
Black hole jets can influence star formation in galaxies - dnetesn
http://phys.org/news/2016-11-black-hole-jets-star-formation.html
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antognini
This is a fairly technical paper, so it may be useful to provide a little more
context as to what the authors are doing. There are currently a number of open
questions in the field of galaxy formation, and there have been for quite some
time. Most of these questions center around a number of strange observations.

One open question is the origin of the M-sigma relation. This is a fairly
strong correlation that is observed between the masses of galaxies and the
masses of the supermassive black holes (SMBHs) that reside at their centers.
It is not known why a small object at the very center of a galaxy would seem
grow in lockstep with the global structure of the galaxy, many thousands of
light-years away.

Another open question is why massive galaxies have the masses that they do.
There is a joke in the galaxy formation community that there are only two
problems with galaxy mass predictions: predicting the mass of high-mass
galaxies, and predicting the mass of low-mass galaxies. Under standard models,
massive galaxies are predicted to be much more massive than currently
observed. Somehow, the surrounding gas in the intergalactic medium does not
get accreted onto these galaxies.

These observations have motivated the theory of "AGN feedback." The idea here
is that the SMBH at the center of a galaxy accretes gas from the surrounding
interstellar medium (ISM). As this gas falls onto the SMBH, it (somehow) forms
a jet, which then interacts with the ISM of the rest of the galaxy. We often
see these jets in radio wavelengths, where they're called FR I and FR II
sources. (I found a few new ones myself in my very first paper [1].) These
AGN-powered jets then (somehow) interact with the ISM in such a way as to
regulate the growth of the galaxy. They perhaps quench the flow of gas from
the intergalactic medium onto the galaxy. This then (hopefully) causes the
galaxy to not get too big, and the SMBH to grow in step with the growth of the
galaxy.

But there's are a lot of hand waving that goes with AGN feedback as its
currently understood. Firstly, it's not clear how the SMBH actually forms a
jet in the first place and what the jet is made of. (There are good theories
like the Blandford-Znajek mechanism, but I don't think they've been
definitively proven.) And it's not well understood how the jet itself actually
interacts with the ISM. It can heat up the ISM in a bubble somewhere, but it's
not obvious how that quenches inflows onto the galaxy in other places.
Furthermore, it's thought, but not definitively known, that these jets can
promote star formation.

The galaxy studied in this paper, IC 5063, seems to be a good candidate to
study because the jet happens to pass nearly through the plane of the galaxy,
so the interaction between the jet and the ISM is fairly large. With the ALMA
telescope now starting to collect science data, it's possible to observe this
interaction at much higher resolution than was before possible.

Based on my reading of this paper, the main result seems to be that the jet-
driven wind is partially optically thin rather than optically thick. This
means that earlier estimates of the molecular mass of the jet-driven winds
were too high, by about an order of magnitude. But this seems to be a
preliminary result, and the authors will do a more thorough calculation when
the rest of the ALMA data comes in.

[1]:
[http://adsabs.harvard.edu/abs/2012ApJ...756..116A](http://adsabs.harvard.edu/abs/2012ApJ...756..116A)

~~~
JumpCrisscross
Do the jets create galaxy-wide magnetic fields? Is the intergalactic medium
charged?

~~~
antognini
The ISM is not charged. Most of it is ionized, however.

The jet itself has a magnetic field that is largely parallel to the jet,
though it gets tangled up in the "bubble" that the jet blows in the ISM. The
bubbles can be quite large (comparable to the size of the galaxy itself), but
are usually outside the galaxy. I don't believe that the jet much changes the
magnetic field of the ISM anywhere away from the jet.

------
Pica_soO
Imagine if you could influence the direction a black hole aims- what a
fantastic interstellar raygun this would make.

First sign of intelligent life is it wiping itself from the galactic map.

~~~
JumpCrisscross
Genuinely curious now. What is the ratio between the energy it takes to rotate
a black hole and the energy it takes to make a new one with the correct
orientation?

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visarga
Engines of destruction and creation. Wonderment

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thesz
If anyone read the New Cosmogony by Stanislaw Lem, he would instantly conclude
that higher powers are not quite fond of organic life, just from the existence
of such beams. The fact that rays can wipe out stars (or, at least, preclude
their formation) only strengthen that conclusion as stars are necessary for
organic life to form.

