Scientists propose massive observatory constellation orbiting the sun

A constellation of gravitational wave observatories could pinpoint the incredibly faint signals from merging black holes.
Chris Young
An artist's impression of gravitational waves.
An artist's impression of gravitational waves.

vchal / iStock 

Since 2015, scientists have detected about 100 black hole mergers thanks to gravitational waves emanating from the cataclysmic events.

That's only a tiny fraction of the hundreds of thousands of black hole mergers that scientists believe take place every year.

Now, a team of scientists from the International School for Advanced Studies in Italy (SISSA) has published a new paper in The Astrophysical Journal detailing how a constellation of interferometers could allow astronomers to detect many more black hole mergers than is possible with current technologies.

A constellation of space-based interferometers

Interferometers are instruments used across many different fields of science and engineering to measure the way two different light waves interfere with one another. The researchers behind the new paper proposed building a constellation of space-based interferometers to detect black hole mergers.

"A constellation of space interferometers orbiting the Sun could enable us to see subtle fluctuations in the gravitational background signal, thus allowing us to extract valuable information about the distribution of black holes, neutron stars, and all other sources of gravitational waves in the universe," Giulia Capurri, a Ph.D. student from SISSA and the first author on the study, explained in a press statement.

Scientists typically refer to those individual fluctuations as anisotropies, and interferometers could allow researchers to pick them out and measure them with greater accuracy than ever before. A constellation of interferometers, meanwhile, could allow for a whole new level of accuracy potentially leading to great scientific breakthroughs.

Detecting ripples in space time

Right now, gravitational waves, also commonly called ripples in space time, from black hole mergers are difficult to detect because they all blend together into noise that is almost impossible to parse and measure as individual waves. Scientists call this noise the stochastic gravitational-wave background (SGWB).

NASA aims to launch its Laser Interferometer Space Antenna (LISA) in the near future, a space-based gravitational wave observatory aimed at detecting black hole mergers and other phenomena. However, Capurri argues that "identifying [anisotropies] requires a very high level of angular resolution not possessed by current and next generation survey instruments."

In their paper, the researchers outline how their constellation of several LISA-like detectors could combine their observations to effectively isolate anisotropies. The researchers say their idea would allow for a much higher resolution, which would be crucial for detecting such faint signals amid the noise of the SGWB.

The complete study was published in The Astrophysical Journal and can be found here.

Study abstract:

Many recent works have shown that the angular resolution of ground-based detectors is too poor to characterize the anisotropies of the stochastic gravitational-wave background (SGWB). For this reason, we asked ourselves if a constellation of space-based instruments could be more suitable. We consider the Laser Interferometer Space Antenna (LISA), a constellation of multiple LISA-like clusters, and the Deci-hertz Interferometer Gravitational-wave Observatory (DECIGO). Specifically, we test whether these detector constellations can probe the anisotropies of the SGWB. For this scope, we considered the SGWB produced by two astrophysical sources: merging compact binaries, and a recently proposed scenario for massive black hole seed formation through multiple mergers of stellar remnants. We find that measuring the angular power spectrum of the SGWB anisotropies is almost unattainable. However, it turns out that it could be possible to probe the SGWB anisotropies through cross-correlation with the cosmic microwave background (CMB) fluctuations. In particular, we find that a constellation of two LISA-like detectors and CMB-S4 can marginally constrain the cross-correlation between the CMB lensing convergence and the SGWB produced by the black hole seed formation process. Moreover, we find that DECIGO can probe the cross-correlation between the CMB lensing and the SGWB from merging compact binaries.

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