摘要:

The gravitational wave spectrum covers many decades in frequency. Sources in the audio-frequency regime above 1 Hz are accessible to ground-based detectors while sources in the low-frequency regime can only be observed from space because of the unshieldable background of local gravitational noise on the ground and because ground-based interferometers are limited in length to a few kilometers. Laser interferometry is a promising technique to observe the minute distance changes caused by gravitational waves, but the actual implementation is very different on ground and in space. An overview of LISA and other detectors will be given. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.57429

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The Laser Interferometer Space Antenna (LISA) will be capable of detecting gravitational waves with frequencies from 0.1 mHz to 1 Hz by using laser interferometers to monitor changes in the distances between test masses in spacecraft separated by five million km. LISA will detect strains as low as10−23with a one year observation time and a signal-to-noise ratio of five. The sensitivity will be sufficient to detect gravitational waves from sources connected with massive black holes in the centers in many galaxies, and from many binary systems within the Milky Way galaxy. Under the concept presented, LISA will be formed by three spacecraft at the vertices of an equilateral triangle. The orbits are chosen so that the triangle formation trails the Earth by 20 degrees. Each spacecraft will contain two independent payloads containing a test mass, laser and 30 cm diameter telescope for the transmission and reception of laser signals. Two independent Michelson interferometers will be formed allowing both polarizations of gravitational waves to be detected. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.57401

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The three LISA spacecraft must monitor changes in their relative separation to about 10 pm. The various operating modes during the mission lifetime will be summarized, and the science mode will be described in detail. The science operations involve the optical system, the attitude and position control system, the on-board processing for signal extraction, telemetry and ground operations. The instrumental origins of the anticipated LISA sensitivity curve will also be described. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.57410

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A CAD representation of the LISA payload has been developed and a finite element analysis conducted. The design closely follows the configurations developed by the science working teams, with independent pointing adjustment of the two telescopes. However, the accommodation of certain systems boxes needs further thought, with perhaps a reduction in unit sizes or transfer to a position on the Spacecraft main structure. Initial modal analysis has given an eigenfrequency for the payload of 50 Hz in the launch configuration. This is encouraging for a later design stage, when analysis of the combined Spacecraft and Payload is conducted, and consideration given to the dynamic characteristics of the multi-spacecraft stack. The principle adopted in the design is to restrain the payload for launch (with the pointing adjustment actuators carrying no load) and to remove the restraints after the spacecraft has been deployed. The finite element model has been linked with thermal modelling data, enabling sensitivity to temperatures to be assessed. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.57418

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The current LISA concept has three spacecraft each with two telescope arms protected by a ‘Y’-shaped’ tube. Thermal mathematical models were established using ESARAD and ESATAN using the latest configuration drawings and design details contained within v0.3 of the Payload Definition Document. The thermal design was refined and the sensitivity of the optics bench and other payload components to disturbances in solar irradiation and power dissipation was determined and compared with defined requirements. The predicted steady state temperatures were used in a finite element model using I-DEAS to determine thermally induced distortions. This 4500 node model was used as input data to a spread sheet evaluation of the gravitational influence of the payload components at a point arbitrarily chosen to be the center of the one of the payload optics benches. The resultant acceleration due to all of the nodes, initially all at uniform temperature, was calculated as a straight forward vector summation of the influence of each node. This assumes that each could be regarded as an independent point in space defined by a point mass and location as given in the finite element model. The thermally induced distortions were then applied to the model and the resultant acceleration recalculated. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.57419

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Recent surveys suggest that most or all normal galaxies host a massive black hole with 1/100 to 1/1000 of the visible mass of the spheroid of the galaxy. Various lines of argument suggest that these galaxies have merged at least once in our past lightcone, and that the black holes have also merged. This leads to a merger rate of massive black holes of about 1/yrs. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.57433

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

I briefly discuss some issues relevant for the formation of supermassive black holes and give estimates of the event rates for the emission of gravitational waves by coalescing supermassive black hole binaries. I thereby use models which take into account recent improvements in our knowledge of galaxy and star formation in the high-redshift universe. Estimated event rates range from a few to a hundred per year. Typical events will occur at redshift three or larger in galaxies lying at the (very) faint end of the luminosity function at these redshifts. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.57420

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Studies of the cosmic X-ray background indicate that it arises mainly from accretion powered AGNs and that the present-epoch mass density in the form of supermassive black holes must be at least an order of magnitude more than represented by currently active Seyfert galactic nuclei. The black hole mass spectrum of these Seyfert nuclei extends up to∼2×108solar masses. Evidence summarized here suggests that much of the local mass density of compact galactic nuclei is associated with inactive quasar remnants which are now black holes that are substantially more massive than Seyfert nuclei. It is emphasized that such quasar remnant black holes are sufficiently massive to preclude the tidal disruption of any infalling stars, solar sized as well as compact. Any Keplerian orbits about these supermassive black holes would have periods exceeding 7 hours. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.57421

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The gravitational radiation emitted during the final stages of coalescence of stellar mass compact objects with low mass massive black holes is a signal that may be detected by LISA with some confidence, while also offering the possibility of measuring strong field effects in relativity. I consider the uncertainties in estimating the rate of such events, and the possibility of enhanced coalescence rates of low mass black holes with low mass massive black holes due to ongoing star formation in centers of galaxies. I also conjecture that x-ray precursors to coalescence may conceivably be observable in some cases. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.57422

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

If it performs as well as planned, LISA could provide tremendous information on physics and astronomy in the strong field regime of general relativity near black holes. X-ray astronomy has already provided us with tantalizing glimpses of phenomena occurring in the accretion flow onto compact objects in binary systems and active galactic nuclei. Iron K-alpha photons emitted by the accreting plasma provide direct evidence for relativistic motions and gravitational redshifts. In addition, there is evidence for the existence of the event horizon, as well as claims of general relativistic effects being responsible for certain classes of time variability. I review these exciting results, and compare and contrast them with the complimentary information which will be obtained by LISA. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.57423

出版商:AIP    

年代:1998

数据来源: AIP