 |
| Artist’s illustration of M87*’s massive jet rising up from the center of the black hole. Credits: S. Dagnello, NRAO, AUI & NSF. |
Fresh images of the most visually striking void in the cosmos are yielding clues about an enigmatic behavior of black holes. These images offer a glimpse of the origin of a massive stream of plasma that propels into the void from the periphery of the supermassive black hole M87*. This is also the initial instance where the shadow of a black hole and its jet have been observed in the same image. This sight will enable astronomers to deduce the mechanisms that produce these colossal streams of plasma.
Astronomer Ru-Sen Lu from the Shanghai Astronomical Observatory in China explains that while it is known that jets are expelled from the vicinity surrounding black holes, the mechanism behind this phenomenon is not fully understood. To investigate this more accurately, it is necessary to observe the genesis of the jet as near to the black hole as feasible.
As commonly known, black holes do not emit any detectable radiation. Due to their immense density, the gravitational pull is so strong that the space-time curvature surrounding them forms a closed sphere. This makes it impossible for any object to attain a velocity that would enable it to escape. However, the region outside the boundary of the closed sphere, which we term as the event horizon, has a different behavior.
In this region, gravity holds complete dominion, and any material in close proximity is ensnared, spiraling into a disk of matter that gushes onto the black hole like water down a drain. This matter is heated by friction and gravity, causing it to emit light, as depicted in the famous M87* image released in 2019, which was captured by the Event Horizon Telescope (EHT) collaboration using data collected in 2017.
 |
| The new image, revealing the jet generation as well as the shadow and ring around the black hole (inset). (R.-S. Lu/SHAO, E. Ros/MPIfR, S. Dagnello/NRAO/AUI/NSF) |
However, not all of the material is inevitably sucked beyond the event horizon. Some of it grazes the edge before being expelled into space from the black hole's polar regions, forming jets that can travel at a substantial portion of the speed of light and cover vast interstellar distances.
Astronomers believe that this material is redirected from the disk's inner rim along the magnetic field lines outside the event horizon. These magnetic field lines boost the particles' speed, so that when they reach the poles, they are fired out into space at a high velocity.
This is the general picture, but it's challenging to determine the specifics. It is known that M87* has a jet that extends up to 100,000 light-years in radio wavelengths, which is roughly the size of our own galaxy. To investigate the region from which the jets emanate more closely, astronomers united powerful radio telescopes in 2018 to form the Global mm-VLBI Array (GMVA). By collecting data in a longer wavelength than the EHT, the GMVA revealed different information.
According to Lu, M87 has been studied for many decades, and scientists were aware of the jet's existence 100 years ago, but they were unable to put it into perspective. However, with the Global mm-VLBI Array (GMVA) and premier instruments at the National Radio Astronomy Observatory (NRAO) and the Green Bank Observatory (GBO), they can observe the region at a lower frequency, allowing them to observe finer details. As a result, they now realize that there are even more details to uncover.
M87 is situated approximately 55 million light-years from Earth and houses a supermassive black hole that is roughly 6.5 billion times the mass of the Sun. This black hole is currently drawing in matter from a surrounding disk. The image captured by the EHT was significant as it was the first time that the shadow of the black hole was seen - a dark region at the center of a luminous ring of material, which is distorted by the gravitational curvature of space-time.
The new image captured shows a more extensive area of space than the EHT image and exposes that the plasma around M87* is more massive than what was previously seen in the EHT image.
The image also reveals the origin of the jet and new details about how it is launched from the space region around the black hole. The new data confirms that magnetic field lines play a vital role in the launch of material as jets from the black hole's poles.
However, this process is not the only mechanism involved in the generation of the M87 jet. The image indicates that a potent wind originating from the disk, powered by radiation pressure, also contributes to the formation of the jet. Astronomer Toney Minter of the National Radio Astronomy Observatory explains that changing the observing wavelengths from 1.3 millimeters to 3.5 millimeters enables the observation of more of the accretion disk and the jet simultaneously, revealing that the ring around the black hole is 50 percent larger than previously believed.
The recent findings about M87* have opened up new avenues for research, and the researchers intend to continue studying the jet and the region surrounding the black hole. They plan to observe the area at various radio wavelengths to gain further insights into the jet's emissions and the black hole's behavior. Astronomer Eduardo Ros from the Max Planck Institute for Radio Astronomy says that the coming years will be fascinating as they learn more about one of the most enigmatic regions in the Universe.
Reference:
Lu, RS., Asada, K., Krichbaum, T.P. et al. A ring-like accretion structure in M87 connecting its black hole and jet. Nature 616, 686–690 (2023). DOI: 10.1038/s41586-023-05843-w
Tags:
Space & Astrophysics