Archive for the ‘引力波’ Category

引力波能绕过黑洞吗?——引力波本性的思考

星期四, 12月 16th, 2021

科学不能以换灵敏度曲线为本。

能捡漏命名一个物理现象,还是很开心的。

静等花开的日子其实没有那么舒服,特别是在这个周围的造林运动如火如荼的年代。

以下内容发布在 中国科学杂志社 公众号平台:

https://mp.weixin.qq.com/s/cI1aSGwsRJw6hSRkhLEg3w

“昨夜西风凋碧树,独上高楼,望尽天涯路”

2015年,双黑洞绕转并合产生的引力波在穿越13亿光年的时空后,成功抵达地球,被2台地基激光干涉仪捕捉到(参见解读和科普[1,2])。从此,引力波领域开始热闹起来。2017年, 宇宙中的两个中子星亲密接触后,一场宇宙烟花表演被地球上的光学望远镜、伽马暴望远镜、引力波探测器分别记录。这表明天文界、物理界可以携手探索宇宙的精彩(参见解读和科普[3,4])。

“衣带渐宽终不悔,为伊消得人憔悴”

探测器记录的是信号和探测器的相互作用。引力波-电磁波, 二者都是“波”,是因为理论上,它们都满足波动方程,区别在于一个是基于引力场描述,一个是基于电磁场描述。历史上,“光(特定波段的电磁波)是波而不是粒子”的论断经过了长期的理论斗争。这是因为理论学家的创造力是无穷的,例如拉普拉斯可以在1808年用粒子说解释光的双折射现象。无可争辩地推翻了“牛顿的光粒子学说”的证据是1818年由阿拉贡实现光的“泊松斑”实验。从此理论学家再也没有造出能够正入射不透明圆盘,到达圆盘后中心区域的光粒子。相反,光的波动方程预言的衍射现象轻松解释了这个亮斑。 

地上的物理应该和天上的物理是一致的,这是牛顿发现“苹果落地”和“地球围绕着太阳转”是统一规律万有引力定律支配以来,人类的信仰之一。这个信仰至今从未出错。2017年,黑洞照片发布,让天文学家着实兴奋了一次:电磁波也能看到黑洞周围的时空结构了。但是我们仔细看了一下照片,这个电磁波穿过黑洞(“不透明圆盘”)的系统,没有呈现“泊松斑”。

“那人依然在灯火阑珊处?”

引力波如果一定是满足波动方程的波,如果找到合适“不透明圆盘”,那么就一定能产生我们命名为“引力波泊松-阿拉贡亮斑”的现象。唯一能阻挡引力波穿透的圆盘,只有引力自己的奇异产物:黑洞。天上的黑洞没有造成可观测的光学泊松斑的重要原因之一是黑洞的尺寸相对于天上电磁波的波长太大了。探测到的大部分引力波是双黑洞整体运动产生的,因此一定能找到黑洞的尺寸和引力波的波长差不多的系统。剩下的,就只有等待。也许在不久的将来,引力波探测器探测到了一个引力波,但是这个引力波的振幅却在不断变弱,直至消逝。如果消逝的过程是因为地球在引力波衍射图样的空间中穿梭,那么这“独一无二的精彩”将会在可预测的未来,再次在所有引力波烟花中如约再次出现。

图片

引力波泊松-阿拉贡亮斑系统示意图

发表在《中国科学:物理学 力学 天文学》英文版2021年第12期的文章“Poisson–Arago spot for gravitational waves”研究了引力波的衍射现象,得到了史瓦西背景下引力波散射的精确解[5],同期发表了期刊副主编蔡荣根院士的点评文章[6]。作为波动的根本属性,衍射干涉对于引力波不容易实现,因为物质对引力波几乎是透明的,小孔双缝都不容易制造。该文提出,黑洞可以阻挡引力波,发挥类似光学不透明板的作用。该文章还发现,对于目前地面探测器探测到的约百赫兹的引力波,经过衍射体黑洞M87*和银心黑洞,可以完美展示引力波的衍射现象。该文首次发现这种现象,称之为引力波的泊松斑,即观察者、引力波源、衍射体黑洞三点一线,那么正好看到一个亮斑。因为引力汇聚作用,引力泊松斑比相应的光学泊松斑强度更强。如果将来的探测器能长期观察一个引力波源,会发现地球在引力波亮条纹暗条纹间穿行。对于M87*和银心黑洞,该文估计了穿行的时间尺度,结果大约是数天。预期下一代观测器可以看到这个现象。从技术上说,这篇文章的一个主要进展是用古老的波带法处理了一个正入射的发散问题。

[1] Fan X L. The detection of gravitational waves and the new era of multi-messenger astronomy. Sci. China-Phys. Mech. Astron., 59, 640001 (2016). https://doi.org/10.1007/s11433-016-5799-3

[2] 陈雁北, 范锡龙. 爱因斯坦都不敢想象, 我们真的探测到引力波!

