The more we explore the universe, the more awestruck we are by what we find.
Taking a leaf out of a science-fiction script, black holes, the universe’s most enigmatic entities, unveil their existence through astonishing properties. A new study has allowed scientists to reveal previously unknown features of black holes.
Stellar-mass black holes, with a mass equivalent to approximately ten suns, broadcast their presence by devouring matter from their stellar partners. Sometimes, supermassive black holes amass at the cores of certain galaxies, leading to the formation of luminous, compact regions known as quasars.
Their mass surpasses ours by millions to billions. A specific group of stellar-mass black holes, capable of launching highly magnetized plasma jets, earn the name ‘microquasars.’
Groundbreaking Research on Microquasars
A dedicated team of international scientists, featuring UNLV astrophysicist Bing Zhang, presents an observational study on the galactic microquasar, GRS 1915+105. The study, published in Nature, uncovers unprecedented features of a microquasar system.
Using China’s colossal Five-hundred-meter Aperture Spherical radio Telescope (FAST), the team unearthed a Quasi-Periodic Oscillation (QPO) signal in the radio band from a microquasar system for the first time. QPOs serve as vital tools for astronomers to comprehend how stellar systems, including black holes, operate. Although QPOs have been spotted in X-rays from microquasars, discovering them within the radio emission of the system is a novelty.
Explaining the Unique Signal
“This distinct QPO signal boasts a rough period of 0.2 seconds or a frequency of around 5 Hertz,” said Wei Wang, a professor from Wuhan University, China, who spearheaded the discovery. “The signal doesn’t always manifest and appears only under unique physical conditions. We were fortunate to detect the signal twice—in January 2021 and June 2022.”
Zhang, director of the Nevada Center for Astrophysics and one of the study’s key contributors, suggests that this distinctive feature could be the first proof of a ‘jet’ launched by a galactic stellar-mass black hole. Under specific circumstances, some black hole binary systems can trigger a jet—concurrent streams of charged matter and a magnetic field racing close to light speed.
Understanding the QPO Signals
“Within black hole systems, X-rays typically investigate the black hole’s surrounding accretion disk, while radio emissions explore the jet launched from the disk and the black hole,” Zhang clarified. He proposed that the jet might undergo precession, causing it to change its direction and return to the original path every 0.2 seconds, thereby creating a temporal modulation.
Zhang attributes this phenomenon to a potential misalignment between the black hole’s spin axis and its accretion disk. However, he also mentions that other possibilities could exist, and further observations will yield more insight into these cryptic QPO signals.
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