Mystery of the Hidden Cosmos


By Bogdan A. Dobrescu /Don Lincoln B. A. ドブレスク /D. リンカーン
English 日本語 日本語
The beautiful spinning pinwheel of the Andromeda galaxy, our celestial neighbor, poses a mystery. The breakneck speed of its rotation cannot be explained by applying the known laws of physics to the disk’s visible matter. By rights, the gravity generated by the galaxy’s apparent mass should cause the stars in the periphery to move more slowly than they actually do. If the visible matter was all there was, Andromeda, and nearly all such quickly rotating galaxies, simply should not exist.  天の川銀河の隣にある,美しい回転花火のようなアンドロメダ銀河は大きな謎を突きつける。その猛烈な回転スピードは,見えている物質からなる銀河円盤に既知の物理法則を適用することでは説明できない。この銀河の見えている物質の質量によって生じる重力では,周辺部にある星の動きは実際よりも遅いはずだ。見えている物質しかないのなら,アンドロメダも他の高速回転している銀河も,そもそも存在しないはずなのだ。
Cosmologists believe that some unseen kind of matter—dark matter—surrounds and permeates Andromeda and other galaxies, adding the necessary gravitational force to keep them spinning as observed. Dark matter, which appears to contribute about 25 percent of the universe’s mass, would also explain other aspects of the cosmos, including the exceedingly fast motion of galaxies within clusters of galaxies, the distribution of matter arising when two clusters collide and the observation of gravitational lensing—the bending of light by gravity—of distant galaxies.  アンドロメダなどの銀河は何らかの見えない「暗黒物質(ダークマター)」に包まれ満たされていて,観測されている回転の維持に必要な重力が補われていると信じられている。暗黒物質は宇宙の質量のうち約25%を占めているらしく,銀河団内での銀河の速すぎる動き,2つの銀河団が衝突する際の物質分布,遠くの銀河に対する重力レンズ効果(重力によって光が曲げられる)の観測結果など,宇宙の他のいくつかの面も説明する。
The simplest theories of dark matter postulate a single kind of as yet undiscovered particle contributing the unseen mass. But despite decades of searching for direct evidence of the dark matter particle, no one has been able to prove its existence. Further, a few discrepancies remain between astronomical observations and this simple theory. The combination of these residual disagreements with the failure to detect this elusive substance has led some scientists to question the traditional theories and imagine a more complicated form of dark matter. Instead of a single type of particle, dark matter might be made of a wider array of dark species. After all, ordinary matter comes in many forms—maybe dark matter is similarly complex.  最も単純な暗黒物質の理論はダークな質量を占める未発見の粒子が1種類あるという前提に立つ。しかし,20年以上の証拠探しにもかかわらず,暗黒物質粒子の存在は証明できていない。さらに,この単純な理論と天文学の観測結果とはわずかにずれている。
Over the past few years scientists have increasingly come to suspect that several varieties of dark matter exist and, perhaps even more intriguing, that previously unsuspected forces act strongly on dark matter and very feebly (or not at all) on ordinary matter. Recent observations of colliding galaxies may provide preliminary support for this hypothesis, and such forces could help explain some of the discrepancies between the basic dark matter model and observations. If complex dark matter exists, it would make for a more interesting and intricate universe than cosmologists usually imagine.  ここ数年,暗黒物質が何種類も存在し,もっと興味深いことに,予想されていなかった力があって,暗黒物質には強く,通常の物質には非常に弱く作用している(あるいはまったく作用しない)との見方が強くなっている。