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每周学术报告

周五下午

2008年 最新学术报告

Journal Club

Galaxy  Cosmology

AGN  VLBI Astrophysics



时间:
9月19 星期二 下午200
报告人:Professor Gianfranco Bertone (IAP, France)
报告题目:Particle dark matter: what comes next
地点:三楼中会议室

Dark matter may not be completely dark. They may annihilate and decay into visible sectors (gamma ray photons, positrons, cosmic ray protons, etc) and may also collide with nucleons. For these reasons, dark matter particles could leave distinguishable signatures in underground detectors, the Sun and planets, galactic center, drawf galaxies, the cosmic backgrounds, the reionization epoch or the middle of nowhere. This provides us hope to see the otherwise "dark" matter and the underlying fundamental physics. Dark matter detection (indirect detection through astrophysical observations and direct detection through experiments) is a booming and exciting area in modern astrophysics and physics. This year is particularly exciting, thank to the launch of Fermi gamma ray telescope (previously known as GLAST) and operation of the large hadron collider (LHC).


时间:9月5日下午2:00(Friday)
报告题目:Accretion states in ultraluminous X-ray sources and stellar-mass black holes
报告人:Dr. Robert Soria (Mullard Space Science Laboratory, University of College London)
地点:3楼中会议室

A
BSTRACT

Spectral state transitions from accreting black holes (BHs)
are an indirect way to estimate the mass accretion rate and the BH mass. Stellar-mass BHs tend to be dominated by a thermal disk (disk-blackboby spectrum) when they are in a luminous state, and a Comptonizing region
(power-law spectrum) at lower accretion rates.
Ultraluminous X-ray sources (ULXs) show different states, and do not seem to have a pure disk state. It is not clear whether this is due to a fundamental difference in the accreting BH mass, the mass transfer rate, or the type of donor star. It is also unclear whether AGN accretion states are more similar to those of stellar-mass BHs or ULXs.

时间:8月25日 上午10:30
报告人:Eric Silver (Harvard-Smithsonian CfA)
报告题目:APEX, The Astrophysical Polarimetric Explorer
地点:3楼中会议

时间:8月8日上午 9:30
报告题目:SEARCHES FOR LIFE IN THE UNIVERSE
报告人:Professor J.V. NarlikarInter-University Centre for Astronomy and Astrophysics, India , IUCCA)
地点:楼中会议室

ABSTRACT

This talk will begin with a description of how vast is our
universe. It will then speculate on the possibility of life in it, preferably of the advanced type. Mention will be made of attempts to contact such advanced extra-terrestrials. It will be argued that this may be a long drawn out procedure. In the second part of the talk there will be a brief description of attempts by Indian scientists led by the speaker to sample air from heights up to 40 km above the Earth's surface.
Microorganisms have been found in these air samples, raising the
intriguing possibility that they may be extra-terrestrial.

时间:8月8日上午 9:30
报告题目:SEARCHES FOR LIFE IN THE UNIVERSE
报告人:Professor J.V. NarlikarInter-University Centre for Astronomy and Astrophysics, India , IUCCA)
地点:三楼中会议室

ABSTRACT

This talk will begin with a description of how vast is our
universe. It will then speculate on the possibility of life in it, preferably of the advanced type. Mention will be made of attempts to contact such advanced extra-terrestrials. It will be argued that this may be a long drawn out procedure. In the second part of the talk there will be a brief description of attempts by Indian scientists led by the speaker to sample air from heights up to 40 km above the Earth's surface.
Microorganisms have been found in these air samples, raising the
intriguing possibility that they may be extra-terrestrial.


