First image of a black hole expelling a powerful jet
A stunning new image of a supermassive black hole could help scientists solve the mystery of how these hungry behemoths fire off jets of accelerated particles out into the cosmos. Taken in 2018 by a network of radio telescopes around the world, the image is focussed on Messier 87 — a galaxy that lies some 55 million light years from our Milky Way.
Messier 87 was also the subject of the first-ever published photograph of a black hole, which was released back in 2019. The newer image, however, reveals new details not visible in its predecessor — including a much larger ring around the hole and, for the first time, the connection between this and one of the particle jets thundering away from the black hole.
What are black holes?
Black holes are regions of where the fabric of spacetime is so deformed by concentrated mass that, beyond their “event horizon”, nothing — not even light — can escape their gravity.
Typically, black holes weigh in at around 5–10 times the mass of our Sun, being constrained by the size of the star that collapsed to form them in the first place.
However, astronomers have also found that most galaxies also contain “supermassive” black holes at their very centre — staggering concentrations of matter that can contain millions or even billions of times the mass of the Sun.
According to NASA, “One possible mechanism for the formation of supermassive black holes involves a chain reaction of collisions of stars in compact star clusters. [This] results in the buildup of extremely massive stars, which then collapse to form intermediate-mass black holes.
“The star clusters then sink to the centre of the galaxy, where the intermediate-mass black holes merge to form a supermassive black hole.”
While black holes are famous for gobbling up matter from their immediate surroundings, they are also capable, counterintuitively, of being the source of emissions.
For example, British physicist Stephen Hawking argued that a weird phenomena could allow black holes to “evaporate” mass slowly over time.
This emission is named Hawking radiation, in his honour. See the fact box, right, for a quick explanation of how this works.
Less subtly, supermassive black holes are also capable of powering phenomena known as quasars.
These are extremely luminous active galactic nuclei that burn as brightly as would a trillion stars packed into a volume about the size of the solar system.
In fact, a recent study of 48 quasars and their surrounding galaxies concluded that these light shows are ignited by galactic “fender-benders”.
Interactions between galaxies pushes into their central supermassive black holes gas that would otherwise orbit at a “safe” distance from the hungry nuclei.
As the gas spirals towards the event horizon, friction causes it to heat up and emit radiation — forming a quasar signal that can be seen far across the universe.
Alongside radiation, black holes are also capable of emitting two powerful jets of matter at nearly the speed of light out into space in opposite directions.
These are suspected to be caused by the “accretion disk” of matter spiralling into the hole generating twisted magnetic fields — which in turn accelerate particles along the disk’s axis.
Zooming in on the black hole and jet of Messier
The new study — which focussed on the supermassive black hole at the heart of the galaxy Messier 87 (M87) — was undertaken by Dr Ru-Sen Lu from Shanghai Astronomical Observatory in China and his colleagues.
Dr Lu said: “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.”
M87’s central blackhole — which is a whopping 6.5 billion times more massive than our Sun — lies some 55 million light years away.
The researchers analysed observations of M87 taken back in 2018 by a network of radio telescopes around the world — including the Global Millimetre VLBI Array (which comprises 14 sites in Europe and North America, the Atacama Large Millimeter/submillimeter Array (in Chile) and the Greenland Telescope — working together to act as a “virtual” Earth-sized telescope.
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The image formed by these telescopes shows, for the first time, how the base of a jet connects with the matter swirling around the supermassive black hole from which it formed.
Previously, it had only been possible to image these two parts individually.
Paper co-author and astrophysicist Professor Jae-Young Kim of the Kyungpook National University in South Korea explained: “This new image completes the picture by showing the region around the black hole and the jet at the same time.”
Also included in the picture is what scientists call the “shadow” of the supermassive black hole.
This is delineated by a ring-like structure of light surrounding the hole, created when some of the light emitted from the accretion disc of matter falling in the hole is bent and captures around the hole.
This phenomena may be familiar from the first-ever direct photograph of a black hole (M87, again, in fact) which was published by the Event Horizon Telescope (EHT) collaboration back in 2019.
Unlike that previous image, however, the new observations of M87 show light being emitted at a longer wavelength — 3.5 millimetres, as opposed to the 1.3 mm seen by EHT — with the ring around the black hole also appearing around 50 percent larger in the new image.
Paper co-author Dr Thomas Krichbaum of the Max Planck Institute for Radio Astronomy in Bonn, Germany, said: “At this wavelength, we can see how the jet emerges from the ring of emission around the central supermassive black hole.”
With their initial study complete, the researchers are now looking to use the same network of radio telescopes to learn more about how black hole jets are formed.
Paper author and Max Planck astronomer Professor Eduardo Ros explained: “We plan to observe the region around the black hole at the centre 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.
The full findings of the study were published in the journal Nature.
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