Soon We’ll Detect Extreme Objects Producing Gravitational Waves Continuously

An artist's concept of a binary pair where a smaller star is feeding material to a neutron star. Perturbations in the neutron star may be sending a constant wash of gravitational waves through space. Courtesy Gabriel Pérez Díaz, SMM (IAC)
An artist's concept of a binary pair where a smaller star is feeding material to a neutron star. Perturbations in the neutron star may be sending a constant wash of gravitational waves through space. Courtesy Gabriel Pérez Díaz, SMM (IAC)

The cosmic zoo contains objects so bizarre and extreme that they generate gravitational waves. Scorpius X-1 is part of that strange collection. It’s actually a binary pair: a neutron star orbiting with a low-mass stellar companion called V818 Scorpii. The pair provides a prime target for scientists hunting for so-called “continuous” gravitational waves. Those waves should exist, although none have been detected—yet.

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Gravitational Wave Observatories Could Search for Warp Drive Signatures

Artist's impression of a Dyson Sphere. The construction of such a massive engineering structure would create a technosignature that could be detected by humanity. Credit: SentientDevelopments.com/Eburacum45
Artist's impression of a Dyson Sphere. The construction of such a massive engineering structure would create a technosignature that could be detected by humanity. Credit: SentientDevelopments.com/Eburacum45

In 2016, scientists at the Laser Interferometer Gravitational-Wave Observatory (LIGO) announced that they had made the first confirmed detection of gravitational waves (GWs). This discovery confirmed a prediction made a century before by Einstein and his Theory of General Relativity and opened the door to a whole new field of astrophysical research. By studying the waves caused by the merger of massive objects, scientists could probe the interior of neutron stars, detect dark matter, and discover new particles around supermassive black holes (SMBHs).

According to new research led by the Advanced Propulsion Laboratory at Applied Physics (APL-AP), GWs could also be used in the Search for Extraterrestrial Intelligence (SETI). As they state in their paper, LIGO and other observatories (like Virgo and KAGRA) have the potential to look for GWs created by Rapid And/or Massive Accelerating spacecraft (RAMAcraft). By combining the power of these and next-generation observatories, we could create a RAMAcraft Detection And Ranging (RAMADAR) system that could probe all the stars in the Milky Way (100 to 200 billion) for signs of warp-drive-like signatures.

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Black Holes Shouldn’t be Able to Merge, but Dozens of Mergers Have Been Detected. How Do They Do It?

black holes in a globular cluster
This is an artist’s impression created to visualize the concentration of black holes at the center of globular cluster NGC 6397. Credit: ESA/Hubble, N. Bartmann

Who knows what lurks in the hearts of some globular clusters? Astronomers using a collection of gravitational wave observatories found evidence of collections of smaller black holes dancing together as binaries in the hearts of globulars. What’s more, they’ve detected an increased number of gravitational wave events when some of these stellar-mass black holes crashed together.

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Hubble Examines the Wreckage From the 2017 Kilonova

Artist's impression of two neutron stars colliding, known as a "kilonova" event. Credits: Elizabeth Wheatley (STScI)

In August 2017, astronomers observed a Gravitational Wave (GW) signal that resulted from the merger of two neutron stars – known as a “kilonova” event. The aftermath of this event (GW170817) was studied by 70 ground-based and space-based observatories in multiple wavelengths. This was the first time astronomers observed a binary neutron star merger in terms of electromagnetic radiation (particularly gamma rays) and GWs. The energy released by this merger was comparable to that of a supernova, leading astronomers to theorize that it must have resulted in a black hole.

Two years later, the Hubble Space Telescope observed the remnant and noted the powerful afterglow and gamma-ray bursts (GRBs) created by the merger, which was consistent with a black hole. However, it would take several more years of analysis before scientists could draw a complete picture of what resulted from this explosive event. Using data from Hubble and several radio observatories, a team of researchers detected a rapidly-rotating disk of material around the black hole and a structured relativistic jet emanating from it.

