[ExI] SETI reviews the Drake equation

[Stuart LaForge]

Quoting BillK:

> Yes, I wondered about the likelihood of the radio jet remaining
> constantly pointed at the Earth.

At this point I highly doubt that it would always be pointed at the  
Earth. If it were, that would either be very strong evidence that we  
live in a simulation or some crazy new physics that we just don't  
understand.

> Also it isn't a gamma ray burst. It's only a radio jet from
> 26,000 light years away with a lot of interstellar dust and gas
> between. So much dust that we can't see the source in the optical
> band. Doesn't that mean the radio jet would have little effect on the
> Earth?

You are right it isn't a gamma ray burst. Gamma ray bursts are very  
short lasting less than a minute and are believed to be caused when  
stellar mass black holes form during hypernovas. On the other hand, a  
quasar/blazar beam is formed by a super massive black hole within an  
active galactic nucleus. When a quasar gets its beam going, the  
resultant gamma rays, x rays, and so forth can last for years.

https://astroquizzical.com/astroquizzical/how-are-gamma-ray-jets-being-generated-from-black
https://arxiv.org/abs/1802.04714


The wimpy radio jet we are seeing now is because our galactic nucleus  
is not active. The black hole in the center does not have that big of  
an accretion disc to fuel its jet. The more gas swirling around the  
black hole, the more ions are produced in the friction heated gas as  
it swirls down into the black hole. These ions are forced to travel in  
a smaller and smaller spiral path as they get pulled down into the  
black hole like the vortex in your tub when you pull the drain plug.  
These electrically charged particles being accelerated into circular  
paths produce a helical magnetic field approximately perpendicular to  
the disk and parallel to the axis of the black hole's rotation.

This is called the synchrotron mechanism of x ray formation by  
quasars. According to Maxwell, the strength of the magnetic field is  
proportional the current or the number of ions and free electrons  
zipping around in the spiral path in a given time. The more gas, the  
stronger the magnetic field. As these ions get whipped around in these  
ever narrowing circular paths, they radiate electromagnetic waves  
similar to a free-electron laser with  a frequency dependent on the  
radius of the ions' circular path around the black hole.

A competing theory suggests x rays from quasars are formed by Compton  
scattering of the radio beam off of CMB photons. I am less clear how  
that mechanism is supposed to work but this might be a jumping off  
point for those who are curious:

https://iopscience.iop.org/article/10.1086/510452/fulltext/

In any case, active galactic nuclei or super massive black holes with  
large dense accretion disks radiate collimated beams of  
electromagnetic radiation with a wide frequency range from radio waves  
and microwaves all the way up to x rays and gamma rays like a gigantic  
wide-spectrum laser. The magnetic fields extending from the poles of  
the black hole also accelerate some of the ions into gigantic particle  
jets that move at almost the speed of light and can stretch for  
hundreds of thousands of light years for the biggest most powerful  
quasars.

https://iopscience.iop.org/article/10.1086/510452/fulltext/


So yes, right now Sagittarius A* does not have enough fuel for its  
radio jet to affect the Earth from that distance. But let the black  
hole start siphoning gas off of one of the supergiant stars found  
orbiting it in the galactic core and we are bound to see some  
fireworks. The question of the dust that obscures the galactic core  
from our optical telescopes is a good one. I don't know how effective  
the dust would be in shielding us from the quasar beam if Sagittarius  
A* starts feeding again. The beam is likely to cause one hell of a  
particle wind that could end up blowing all dust right out of the  
galaxy.

Stuart LaForge