Black holes, the most puzzling entities in the universe, often seem as if they have jumped straight from the pages of a sci-fi novel.
Stellar-mass black holes, around 10 times the mass of our sun, often give away their location by consuming material from nearby stars.
At times, supermassive black holes gather at the core of galaxies to form brilliantly compact regions called quasars, with masses equal to millions or billions of our sun.
A smaller subset of stellar-mass black holes can even launch jets of highly magnetic plasma, earning them the title of microquasars.
Revealing the Unseen Features of Microquasars
An international team of researchers, including astrophysicist Bing Zhang from UNLV, has undertaken an observational study of a specific microquasar named GRS 1915+105.
Using the huge Five-hundred-meter Aperture Spherical radio Telescope (FAST) in China, they discovered characteristics of this microquasar system previously unseen.
The team found a quasi-periodic oscillation (QPO) signal in the radio band from the microquasar system, marking the first such discovery.
Astronomers use QPOs to understand the functioning of stellar systems like black holes. While QPOs have been detected in X-rays from microquasars, finding them as part of the system’s radio emission is a unique observation.
“The unique QPO signal has a rough period of 0.2 seconds or about 5 Hertz frequency,” said Wei Wang from Wuhan University in China, who led the discovery team.
“Such a signal appears only under specific physical conditions. We were fortunate to capture this signal twice – in January 2021 and June 2022.”
Connecting QPOs and Black Hole Jets
According to Bing Zhang, the QPO signal could provide the first evidence of a “jet” activity from a stellar-mass black hole in our galaxy.
Some black hole binary systems, under certain conditions, launch a jet—fast-moving parallel beams of charged matter and magnetic fields.
Zhang explains, “In black hole systems, X-rays usually explore the accretion disk around the black hole, while radio emissions investigate the jet launched from the disk and the black hole.
The mechanism inducing temporal modulation in a relativistic jet isn’t fully understood yet, but one plausible explanation could be the jet undergoing precession – meaning it points in varying directions, returning to its original direction every 0.2 seconds.”
This effect might be caused by a misalignment between the spin axis of the black hole and its accretion disk (a bright, hot spin of gases surrounding the black hole), possibly due to spacetime dragging near a rapidly spinning black hole.
“Other possibilities exist, however, and continued observations of this and other galactic microquasar sources will provide more insight into these enigmatic QPO signals,” said Zhang.
The study was published in Nature.
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