 

时间:722日 星期二 下午200
地点:三楼中会议室
报告人:
Dr. Yanlin Wu (Cornell University, USA)
题目:Spitzer Mid-Infrared Observations of Blue Compact Dwarf Galaxies

Abstract

Blue Compact Dwarf Galaxies (BCDs) are galaxies that are characterized by their blue optical colors, low luminosities and small sizes. BCDs are found to typically have low, subsolar, metallicities and proposed to be used as local laboratory to study the star formation in the early univesre. The unprecendented sensitivity of the Spitzer Space Telescope has enabled us for the first time to detect a large sample of these low luminosity systems, proving the presence/absence of the Polycyclic Aromatic Hydrocarbon features. In addition, using the high-resolution spectroscopy, we study the elemental abundances of neon and sulfur in BCDs and compare with the results from optical studies. Finally, we also analyse the FIR/radio correlation in low luminosity galaxies and expand the discussion to the mid-IR.


 

时间:721日 星期一 下午200
地点:三楼中会议室
报告人:
Professor Xiaohui Fan (University of Arizona, USA)
题目:The Highest Redshift Quasars and the End of Reionization

Abstract:


Luminous quasars at high redshift provide direct probes of the evolution of supermassive black holes (BHs) and the intergalactic medium (IGM) at early cosmic time. Over the last six years, more than 20 quasars have been discovered at z>6 from various wide-field surveys. Two main results emerge from the studies of these quasars. Detections of such objects indicate the existence of billion M_sun BHs merely a few hundred Myrs after the first star formation in the Universe. They are surrounded by metal-enriched gas and young galaxies with intense star formation, providing the strongest constraints on early growth of supermassive BHs and co-evolution with their host galaxies.

Meanwhile, Absorption spectra of the highest redshift quasars reveal complete Gunn-Peterson absorption, indicating a rapid increase in the IGM neutral fraction, marking the end of the reionization epoch at z~6, suggesting a peak of reionization activity and emergence of the earliest galaxies and AGNs at 6<15. These results strongly suggest that crucial changes are happening at z~6-7. A number of ambitious near-IR surveys aiming at finding quasars at z>7 will likely produce the first detection of quasars in this crucial epoch in the next few years.


时间:74 星期五 下午200
地点:三楼中会议室
报告人:
Dr. Kang Xi (MPIA, Germany)
题目:Modeling satellite galaxy kinematics and luminosity


时间:620 星期五 下午200
地点:三楼中会议室
报告人:Prof. Jin LipingJilin University
题目:Evolution of solar nebula and planet masses


时间:619 星期四 上午1000
地点:三楼中会议室
报告人:Prof. David Burrows(Dept. of Astronomy & Astrophysics, Penn State University)
题目:Highlights of the Swift GRB Mission


时间:523 星期五 下午200
地点:三楼中会议室
报告人:Dr. Tian Wenwu from NAOC
题目:通过HI+CO谱线观测决定河内超新星遗迹和相关联天体的距离


时间:523 星期五 上午1000
地点:三楼中会议室
报告人:徐仁新(Department of Astronomy, Beijing University
题目:Pulsars and Quark Stars


时间:520 星期二 下午300
地点:三楼中会议室
报告人:Dr. Yan, Huirong 闫慧荣

 (Canadian Institute for Theoretical AstrophysicsCITA)
题目:Nonlinear Cosmic Ray transport and acceleration in MHD turbulence


时间:59 星期五 下午300
地点:三楼中会议室
报告人:Prof. Wang Bin 王斌 ( Fudan University
题目:Black Holes in the LHC


时间:59 星期五 上午1000
地点:三楼中会议室
报告人:
Prof. Li cheng   SHAO&MPA
题目:Connections of galaxy-galaxy interactions to the formation of stars,

      the accretion of black holes,  and the structural changes of galaxies


时间:428 星期二 下午200
地点:三楼中会议室
报告人:
陈学雷 (CHEN, Xuelei)
题目:Dark age, first stars and reionization


时间:424 星期四 下午200
地点:三楼中会议室
报告人:
Jiasheng Huang (Harvard-Smithsonian CfA)
题目:ULIRGs at high redshifts


时间:417 星期四 上午9:30am
地点:三楼中会议室
报告人:Pro.Richard ManchesterAustralia Telescope National Facility,

