September 6, 2013
Black Hole Jets Expelling Gas From Host Galaxy
April Flowers for redOrbit.com - Your Universe Online
A worldwide network of radio telescopes has allowed astronomers to find strong evidence that a powerful jet of material, propelled to nearly light speed by the central black hole of a galaxy, is blowing massive amounts of gas out of the host galaxy. The scientists say the process is limiting the growth of the black hole and the rate of star formation in the galaxy. That makes the process a key to understanding how galaxies develop.
According to prevailing theories, galaxies should be more massive and have more stars than is actually the case. Two major mechanisms have been proposed that would slow or halt the process of mass growth and star formation: pushback from the jets powered by the galaxy’s central, massive blackhole, and violent stellar winds from bursts of star formation.
"With the finely-detailed images provided by an intercontinental combination of radio telescopes, we have been able to see massive clumps of cold gas being pushed away from the galaxy's center by the black-hole-powered jets," said Raffaella Morganti, of the Netherlands Institute for Radio Astronomy and the University of Groningen.
Galaxy 4C12.50, nearly 1.5 billion light-years from Earth, was chosen for study because it is at a stage where the black hole "engine" that produces the jets is just turning on. The concentration of mass in a black hole is so dense that not even light can escape, and material is pulled in towards it, forming a swirling disk surrounding the black hole. The tremendous gravitational energy of the black hole is tapped by processes in the disk to propel material outward from the disk's poles.
The team's findings were published in a recent issue of Science.
The scientists found clumps of hydrogen gas moving outward from the galaxy at just over 600 miles a second at the ends of both jets. The clouds are massive: one is approximately 16,000 times the mass of our Sun, while the other is 140,000 times the mass. According to the scientists, the larger cloud is roughly 160 by 190 light-years in size.
"This is the most definitive evidence yet for an interaction between the swift-moving jet of such a galaxy and a dense interstellar gas cloud," Morganti said. "We believe we are seeing in action the process by which an active, central engine can remove gas - the raw material for star formation - from a young galaxy," she added.
According to observations, the jets from the galaxy's core can stretch and deform clouds of interstellar gas to expand their "pushing" effect beyond the narrow width of the jets themselves. At the current stage of development for 4C12.50, the jets may turn on and off, and thus periodically repeat the process of removing gas from the galaxy.
Using the Atacama Large Millimeter/submillimeter Array (ALMA), another team of scientists announced in July that they had found gas being blown from a more nearby galaxy, called NGC 253, by an intense burst of star formation.
"Both processes are thought to be at work, often simultaneously, in young galaxies to regulate the growth of their central black holes as well as the rate at which they can form new stars," Morganti said.
The current team combined the signals from radio telescopes in Europe and the US to essentially make one giant, intercontinental telescope. The US telescopes included the National Science Foundation's Very Long Baseline Array (VLBA) - a continent-wide system of radio telescopes ranging from Hawaii, across the U.S. mainland, to St. Croix in the Virgin Islands - and one antenna from the Karl G. Jansky Very Large Array (VLA) in New Mexico.
In Europe, they used telescopes in Effelsberg, Germany; Westerbork, the Netherlands; and Onsala, Sweden. Such a far-flung system created extremely high resolving power – the ability to see fine detail – and was essential to pinpointing the location of the gas clouds affected by the galaxy's jets.