Powered by a supermassive black hole, the bright quasar spews out radiation that pushes away clouds of gas in its vicinity, creating winds reaching speeds of around 58 million kilometers per hour. 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 feeding supermassive black holes at the hearts of so-called “active galactic nuclei” or “AGN” may play in shaping the wider world. galaxies around them.
The scientists made their findings using eight years of data on the quasar SBS 1408+544, located 13 billion light-years away in the constellation Bootes. These data were collected as part of the Black Hole Mapper echo mapping project by the Sloan Digital Sky Survey (SDSS). Light from SBS 1408+544 traveled 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 heart of most galaxies, not all of these power quasars. Quasar black holes are surrounded by matter in a flattened swirling cloud called an “accretion disk”, which gradually supplies them with material.
The enormous gravitational influence of the quasar’s central supermassive black hole causes friction and tidal forces that heat the mass of the accretion disk, causing it to glow intensely. In addition, matter that is not fed into the supermassive black hole is directed to the poles of cosmic titania by strong magnetic fields, where it is accelerated to speeds close to the speed of light and ejected as highly collimated jets. These dual jets from each pole of the black hole are also accompanied by emissions of electromagnetic radiation.
Not only does this radiation make some quasars brighter than the combined light of all the stars in the galaxies around them, but this light also shapes those galaxies and offers astronomers a useful gauge for measuring the effect of black holes on galaxies in general.
“The material in it [accretion] the disk is always falling into the black hole, and the friction of that tug and pull heats it up and makes it very, very hot and very, very bright,” team leader and University of Wisconsin-Madison astronomy professor Catherine Grier said in an interview. “These quasars are really luminous, and because there is a large temperature range from the interior to the far reaches of the disk, their emission covers almost the entire electromagnetic spectrum.”
The bright light from this particular quasar allowed Grier and colleagues to observe 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 carbon atoms.
The team found that every time they measured this absorption spectrum during 130 observations of SBS 1408+544, there was a shift from the correct position of the carbon absorption “shadow”. This increased over time as radiation from the quasar dislodged material from its surroundings. This material created supermassive black hole winds that reached speeds of up to 36 million miles per hour (58 million kilometers per hour), about 45,000 times the speed of sound.
“This shift tells us that the gas is moving fast and getting faster,” 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 reflected from the accretion disk.”
Scientists had suspected that they had seen 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 orbit around them 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 their fuel, ending their days as quasar machines.
This could turn an active galaxy into a quiet one like the Milky Way, which, in addition to forming stars very slowly, 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 rather than push it away, triggering new bouts of star formation in their host galaxies.
Black hole winds like the ones the team saw could also travel beyond the edges 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 small compared to their galaxies,” Grier said. “That doesn’t mean they can’t ‘talk’ to each other, and it’s the way they talk to each other that we’ll have to take into account when we model the effects of these kinds of black holes.”
The team’s research was published in June in The Astrophysical Journal.