 CSIRO
题目:Pulsars and Gravity


时间:415 星期二 下午300
地点:三楼中会议室
报告人:周旭,朱镇熹

  (中国南极天文中心,国家天文台,紫金山天文台)
题目:中国首次南极天文观测


时间:411 星期五 下午200
地点:三楼中会议室
报告人:
张同杰(北京师范大学)
题目:Weak lensing and dark energy cosmology


时间:49 星期三 下午200
地点:三楼中会议室
报告人:
Prof. Chris Done, Durham University, UK
题目:Accreting black holes


时间:43 星期四 下午200
地点:三楼中会议室
报告人:
Prof. Kinwah Wu (Mullard Space Science Laboratory, University

    College London, UK)
题目:Emission from Accretion and Outflows of Black Holes: General

 Relativistic Radiative Transfer


时间:328 星期五 下午200
地点:三楼中会议室
报告人:李淼 (科大)
题目:暗能量


时间:229 星期五 下午200
地点:三楼中会议室
报告人:August E. Evrard (University of Michigan)
题目:Before the Deluge: Cosmology from Galaxy Cluster Surveys


报告总目录

2004

2005

2006

2008天文学

暑期高级讲座


 

 

 

 

 

 

 

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银河系的中心超大质量黑洞的最强有力证据

    中国科学院百人计划入选者,我台天体物理研究室研究员沈志强博士领导的一个国际天文研究小组,通过对位于我们银河系中心被称为人马座A*Sgr A*)的神秘射电发射源的高空间分辨率观测,发现了支持我们太阳系所在的银河系的中心存在超大质量黑洞观点的迄今为止最令人信服的证据。

     该研究成果刊登在113出版的英国《自然》周刊上。(详见Nature2005年,438期,62

沈志强及其合作者,包括美国国家射电天文台台长鲁国鏞,美国加州理工学院的梁茂昌,美国哈佛——史密松天体物理中心的贺曾樸(现任中国台湾天文暨天文物理研究所所长)和赵军辉,利用国际先进的甚长基线干涉阵(VLBA)于2002113成功获得了Sgr A*3.5毫米波长上的首个图像,并进而确定该源的真实直径与地球轨道半径相当。也就是说,这个至少40万倍於太阳质量的Sgr A*所占区域的直径只有1.5亿公里,由此推断出的最小质量密度比任何目前已知的黑洞候选者的密度都要大了一万亿倍以上,强烈地支持Sgr A*是超大质量黑洞的物理解释。

更令人兴奋的是,这是天文学家第一次看到距离黑洞中心如此近的区域。根据爱因斯坦的广义相对论,超大质量黑洞的强引力场会致使经过其边缘的光线发生弯曲,使其中央出现一个相对于周围亮环状辐射显著变暗的阴影。对红外波段观测到的Sgr A*周围的年轻大质量恒星的轨道运动的研究表明,Sgr A*的质量约相当于400万个太阳的质量。这样的话,Sgr A*黑洞的阴影直径是其在3.5毫米的辐射区域大小的一半。因此,未来在1毫米或更短波长上的观测将很有希望触及与阴影直径可比拟的区域,这为检验广义相对论提供了一个有力的工具。

    Sgr A*所在的银河系中心距我们太阳系约26000光年(1光年等于光在一年时间内穿越的空间距离,相当于10万亿公里),其发出的射电波信号虽然能穿透遮挡着可见光的尘埃,但却要受到星际等离子体介质的散射影响,使得直接测得的源的视大小比真实的要大。这与雨夜的街灯看上去比平时大是一个原理。从1997年开始,该研究小组对Sgr A*开展了大量的VLBA观测研究,并发展了一套数据分析方法以提高测量的精确度,为最终测得Sgr A*的大小打下了基础。

黑洞概念的科学提出是在一个世纪前,如何从观测上证明黑洞的真实存在是现代天体物理学中最具挑战性的课题之一。近几年的空间天文卫星和地面大型天文仪器已经发现了很多黑洞候选者,其中19742月发现的位于银河系中心的致密射电源Sgr A*因其距离我们最近,而被公认为是研究黑洞物理的最佳目标。

 

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