The cosmic zoo contains objects so bizarre and extreme that they generate gravitational waves. Scorpius X-1 is part of this strange collection. It’s actually a binary pair: an orbiting neutron star with a low-mass stellar companion called V818 Scorpii. The pair is a prime target for scientists looking for so-called “continuous” gravitational waves. These waves should exist, although none have been detected, yet.
“Scorpius X-1 is one of the most promising sources for detecting these continuous gravitational waves,” said Professor John Whelan from the School of Mathematical Sciences at the Rochester Institute of Technology. He is the principal investigator of the RIT group in the LIGO Science Collaboration, which is part of a group of scientists focused on the direct detection of gravitational waves. LIGO is the Gravitational Wave Laser Interferometer Observatory, located in Washington State and Louisiana. Virgo (in Italy) and KAGRA (in Japan) also search for gravitational waves, often in conjunction with LIGO.
Scorpius X-1 Gravitational Wave Hunt
Whelan’s team used data from the third LIGO-Virgo observing campaign in their search for continuous gravitational waves from Scorpius X-1. “It’s pretty close at just 9,000 Light years away,” Whelan said. “We can see it very clearly in X-rays because the gaseous matter of the companion star is fired at the neutron star.”
Despite its brightness, the team did not detect a continuous sweep of gravitational waves from Scorpius X-1. That doesn’t mean the waves aren’t there. In fact, their data provides important goalposts as they forecast more sightings of the pair. This helped them improve their research methodology and should eventually lead to the detection of these elusive waves.
“This research has provided the best constraint so far on the possible strength of the gravitational waves emitted by Scorpius X-1,” said Jared Wofford, who holds a PhD in science and technology in astrophysics. candidate. “For the first time, this research is now sensitive to models of the system’s possible torque equilibrium scenario, which states that the torques of the gravitational wave and material accretion on the neutron star are in equilibrium. In the coming years, we expect better sensitivities from more data taken by the Advanced LIGO observation series probing deeper into the torque balance scenario in hopes of making the first detection of continuous wave.
The Scorpius X-1 System
Scorpius X-1 is the most powerful X-ray source in our sky (after the sun). Astronomers discovered it in 1962 when they sent a sounding rocket into space with an X-ray detector. Over the years, they discovered that its strong X-ray emissions came from a neutron star of solar mass 1.4 which engulfs matter from its smaller companion of solar mass 0.4. The neutron star’s strong gravitational field accelerates stellar material as it falls onto the star. This superheats the material and causes it to emit X-rays.
While the system is a strong X-ray emitter and is bright in optical light, it is actually classified as a low-mass X-ray binary. Both objects have an orbital period of 18.9 hours. It is not known whether they formed together early in their history. Some astronomers suggest they might have met when a supermassive star and the smaller companion met up close in a globular cluster environment. The larger companion eventually exploded in a supernova, creating the neutron star.
Using Gravitational Waves to Understand the Scorpius X-1 Binary Pair
Most of us are familiar with gravitational waves generated by black hole and/or neutron star mergers. The first detection of these waves was in 2015. Since then, LIGO and its sister facilities KAGRA and Virgo have regularly detected these “stronger” waves. It is important to remember that these detections record specific collisions, essentially “one-time” events. However, they are not the only sources of gravitational waves in the universe. Astronomers believe that massive objects that spin hundreds of times per second, like neutron stars, can produce weaker continuous waves that should be detectable.
So what could be causing the waves in a neutron star/companion star binary pair? Look at the outer structure of neutron stars. Scientists describe them as uniformly smooth objects with strong gravitational and magnetic fields. However, they may have tiny surface irregularities (called “mountains”). These protrude only a fraction of a millimeter above the surface of the neutron star’s “crust”. The mountains are really deformations in this crust. They are created by extreme stresses in the electromagnetic field of the neutron star.
It is also possible that these distortions occur when the rotation of the object slows down. Or maybe when its rotation suddenly speeds up. Whatever their form, they affect the magnetic and gravitational fields of the neutron star. This may be what causes the gravitational waves. If so, these mountains may be small, but their influence could be big.
The challenge now is to measure these waves. Ultimately, astronomers will detect a constant “washing” of waves coming from Scorpius X-1. Their data will tell them more about the neutron star itself. It should also give clues to the dynamics of the binary pair as the members orbit each other.
Quote: Scorpius X-1: Astronomers may soon detect extreme objects producing continuous gravitational waves (2023, January 31) Retrieved February 1, 2023 from https://phys.org/news/2023-01-scorpius-x- astronomers-extreme-gravitational .html
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