A bright quasar, powered by a supermassive black hole, emits radiation that pushes clouds of gas away from its surroundings, generating winds at speeds of about 58 million kilometers per hour. Oh, and the quasar is also almost as old as the universe itself.
The discovery, made by a team of scientists led by astronomers from the University of Wisconsin-Madison, demonstrates the role that feeding supermassive black holes at the hearts of so-called “active galactic nuclei” or “AGNs” can play in shaping the broader galaxies around them.
The researchers came to their findings based on eight years of data on the quasar SBS 1408+544, located 10.8 billion light-years away in the Bootes constellation. This data was collected by the Black Hole Mapper Reverberation Mapping Project, conducted by the Sloan Digital Sky Survey (SDSS). The light from SBS 1408+544 has been traveling to Earth for almost 11 billion years; that’s almost as long as the 13.8 billion year old universe has existed.
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Although supermassive black holes with masses equivalent to millions or sometimes billions of suns are thought to exist at the core of most galaxies, not all of these quasars are capable of increasing their power. Quasar black holes are surrounded by matter in an oblate, swirling cloud called an “accretion disk,” which 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. Furthermore, matter that is not carried to the supermassive black hole is channeled by powerful magnetic fields to the poles of the cosmic Titan, where it is accelerated to near-light speeds and shot out as highly collimated jets. These twin 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 provides astronomers with a useful gauge for measuring the influence black holes have on galaxies in general.
‘The material in there [accretion] “The disk is always falling into the black hole, and the friction from that pulling and tugging heats up the disk and makes it very, very hot and very, very bright,” team leader and astronomy professor Catherine Grier of the University of Wisconsin-Madison said in an interview. “These quasars are really luminous, and because there’s a large temperature range from the interior to the far parts of the disk, their emission spans almost the entire electromagnetic spectrum.”
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 that light was 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 material away from the environment. This material formed the supermassive black hole winds that reached speeds of up to 58 million kilometers per hour, which is about 45,000 times the speed of sound.
“That shift tells us that the gas is moving fast, and faster and faster,” said Robert Wheatley, co-leader of the team and a University of Wisconsin-Madison astronomy graduate. “The wind is speeding up because it is being pushed by radiation blown off the accretion disk.”
Scientists have previously suspected that they have observed accelerating supermassive black hole winds, but this is the first time the observation has been supported by hard evidence. Such cosmic winds are of great interest to astronomers because the gas they drift serves as building blocks for stars. That means that, if black hole winds are powerful enough, they can cut off star formation, “killing” their host galaxies. They can also defuel central supermassive black holes, ending their days as quasar machines.
That could turn an active galaxy into a quiet galaxy like the Milky Way, which not only forms stars very slowly, but also has a ‘sleeping gigantic’ 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 that of a human eating a grain of rice every million years. Alternatively, the winds from supermassive black holes could compress gas instead of pushing it away, triggering new bouts of star formation in their host galaxies.
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Black hole winds like those observed by the team can also travel beyond the outer edges of their galaxies and affect neighboring galaxies, and ultimately the neighboring supermassive black holes at the heart of those galaxies.
“Supermassive black holes are big, but they are very small compared to their galaxies,” Grier said. “That doesn’t mean they can’t ‘talk’ to each other, and this is a way in which one can talk to the other that we will have to take into account when we model the effects of these types of black holes.”
The team’s research was published in June in The Astrophysical Journal.
Editor’s note: The quasar SBS 1408+544 is 10.8 billion light-years away. This article has been updated to reflect that.