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enter image description here

I am referring to this picture published here. Apparently super massive black holes emit radiation and matter in astrophysical jets. And these jets can form galaxies. I have some questions:

  1. Isn't throwing out matter contrary to what a black hole is supposed to do? I imagine that the collapsing stars and gas falling into black hole would get super-heated and would emit energy as radiation but why would it throw out matter?

  2. The matter is said to leave at near speed of light. Can such fast moving jet condense to form a galaxy? If it does, shouldn't it be a stretched, thin thread like structure and not a Spiral galaxy as shown in the illustration?

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    $\begingroup$ Link to the original story (or better still, a journal paper) - it is impossible to write a sensible commentary on some artists impression. I almost guarantee that the astronomers will not have said anything is "zapping" something "into existence". $\endgroup$ – Rob Jeffries Dec 2 '14 at 15:00
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  1. No, throwing matter out isn't contrary to a BH; there is often an accretion disc surrounding the black hole and that is what forms the jet.
  2. No, the ejected material cannot condense to form a galaxy. A galaxy requires the material to be gravitationally bound to some central point, a jet moving at $\sim c$ is moving too fast to be gravitationally bound to anything.

As to the shape of the jet, it should be a stream, as evidenced by the Hubble Space Telescope image of Messier 87 (M87): enter image description here

but this is nowhere near the spiral shape of a galaxy.

The artist's impression of the situation is to show that the jet (the bright object in the upper left) from the black hole is illuminating a nearby galaxy (the object towards the right of your image). What researchers have further found is that the particular quasar, called HE0450-2958, appears to be inducing a high star formation rate in a nearby galaxy--a rate of about 100 times what is found in the Milky Way! It is based on this that the (likely misleading) title of the article Black Hole Caught Zapping Galaxy into Existence? is given.

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Black holes do explode after their life is over, thus vomiting out all the matter they ingested. Apologies for not providing credible explanation for my claim (in the form of mathematical equations). I read that (that black holes do explode) in Stephen Hawking's book titled Black Holes And Baby Universes. He stated that there is an inverse relation between the mass of a black hole and it's life expectancy.

Very "light" black holes have a life expectancy in the range of 10^18 years while very "heavy" black holes have a life expectancy between 10^12 or so years. This is what my rough recollection is. Read the original book if you want precise values.

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    $\begingroup$ The universe is on the order of $10^{10}$ years old, much shorter than the time scale for black hole evaporation. $\endgroup$ – George G Dec 2 '14 at 16:01
  • $\begingroup$ True. Notice that a) I did not state that as a fact. I stated that I read it in Hawking's book of given title. And b) I (or Hawking) did not state that any black hole has actually evaporated or not after the formation of universe. What I stated (and was probably misinterpreted) was that the life expectancy of the black holes is in the given range (again I stated clearly that I do not know the exact values), not that it has already happened. $\endgroup$ – Imran Roy Dec 2 '14 at 16:23
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    $\begingroup$ Well, you posted it as an answer and it does not address the question. $\endgroup$ – George G Dec 2 '14 at 17:14
  • $\begingroup$ This answer doesn't really seem to address the issue OP has. $\endgroup$ – Kyle Kanos Dec 2 '14 at 17:30

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