棕矮星（Brown dwarf）是類恆星天體的一種，它們是所謂「失敗的恆星」，與一般恆星不同，棕矮星由於質量不足，不能像正常恆星那樣通過氫核聚變維持光度，無法成為主序星。但它們的內部及表面均呈對流狀態，不同的化學物質並不會在內部分層存在。研究表明，小於13倍木星質量的天體不會發生氘核聚變，而大於75倍木星質量的天體會產生氫核聚變[1]，因此如果只從質量上區分，棕矮星為處於13倍木星質量與75倍木星質量之間的天體。現時人們仍在研究棕矮星在過往是否曾經在某位置發生過核聚變，已知的是，質量大於13個木星的棕矮星可融合氘。棕矮星的許多性質與太陽系外巨行星（EGP）相似，因此也有人將它們統稱為具有亞恆星質量的天體（SMO）。
歷史
1960年代天文學家們已經在理論上都預測了棕矮星的存在[2][3]。棕矮星原先被稱為「黑矮星」，代表在字宙間漂浮的類恆星天體或質量不足以發生核反應的天體。但「黑矮星」一詞現時是指一些停止發光，並已死亡的白矮星。
早期的恆星模型指出，一個天體欲成為真恆星，必須擁有80個以上的木星質量，以產生核反應。「棕矮星」的理論最初於1960年代早期提出，指其數量可能比真恆星多，由於未能發光，要尋找也頗為困難。它們會釋出紅外線，可憑地面的紅外線偵測器來偵測，但由提出至證實發現足足用了數十年。
近期的研究則指出，恆星能發光發熱除取決於質量外，也包括其內含的化合物。一些棕矮星的質量達到90個木星仍不能點燃內部的氫。還有當一團星雲塌縮時，除產生恆星外，也會產生不發光的棕矮星，其質量少於13個木星。
首個棕矮星於1995年得到證實，到2006年已經發現了三百多顆，並在1999年發現了第一個雙棕矮星系統[4]，軌道周期約為6天。棕矮星被認為是銀河系中數目最多的天體之一，較接近地球的棕矮星是印第安座υ星，該恆星系統擁有兩顆棕矮星，距離太陽12光年。
棕矮星的形成
關於棕矮星形成的機制天文學家們眾說紛紜，比較常見的有拋射理論、前恆星核的光致侵蝕理論、不透明度制約的分裂理論、原恆星盤的不穩定性理論等。拋射理論認為，棕矮星是由於低質量的原恆星胚在還沒有達到產生氫核聚變所需的質量前，與其它天體發生了碰撞而被拋射出前恆星核所形成的[5][6]，這一理論部分地得到了雙棕矮星系統的證實。前恆星核的光致侵蝕理論基於大質量恆星的輻射對前恆星核的光致侵蝕作用，能夠解釋處於電離氫區中的棕矮星的形成機制。棕矮星也可能由大質量的原恆星盤在其它恆星的引力作用下發生碎裂而產生[7]。這些理論每個都只能解釋部分棕矮星的形成，研究棕矮星周圍的恆星盤可以有效地檢驗上述理論。

