A bright quasar powered by a supermassive black hole shoots out radiation that pushes clouds of gas into its surroundings to generate winds reaching speeds of about 36 million miles per hour (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, shows the role that powering supermassive black holes at the hearts of so-called “active galactic nuclei” or “AGN” can play in sculpting a wider galaxies around them.
The researchers made their findings using eight years of data on the quasar SBS 1408+544, located 13 billion light-years away in the constellation Volovar. This data was collected by the Black Hole Mapper Reverberation Mapping Project carried out by the Sloan Digital Sky Survey (SDSS). Light from SBS 1408+544 has been traveling to Earth for 13 billion years; that’s almost as long as the universe has existed at 13.8 billion years.
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Although 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 quasars. Quasar black holes are surrounded by matter in a flattened, rotating cloud called an “accretion disk,” which gradually feeds them material.
The immense gravitational influence of the quasar’s central supermassive black hole causes friction and tidal forces that heat the material in the accretion disk, causing it to glow intensely. In addition, matter not fed by the supermassive black hole is driven to the cosmic titan’s poles by powerful magnetic fields, where it is accelerated to near-light speed and ejected as highly collimated jets. These twin jets from each pole of a black hole are also accompanied by emissions of electromagnetic radiation.
This radiation not only makes 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 measure for astronomers to measure the influence that black holes have on galaxies as a whole.
“The material in it [accretion] the disc is always falling into the black hole, and the friction from that tugging and tugging heats the disc and makes it very, very hot and very, very bright,” team leader and University of Wisconsin-Madison astronomy professor Kathryn Greer said in a statement. “These quasars are truly luminous, and because there is a large range of temperatures from the interior to the far reaches of the disk, their radiation covers almost the entire electromagnetic spectrum.”
The bright light from this particular quasar allowed Greer and his colleagues to trace the winds of gaseous carbon. This was done by measuring gaps in the broad spectrum of electromagnetic radiation emitted by the quasar, which indicated that the light was being absorbed by the 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 correct position of the carbon absorption “shadow”. This increases over time as radiation from the quasar repels the material around it. This material forms the supermassive black hole winds, which reach speeds of up to 36 million miles per hour (58 million kilometers per hour), which is about 45,000 times the speed of sound.
“This change tells us that the gas is moving fast and faster all the time,” said team co-leader and University of Wisconsin-Madison astronomy graduate student Robert Wheatley. “The wind accelerates because it is pushed by radiation that is ejected from the accretion disk.”
Scientists have suspected that they have spotted accelerating supermassive black hole winds before, but this is the first time the observation has been backed up with hard evidence. Such cosmic winds are of great interest to astronomers because the gas they blow away serves as the building blocks of stars. This means that if black hole winds are strong enough, they can interrupt star formation, thereby “killing” their host galaxies. They can also deprive central supermassive black holes of fuel, ending their days as quasar machines.
This can 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, winds from supermassive black holes could compress the gas instead of expelling it, triggering new bouts of star formation in their host galaxies.
Black hole winds like the kind observed by the team could also travel beyond the outskirts of their galaxies, affecting neighboring galaxies and, ultimately, the neighboring supermassive black holes at the heart of those galaxies.
“Supermassive black holes are big, but they’re really small compared to their galaxies,” Greer said. “That doesn’t mean they can’t ‘talk’ to each other, and it’s a way for one to talk to the other that we’ll need to account for when we model the effects of these types of black holes.”
The team’s research was published in June in The Astrophysical Journal.
