REPUBLIKA.CO.ID, JAKARTA — Astronomers noticed mysterious changes in jets of highly magnetic plasma detonated by black hole tiny bits that feed on gas and dust. Such periodic changing features on the jet, occurring within a fraction of a second, have been detected by the Five-hundred-meter Aperture Spherical Radio Telescope (FAST) in China.
Reported Space on Tuesday (2/8/2023), astronomers learned that the strange flashing object called GRS 1915+105 consists of ordinary stars orbiting a stellar black hole. These stellar black holes are black holes that are born after a massive star dies.
As the star orbits the black hole, some of the material is sucked into the cosmic monster, which fails to swallow all of the material and instead accelerates some of it into a jet that appears to shoot from its poles. The team behind the observations think that the measurable change in the jet’s energy may be due to the fact that the black hole’s rotation is out of sync with its accretion disk, the disk of material orbiting the black hole’s location. That can cause the jet to wobble almost like a spinning cosmic top.
As the jet moves away, its energy drops. A split second later, it was back to normal as the system cycled back. Wei Wang, a professor of astrophysics at Wuhan University in China and lead author of the study said in a statement the strange signal had a roughly 0.2-second period or a frequency of about 5 Hertz.
“Such signals are not always present and only appear under special physical conditions. Our team was lucky enough to catch the signal twice in January 2021 and June 2022 respectively,” said Wang.
GRS 1915+105 is what researchers call a microquasar, a star-scale version of a quasar. Quasars are very bright galactic hearts containing supermassive black holes that are millions or even billions of times more massive than the sun.
This cosmic colossus attracts matter around it with its enormous gravitational force. Some of this matter falls past the black hole’s event horizon, the point of no return from which not even light can escape.
However, some matter escapes this fate and is instead funneled to the black hole’s poles, radiating out into space in the form of super-energy beams. This also happens in microquasars, although on a much smaller scale.
Officially called quasi-periodic oscillations (QPO), the changes seen in GRS 1915+105 have never been seen in radio waves from such a black hole before. QPOs are useful for understanding the physics of black holes and surrounding systems, so observations of this shifting microquasar, located some 28,000 light years from Earth towards the constellation Aquila, can shed light on the eating habits of smaller black holes.
These QPOs, visible in radio waves, could be the first evidence of a jet change of this type, but what exactly causes these oscillations remains a mystery. Bing Zhang, an astronomer at the University of Nevada and co-author of the study said that in accretion black hole systems, X-rays usually probe the accretion disk around the black hole while radio emissions usually probe the disk-launched jets and black holes.
“A detailed mechanism for inducing temporal modulation in relativistic jets was not identified, but one plausible mechanism is that the jet is under precession, meaning the direction of the jet regularly points in a different direction and returns to its original direction every about 0.2 seconds. ,” said Zhang.
This effect may be caused by a misalignment between the black hole’s spin axis and the bright disk of hot, gas and dust around it. This would arise as a result of the fact that as a stellar-mass black hole rotates, it drags the fabric of spacetime with it (an effect called Lense) Thirring which is just frame dragging.
“However, there are other possibilities, and follow-up observations of this and other galactic microquasars will bring more clues to understanding this mysterious QPO signal,” said Zhang.
2023-08-02 15:05:56
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