题目：Extremely large mass ratio inspirals: gravitational waves from our galactic centre

主讲人：Pau Amaro Seoane 教授（西班牙瓦伦西亚理工大学）

时间：8月16日、18日，9月13日、15日，晚上19:00-20:30

会议ID：（腾讯会议）885 406 272

联系人：杨捷

课程内容：

The detection of the gravitational waves emitted in the capture process of a compact object by a massive black hole (MBH) is known as an extreme-mass ratio inspiral (EMRI), it represents a unique probe of gravity in the strong regime, and it is one of the main targets of the Laser Interferometer Space Antenna (LISA). The possibility of observing a compact-object EMRI at the Galactic Center (GC) when LISA is taking data is very low. However, the capture of a brown dwarf, an X-MRI, is more frequent because these objects are much more abundant and can plunge without being tidally disrupted. An X-MRI covers some ∼10^8 cycles before merger, and hence stays on band for millions of years. About 2 ×10^6 yrs before merger they have a signal-to-noise ratio (SNR) at the GC of 10. Later, 10^4 yrs before merger, the SNR is of several thousands, and 1000 yrs before the merger a few 10^4. Based on these values, this kind of EMRIs is also detectable at neighbor MBHs, albeit with fainter SNRs. We calculate the event rate of X-MRIs at the GC taking into account the asymmetry of pro- and retrograde orbits on the location of the last stable orbit (LSO). We estimate that at any given moment, and using a conservative approach, there are of the order of ≳20 sources in band. From these, ≳5 are circular and are located at higher frequencies, and about ≳15 are highly eccentric and are at lower frequencies. Because of their proximity, X-MRIs represent a unique probe of gravity in the strong regime. The mass ratio for a X-MRI at the GC is q ∼10^8 , i.e., 3 orders of magnitude larger than stellar-mass black hole EMRIs. Since backreaction depends on q , the orbit more closely follows a standard geodesic, which means that approximations work better in the calculation of the orbit. X-MRIs can be sufficiently loud so as to track the systematic growth of their SNR, which can be high enough to bury that of MBH binaries.

个人简介：

Pau Amaro Seoane是西班牙瓦伦西亚理工大学（Universitat Politècnica de València） 教授，在西班牙获得理论物理学（粒子物理学）学士学位后，转到海德堡攻读理论天体物理学博士学位，着重于密集恒星系统和超大质量黑洞生长问题的研究。Pau与波茨坦马克斯普朗克引力物理研究所所长Bernard Schutz教授和 Curt Cutler博士一起合作从事广义相对论，特别是引力波天文学的研究。他们的引力波天文研究和技术小组领导了西班牙在LISA探路者任务和未来LISA探测计划中的工作。他与同事Carlos Sopuerta一起共同担任了LISA联盟引力波天文学课题组中的极端质量比双黑洞旋进系统（EMRIs）研究小组的主席。