The Cosmic Zoo contains objects so strange and extreme that they generate gravitational waves. Scorpius X-1 is part of that strange group. It’s actually a binary pair: an orbiting neutron star with a low-mass stellar companion called V818 Scorpii. The pair provides a primary target for scientists looking for so-called “persistent” gravitational waves. These waves must exist, although none have been detected, yet.
“Scorpius X-1 is one of the most promising sources for detecting these persistent gravitational waves,” said Professor John Whelan of the Rochester Institute of Technology’s School of Mathematical Sciences. He is the Principal Investigator of the RIT Group in the LIGO Scientific Collaboration, and is part of a group of scientists focused on the direct detection of gravitational waves. LIGO is a laser gravitational wave observatory, located in Washington and Louisiana. Virgo (in Italy) and KAGRA (in Japan) also search for gravitational waves, often in conjunction with LIGO.
The search for gravitational waves in Scorpius X-1
Whelan’s team used data from the third round of LIGO-Virgo observations in their search for persistent gravitational waves from Scorpius X-1. “It’s relatively close at only 9,000 light-years away,” Whelan said. And we can see it very clearly in X-rays because the gaseous substance is from a companion star to the neutron star.
Despite its brightness, the team did not detect Scorpius X-1’s constant wash of gravitational waves. This does not mean that waves do not exist. In fact, their data provides important targets as they plan further observations of the pair. It helped them improve their research methodology and should eventually lead to the discovery of these elusive waves.
“This research has yielded the best constraint yet on the potential strength of gravitational waves emitted by Scorpius X-1,” said Jared Wofford, PhD, Astrophysical Sciences and Technology. candidate. “For the first time, this research is now sensitive to models of the system potential torque equilibrium scenario, which states that the gravitational wave torques and the accumulation of matter in the neutron star are balanced. In the coming years, we expect even better sensitivities from more data obtained through LIGO’s advanced observations are delving deeper into the torsion equilibrium scenario in hopes of making the first continuous wave detection.”
Artist’s conception of the neutron star shows an outline of its magnetic field and possible jets of material escaping from the poles. In the Scorpius X-1 system, the neutron star is paired with a low-mass star. Matter seeps from the younger star to the surface of the neutron star. Irregularities on the surface of a neutron star may play a role in the formation of gravitational waves. Credit: Kevin Gill, Attribution 2.0 Generic (CC BY 2.0)
Scorpius X-1 System
Scorpius X-1 is the most powerful X-ray source in our sky (after the Sun). It was discovered by astronomers in 1962 when they sent a sounding rocket with an X-ray detector into space. Over the years, they have discovered that the powerful X-ray emissions are coming from a 1.4-solar-mass neutron star that is gobbling up material flowing from its smaller 0.4-solar-mass companion. The strong gravitational field of a neutron star accelerates interstellar matter as it falls on the star. This heats the matter 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 system. The two objects have an orbital period of 18.9 hours. It is unclear if they formed together earlier in their history. Some astronomers suggest that they might have met when a massive star encountered its young close companion in a globular cluster environment. The larger companion eventually exploded as 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 merging black holes and/or neutron stars. The first detection of these waves occurred in 2015. Since then, LIGO and its sister facilities KAGRA and Virgo have detected these “stronger” waves regularly. 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 rotate hundreds of times per second, such as neutron stars, can produce weaker detectable continuous waves.
So what could be causing the ripples 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 small surface irregularities (called “mountains”). These protrude only fractions of a millimeter above the surface of the “shell” of the neutron star. The mountains are actually distortions in that crust. They are created by intense pressures in the electromagnetic field of the neutron star.
It is also possible that these deformities occur when the rotation of the body slows down. Or maybe when it suddenly sped up. Regardless of how they form, they influence the magnetic and gravitational fields of the neutron star. This may be what is causing it. gravitational waves. If so, those mountains may be small, but their impact could be huge.
Provided by Universe Today