's radial velocity are very small. Also, to obtain good (scientifically not too doubtful anymore) values for both orbital period and mass of an extrasolar planet, one has to watch that system for several revolutions of that planet. I don't know what's the mass of that star compared to sun, but since I don't suppose it's much more massive, to use that wobble method that star's radial velocity would have to be measured from time to time for at least a few decades to come (maybe a century) before any meaningful data would result from that method.

VanderL
2003-Nov-16, 04:28 PM
Thanks,

I checked other sites as well to find out about the "gap" detection but I couldn't find anything useful. I wouldn't know how long it takes to make the "wobble" measurements, but this would surely be a star that has to be included in any survey.
The article is also very vague about why this star is "on the cusp of becoming a main-sequence star".
What does this phrase mean?

IonDrive
2003-Nov-18, 06:00 PM
If you look at Hertzsprung-Russel-Diagram, that is a diagram where you plot the brightness of stars vs. their "color" ( = surface temperature), you will find that many stars are situated in a relatively thin band reaching from bright blue stars to dim red ones. Stars who are in the stage of stable hydrogenium fusion are situated there and most of them are there because this stage is simply the by far longest stage in the lifespan of each star. This area is called the main sequence. "On the cusp of becoming a main sequence star" simply means that this star is just initiating this phase of stable H burning. (Before the fusion process becomes stable, newborn stars are situated a little above the main sequence, they are a little brighter and redder than their older counterparts.)

VanderL
2003-Nov-19, 06:05 PM
Thanks for the explanation, what is this star using as energy source (before becoming a main sequence star), and how does this change actually occur, because the hydrogen must already exist at the core for it to "ignite" in a fusion reaction. I also read about stars that have changed "color" in mere decades, like FG Sagittae that changed from blue to yellow since 1955. Does this mean that the lifespan of a star is not as long as we think, or that the Hertzsprung-Russell diagram tells us something different about what makes stars shine?
Cheers.