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Simulate gravitational waves produced by black holes , That sounds terrible , It must take a lot of computing power ？

exactly , Discover the gravitational waves predicted by Einstein , Humans use it 100 year , And using supercomputing to simulate it exactly , People use 90 year ！

1915 year , Einstein published general relativity , And then physicists predicted , A merger of two black holes produces Gravitational waves .

until 2005 year , Scientists got the first Black holes merge numerical solutions , And it's done off and on with supercomputing 2 Months .

But now , You just need one macOS or Linux System laptop , You can also calculate black hole mergers , It's the one with animation .

This is a Ph.D. program from Caltech Vijay Varma Developed a Python package , It is used to simulate how two black holes radiate gravitational waves during rotation , And the whole process of their merger .

The installation method is so simple that it can even be done through PyPI Direct installation ：

pip install binaryBHexp

And then you just type in a bunch of parameters , You can simulate gravitational waves on your laptop . Even drag the animation with the mouse , comprehensive 360 Watch the black hole merging process ：

You think that's all ？ No no no , These are just “ By-product ” nothing more .

real “ The main course ” yes , This doctor uses AI Developed By far the most accurate Black hole merging model , And it greatly shortens the simulation time .

Now physicists are going to use this technique to simulate more complex black hole merging processes , help Gravitational wave interference observatory （LIGO） More gravitational waves can be found , Or to test general relativity , Or find its flaws .

△ LIGO

With this work , The doctor has been in the top journals 《 Physical Review Letters 》 A number of papers have been published .

Why simulate gravitational waves

Since gravitational waves can be found experimentally , Why do we have to simulate it numerically ？ Before we get to know the problem , We have to solve a problem first ：

How do we observe gravitational waves ？

Einstein's general theory of relativity , The gravitational wave is “ Ripples of time and space ”, It's the disturbance of a mass object to space-time when it's moving .

however , Gravitational waves are so weak . Only Black hole merging Such incidents , To radiate the gravitational waves that we find .

Black hole merging is now recognized as The strongest gravitational wave source , Because the black hole itself is just a strong gravitational source , So in the merger process , They only radiate gravitational waves .

In order to observe gravitational waves , come from Caltech and MIT A group of physicists , We set up a laser interference gravitational wave observatory LIGO.

This place is dedicated to detecting gravitational waves , It seems that there are two right angle distribution “L” Arm shaped . When gravitational waves appear , The laser in each arm , Will measure the relative difference in arm length .

This process is very difficult , Because every day LIGO Will receive a lot of weak signals with a lot of noise .

Assistant professor from the University of Massachusetts Scott E. Field Explain this ：

The difficulty , It's like trying to listen to music on your mobile phone in a noisy restaurant .

I only know the content of the song , In order to find it more easily in the background noise .

in other words , We have to find a way to simulate it numerically , And then we can detect it .

This is the significance of numerical simulation of gravitational waves .

After all , Only a few gravitational waves have been detected , Not even what it looks like Completely understand , Different quality 、 What kind of gravitational wave does rotation and revolution speed produce , We need to solve the very complex general relativity equation to simulate .

But in the numerical simulation of gravitational waves , Physicists are having trouble again ——

Using supercomputing to solve the general relativity equation , Can only Faster Simulate some of the gravitational wavelengths , It's the mass ratio Less than 10：1 The gravitational waves produced by the merging of two black holes in the universe .

For the merging of these black holes , From the University of Massachusetts Gaurav Khanna Express ：

It's like simulating the interaction between a big ship and a small sailing boat , After all, the latter will hardly affect the route of the giant ship .

But for another part of the black hole , That is, the mass ratio is greater than 10：1 The gravitational waves produced by the merging of two black holes in the universe , The amount of computation required for simulation is too large .

2005 year , Physicists used supercomputers to simulate 2 Months , And then we get a numerical solution . For a mass ratio greater than 10：1 The situation of , It may take years for Supercomputing , This is obviously unrealistic .

So the mass ratio is greater than 10：1 The two black holes of the merger , Can't really detect their gravitational waves ？

There is actually another way —— simplified calculation .

These physicists from the University of Massachusetts , I hope to use machine learning to simplify the calculation process .

They even made a real Python tool kit , And from the research results , It has been successfully simulated that the mass ratio is 3：1 The merging process of black holes .

The calculated results are consistent with those of supercomputing simulation , The accuracy is no less than 1%.

One command simulates black hole merging

This visualization tool that simulates black hole merging is called binaryBHexp.

The installation process is very simple , I've said that before . It's also very simple to use .

Because the merging of black holes only depends on the following physical quantities ： quality 、 Angular momentum 、 Revolution speed .

Enter these values into the command ：

binaryBHexp --q 2 --chiA 0.2 0.7 -0.1 --chiB 0.2 0.6 0.1

Parameters q It's the mass ratio of two black holes ,chiA and chiB Then there are the rotation and revolution speeds of the two black holes （ All have been normalized ）.

Different parameters lead to different black hole merging phenomena .

For example, the following set of parameters , It shows that gravitational waves are huge “ Recoil ”, Its energy can accelerate the black hole to the speed of light 1/100, Throw it out of the galaxy ：

binaryBHexp --q 1.34 --chiA 0.62 -0.27 0.34 --chiB -0.62 0.27 0.34

Target stars, sea

On the ground LIGO It's not enough for physicists .

On earth, , The length of the two interference arms used to measure gravitational waves is limited , If we build a probe into space , So the interference arm can be as long as 100 More than kilometers , Greatly improve the detection accuracy .

This is the European Space Agency ESA and NASA Imagine a space-based gravitational wave exploration program LISA, Due in 2035 launch .

In space , The improvement of accuracy can let us see black hole merging events with larger mass ratio , For example, the mass ratio exceeds 100 The situation of Wan .

Because there might be in the center of the galaxy 10 Hundreds of millions of solar mass black holes , When it sucks ordinary black holes into it , This kind of super mass ratio merging event will occur .

On the other side , Physicists are preparing for numerical computation .

Scott Field and Gaurav Khanna The professor expects to publish a larger mass ratio calculation model in this summer arxiv On , I don't know what surprise it will bring .

Project address ：
https://vijayvarma392.github.io/binaryBHexp/

Reference link ：
[1]https://www.quantamagazine.org/new-black-hole-math-closes-cosmic-blind-spot-20210512/ 
[2]https://phys.org/news/2019-01-physicists-supercomputers-ai-accurate-black.html 
[3]https://phys.org/news/2020-03-method-black-holes-galaxies.html 
[4]https://pypi.org/project/surfinBH/ 
[5]https://pypi.org/project/binaryBHexp/ 

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