MIT's next-gen gravitational-wave detector will replace LIGO

Construction of a sizable detector capable of detecting gravitational-wave signals from events like the merging of black holes and neutron stars is underway.
Shubhangi Dua
Artist’s impression of a Cosmic Explorer observatory

Soon, an instrument could answer the most puzzling questions in cosmology as far back as the early universe.

The Massachusetts Institute of Technology recently unveiled its plans to build the next-generation gravitational-wave detector that aims to pick up ripples in space-time from the early universe.

MIT stated that this included detecting surges from gravitational-wave sources such as merging black-hole and neutron stars every few days. In order to implement the device, the detectors in the observatory will be extended to cover the expanse of a small city.

Larger than LIGO

statement by the university says that the project is focusing on designing and building a more significant and sensitive gravitational-wave observatory, aiming to replace existing observatories like the Laser Interferometer Gravitational-wave Observatory (LIGO).

MIT and Caltech operate LIGO. The 'L' stands for 'listen,' inferring that the instrument listens to cosmic ripples using two lasers, which are concentrated beams of light. 

An indication of the difference in the beams' arrival time can suggest the gravitational wave passed through the L-shaped detector. LIGO's two detectors are placed in different locations in the United States. Virgo in Italy and KAGRA in Japan are the other set of sensors known so far. 

Matthew Evans, Cosmic Explorer's executive director and a professor of physics at MIT, cited the difference between the MIT detector and LIGO, stating that the Cosmic Explorer is, in some sense, a giant LIGO. 

"The LIGO detectors are four kilometers long for each arm, and Cosmic Explorer will be 40 kilometers on a side, so 10 times larger. The signal we get from a gravitational wave is essentially proportional to the size of our detector, and that's why these things are so big."

Evans explained: "Bigger is better, up to a point. At some point, you've matched the length of the detector to the wavelength of the incoming gravitational waves. And then, if you continue making it bigger, there are really diminishing returns in terms of scientific output. It's also hard to find sites to build that large of a detector. When you get too big, the curvature of the Earth starts to become an issue because the detector's laser beam has to travel in a straight line, and that's less possible when a detector is so large that it has to curve with the Earth."

Next-gen detector to trace billions of years into the past

MIT has developed initial iterations of algorithms designed to scout for potential locations in the western United States. They further intend to replace LIGO observatories by the mid-2030s with this new next-generation project that's bigger and likely to witness gravitational waves.

The researchers aim to observe sources such as black holes and the collision of neutron stars that are much farther away, seeking billions of years back, unlike the LIGO, which can trace back to 1.5 billion years. 

"That seems far away, but compared to the size of the universe, which is about 13 to 14 billion years old, that's pretty nearby," Evan said. "That means we are missing important steps in the history of the universe, one of which is "Cosmic Noon," where most of the stars in the universe were formed."

Around three billion years after the universe's birth, accessing sources from that era would offer valuable insights into the formation of black holes and neutron stars, shedding light on their origins within stellar systems.

Evan hopes to glimpse the universe when it was just a billion years old during the Epoch of Reionization, when atoms were ionized and galaxies started to form.

He believes that the Cosmic Explorer would be sensitive to the mergers of black holes and neutron stars up to those distances and even farther.

Potential research

The observatory can also test Einstien's theory of relativity; though it is attached with significant uncertainties, it can still be precisely measured with the Cosmic Explorer.

"Finally, many measurements get better the more sources you have. We think Cosmic Explorer could detect hundreds of thousands of black hole binaries and up to a million neutron star mergers per year," Evan added.

In the upcoming three years, MIT researchers intend to finalize a comprehensive design that includes the integration of a vacuum system and the development of a robust architectural and infrastructural plan.

They are working in collaboration with the space mission, LISA, being run by the European Space Agency and the Einstein Telescope in Europe.

"All these groups are colleagues rather than competitors, who we anticipate working with. In this field, you get farther by working together. It's kind of a global effort to build these next-generation gravitational wave detectors, and it's global science," Evan stated. 

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