首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
外语
The earliest known galaxies in the universe, which formed during the universe’s "dark age" nearly 13 billion years ago, have bee
The earliest known galaxies in the universe, which formed during the universe’s "dark age" nearly 13 billion years ago, have bee
admin
2010-09-25
56
问题
The earliest known galaxies in the universe, which formed during the universe’s "dark age" nearly 13 billion years ago, have been spied by two teams of astronomers.
The discoveries, reported separately in this week’s issue of the journal Nature, suggest that galaxies were forming just 700 million years after the birth of the universe.
Theory holds that the universe formed 13.7 billion years ago when an extremely dense concentration of mass rapidly expanded in an event known as the big bang.
The universe has been expanding ever since, so astronomers are able to age galaxies by computing how much the wavelength of their light has stretched—or redshifted--as the expansion takes the galaxies farther from Earth. The redder the light is, the older and more distant the galaxy is.
The detection of such ancient galaxies adds intrigue(神秘色彩) to theories of how the very first galaxies formed, according to astronomers.
Were there many large, young galaxies in the early universe that are obscured from astronomers’ view by abundant gases absorbing their light? Or were galaxies rare and small way back then, as a prevailing theory suggests, and later clumped together to form larger galaxies such as the Milky Way?
"We believe that we need both these processes to explain what we see," Masanori Iye, a professor at the National Astronomical Observatory of Japan, said in an email.
The galaxy, called IOK-1, formed about 750 million years after the big bang—60 million years closer to the event than the previous record holder.
Given the number of galaxies found during a later epoch about 810 million years ago, the researchers had expected to find as many as six galaxies like IOK-1. But the comparative rarity(稀有) of objects like IOK-1 means that the universe must have changed significantly over the 60 million years that separate the two epochs, the team suggests.
Iye and colleagues believe that they are witnessing the last phase of a process known as reionization(再次电离).
According to Iye, about 380,000 years after the fiery hot big bang, the universe cooled so much that protons and electrons recombined to form neutral hydrogen. This is known as the beginning of the dark age of the universe, because neutral hydrogen absorbs the light from stars.
As more galaxies stared to form about 300 million years later, the hot stars heated the intergalactic(银河间的) medium and gradually reionized the neutral hydrogen back to protons and electrons. The ionized hydrogen then became more transparent, allowing the galaxies light to pass through.
Iye said the new results support the idea that neutral hydrogen was still abundant 750 million years after the big bang, blocking even older galaxies from view. "We are starting to see the last phase of cosmic reionization, or the dawn of the cosmic dark age," he said.
Iye added that the discovery also supports the "hierarchical" theory of galaxy formation, which suggests that big, bright galaxies formed as smaller galaxies collided and merged. "The epoch we have probed is yet in this critical stage," he said.
According to the passage, the "hierarchical" theory of galaxy formation suggests that big, bright galaxies formed as ______.
选项
答案
smaller galaxies collided and merged
解析
根据题干中的关键词“hierarchical”theory定位到最后一段,可得答案。
转载请注明原文地址:https://kaotiyun.com/show/5Qz7777K
0
大学英语六级
相关试题推荐
Wateristasteless,odorless,andnearlycolorless(ithasaslighthintofblue).Itisa【C1】______thatisessentialtoallkn
A、HeboughtthemfromHenry.B、Heboughtthematabookstore.C、Hefoundthemlyinginaquietstreet.D、Hetookthemfromacar
PresidentCoolidge’sstatement,"ThebusinessofAmericaisbusiness",stillpointstoanimportanttruthtodaythatbusinessi
A、Theyneedcareandaffection.B、Theyarefondofround-the-worldtrips.C、Theyaremostlyfrombrokenfamilies.D、Theyarelik
A、Hewentmountain-climbinglastyear.B、Hehasn’ttraveledaroundtheworldyet.C、Healwayswantstoclimbthatmountain.D、He
ThewritingoftheConstitutionoftheUnitedStatesisanactofsuchgeniusthatphilosophersstillwonderatitsaccomplishme
TheUnitedNationswasfoundedto______(维护世界和平、促进繁荣以及保护人权).
Tobetterunderstandthenegotiationpracticesofothercultures,itisimportantforustobeawareofthestandardnegotiation
A、Theyarehusbandandwife.B、Thewomanisaguesttotheman’shouse.C、Themanisaguesttothewoman’sflat.D、Theyarefat
OnceTwainreuniteswiththemotherland,___________________(它可以享受到比香港更多的自治权).
随机试题
在行肝叶或肝段切除术时,须在第一肝门处理肝蒂内各结构,其位置关系是()
________是由商品的生产成本(k)加平均利润()构成的。 生产价格形成后,价值规律作用的表现形式发生了变化。生产价格形成前,商品价格围绕________上下波动。生产价格形成后,商品价格就围绕________上下波动。
从年龄分布来看,死亡率最高的是
具有司眼睑开合的经脉是
下列不属于体内产生的色素是
王某于2004年8月与保险公司签订一份人身保险合同,被保险人为其8周岁的儿子王强,未指定受益人。至2007年8月,王某已支付了3年的保险费。当年9月,王强患病住院,由于医院的重大失误致王强终身残废。依照《保险法》的规定,下列有关本案的表述,不正确的是:
【2007年真题】根据《工程造价咨询企业管理办法》,下列属于工程造价咨询企业业务范围的是()。
货币型理财产品具有投资期()的特点。
(2007年真题)集合{0,1,2,3}的子集的个数为[]。
【S1】【S7】
最新回复
(
0
)