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Feasting Black Hole Blows Bubbles

A monstrous black hole's rude table manners include blowing huge bubbles of hot gas into space. At least, that's the practice of the supermassive black hole residing in the hub of the nearby galaxy NGC 4438 in the Virgo Cluster, 50 million light-years from Earth.

These NASA Hubble Space Telescope images of the galaxy's central region clearly show one of the bubbles rising from a dark band of dust. The other bubble, emanating from below the dust band, is barely visible, appearing as dim red blobs in the close-up picture of the galaxy's hub.

These extremely hot bubbles are caused by the black hole's voracious eating habits. The eating machine is engorging itself with a banquet of material swirling around it in an accretion disk (the white region below the bright bubble). Some of this material is spewed from the disk in opposite directions. Acting like high-powered garden hoses, these twin jets of matter sweep out material in their paths. The jets eventually slam into a wall of dense, slow-moving gas, which is traveling at less than 223,000 mph (360,000 kph). The collision produces the glowing material. The bubbles will continue to expand and will eventually dissipate. Compared with the life of the galaxy, this bubble-blowing phase is a short-lived event.

The bubble is much brighter on one side of the galaxy's center because the jet smashed into a denser amount of gas. The brighter bubble is 800 light-years tall and 800 light-years across.

Astronomers are concluding that monstrous black holes weren't simply born big but instead grew on a measured diet of gas and stars controlled by their host galaxies in the early formative years of the universe.

These results, gleaned from a NASA Hubble Space Telescope census of more than 30 galaxies with its powerful "black hole hunting" spectrograph, are painting a broad picture of a galaxy's evolution and its long and intimate relationship with its giant central black hole.

Though much more analysis remains, an initial look at Hubble evidence favors the idea that titanic black holes did not precede a galaxy's birth but instead co-evolved with the galaxy by trapping a surprisingly exact percentage (0.2%) of the mass of the bulbous hub of stars and gas in a galaxy.

This means that black holes in small galaxies went relatively undernourished, weighing in at a mere few million solar masses. Black holes in the centers of giant galaxies, some tipping the scale at over one billion solar masses, were so engorged with infalling gas that they once blazed as quasars, the brightest objects in the cosmos.

The bottom line is that the final mass of a black hole is not primordial; it is determined during the galaxy formation process. "This supports the original theory of why black holes are important and how they got their masses. It suggests that the major events that made a galaxy and the ones that made its black hole shine as a quasar were the same events," says John Kormendy of the University of Texas at Austin. "These results are a catalyst that help to tie together many lines of investigation on galaxy formation into a more believable and coherent picture."

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