Tiny crystal device could stimulate gravitational wave detectors to reveal birth cries of black holes

In 2017, astronomers witnessed the birth of a black hole for the first time. Gravitational wave detectors picked up the ripples in space-time caused by the collision of two neutron stars to form the black hole, and other telescopes then observed the resulting explosion.

But the true detail of the black hole’s formation, the movements of matter in the moments before it was sealed within the black hole’s event horizon, have remained unnoticed. This is because the gravitational waves rejected in these last moments had such a high frequency that our current detectors cannot pick them up.

If you could watch ordinary matter turning into a black hole, you would see something similar to the Big Bang played backwards. Scientists who design gravitational wave detectors have worked hard to figure out how to improve our detectors to make this possible.

Today our team is publishing an article that shows how this can be done. Our proposal could make detectors 40 times more sensitive to the high frequencies we need, allowing astronomers to listen to matter as it forms a black hole.

It’s about creating strange new packets of energy (or “quanta”) that are a mixture of two types of quantum vibrations. Devices based on this technology could be added to existing gravitational wave detectors to achieve the additional sensitivity needed.

Quantum problems

Gravitational wave detectors like the Laser Interferometer Gravitational-wave Observatory (LIGO) in the United States use lasers to measure incredibly small changes in the distance between two mirrors. Because they measure changes 1,000 times smaller than the size of a single proton, the effects of quantum mechanics – the physics of individual particles or energy quanta – play an important role in how these detectors work. .

Two different types of quantum energy packets are involved, both predicted by Albert Einstein. In 1905 he predicted that light comes in packets of energy which we call photons; two years later, he predicted that heat and sound energy come in packets of energy called phonons.

Photons are widely used in modern technology, but phonons are much more difficult to exploit. Individual phonons are usually overwhelmed by a large number of random phonons which are the heat of their surroundings. In gravitational wave detectors, phonons bounce inside the detector’s mirrors, degrading their sensitivity.

Five years ago, physicists realized that you could solve the problem of insufficient high frequency sensitivity with devices that combine phonons with photons. They have shown that devices in which energy is transported in quantum packets that share the properties of phonons and photons can have quite remarkable properties.

These devices would involve a radical change to a familiar concept called “resonant amplification”. Resonant amplification is what you do when pushing a playground swing – if you push at the right time, all of your little pushes create a big swing.

The new device, called a “white light cavity,” would amplify all frequencies equally. It’s like a swing that you could push at any time and end up with big results.

However, no one has yet figured out how to make one of these devices, as the phonons inside would be overwhelmed by random vibrations caused by the heat.

Quantum solutions

In our article, published in Communications physics, we show how two different projects currently underway could do the job.

The Niels Bohr Institute in Copenhagen has developed devices called phononic crystals, in which thermal vibrations are controlled by a crystalline structure cut into a thin membrane. The Australian Center of Excellence for Engineering Quantum Systems has also demonstrated an alternative system in which phonons are trapped inside an ultrapure quartz lens.

We show that these two systems meet the requirements to create the “negative dispersion” – which spreads light frequencies in an inverted rainbow pattern – necessary for white light cavities.

The two systems, added to the back end of existing gravitational wave detectors, would improve sensitivity to frequencies from a few kilohertz by the 40 times or more needed to listen for the birth of a black hole.

And after?

Our research does not represent an instant solution to improve gravitational wave detectors. There are enormous experimental challenges in turning these devices into practical tools. But it does offer a path to the 40-fold improvement in the gravitational wave detectors needed to observe births in black holes.

Astrophysicists have predicted complex gravitational waveforms created by the convulsions of neutron stars as they form black holes. These gravitational waves could allow us to listen to the nuclear physics of a collapsing neutron star.

For example, it has been shown that they can clearly reveal whether the neutrons in the star stay as neutrons or if they break down into a sea of ​​quarks, the smallest subatomic particles of all. If we could watch neutrons transform into quarks and then disappear in the black hole singularity, it would be exactly the reverse of the Big Bang where, out of the singularity, particles emerged that continued to create our universe.

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This article is republished from The Conversation under a Creative Commons license. Read the original article.