Galaxy Collisions Give Birth to Quasars

HammerSun

Demolition derby. Observations of distant quasars reveal they originated from the collisions of massive galaxies.
Credit: (Top) NASA/ESA/Hubble Heritage (STScI/AURA)/A. Evans (U.VA/NRAO/Stony Brook U.); (Bottom ) E. Treister/K. Teramura (IfA/U.HI)


Peering behind thick clouds of cosmic gas and dust, researchers believe they have finally determined the origins of quasars, the brightest and most powerful objects in the universe. X-ray and infrared observations of over 200 distant galaxies, coupled with images taken in visible light, reveal that quasars form when two galaxies smash into each other and their central black holes merge. The new observations also suggest that quasars were more common in the early universe than previously thought.

Astronomers discovered quasars, short for quasi-stellar objects, in the 1950s. Only about the size of our solar system, quasars easily outshine entire galaxies and can burn for 100 million years. For decades, however, astronomers could not figure out what generated these cosmic beacons. The obvious suspects were supermassive black holes, which anchor the cores of practically all galaxies, can devour gigantic amounts of matter, and are known to produce huge jets of particles and energy. But many galaxies—including the Milky Way—host supermassive black holes yet don't generate quasars.

Perhaps the younger quasars were hiding. At least, that's what astronomers began to suspect in the late 1990s when they noticed that some galaxies whose central cores were obscured by huge clouds of dust seemed to emit the same kind of radiation and produced similar levels of energy as quasars.

To peek behind the dust, astronomer Ezequiel Treister of the University of Hawaii, Honolulu, and colleagues first selected about 200 candidate galaxies out of 100,000 images taken by the Hubble Space Telescope. Then they trained the Chandra and Spitzer space telescopes, which can see in x-ray and infrared light, respectively, on the galaxies' obscured cores. The candidates ranged out to a distance of about 11 billion light-years—back to a time when the universe was only 2.7 billion years old. The new observations revealed hidden quasars in every one of the galaxies, the team reports online today in Science. What's more, by studying the shape of the galaxies in the Hubble images, the astronomers found that they all had arisen from the mergers of two massive galaxies and their central black holes.

Taken together, the data paint a picture of how quasars form. "Suddenly it all made sense," says astronomer and co-author Priyamvada Natarajan of Yale University. When two big galaxies merge, she explains, their supermassive black holes combine. The new black hole, which weighs as much as billions of suns, begins devouring everything in its vicinity. For up to 100 million years, this activity is shrouded by the dust kicked up by the galaxy merger. But eventually, the black hole consumes enough of the dust that the powerful and brilliant particle jets blasting out from its poles can break into the open. After another 100 million years, the quasar exhausts its fuel and goes dark, becoming just a garden-variety, billion-solar-mass or so black hole.

In the early universe, collisions—and hence quasars—occurred more often because galaxies were packed much more closely together. For many years, Treister says, astronomers doubted that obscured quasars were very common. "Now," he says, "we are seeing them everywhere."

The findings provide "powerful insights into how quasars form and evolve," says astronomer Amy Barger of the University of Wisconsin, Madison. The notion that obscured quasars are the byproduct of galaxy mergers has been around for quite a while, adds astronomer Christopher Reynolds of the University of Maryland, College Park. "But it is amazing that the fraction of obscured quasars tracks the galaxy-merger rate so well," he says. "It means that there isn't much room for other mechanisms to produce obscured quasars."

S.A.S

机翻的
凝视宇宙背后的气体和尘埃，研究人员相信，他们终于确定了类星体的起源，宇宙中最明亮和最强大的对象浓云。透视和200多个红外观测遥远星系，在可见光拍摄的图像，加上显示，类星体的形式当两个星系粉碎互相其中央的黑洞合并。新的观测还表明，类星体更在早期宇宙中常见的比以前想象。

天文学家发现了类星体，为半短恒星的对象，在20世纪50年代。只关心我们的太阳系的大小，类星体容易一枝独秀整个星系和可刻录为1.00亿年。几十年来，但是，天文学家无法弄清这些宇宙生成的信标。最明显的犯罪嫌疑人超大质量黑洞，有固定的几乎所有星系的核心，可以吞噬物质的巨大数额，并且能够产生粒子和能量巨大的飞机。但是，许多星系，包括银河系在内的主机超大质量的黑洞还不会产生类星体。

也许年轻的类星体藏身。至少，这就是天文学家开始怀疑在90年代末的时候，他们发现有些星系的中央核心被巨大的尘埃云掩盖，似乎发出的辐射和生产同类的类星体的能源类似的水平。

后面的尘土，天文学家埃茨基埃尔的夏威夷，檀香山，和同事大学Treister偷看第一选择了约200米的由哈勃太空望远镜拍摄的图像候选人十万星系。然后，他们训练了斯皮策和钱德拉太空望远镜，可以看到X射线和红外光，分别在该星系核模糊。不等的候选人出约11亿光年的距离，多年回到当时宇宙只有2.7亿年。新的观测显示，隐藏在每一个类星体的星系研究报告称，今天的在线科学。更重要的是，通过研究在哈勃图像形状的星系，天文学家们发现他们都已经由两个巨大的星系合并，其中央的黑洞出现。

两者合计，数据描绘一幅图片类星体是如何形成。 “突然，一切都很有道理，说：”天文学家和共同作者之一，耶鲁大学Priyamvada纳塔拉詹。当两个大的星系合并时，她解释说，他们的超大质量的黑洞合并。新的黑洞，其重量多达数十亿个太阳，开始吞噬附近的一切。长达1.00亿年，这项活动是由灰尘笼罩踢的星系合并了。但最终，黑洞消耗足够的尘埃和灿烂的强大粒子喷射飞机从它的两极，可以很快打入公开。再过1.00亿年，这个类星体的燃料和废气去黑暗，成为只是一个普通的，亿个太阳质量的黑洞左右。

在早期宇宙中，碰撞，因此类星体，多了一些，因为星系爆满更加密切地合作。多年来，Treister说，天文学家怀疑，模糊了类星体，也很普遍。 “现在，”他说，“我们看到他们无处不在。”

调查结果提供“为类星体是如何形成和演变强大的见解，说：”天文学家艾米巴里耶威斯康星大学麦迪逊分校。模糊的概念，类星体是星系合并的副产品已相当长一段时间左右，增加了天文学家克里斯托弗的学院公园市马里兰大学的雷诺兹。 “但令人惊讶的是模糊的一小部分类星体跟踪星系合并率这么好，”他说。 “这意味着没有其他办法产生很大的空间遮蔽类星体。”

baiseniao

机翻能翻到这样很八错了。