Light riddle Halos of mysterious dark matter could be hiding large numbers of unseen stars on the fringes of galaxies, according to a new study.
The discovery, reported in the journal Nature, could explain why there's more light in the universe than there are stars to produce it.
"Existing explanations such as very distant far away galaxies and nearer very faint galaxies can't explain this discrepancy, " says lead reseracher Professor Ned Wright of the University of California.
"The idea of not-so-far-away faint galaxies (producing this light) is off by a factor of about ten, while the 'distant galaxies' hypothesis is off by a factor of about a thousand."
In large clusters of galaxies, astronomers have found much higher percentages of this light discrepancy, as high as 20 per cent.
To solve the riddle, Wright and colleagues used NASA's Spitzer infrared space telescope to map a region of the sky ten billion light years away in the constellation Bo?tes.
Blocking out the light
"There were a large number of galaxies in that field, so we cut out the light from those galaxies by masking them, " says Wright.
"We ended up with a picture of the sky, with all the galaxies cut out which you expect to be perfectly uniform and dark, but we still see small amounts of light coming from somewhere."
Wright and colleagues measured this unexplained light, which they call fluctuations, and found it appeared to be coming from stars hidden in the halos of dark matter surrounding galaxies.
"Galaxies are collections of stars that sit inside a more extended halo of dark matter, " says Wright.
"We can't see the dark matter but we know it's there because of its gravitational impact on the galaxy."
Flung out by gravity
Wright and colleagues, contend that about one star in every thousand are flung out of their galaxies by the gravitational perturbations produced during galactic mergers.
"When these galaxies merge not all of the stars end up in the merged galaxy, " says Wright. "It's these stars, which end up hidden in the dark matter, that are providing the additional light we're seeing."
He says he always felt galaxies were a lot fuzzier than expected.
"This fuzziness means there no sharp edge to the galaxy boundary."
黑色物质隐藏了孤独恒星的光芒
研究表明，神秘黑色物质的光晕可能会隐藏大部分分部在银河系边缘的看不见的星体的光芒。这个发现，发布在《自然》杂志上，能够解释在宇宙中的光芒比星体产生的光芒更多。现有的解释例如离银河系太远，或者离银河系太近都不能解释这种矛盾，来自加利福尼亚大学的研究教授Ned Wright说。离巨大的银河系不太远的观点，是十分之一的因素，然而离银河系太远的假设是千分之一的因素。在成群的银河系中，宇航员们发现这种光芒相差很高的比例，高达20%。为了解开谜底，Wrigth和他的同事们用NASA的箭头式弹头红外空间望远镜在牧牛座星群周围绘出了一个10亿光年远的区域。 阻塞光线 在那片区域中有许多星系，因此为了掩饰它们，我们切断了来自这些星系的光芒。我们把天空做成图片的形状，切断所有的星系，你可以看见的是完全的统一和黑暗，但我们仍然能看见不知来自何方的少量的光芒。Wrigth和他的同事们检测这不知名的光线，称它们为波动，还发现了这不知名的光线看似来自隐藏在围绕着星系的黑色物质光晕后的星体。星系是星体的聚集，是一个更有扩张性的黑色物质的光晕。Wright说。我们看不见这种黑色物质，但是我们知道它的存在，因为它的重力对星系的影响。 靠重力抛出 Wright和他的同事们主张说一千颗星星中大约有一颗被抛出它们的星群，通过在银河系合并中所产生的重力扰动来实现。当这些星系合并时，并不是所有的的星体都能完成合并，Wright说，在这些星体中，被黑色物质隐藏的星体就产生了我们所看到的额外的光线。他说他感觉到星系比他想象中的更模糊。这种模糊性意味着银河边界没有明确的界限。
