An illustration of cosmic winds blowing from a supermassive black hole.
(Image credit: NASA/CXC and Nahks Tr’Ehnl)
A bright quasar, powered by a supermassive black hole, is blasting out radiation that pushes away clouds of gas in its surroundings to generate winds reaching speeds of around 36 million miles per hour (58 million kilometers per hour). Oh, and the quasar is also nearly as old as the universe itself.
The discovery, made by a team of scientists led by University of Wisconsin–Madison astronomers, shows the role that feeding supermassive black holes at the hearts of so-called “active galactic nuclei,” or “AGNs,” can play in sculpting the wider galaxies around them.
The researchers arrived at their findings using eight years of data about the quasar SBS 1408+544, located 13 billion light-years away in the constellation Bootes. This data was collected by the Black Hole Mapper Reverberation Mapping Project carried out by the Sloan Digital Sky Survey (SDSS). The light from SBS 1408+544 has been traveling to Earth for 13 billion years; that’s almost as long as the 13.8 billion-year-old universe has existed.
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While supermassive black holes with masses equivalent to millions, or sometimes billions, of suns are thought to exist at the hearts of most galaxies, not all of these power up quasars. Quasar black holes are surrounded by matter in a flattened swirling cloud called an “accretion disk” that gradually feeds them material.
The immense gravitational influence of a quasar’s central supermassive black hole causes friction and tidal forces that heat the matter of the accretion disk, causing it to glow intensely. Additionally, matter that is not fed to the supermassive black hole is channeled to the poles of the cosmic titan by powerful magnetic fields, where it is accelerated to near-light speeds and blasted out as highly collimated jets. These dual jets from each black hole pole are also accompanied by emissions of electromagnetic radiation.
Not only does this radiation make some quasars brighter than the combined light of every star in the galaxies around them, but this light also shapes those galaxies and offers a useful gauge for astronomers to measure the influence black holes have on galaxies in general.
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“The material in that [accretion] disk is always falling into the black hole, and the friction of that pulling and pulling heats up the disk and makes it very, very hot and very, very bright,” team leader and University of Wisconsin–Madison astronomy professor Catherine Grier said in a statement. “These quasars are really luminous, and because there’s a large range of temperatures from the interior to the far parts of the disk, their emission covers almost all of the electromagnetic spectrum.”
An image of the supermassive black hole powered quasar SBS 1408+544 in the constellation Bootes (Image credit: Jordan Raddick and the SDSS collaboration)
The bright light from this particular quasar allowed Grier and colleagues to track winds of gaseous carbon. This was done by measuring gaps in the broad spectrum of electromagnetic radiation emitted by the quasar, which indicated light being absorbed by carbon atoms.
The team found that every time they measured this absorption spectrum over 130 observations of SBS 1408+544, there was a shift from the rightful position of the carbon absorption “shadow.” This increased over time as radiation from the quasar pushed away material from around it. This material formed the supermassive black hole winds that reached speeds of up to 36 million miles per hour (58 million kilometers per hour), which is about 45,000 times the speed of sound.
“That shift tells us the gas is moving fast, and faster all the time,” said team co-leader and University of Wisconsin–Madison astronomy graduate Robert Wheatley. “The wind is accelerating because it’s being pushed by radiation that is blasted off of the accretion disk.”
The supermassive black hole at the heart of the Milky Way Sgr A* seen in polarized light is a dormant giant (Image credit: EHT Collaboration)
Scientists have suspected that they have spotted accelerating supermassive black hole winds before, but this is the first time that observation has been backed up with hard evidence. Such cosmic winds are of great interest to astronomers because the gas they shift around serves as the building blocks of stars. That means, if black hole winds are powerful enough, they can cut off star formation, thereby “killing” their host galaxies. They can also deprive central supermassive black holes of fuel, ending their days as quasar machines.
That could turn an active galaxy into a quiet galaxy like the Milky Way, which, in addition to forming stars at a very slow rate, also has a “sleeping giant” black hole at its heart. Sagittarius A* (Sgr A*), our black hole, is surrounded by so little matter that its diet of gas and dust is equivalent to a human eating a grain of rice every million years. Alternatively, the winds from supermassive black holes could compress gas rather than push it away, which would trigger new bouts of star formation in their host galaxies.
Black hole winds like the kind seen by the team could also travel beyond the outskirts of their galaxies, influencing neighboring galaxies and, eventually, the neighboring supermassive black holes at the heart of those galaxies.
“Supermassive black holes are big, but they’re really tiny compared to their galaxies,” Grier said. “That doesn’t mean they can’t ‘talk’ to each other, and this is a way for one to talk to the other that we will have to account for when we model the effects of these kinds of black holes.”
The team’s research was published in June in The Astrophysical Journal.
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Robert Lea is a science journalist in the U.K. whose articles have been published in Physics World, New Scientist, Astronomy Magazine, All About Space, Newsweek and ZME Science. He also writes about science communication for Elsevier and the European Journal of Physics. Rob holds a bachelor of science degree in physics and astronomy from the U.K.’s Open University. Follow him on Twitter @sciencef1rst.
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