Treading in the Footsteps of Galilei

Professor Achim Stahl Copyright: © Barbara Brixhe

RWTH Professor Achim Stahl on the large-scale research project Einstein Telescope  – Funding has been provided by the Bundestag for a feasibility study

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The major European research project "Einstein Telescope" is set to provide us with unprecedented insights into the universe

The major European research project "Einstein Telescope" aims to provide unprecedented insights into the universe, with astrophysicists hoping to gain completely new knowledge about the Big Bang, black holes, supernovas and more. We spoke to Professor Achim Stahl, Head of the III Physics Institute B at RWTH Aachen University, about gravitational waves, dying stars and the significance of the project for science.

What is the Einstein Telescope?

Prof. Achim Stahl: An astrophysical project for basic research. We call it a telescope because it detects gravitational waves from space. Technically speaking, they are underground laser installations, which of course don't look like a telescope. So the name comes from the function of being able to observe events that come to us from the universe.

Gravitational waves are...

Stahl: ...periodic lengthening and shortening of space. Predicted by Einstein in his theory of relativity about 100 years ago, they were experimentally detected for the first time in 2015 with the second-generation telescopes. We are now planning the next generation - they are around ten times as sensitive. With this generation, we want to go back to the times when the first structures were formed in the universe and when stars were first formed.

How can events be derived from waves?

Stahl: The theory of relativity has taught us that space shortens around very concentrated masses. Obviously around black holes, but also around compact stars. This means that if you dropped a scale into a black hole, it would gradually become shorter. This is static, so it does not yet make a wave. If two black holes orbit each other, the distance shifts permanently. This periodic change spreads through the entire universe in the form of waves. It can run through the entire universe for hundreds of millions of years without really experiencing any change. It would also simply pass through the earth. However, the earth would be compressed a little and then pulled apart again - and we can register this using laser light in special detectors. The fascinating thing about the technology is that we can detect changes in distance that are much smaller than the diameter of an atomic nucleus - with today's telescopes over a measuring distance of three or four kilometers, with the Einstein telescope it will be ten kilometers.

  Einstein-Teleskop Copyright: © Marco KraanNikhef

What is the insight that you are looking for?

One question we would like to answer, for example, is the formation of black holes. We know that there are stars that explode, which are known as supernovae. Particularly heavy stars that go supernova collapse into a black hole, which then carries the mass of about half of this star, the rest is blown off. But we also know that there are black holes at the center of galaxies that carry hundreds of millions of masses of stars and they are certainly not the result of the death of a single star. So one question is: how did these black holes form? They could be much older, even a result of the Big Bang, so they would have had enough time to grow to these masses. With the Einstein telescope, we will be able to measure how far away the black holes are and thus determine their age. This will make it possible to determine whether a black hole originates from a star death or the early phase of the universe.

Would the realization of the Einstein Telescope be a further step in a long development or a real "game changer"?

It would clearly be a very big step. There was a first generation whose sensitivity was not yet sufficient to detect gravitational waves at all. The second generation succeeded in doing this; we were able to detect black holes weighing 120 to 140 solar masses for the first time. That was the experimental proof that there are black holes that are heavier than stars, which can have a maximum weight of 30, perhaps 40 solar masses, otherwise they would be unstable. And now the third generation of telescopes is to follow. So we're not talking about a continuous development, but about real milestones, each spanning around 20 years.

Are there any other highlights that the second-generation telescopes have discovered?

An event involving a neutron star was very revealing. Based on the measured gravitational waves, we were able to determine where the event took place and then optical, gamma, radio and infrared telescopes could be pointed at it. This made it possible to observe the afterglow of the merger and thus prove that large quantities of heavy elements were produced. Broken down to alchemy, you could say that we have solved the riddle of how gold is created. The gold that we find here on Earth was created in such neutron star collisions. When the earth was formed, there must have been such an event somewhere in the immediate vicinity - in the astronomical sense.

So if new elements are created in particle collisions in neutron stars, shouldn't we expect gold to be created in particle collisions at CERN as well?

Well, gold won't be produced. But yes, the production of heavier elements can be demonstrated in these particle collisions. However, you wouldn't get much more than heavy hydrogen and helium.

What significance would the Einstein Telescope have for the region?

First of all, of course, an immense economic significance. We are expecting to create around 3,000 jobs during the construction phase and a good 1,000 during the operational phase - only a small proportion of these will be jobs for scientists, with technical and administrative staff in particular being required. Against the background of regional structural change, this would be a huge step. There will also be a major economic effect through technology transfer. If you look again at CERN, you can see how industrial and research parks have settled in a region that used to be dominated by agriculture. From a technological point of view, a gravitational wave telescope with lasers at its center is even more advanced than what CERN is doing. It is reasonable to expect that all of this would contribute significantly more to structural change than the thousands of jobs.

What is the status of the Einstein Telescope?

We have managed to get on the roadmap for major European research projects. A kind of bidding competition is currently underway: which region can submit the best concept - including a financing concept. Apart from us with the border triangle, Sardinia in particular is still in the running. Our big advantage is that the Dutch have already approved 50 percent of the construction costs. In addition, the state of North Rhine-Westphalia and Belgium have clearly positioned themselves in favor of the telescope; now it is up to the Federal Ministry of Education and Research, which would have to approve around 350 million euros of the total costs of around 1.8 billion euros.

Now, for the first time, there is a promise that - subject to an approved federal budget - money will come from the federal government...

Exactly - a very important signal, not least thanks to the great commitment of Ye-One Rhie, member of the Bundestag, and other politicians from the region. We are talking about funds for the planning phase, three million euros for 2024 and a further six million for 2025. And even if it is not the ministry but parliament that has decided that we should receive these funds, it is a first big step towards the commitment that is still missing. And once we have a financing concept, I believe it will also be relatively clear what the location decision will be.

It is the soil as well as the possible financing concept that predestines the area for this project.

Exactly, the marl soil that we have here is a very soft rock that absorbs disturbances coming from below or above. The layer here in the border region is very thick, around 50 meters, before there is an abrupt jump to hard sandstone, which are ideal conditions. At the moment, we are intensively researching the subsurface here to determine the ideal positioning. This makes the Einstein Telescope a real-life laboratory for geologists and geophysicists, as a region is rarely studied so intensively.

How enthusiastic are researchers about this project?

Totally enthusiastic. The Einstein telescope is a fantastic option. A completely new medium will be added, and completely new observations will be possible, giving science a completely extraordinary perspective. A feeling like Galileo must have had when he was able to look into the universe for the first time through newly cut lenses