a simulation of the powerful jets generated by supermassive black holes at the centers of the largest
1 explains why some burst
2 as bright
3 visible across the universe, while others fall apart and never pierce the halo of the
4. about 10 percent of all galaxies with active
5 - all presumed to have supermassive black holes within the central
6 - are observed to have jets of gas
7 in opposite directions from the core. the hot ionized gas is propelled by the twisting magnetic fields of the rotating black hole, which can be as large as several billion suns.
a 40-year-old puzzle was why some jets are hefty and punch out of the galaxy into intergalactic space, while others are narrow and often fizzle out before reaching the edge of the galaxy. the answer could shed light on how galaxies and their central black holes evolve, since
8 jets are thought to
9 the galaxy and slow star formation, while also slowing the infall of gas that has been feeding the
10 black hole. the model could also help
11 understand other types of jets, such as those produced by individual stars, which we see as gamma-ray bursts or pulsars.
"whereas it was rather easy to reproduce the stable jets in simulations, it turned out to be an extreme challenge to explain what causes the jets to fall apart," said university of california, berkeley theoretical astrophysicist alexander tchekhovskoy, a nasa einstein postdoctoral fellow, who led the project. "to explain why some jets are
12, researchers had to resort to explanations such as red giant stars in the jets' path loading the jets with too much gas and making them heavy and unstable so that the jets fall apart."
by taking into account the magnetic fields that generate these jets, tchekhovskoy and colleague omer bromberg, a former lyman spitzer jr. postdoctoral fellow at princeton university, discovered that magnetic instabilities in the jet determine their fate. if the jet is not powerful enough to
13 the surrounding gas, the jet becomes narrow or collimated, a shape
14 to kinking and breaking. when this happens, the hot ionized gas
15 through the magnetic field spews into the galaxy,
16 a hot bubble of gas that generally heats up the galaxy.
powerful jets, however, are broader and able to punch through the surrounding gas into the intergalactic medium. the determining factors are the power of the jet and how quickly the gas
17 drops off with distance, typically dependent on the mass and
18 of the galaxy core.
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