Black hole and its jet imaged together for 1st time
We’ve all seen the incredible images of black holes, including the first direct images of these mysterious objects, first released in 2019. Now astronomers have obtained another first: an image showing both a supermassive black hole at the center of a distant galaxy, and its powerful jet. The massive black hole is in the center of galaxy Messier 87, which is 55 million light-years away. It’s the same black hole imaged initially by the Event Horizon Telescope (EHT) in 2019. An international group of astronomers released the new image on Wednesday, April 26, 2023.
The Event Horizon Telescope took the previous images of this black hole. But this time, astronomers used multiple telescopes to obtain the new image: the Global mm-VLBI Array (GMVA), the Atacama Large Millimeter/submillimeter Array (ALMA) and the Greenland Telescope (GLT). The European Southern Observatory (ESO) is a partner of ALMA.
The astronomers first conducted the observations in 2018. They have been combining the data from the multiple telescopes together since then.
A black hole and its powerful jet
This is the first time that astronomers have captured both a black hole and its jet – called a relativistic jet – in the same image. Scientists have long known that black holes can emit these huge jets. But how they form still isn’t well understood. Ionized matter within the jets moves at close to the speed of light. As lead author Ru-Sen Lu from the Shanghai Astronomical Observatory in China stated:
We know that jets are ejected from the region surrounding black holes. But we still do not fully understand how this actually happens. To study this directly we need to observe the origin of the jet as close as possible to the black hole. Thanks to ALMA’s location and sensitivity, we could reveal the black hole shadow and see deeper into the emission of the jet at the same time.
We think of black holes as powerful objects that suck in material that can never escape. Not even light can leave a black hole. That is basically true, but black holes can also have huge rings of matter – called accretion disks – that swirl around them. The new images show the base of a jet connected to the ring surrounding the black hole. Co-author Jae-Young Kim, from the Kyungpook National University in South Korea and the Max Planck Institute for Radio Astronomy in Germany, said:
This new image completes the picture by showing the region around the black hole and the jet at the same time.
New image shows unprecedented detail
The new image shows details not previously seen together in any photos of black holes. You can clearly see the jet expelled from the black hole. You can also see the ring of material and the black hole’s shadow. The shadow is a two-dimensional dark zone caused by the strong gravity of the black hole. It is the pitch-black darkness in the center of the accretion disk, in the singularity region. A singularity itself, however, isn’t so much a place as it is a condition, where gravity is so intense that spacetime itself breaks down.
The material in the ring becomes heated as it orbits the black hole. As a result, it emits light. That is why we can see it, even though the black hole itself is black and invisible. We see the matter orbiting the black hole as a ring, because the gravity of the black hole bends the light. In the shadow region, however, nothing is visible at all.
Previously, the Event Horizon Telescope imaged the black hole at a wavelength of 1.3 mm. But now, the new network of telescopes was able to obtain an image at a longer wavelength of 3.5 mm. That allows more details to be seen. Thomas Krichbaum of the Max Planck Institute for Radio Astronomy said:
At this wavelength, we can see how the jet emerges from the ring of emission around the central supermassive black hole.
Larger accretion disk
The size of the accretion disk is also larger in the new image. It looks about 50% larger than it did in the previous Event Horizon Telescope image. The researchers say that is because the new image is simply able to resolve more of the material in the accretion disk. This also provides clues as to how the accretion disk formed. As Keiichi Asada from the Academia Sinica in Taiwan noted:
To understand the physical origin of the bigger and thicker ring, we had to use computer simulations to test different scenarios.
Future observations of the Messier 87 black hole
The researchers plan to use the same network of telescopes to keep observing the black hole. This should help astronomers better understand how the powerful jets originate. Eduardo Ros from the Max Planck Institute for Radio Astronomy said:
We plan to observe the region around the black hole at the center of M87 at different radio wavelengths to further study the emission of the jet. The coming years will be exciting, as we will be able to learn more about what happens near one of the most mysterious regions in the universe.
Bottom line: For the 1st time, astronomers have taken an image of a black hole that shows both the black hole and a powerful jet of material being blasted away from it.