Black Holes May Not Grow Beyond Certain Limit

xyz writes "Do black holes increase in size indefinitely? According to an analysis by astronomers at Yale and the European Southern Observatory, the maximum size a black hole may reach is only few tens of billion of solar masses. The limit was calculated using an analysis of what may happen to the gas surrounding a black hole which has reached few tens of billions of solar masses. It is thought that black holes of such size heat the surrounding gas to a temperature where the radiation pressure begins blowing outer layers into space."

Comments

Re:Interesting repercussions

[Bemopolis]

or one, does this means that stars are continously recycled by the black hole believed to be at the center of each galaxy? i.e. They get sucked in, crushed, then ejected as gassous emmisions which then collect and reform as a new star.

What happens, roughly, is that stars that stray too close to the black hole are torn apart by the tidal forces, their constituent gas adding to a large torus of gas orbiting the black hole. Some fraction of this torus loses enough angular momentum to either fall into the event horizon of the black hole, lost "forever" (astronomically speaking), or a grazing collision that gives it enough energy to avoid being sucked in. This gas can form a galactic wind of sorts: that flow becomes collimated by the high spin rate of the black hole and the torus of gas around it. This produces jets like those seen emanating from the core of M87. That gas, with its high temperature and flow rate, will not cool to a low enough temperature to coalesce into new stars any time "soon" (astronomically speaking.)

Now, there are flows that involve gas being ejected from the disk of the galaxy with less energy, which can rain back down onto the disk and contribute to newly-formed stars. But these "champagne flows" are usully caused not by the energetics of the central black holes, but rather the collective stellar winds from the stars in the disk; for example, the galactic superwind of M82

In both cases, the thermal energy of the ejecta is insufficient to explain the gravitational anomalies you mention.

Re:Tens of billion?

[gv250]

There are 10^11 stars in the galaxy. That used to be a huge number. But it's only a hundred billion. It's less than the national deficit! We used to call them astronomical numbers. Now we should call them economical numbers.
Richard Feynman, US educator & physicist (1918 - 1988)
http://www.quotationspage.com/quote/26930.html