Paint it Black

Some time ago I mentioned that galaxies appear to form around supermassive black holes in an act of co-evolution. Once formed, the black holes act as 'hearts' to the galaxies, pumping energy out at regular intervals to regulate the growth of the black holes themselves, as well as promoting star formation. When they reach a certain size they eject hot plasma. This heat slows the formation of new stars and the growth of the black hole itself.

Another neat trick they seem to do is shoot out jets of high energy particles and fast moving gas. These travel at nearly the speed of light and emit radio waves. It has been speculated that most massive galaxies which contain black holes may have gone through an active stage where they spewed out jets, before settling down in the later history of the universe. In the early history of the universe these jets had a tendency to hit other galaxies, in the process carrying cold, neutral hydrogen gas and, intriguingly, water vapour. Cold gas happens to be a critical ingredient for star birth and these jets appear to have set off stellar baby booms.

One of the big questions in Cosmology has been which came first?, the supermassive black holes which we now see at the centre of galaxies, or the galaxies themselves. Now, new research published in the journals Astronomy & Astrophysics and Astrophysical Journal by David Elbaz of the Center for Nuclear Studies of Saclay may have provided an answer. A quasar (a type of black hole which releases incredibly intense jets of energy) was observed five billion light years away. It just so happens that this particular black hole doesn’t appear to have a galaxy around it. Elbaz and his team then noticed that a neighbouring galaxy was in the midst of a frantic burst of star formation at a rate of 350 suns per year. The reason for this is that the quasar is blasting the galaxy with a ray of particles and gas. In doing so it was effectively creating a host galaxy for itself since the two objects are on course to merge with each other. An article in science daily states:

Earlier observations had shown that the companion galaxy is, in fact, under fire: the quasar is spewing a jet of highly energetic particles towards its companion, accompanied by a stream of fast-moving gas. The injection of matter and energy into the galaxy indicates that the quasar itself might be inducing the formation of stars and thereby creating its own host galaxy; in such a scenario, galaxies would have evolved from clouds of gas hit by the energetic jets emerging from quasars.

"The two objects are bound to merge in the future: the quasar is moving at a speed of only a few tens of thousands of km/h with respect to the companion galaxy and their separation is only about 22 000 light-years," says Elbaz. "Although the quasar is still 'naked', it will eventually be 'dressed' when it merges with its star-rich companion. It will then finally reside inside a host galaxy like all other quasars." Hence, the team have identified black hole jets as a possible driver of galaxy formation, which may also represent the long-sought missing link to understanding why the mass of black holes is larger in galaxies that contain more stars

Elbaz says stars probably don’t form this way in our region of the universe since it is home to old galaxies and hardly any quasars (which would have a destructive effect on life if it got in the way). But “it might have had a substantial impact on galaxy formation in early times,” about 10 billion to 12 billion years ago, when most galaxies were born and quasars were much more common.

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