A worldwide network of telescopes has produced an image of a jet of radio waves appearing to blast out from the centre of a supermassive black hole at over 15 times the speed of light.
One year ago, scientists at observatories around the world teamed up to produce the first-ever image of a black hole’s shadow. But the Event Horizon Telescope collaboration can produce more than just an image of a cosmic doughnut. During its April 2017 observing run, it also took an image of a blazar—a supermassive black hole blasting a jet of radiation toward Earth, allowing astronomers peer inside and image the radio jet in the best resolution yet.
Understanding these black hole jets and how they form is of central importance to astrophysicists today, and a popular way to study them is very long baseline interferometry (VLBI). VLBI is a method that combines the observations of radio telescopes located around the world—effectively creating a much larger telescope—in order to increase the overall resolution with which they can make out distant objects. Each telescope records the radiation coming in from a source and the exact time that the radiation arrived. Computer algorithms combine and, in a sense, focus the data into a high-resolution image.
The most famous use of VLBI came from the Event Horizon Telescope, a worldwide effort to create an image of the dark circle at the centre of a black hole. Eight radio telescopes took data for two weeks back in 2017, and the collaboration presented the now-iconic image of the centre of galaxy M87 last April. Though the M87 image helped scientists better understand jet formation, it didn’t directly link the black hole to its jet, according to the study published today in Astronomy and Astrophysics. But they observed other targets as well, including a bright source of radio waves called blazar 3C 279, billions of light-years away.
Today, scientists are releasing the results of their analysis of 3C 279, led by Jae-Young Kim at the Max Planck Institute for Radioastronomy in Germany. The EHT imaged the object on April 5, 6, 10, and 11 of 2017, and scientists in the following years worked to combine the observations to combine and analyse the actual data.
These observations imaged the jet down to a half a light-year in resolution. The structure appeared twisted at its base and had smaller substructural components moving perpendicular to our field of view. It even changed over the course of the few days of the observing window. Two of the jet components appeared to be moving faster than the speed of light, 15 and 20 times light speed, in fact. They’re not really moving faster than the speed of light; they just appear to be doing so in the sky, an effect I explain here. Together, the observations suggest that the jet could be a bent or rotating emission of shockwaves produced by instabilities in its plasma.
One physicist who was not involved in the study, postdoctoral researcher Konstancja Satalecka at DESY in Germany, told Gizmodo that the measurements are compelling on their own but will be even more exciting when combined with other radiation wavelengths, such as gamma rays. Gamma ray emissions from jets are associated with new features forming and could also be correlated with more mysterious outbursts like neutrinos and cosmic rays.
“Since the EHT observations were taken during a time when 3C 279 showed high variability in gamma rays, I am really excited about the subsequent publication where the multi-wavelength data will be used to model the processes in the jet,” she told Gizmodo in an email. “Hopefully we can pinpoint the location of the gamma-ray emission region and learn more about the acceleration and emission mechanisms responsible for their production.”
This jet is just one example, Satalecka explained, of a family of objects that can show huge variation. This means that the results here can’t be generalized to other active galactic nuclei—galaxies whose centres are also blasting out radiation. Still, it’s a step toward understanding how these jets form.
Scientists are continuing to analyse the data from the April 2017 run and hope to eventually produce an image or even a video of our own galaxy’s central black hole. The ongoing covid-19 pandemic has put this month’s EHT run on hold, so EHT scientists are working to further analyse data taken in 2017 and 2018. An expanded run with 11 observatories is scheduled for March 2021.