Image: Pablo Garcia (NASA/MSFC)
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After decades of effort, scientists have finally discovered the secret mechanism that powers the brightest light shows in the universe, emitted by absurd energetic rays that shoot out of explosive galaxies known as blazars, a new study reports.
The breakthrough was made possible by a new space mission that can see for the first time the mind-boggling physics that fuel these astrophysical jets, which are made of ultrafast particles and can shine with the brightness of 100 billion suns.
While our own galaxy, the Milky Way, is currently in a sleepy phase, many other “active” galaxies are bursting at the seams with energetic matter replenished by the supermassive black holes lurking at their centers. Intense interactions between the massive black holes and their gaseous environment can cause radiant jets to erupt from these galaxies at nearly the speed of light; some jets extend more than a million light years into deep space.
Blazars are active galaxies with jets pointing directly at Earth. These objects are many millions or billions of light years away, so they don’t pose any risk to our planet, although their jets are so bright that they can be seen even over those vast distances. Thousands of blazars have been observed by astronomers, but until now no one has been able to explain the precise mechanisms that make them so overwhelmingly bright.
Scientists led by Ioannis Liodakis, a Gruber Fellow at the Finnish Center for Astronomy with the European Southern Observatory at the University of Turku, were finally able to solve this mystery thanks to the Imaging X-ray Polarimetry Explorer (IXPE), a joint mission between NASA and the Italian space agency launched into orbit in December 2021.
Liodakis and his colleagues used IXPE to examine an extremely bright blazar called Markarian 501, which is more than 300 million light-years from Earth. Because IXPE is the first mission to capture a pattern called polarization in X-ray light, the researchers were able to show that the particles in these jets are supercharged by shock fronts, revealing a long-standing “unanswered question” about the dynamics of these brilliant objects, according to a study published on Wednesday in Nature.
“We know these wells from the 1960s,” Liodakis said in an email to Motherboard, referring to blazar jets. “They are among the brightest objects in X-rays, and for years we didn’t know how the X-rays are made. We had a few theories, but the radio and optical data we could get can’t tell us much.”
“That’s because those come far from the accelerator site, while X-rays come straight from the heart of the accelerator,” he continued. “They really let us look at the acceleration area and the physical conditions there, making them the ideal tool to answer our questions.”
Put another way, each band of the light spectrum tells a different story about the nature of these jets, and scientists have missed the most important chapter on X-rays. In particular, researchers have tried to capture the polarization of X-rays in the jets, which is essentially a pattern embedded in the configuration of light waves that contains information about how and where the light was produced.
While scientists have long been able to study the polarization of blazarjets in many different bands of the light spectrum, only IXPE can resolve these patterns in the kind of high-energy X-ray light that illuminates the initial process that sends the jet particles flying. into deep space with unthinkable energies. Liodakis said the mission has been on astronomers’ wish list for decades, and that the observations helped open “a new window on the universe” that allowed scientists “to make the observations and, after all these years, immediately test our models.”
Indeed, IXPE’s view of Markarian 501, which was captured in March 2022, suggests that the particles in a jet are accelerated when they collide with slower-moving material in the galaxy, creating a shock wave that spreads through the jet and stimulates the particles. to incredibly high energy levels. Particles traveling in this wave produce highly polarized X-ray light; as they pass it, their emission becomes less polarized.
These results confirm models that predicted the central role of shock waves in driving these cosmic particle accelerators, which are natural laboratories for studying the behavior of light and matter at extremely high energies. To that end, Liodakis and his colleagues hope that IXPE and similar instruments will continue to reveal the secrets of blazars and their pyrotechnic jets, including Markarian 501.
“Our observations were made when Markarian 501 was in a sort of intermediate activity state,” Liodakis said. “Those sources are always active, but there are times when they go into these outbursts that can make them more than 100 times brighter. We’re not sure if our findings apply in those states.
“We have more observations planned that will hopefully happen soon, and we’ll be able to figure out what’s going on inside the jets during these outbursts,” he concluded.