天文學家發現“超級木星”

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天文學家發現“超級木星”

英國每日郵報報導,近日天文學家發現了一顆名為“超級木星”的新行星，或可以幫助科學家提出關於行星形成的新觀點。一直以來，科學家都認為大型恆星在由塵埃氣體組成的旋轉盤中產生新行星，但直到最近的這項發現才證實這個行星形成的觀點可能是正確的。這顆新行星是由位於夏威夷莫納克亞山頂的日本斯巴魯8米望遠鏡觀測到的，它比太陽系最大的行星木星還要大13倍，該行星正環繞著一顆名為仙女座k的恆星運行。



天文學家發現“超級木星”

這顆恆星距離地球170光年遠，質量是太陽的2.5倍以上。基於科學家的觀測，這顆超級木星的形成方式與普通的低質量外來行星並無差異，在行星形成的嬰儿期，吸收環繞恆星的“原行星盤”的物質而聚集自身的質量。最初科學家認為，由於這顆新行星的環繞軌道比海王星環繞太陽軌道略微寬一點，因此可以與太陽系內行星軌道相比較，因此它的形成方式可能也類似於太陽系內的行星形成。



天文學家發現“超級木星”

之前發現的LkCa15b距離地球450光年遠，據稱它利用外圍的氣體和塵埃“自我建造”（藝術家印像圖）。超級木星的恆星，仙女座k是一顆相對年輕的恆星，大約只有3000萬年曆史，因此它的形成周期可能更類似於小行星。但超級木星並非目前發現的第一顆新行星，僅僅只是照片拍攝到的眾多行星之一。與之前發現的800顆行星的方式有所不同，這次天文學家是利用紅外技術捕捉到這些圖像。天文學家利用的光學方法結合了自適應光學和一種名為多孔障板干涉法的技術。



天文學家發現“超級木星”

這種技術是利用一塊多空的小型障板放在所要收集的光線所經過的路徑，然後通過大型望遠鏡光線集中。利用這種方法科學家能夠操控光波長。在此之前，科學家利用這種方法還發現了另一顆行星——LkCa15b,一顆被冷卻的塵埃和氣體包圍的炙熱原行星。據稱，LkCa15b未來也將發展成為類似超級木星的氣體巨星。

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This ESOCast video shows how astronomers, for the first time, were able to directly follow the motion of an exoplanet as it moved from one side of its host star to the other. The planet has the smallest orbit so far of all directly imaged exoplanets, lying almost as close to its parent star as Saturn is to the Sun. Scientists believe that it may have formed in a similar way to the giant planets in the Solar System. Because the star is so young, this discovery proves that gas giant planets can form within discs in only a few million years, a short time in cosmic terms.

Only 12 million years old, or less than three-thousandths of the age of the Sun, Beta Pictoris is 75% more massive than our parent star. It is located about 60 light-years away towards the constellation of Pictor (the Painter) and is one of the best-known examples of a star surrounded by a dusty debris disc.

Earlier observations showed a warp of the disc, a secondary inclined disc and comets falling onto the star. "Those were indirect, but tell-tale signs that strongly suggested the presence of a massive planet, and our new observations now definitively prove this," says team leader Anne-Marie Lagrange. "Because the star is so young, our results prove that giant planets can form in discs in time-spans as short as a few million years." Recent observations have shown that discs around young stars disperse within a few million years, and that giant planet formation must occur faster than previously thought. Beta Pictoris is now clear proof that this is indeed possible.

The team used the NAOS-CONICA instrument (or NACO [2]), mounted on one of the 8.2-meter Unit Telescopes of ESO's Very Large Telescope (VLT), to study the immediate surroundings of Beta Pictoris in 2003, 2008 and 2009. In 2003 a faint source inside the disc was seen (eso0842), but it was not possible to exclude the remote possibility that it was a background star. In new images taken in 2008 and spring 2009 the source had disappeared!

The most recent observations, taken during autumn 2009, revealed the object on the other side of the disc after a period of hiding either behind or in front of the star (in which case it is hidden in the glare of the star). This confirmed that the source indeed was an exoplanet and that it was orbiting its host star. It also provided insights into the size of its orbit around the star.

The planet has a mass of about nine Jupiter masses and the right mass and location to explain the observed warp in the inner parts of the disc. "Together with the planets found around the young, massive stars Fomalhaut and HR8799, the existence of Beta Pictoris b suggests that super-Jupiters could be frequent byproducts of planet formation around more massive stars," explains Gael Chauvin, a member of the team.

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螣蛇廿一，即仙女座κ（Kappa Andromedae，Kappa And），是仙女座中的一顆恆星。
螣蛇廿一是一顆藍白色B型次巨星，視星等為+4.15，根據依巴谷衞星的視差量測資料，它距離地球大約158光年或52秒差距。

在中國該恆星屬於室宿的螣蛇星官，「螣蛇」是中國神話中一種能飛行的蛇。
「螣蛇廿一」代表該恆星是螣蛇星官的第二十一顆恆星。

行星系統
2012年11月在螣蛇廿一旁以直接攝影法發現了一個質量約是木星12.8倍的高溫氣體巨行星（Kappa Andromedae b，Kappa And b），
因此被命名為超級木星'Super Jupiter'。
與母恆星的投影距離大約是55 ± 2天文單位。根據光譜觀測資料推測，該行星表面溫度高達1700 K。

The "super-Jupiter" companion, Kappa Andromedae b (upper left)