

Bizarre Star Could Host a Neutron Star in Its Core - deeths
http://www.scientificamerican.com/article.cfm?id=bizarre-star-could-host-a-neutron-star-in-its-core

======
ChuckMcM
original paper:
[http://adsabs.harvard.edu/full/1989ApJ...346..277E](http://adsabs.harvard.edu/full/1989ApJ...346..277E)
discussing the concept. Fusion would happen on the surface of the neutron
star. An interesting concept. I suppose if a neutron star entered a gas cloud
you could get one of these.

Edit: Not the _original_ paper but a follow on how these stars would work,
refuting other papers that said they were impossible :-)

------
JoeAltmaier
Could use them as cardinal points in a galactic map, if they're that rare.
Maybe they are actually galactic navigational beacons!

------
TrainedMonkey
Found more detailed explanation of what they are:
[http://cow.physics.wisc.edu/~ogelman/guide/tz/](http://cow.physics.wisc.edu/~ogelman/guide/tz/)

~~~
deeths
Great link!

The TL;DR:

Because the density of the neutron star and the Red Giant are so different
(average Red Giant density is about the same density as water), the neutron
star can keep a distinct structure/orbit for 1000 years or so. When it gets to
the core, fusion occurs in a halo around the neutron star instead of through
the normal sort of fusion you'd get in a Red Giant core. This leads to a
different ratio of nuclear isotopes, which is how you can determine these
objects aren't typical Red Giants.

The resulting objects survive around 70 million years before the neutron star
core absorbs enough mass to turn into a black hole (one of the other linked
papers in this thread had some discussion on how long they might be stable).
However, the predicted rate of birth/death of these objects indicates there
may be a few of these in the galaxy at any given time.

------
mrfusion
So as a follow up question. What happens if a black hole falls into a super
nova? And bonus question: what happens if a black hole falls into a neutron
star?

~~~
analog31
Thinking as a physics generalist but not an astronomer, I'd describe these
things as:

1\. Super nova happens near a black hole. Stuff (including photons) that
emanate with a speed and direction sufficient to overcome the escape velocity
of the system will have happy sailing. Photons at the speed of light, massive
stuff slowed down. The rest will be sucked into the hole. The result would be
a directional burst that favors photons over massive material.

2\. Same as saying that a neutron star falls into black hole.

------
brianpgordon
Where does fusion occur then? At the surface of the neutron star? Or is the
star supported by the kinetic energy of matter falling onto the inner star?

~~~
TrainedMonkey
Both. Red giants exhausted supply of hydrogen in the core, so fusion is
switched to shell. This causes pressure/temperature of red giant to drop
dramatically and radius to balloon. Neutron stars are incredibly dense, so
under certain conditions collision of red giant with neutron start could work
out.

------
larubbio
I wished the article went into more detail about how it could form. My hazy
memory of astronomy from college, I thought matter falling onto a neutron star
from a companion star was how a type IIa supernova occurred. How would the
neutron star be "swallowed" without triggering the nova?

~~~
TrainedMonkey
I am not sure if we understand formation process of such stellar objects in
general (Or possibly many processes). According to wikipedia one theory is
slow orbit degradation of binary system containing neutron star and red dwarf:
[http://en.wikipedia.org/wiki/Thorne%E2%80%93%C5%BBytkow_obje...](http://en.wikipedia.org/wiki/Thorne%E2%80%93%C5%BBytkow_object)

This makes me want to see a simulation of this happening.

