In the Dark

Some interesting astronomy news emerged this evening relating to a paper published in 30th June issue of the journal Nature. The press release from the European Southern Observatory (ESO) is quite detailed, so I’ll refer you there for the minutiae, but in a nutshell:

A team of European astronomers has used ESO’s Very Large Telescope and a host of other telescopes to discover and study the most distant quasar found to date. This brilliant beacon, powered by a black hole with a mass two billion times that of the Sun, is by far the brightest object yet discovered in the early Universe.

and the interesting numbers are given here (with links from the press release):

The quasar that has just been found, named ULAS J1120+0641 [2], is seen as it was only 770 million years after the Big Bang (redshift 7.1, [3]). It took 12.9 billion years for its light to reach us.

Although more distant objects have been confirmed (such as a gamma-ray burst at redshift 8.2, eso0917, and a galaxy at redshift 8.6, eso1041), the newly discovered quasar is hundreds of times brighter than these. Amongst objects bright enough to be studied in detail, this is the most distant by a large margin.

When I was a lad, or at least a postdoc, the most distant objects known were quasars, although in those days the record holders had redshifts just over half that of the newly discovered one. Nowadays technology has improved so much that astronomers can detect “normal” galaxies at even higher redshifts but quasars remain interesting because of their extraordinary luminosity. The standard model for how a quasar can generate so much power involves a central black hole onto which matter falls, liberating vast amounts of gravitational energy.

You can understand how efficient this is by imagining a mass falling onto a black hole of Mass from a large distance to the horizon of the black hole, which is at the Schwarzschild radius . Since the gravitational potential energy at a radius is the energy involved in bringing a mass from infinity to the horizon is a staggering , i.e. half the rest mass energy of the infalling material. This is an overestimate  for various reasons but it gives you an idea of how much energy is available if you can get gravity to do the work; doing the calculation properly still gives an answer much higher than the amount of energy that can be released by, e.g., nuclear reactions.

The point is, though, that black holes aren’t built in a day, so if you see one so far away that its light has taken most of the age of the Universe to reach us then it tells us that its  black hole must have grown very quickly. This one seems to be a particularly massive one, which means it must have grown very quickly indeed. Through observations like this  we learn something potentially very interesting about the relationship between galaxies and their central black holes, and how they both form and evolve.

On the lighter side, ESO have also produced the following animation which I suppose is quite illustrative, but what are the sound effects all about?