Planet Projected at Solar System's Edge
Kyoko Hasegawa, AFP
http://dsc.discovery.com/news/2008/02/28/planet-solar-system.html
Feb. 28, 2008 -- Scientists at a Japanese university said Thursday they believed another planet up to two-thirds the size of the Earth was orbiting in the far reaches of the solar system.
The researchers at Kobe University in western Japan said calculations using computer simulations led them to conclude it was only a matter of time before the mysterious "Planet X" was found.
"Because of the very cold temperature, its surface would be covered with ice, icy ammonia and methane," Kobe University professor Tadashi Mukai, the lead researcher, told AFP.
The study by Mukai and researcher Patryk Lykawka will be published in the April issue of the Astronomical Journal.
"The possibility is high that a yet unknown, planet-class celestial body, measuring 30 percent to 70 percent of the Earth's mass, exists in the outer edges of the solar system," said a summary of the research released by Kobe University.
"If research is conducted on a wide scale, the planet is likely to be discovered in less than 10 years," it said.
Planet X--so called by scientists as it is yet unfound--would have an oblong elliptical solar orbit and circle the sun every thousand years, the team said, estimating its radius was 15 to 26 billion kilometers.
The study comes two years after school textbooks had to be rewritten when Pluto was booted out of the list of planets.
Pluto was discovered by the American astronomer Clyde Tombaugh in 1930 in the so-called Kuiper belt, a chain of icy debris in the outer reaches of the solar system.
In 2006, nearly a decade after Tombaugh's death, the International Astronomical Union ruled the celestial body was merely a dwarf planet in the cluttered Kuiper belt.
The astronomers said Pluto's oblong orbit overlapped with that of Neptune, excluding it from being a planet. It defined the solar system as consisting solely of the classical set of Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
The team noted that more than 1,100 celestial bodies have been found in the outer reaches of the solar system since the mid-1990s.
"But it would be the first time to discover a celestial body of this size, which is much larger than Pluto," Mukai said.
The researchers set up a theoretical model looking at how the remote area of the solar system would have evolved over the past four billion years.
"In coming up with an explanation for the celestial bodies, we thought it would be most natural to assume the existence of a yet unknown planet," Mukai said.
"Based on our hypothesis, we calculated how debris moved over the past four billion years. The result matched the actual movement of the celestial bodies we can observe now," he said.
He was hopeful about research by Kobe University, the University of Hawaii and Taiwan's National Central University.
"We are expecting that the ongoing joint celestial observation project will eventually discover Planet X," Mukai said.

由於月球很細所以能反光也很少, 但月球在近水平上升時有時看上去也像一個小太陽, 這是角度問題
當planet-x近地球時因為面積巨大能反光也強很多, 它本身可能都有自己的月亮, 所以可能看上去會唔只兩個太陽
估一下, 如果它們的position係咁嘅時侯
太陽 > 地球 > Planet-X
到時地球可能真的會有一段時間沒有夜晚的
重有Planet-X話係差唔多以經死亡的星所以沒有光, 沒有很多星體像太陽一様.
要等它近太陽系時才能用紅外線望遠鏡望到小許"黑影"
夠景有冇Planet-X我地好快就會知, 唔需要爭論有定冇.

NASA has been reported in 2003年  遍號#2003UB313

The Dark Star:
The Planet X Evidence
© Timeless Voyager Press 2005
ISBN number 1-892264-18-8


Author Andy LloydAndy Lloyd's work on the subject of Nibiru has become essential reading for anyone who has studied the theories of Zecharia Sitchin.  After 6 years of research, the Dark Star Theory is finally available in book format, available through all good book shops. 'The Dark Star' is 328 pages long, is beautifully illustrated and fully referenced.  An awful lot of work has gone into the book.  Its purpose is to establish the facts about Planet X in a clear and understandable way.
At the end of this book, your understanding and appreciation of the outer solar system will be greatly enhanced.  You will have the facts at your fingertips when discussing the potential existence of Planet X.  You will know WHY this object is for real, and why that is so significant for us all.
The feedback I have received about the book makes the following point very clear:  That complex scientific material has been presented in a way that was easily readable, and enjoyable.

The book will stretch your mind to possibilities you have never considered!

↓↓↓↓↓↓↓↓↓↓↓



In Darkstar16 I looked at the depiction of Leo at Nimrud Dag in Turkey, and analysed the celestial positions of the stars on the frieze.  It quickly became evident that the star shown within the upturned crescent moon could not be Regulus, as had previously been assumed.  Instead, the placement of a star within a crescent presented us with a new possibility, that of the projected arrival of Nibiru in Leo.  The positioning of the other planets in the constellation allowed us to date this event to 2BC.  What was unclear was whether this frieze was designed to predict an event, or to record one.  Given the construction of a 'star shaft' at a different point in the mountain (1), it seemed likely that this Anatolian complex, dating back to about 60BC, was aimed at pinpointing the date of a future event.
That event, I proposed, was the expected appearance of Nibiru, a brown dwarf in an elongated elliptical orbit around the Sun, that was one and the same as the Messianic Star.

早期的恆星模型指出，一個天體欲成為真恆星，必須擁有80個以上的木星質量，以產生核反應。「棕矮星」的理論最初於1960年代早期提出，指其數量可能比真恆星多，由於未能發光，要尋找也頗為困難。它們會釋出紅外線，可憑地面的紅外線偵測器來偵測，但由提出至證實發現足足用了數十年。

下面引用由looseman在 2009/02/25 01:20pm 發表的內容：
the answer is here