Space telescopes uncover supermassive black hole winds
Supermassive black holes are titanic oddities. Usually sited at the core of galaxies and various high-energy phenomena such as quasars, their mass can be anywhere from that of a hundred thousand to billions of suns. Now observations from NASA and ESA space telescopes are shedding light on the incredibly powerful cosmic winds they produce, which can have more energy than an entire galaxy.
Many astronomers believe that supermassive black holes are found at the center of most sizable galaxies, including our own. It's a logical assumption, given the amount of matter that accumulates there. With so many stars and so much gas, it's like a feast for any black holes that develop or migrate there, and it turns out that the growth of these supermassive black holes has an effect on the evolution of their host galaxies. Part of this effect is due to the fierce winds that they generate.
The key to understanding these winds are the tremendous X-rays that the black holes produce as the gases that encounter them blast away at relativistic speeds. Observing these X-rays has allowed astronomers to build up a picture of the winds.
The key finding is that these winds blow away in all directions from the supermassive black holes, instead of tight beams. This was detected by observations carried out by NASA's Nuclear Spectroscopic Telescope Array (NuSTAR), which observes high energy X-rays, and ESA’s XMM-Newton telescope, which looks at low energy X-rays.
The spherical winds were seen blowing from a quasar called PDS 456, which is extremely bright and situated 2 billion light years away. It was studied on five occasions by NuStar and XMM-Newton in 2013 and 2014, which measured the winds traveling at speeds of one-third of the speed of light and emitting X-rays with more energy than a trillion suns.
Such ultra-fast winds had been suspected to exist, but this was the first confirmation. XMM-Newton had previously detected iron atoms pushed by black-hole winds, but these were thought to be the result of beam-like streams emitted from the poles of a black hole.
The latest observations by the space telescopes not only demonstrate that the winds blow in all directions, but also allow scientists to measure the strength, shape, and velocity of the winds, which provides insights into galactic evolution.
According to scientists, this blasting away of gases inhibits the growth of the galaxy by diminishing its capacity to create new stars due to a lack of raw materials. By understanding these winds, astronomers can now measure and predict the extent of this inhibition. The growing theory is that these supermassive black holes evolve with their galaxies, producing a feedback mechanism that regulates galactic evolution.
An interesting side note is that this uniform expansion reinforces observations that show that the more massive a galaxy's central bulge is, the larger the supermassive black hole at its core. Astronomers are also interested in PDS 456 because its distance gives them a glimpse at how the universe looked 10 billion years ago when such phenomena were more common.
"For an astronomer, studying PDS 456 is like a paleontologist being given a living dinosaur to study," says Daniel Stern of NASA's Jet Propulsion Laboratory. "We are able to investigate the physics of these important systems with a level of detail not possible for those found at more typical distances, during the 'Age of Quasars.'"
The results were recently published in the journal Science.