Supermassive Black Hole at the Center of the Milky Way Warps Spacetime into Oval Shape, Study Finds
In a groundbreaking study, astronomers have discovered that the supermassive black hole at the center of our Milky Way galaxy is warping spacetime into an oval shape. This finding sheds new light on the nature of these cosmic behemoths and their impact on the surrounding space.
According to Albert Einstein’s theory of general relativity, massive objects can drag spacetime around them when they spin. This phenomenon, known as “frame dragging,” has been observed in various contexts, including our own spinning Earth. However, the effect is much more pronounced for supermassive black holes, which are millions or even billions of times more massive than our sun. The faster these black holes spin, the more spacetime flattens around them, resulting in an oval shape.
Determining the spin rate of our galaxy’s supermassive black hole, known as Sagittarius A* or Sgr A*, has been a challenge for astronomers. Previous estimates have varied widely. However, a team of astronomers led by Ruth Daly from Penn State University has now employed a method called the “outflow method” to measure Sgr A*’s angular velocity.
The outflow method involves studying how material flows away from a black hole. While black holes are known for pulling material in, they can also emit magnetically collimated jets of matter that produce radio waves. Additionally, hot clumps of plasma generated in the disk of matter around a black hole can radiate in X-rays. These clumps, called plasmoids, form more efficiently when a black hole spins rapidly due to frame dragging. By analyzing archival observations from radio telescopes and NASA’s Chandra X-ray Observatory, Daly’s team determined that Sgr A* is spinning at 60% of the maximum possible value defined by the speed of light.
“Our work may help settle the question of how fast our galaxy’s supermassive black hole is spinning,” said Daly. “Our results indicate that Sgr A* is spinning very rapidly, which is interesting and has far-reaching implications.”
The implications of this discovery are significant. The speed at which a black hole spins affects the power of the collimated jets of radiation it emits. Currently, Sgr A* is relatively inactive, but if a gas cloud or star were to fall into it, its jets could be reignited. Evidence of past activity comes from the Fermi Bubbles, enormous structures of gamma-ray emitting matter extending above and below the plane of our galaxy. These bubbles are believed to be remnants of powerful jets that once emanated from Sgr A*. However, such powerful jets can only occur if the black hole is spinning rapidly.
“Jets powered and collimated by a galaxy’s spinning central black hole can profoundly affect the gas supply for an entire galaxy, which affects how quickly and even whether stars can form,” explained Megan Donahue from Michigan State University. “Measuring the spin of our black hole is an important test of this scenario.”
The findings of this study, published in the January 2024 issue of the journal Monthly Notices of the Royal Astronomical Society, provide valuable insights into the nature and behavior of supermassive black holes. By understanding their spin rates and the impact they have on their surroundings, scientists can gain a deeper understanding of the formation and evolution of galaxies. The study also highlights the importance of continued research in unraveling the mysteries of these cosmic giants and their role in shaping the universe as we know it.
