Fastest and most furious ultraviolet wind found near a black hole
A team led by York University researchers has discovered the fastest wind near a supermassive black hole ever found at ultraviolet wavelengths, driven by the disc of matter, or quasar, surrounding the black hole.
“This quasar has a black hole of 1.7 billion times the mass of the Sun. That’s typical. What’s not typical is that it has gas moving towards us at 30 per cent of the speed of light,” says York Professor Patrick Hall of the Faculty of Science.
The finding is published today in a peer-reviewed paper in The Astrophysical Journal, published by The American Astronomical Society.
The research team includes York graduate student and lead author Lucas Seaton, graduate student Marianna Veltri, and undergraduate student Zezhou Zhu, along with colleagues from the University of Washington Bothell and other members of the Sloan Digital Sky Survey (SDSS) collaboration.
“This quasar, known as J2318 (Jay Twenty-Three Eighteen), can be found in the Great Square in the constellation of Pegasus,” says Seaton. “In terms of its speed, this quasar’s wind could be called a category 79 hurricane,” says Seaton. “Every category of hurricane is about 20 per cent faster than the category below it. Calling it category 79 gives an idea of just how fast it is, but of course this wind is unlike anything on Earth.”
Astronomers have known for close to three decades that every large galaxy has a supermassive black hole at its centre, with a mass from millions to billions of times that of the Sun, although contrary to popular belief they do not eat everything in reach. Matter spiraling into one of these black holes forms a disc far bigger than Earth’s orbit around the Sun and hotter than the surface of the Sun. These discs of hot gas, called quasars, generate enough light to be seen across the observable universe and to drive winds from their surfaces.
“In quasars, we often see winds of gas pushed away from the black hole by the light of the quasar,” says Seaton. “The wind in J2318 can be seen at ultraviolet wavelengths at velocities up to 30 per cent the speed of light. Even faster winds can be seen at x-ray wavelengths, but J2318 is the fastest ever discovered at ultraviolet wavelengths.”
Unlike the differences in gas pressure that drive atmospheric winds on Earth, winds from quasars are pushed at least in part by light itself. Individual packets of light (called photons) bounce off or are absorbed by atoms in the gas and accelerate them.
“Quasars put out so many photons that those tiny pushes add up to extreme velocities,” says Seaton. “The problem is, the photons can also remove all the electrons from the atoms, making them invisible. How to push the gas to the speeds we see while keeping the carbon and silicon ions we see intact… it’s quite a puzzle.”
The discovery relied on data from two components of the SDSS, an international survey of the night sky to which hundreds of astronomers have contributed since its start in 1998, specifically, the SDSS-IV Time-Domain Spectroscopic Survey and the SDSS-V Black Hole Mapper. Veltri flagged the quasar as potentially interesting in SDSS-V in 2023 while an undergrad student at York. After looking at it using software set up by Zhu, Hall realized it had an extremely fast wind.
“Canada has a share of the eight-meter-diameter Frederick C. Gillett Gemini Telescope (also known as Gemini North) in Hawai’i, and we immediately proposed observations with it. They succeeded in confirming its record-breaking wind velocity,” he says, adding that he often involves York undergraduates in research as part of his participation in the SDSS.
He explains that “just as a rainbow spreads the Sun’s light into different wavelengths (colours), the SDSS spreads out the light from certain stars, galaxies, and quasars into what we call their ‘spectra’. From those spectra, with practice, students learn to spot unusual quasars. In the past, only PhD astronomers or graduate students studying for a PhD would have made a discovery like this, but the SDSS enables undergraduates to do so.”
Study co-author, Associate Professor Paola Rodríguez Hidalgo of the University of Washington at Bothell, adds: “Both Patrick and I have been working together and with undergraduate students thanks to the SDSS Faculty and Students Team (FAST) initiative that supports these collaborations. Initiatives like this allow students to focus on research while finishing their undergraduate studies. These students will be the next generation of scientists and are already making scientific discoveries.”
Co-author Liliana Flores, who worked with Professor Rodríguez Hidalgo as an undergraduate at UW Bothell and was a FAST participant, says she was thrilled to contribute to the study of this extreme outflow case. “I was in charge of fitting the absorption profiles in the quasar spectrum to determine their velocity and equivalent widths. Repeated observations revealed that the amount of absorbed light changes over time. Something in the wind conditions must be changing for that to happen.”
Veltri assembled measurements of the brightness of the quasar from 20 years of surveys, starting with the original SDSS. That data shows that J2318 is slowly varying in brightness in a way indistinguishable from other quasars. Only by taking detailed measurements of spectra with SDSS was the wind in J2318 revealed.
Rodríguez Hidalgo calls the discovery exciting. “These extreme outflows carry incredible amounts of energy that can affect the galaxies around them. They serve as a sort of missing link: the elusive feedback between the active central region of a galaxy and the rest of the galaxy. While this process has been included in simulations of galaxy formation for decades, a lot more work needs to be done to understand it from observations and make sure the simulations handle it correctly.”
Searches are continuing for more extremely high velocity outflows from quasars, says Flores. “It won’t be easy to find a faster ultraviolet outflow than that of J2318, but we are continuing this search from the nearby universe to the most distant reaches of the universe that we can see.”
IMAGE: An artist's impression of a quasar. The black dot in the center represents the supermassive black hole at the center of the quasar. The red-and-yellow spiral surrounding it shows the disc of hot gas falling into the black hole. Some of this gas is ejected as the quasar's wind, which is shown in light blue. The size of the disc shown is comparable to the size of our Solar System. Credit NASA/CXC/M. Weiss, Nahks Tr'Ehnl, Nurten Filiz Ak
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