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Shortly Before They Collided, two Black Holes Tangled Spacetime up Into Knots

A binary black hole system, viewed from above. Image Credit: Bohn et al. (see http://arxiv.org/abs/1410.7775)

In February 2016, scientists at the Laser Interferometer Gravitational-Wave Observatory (LIGO) announced the first-ever detection of gravitational waves (GWs). Originally predicted by Einstein’s Theory of General Relativity, these waves are ripples in spacetime that occur whenever massive objects (like black holes and neutron stars) merge. Since then, countless GW events have been detected by observatories across the globe – to the point where they have become an almost daily occurrence. This has allowed astronomers to gain insight into some of the most extreme objects in the Universe.

In a recent study, an international team of researchers led by Cardiff University observed a binary black hole system originally detected in 2020 by the Advanced LIGO, Virgo, and Kamioki Gravitational Wave Observatory (KAGRA). In the process, the team noticed a peculiar twisting motion (aka. a precession) in the orbits of the two colliding black holes that was 10 billion times faster than what was noted with other precessing objects. This is the first time a precession has been observed with binary black holes, which confirms yet another phenomenon predicted by General Relativity (GR).

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Gravitational Waves Will Give Astronomers a new way to Look Inside Neutron Stars

Illustration showing the merger of two neutron stars. Credit: NASA's Goddard Space Flight Center/CI Lab

It’s difficult to study neutron stars. They are light years away and only about 20 kilometers across. They are also made of the most dense material in the universe. So dense that atomic nuclei merge together to become a complex fluid. For years our understanding of the interiors was based on complex physical models and what little data we could gather from optical telescopes. But that’s starting to change.

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Gravitational Waves Near a Neutron Star Could Generate Photons

Artist view of colliding neutron stars. Credit: ESO/L. Calçada/M. Kornmesser

In addition to their intense magnetic fields and copious output of x-ray radiation, neutron stars might have one more trick up their sleeves. They might be able to turn gravitational waves into an extra source of photons.

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A Black Hole can Tear a Neutron Star Apart in Less Than 2 Seconds

Numerical simulation of a black hole-neutron star merger. Credit and ©: K. Hayashi (Kyoto University)

Almost seven years ago (September 14th, 2015), researchers at the Laser Interferometer Gravitational-wave Observatory (LIGO) detected gravitational waves (GWs) for the first time. Their results were shared with the world six months later and earned the discovery team the Noble Prize in Physics the following year. Since then, a total of 90 signals have been observed that were created by binary systems of two black holes, two neutron stars, or one of each. This latter scenario presents some very interesting opportunities for astronomers.

If a merger involves a black hole and neutron star, the event will produce GWs and a serious light display! Using data collected from the three black hole-neutron star mergers we’ve detected so far, a team of astrophysicists from Japan and Germany was able to model the complete process of the collision of a black hole with a neutron star, which included everything from the final orbits of the binary to the merger and post-merger phase. Their results could help inform future surveys that are sensitive enough to study mergers and GW events in much greater detail.

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LISA has Passed a key Review Phase, it’s Time to Actually Design the Final Mission

Any project manager will tell you that a phased review project system is the way to go.  Whether or not you agree with that statement, the process has been widely adopted by space exploration organizations across the globe. They form the basis of many of the best-known projects, and the completion of their phases are events to be celebrated by both the people working on them and the public at large. Now LISA, ESA’s attempt to build a 2.5 million kilometers long interferometer in space, has passed its Feasibility Phase, and is moving on to actually building some prototype technologies.

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Astronomers Could Detect Gravitational Waves by Tracking the Moon's Orbit Around the Earth

An artist view of primordial gravitational waves. Credit: Carl Knox, OzGrav/Swinburne University of Technology

Gravitational waves are notoriously difficult to detect. Although modern optical astronomy has been around for centuries, gravitational wave astronomy has only been around since 2015. Even now our ability to detect gravitational waves is limited. Observatories such as LIGO and Virgo can only detect powerful events such as the mergers of stellar black holes or neutron stars. And they can only detect waves with a narrow range of frequencies from tens of Hertz to a few hundred Hertz. Many gravitational waves are produced at much lower frequencies, but right now we can’t observe them. Imagine raising a telescope to the night sky and only being able to see light that is a few shades of purple.

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