Machine learning decodes tremors of the universe
Neural network analyzes gravitational waves in real-time

Date:
December 9, 2021
Source:
Max Planck Institute for Intelligent Systems
Summary:
Researchers train a neural network to estimate -- in just a few
seconds - - the precise characteristics of merging black holes
based on their gravitational-wave emissions. The network determines
the masses and spins of the black holes, where in the sky, at what
angle, and how far away from Earth the merger took place.



FULL STORY ========================================================================== Black holes are one of the greatest mysteries of our Universe --
for example, a black hole with the mass of our Sun has a radius of
only 3 kilometers. Black holes in orbit around each other give off gravitational radiation - - oscillations of space and time predicted
by Albert Einstein in 1916. This causes the orbit to become faster and
tighter, and eventually, the black holes merge in a final burst of
radiation. These gravitational waves propagate through the Universe
at the speed of light, and are detected by observatories in the USA
(LIGO) and Italy (Virgo). Scientists compare the data collected by the observatories against theoretical predictions to estimate the properties
of the source, including how large the black holes are and how fast
they are spinning. Currently, this procedure takes at least hours,
often months.


==========================================================================
An interdisciplinary team of researchers from the Max Planck Institute for Intelligent Systems (MPI-IS) in Tu"bingen and the Max Planck Institute
for Gravitational Physics (Albert Einstein Institute/AEI) in Potsdam
is using state-of-the-art machine learning methods to speed up this
process. They developed an algorithm using a deep neural network,
a complex computer code built from a sequence of simpler operations,
inspired by the human brain.

Within seconds, the system infers all properties of the binary black-hole source. Their research results were published in the flagship journal
of Physics, Physical Review Letters.

"Our method can make very accurate statements in a few seconds about how
big and massive the two black holes were that generated the gravitational
waves when they merged. How fast do the black holes rotate, how far
away are they from Earth and from which direction is the gravitational
wave coming? We can deduce all this from the observed data and even make statements about the accuracy of this calculation," explains Maximilian
Dax, first author of the study Real-Time Gravitational Wave Science with
Neural Posterior Estimation and Ph.D. student in the Empirical Inference Department at MPI-IS.

The researchers trained the neural network with many simulations --
predicted gravitational-wave signals for hypothetical binary black-hole
systems combined with noise from the detectors. This way, the network
learns the correlations between the measured gravitational-wave data
and the parameters characterizing the underlying black-hole system. It
takes ten days for the algorithm called DINGO (the abbreviation stands
for Deep INference for Gravitational-wave Observations) to learn. Then
it is ready for use: the network deduces the size, the spins, and all
other parameters describing the black holes from data of newly observed gravitational waves in just a few seconds. The high-precision analysis
decodes ripples in space-time almost in real-time -- something that
has never been done with such speed and precision. The researchers are convinced that the improved performance of the neural network as well as
its ability to better handle noise fluctuations in the detectors will make
this method a very useful tool for future gravitational-wave observations.

"The further we look into space through increasingly sensitive detectors,
the more gravitational-wave signals are detected. Fast methods such as
ours are essential for analyzing all of this data in a reasonable amount
of time," says Stephen Green, senior scientist in the Astrophysical
and Cosmological Relativity department at the AEI. "DINGO has the
advantage that -- once trained -- it can analyze new events very
quickly. Importantly, it also provides detailed uncertainty estimates
on parameters, which have been hard to produce in the past using machine-learning methods." Until now, researchers in the LIGO and Virgo collaborations have used computationally very time-consuming algorithms to analyze the data. They need millions of new simulations of gravitational waveforms for the interpretation of each measurement, which leads to
computing times of several hours to months -- DINGO avoids this overhead because a trained network does not need any further simulations for
analyzing newly observed data, a process known as 'amortized inference'.

The method holds promise for more complex gravitational-wave signals
describing binary -- black-hole configurations, whose use in current
algorithms makes analyses very time-consuming, and for binary neutron
stars. Whereas the collision of black holes releases energy exclusively
in the form of gravitational waves, merging neutron stars also emit
radiation in the electromagnetic spectrum. They are therefore also visible
to telescopes which have to be pointed to the respective region of the
sky as quickly as possible in order to observe the event. To do this,
one needs to very quickly determine where the gravitational wave is
coming from, as facilitated by the new machine learning method. In the
future, this information could be used to point telescopes in time to
observe electromagnetic signals from the collisions of neutron stars,
and of a neutron star with a black hole.

Alessandra Buonanno, director at the AEI, and Bernhard Scho"lkopf,
a Director at the MPI-IS, are thrilled with the prospect of taking
their successful collaboration to the next level. Buonanno expects
that "going forward, these approaches will also enable a much more
realistic treatment of the detector noise and of the gravitational
signals than is possible today using standard techniques,"
and Scho"lkopf adds that such "simulation-based inference using
machine learning could be transformative in many areas of science
where we need to infer a complex model from noisy observations." ========================================================================== Story Source: Materials provided by Max_Planck_Institute_for_Intelligent_Systems. Note: Content may be edited
for style and length.


========================================================================== Journal Reference:
1. Maximilian Dax, Stephen R. Green, Jonathan Gair, Jakob H. Macke,
Alessandra Buonanno, Bernhard Scho"lkopf. Real-Time Gravitational
Wave Science with Neural Posterior Estimation. Physical Review
Letters, 2021; 127 (24) DOI: 10.1103/PhysRevLett.127.241103 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/12/211209142542.htm

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