[3] 范锡龙. 贝叶斯引力波多信使天文学. 中国科学: 物理学 力学 天文学, 48, 079804 (2018). https://doi.org/10.1360/SSPMA2018-00102

[4] 陈雁北, 范锡龙. 时空与物质、广义相对论与量子力学的完美结合——深度科普解读双中子星并合多信使观测. 物理, 46(12), 817-827 (2017). https://doi.org/10.7693/wl20171205

[5] Zhang H S, Fan X L. Poisson-Arago spot for gravitational waves. Sci. China-Phys. Mech. Astron., 64, 120462 (2021). https://doi.org/10.1007/s11433-021-1764-y

[6] Cai R-G. A diffraction phenomenon of gravitational waves: Poisson-Arago spot for gravitational waves. Sci. China-Phys. Mech. Astron., 64, 120461 (2021). https://doi.org/10.1007/s11433-021-1792-3

PRL:一个引力波速度测定的新方法

星期日, 12月 18th, 2016

First successful detection of gravitational waves (GW) by LIGO/Virgo opened up a new window on the Universe and gave us unprecedented possiblities of testing gravity. In particular the issue of the speed of gravity, in General   Relativity  equal to the speed of light, became now accessible for experimental tests. Any observational clue that gravitational waves propagate with speed   different from c would mark the breakdown of General Relativity.

In this paper we propose a new method to measure the speed of gravity   assuming that strongly lensed gravitational signal accompanied by its electromagnetic (EM) counterpart   could be detected. The method is based on measuring the difference between strong lensing   time delays registered in GW and EM. The differential setting of our method makes it robust and free from the intrinsic time delays in the source (i.e. different emission times of GW and EM signal).

Strongly lensed GW signals are expected to be registered by the next   generation of interferometric detectors like the Einstein Telescope.

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.118.091102

arXiv:1612.04095

gw-em 测试流程

星期六, 2月 22nd, 2014

1. 根据f-function 产生 injection 的位置: gendist

2. 根据 gw模型产生injection 的波形+data analysis : LAL

3. play with  posterior samples and f-fuunction : hist2d + greedy

LAL 学习

星期二, 6月 18th, 2013

LAL 学习
https://www.lsc-group.phys.uwm.edu/daswg/projects/lalsuite.html

LAAC Data Analysis Training
LALSuite
installing LAL and LALApps
LALSuite Git
LALSuite is comprised of the following components
LAL: Core gravitational wave analysis routines
LALFrame: LAL wrapping of the LIGO/Virgo Frame library
LALMetaIO:LAL wrapping of the MetaIO LIGO_LW XML library
LALXML:LAL wrapping of the libxml2 XML library, currently unused
LALSimulation:LAL routines for gravitational waveform and noise generation
LALBurst:LAL routines for burst gravitational wave data analysis
LALInspiral:LAL routines for inspiral and ringdown CBC gravitational wave data analysis
LALPulsar:LAL routines for pulsar and continuous wave gravitational wave data analysis
LALInference:LAL routines for Bayesian inference data analysis
LALStochastic:LAL routines for stochastic background gravitational wave data analysis
LALApps: Collection of gravitational wave data analysis codes and pipelines utilising the LAL libraries

cbc code 执行命令
https://www.lsc-group.phys.uwm.edu/ligovirgo/cbcnote/BayesianReview/InspnestDocs

universe = standard
executable = lalapps_inspnest
arguments = ” -i LALLIGO -I H1 -C test –inj test_injection.xml -o test_0.dat –srate 2048 –Nsegs 10 –length 100 –Nlive 1000 –Nmcmc 200 –verbose”
error = lalapps_inspnest$(Process).err
output = lalapps_inspnest$(Process).out
log = mycode.log
notification = never
queue

安装 LALSuite
https://www.lsc-group.phys.uwm.edu/daswg/docs/howto/lal-install.html
某机器上第一次安装
先安装有一些别的软件确保LALSuite安装
必须有些手动操作设置    To setup your environment to use the newly-built LAL
分别安装LALSuite 里面的每个包  (顺序和网站上说的不同有时需要不同,因为包的依赖问题,要有耐心测试。。。)
LAL
LALFrame
LALMetalO
LAMXML
LALSimulation
LALBurst
LALPulsar
LALInspiral
LALInference
LALApps   如果不是需要远程登陆本机器操作, 就不用  –enable-condor

最后 别忘了 把 source ${LSCSOFT_ROOTDIR}/etc/lscsoftrc 加到     .bash_profile  里面!

安装LALSuite  note  from Matt
cloned the lalsuite directory (e.g. using “git clone xilong.fan@ligo-vcs.phys.uwm.edu:/usr/local/git/lalsuite.git”)
installed all the parts of lalsuite (lal, lalmetaio, lalxml,lalsimulation, lalinspiral, lalburst, lalpulsar, lalstochastic, lalinference)
checked-out the lalinference_burst branch using “git branch –track lalinference_burst origin/lalinference_burst”
git checkout lalinference_burst

–If that’s what you’ve done then you should currently be in the lalinference_burst branch. You can check what branch you’re in by typing “git branch” and it will list the branches – there will be a * next to the name of the branch that you are in.
–If you want to run codes that have been developed in this branch then you should probably reinstalled all of lalsuite from this branch. So, you should perform “make uninstall” and “make distclean” in all the parts of lalsuite, and then reinstall all of them.

Note: Having the release versions of LALSuite installed from MacPorts will lead to build errors if you try and build LALSuite from the git repository. If you are planning on building LALSuite from git do not installed these ports.

如果安装了怎么办?
卸载!

fantekiMacBook-Pro:~ fanf$ sudo port uninstall lalapps
fantekiMacBook-Pro:~ fanf$ sudo port uninstall LALStochastic
sudo port uninstall LALApps
sudo port uninstall LALInference
sudo port uninstall LALStochastic
sudo port uninstall LALInspiral
sudo port uninstall LALPulsar
sudo port uninstall LALBurst
sudo port uninstall LALSimulation
sudo port uninstall LALMetaiO
sudo port uninstall LALXML
sudo port uninstall LALFrame
sudo port uninstall LAL