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The Question
(Submitted April 15, 1997)
I just finished reading Kip Thorne's book "Black Holes and Time Warps".
I seem to recall an article in the last 6 months or so, I thought from
the NY Times Science pages, about a new theory on collapsing stars that
allowed for black holes to form from stars much smaller than previously
thought. The mechanism as I recall was for a short burst of radiation
release such that the neutron pressure that normally keeps the star from
collapsing is released. I recall that one of the authors was in his
80's and the other in his 90's. Could you give me a reference to this
work?
The Answer
I believe you are referring to a paper by Gerald Brown
with Hans Bethe called "A Scenario for a Large Number of Low-Mass
Black Holes in the Galaxy". The paper was published in the
Astrophysical Journal, volume 423, page 659, in March 1994.
The mechanism they propose "softens" the equation governing
the collapse of a neutron star so that stars with lower mass
that previously thought can produce black holes after a supernova
explosion. Hans Bethe turned 90 years old this past July, and
was presented by the APS with a prize that will be set up in his
name. The prize will be awarded annually to an astronomer or
nuclear physicist (or someone who is both!). Hans considers
himself both an astronomer and a nuclear physicist, and is the
person who explained the generation of energy in the Sun by
the fusion of hydrogen to helium. He won the Nobel prize for
this research in 1967. He is a national treasure, and as
you will see at
http://www.nobel.se/physics/laureates/1967/bethe-bio.html
he is still a vibrant and happy member of the physics community.
In fact, he is still publishing. His latest paper in the
"Ap. J" was in December, on Supernova Shocks.
I'm sorry I don't know the age of the other author of the
paper.
Here's the blurb about the project that appeared in
Physics News Update:
August 25, 1993
WHY DON'T MORE SUPERNOVAS LEAVE BEHIND PULSARS? The
venerable Hans Bethe, pioneer in the study of stellar
nuclear physics for decades, and Gerald Brown of Stony
Brook, propose that some collapsing stars---with masses as
low as 18 solar masses---refrain temporarily from
vanishing into a black hole and instead pause at the
neutron-star level of compactification long enough to
trigger a supernova explosion. The residual core would
thereafter shrink without a trace into a black hole. Bethe
and Brown invoke a hypothesis about neutron stars
introduced in the last few years by Brown and others.
According to this model, as the density at the core of a
collapsing star exceeds three times the density of
ordinary matter, electrons might not necessarily combine
with protons to form neutrons, as was thought, but might
instead spawn K mesons and neutrinos. In place of the
traditional pure neutron matter, the collapsing core would
then be a more compressible mixture of protons and
neutrons, buoyed up for a time by the restless motions of
the neutrinos. When they depart the collapse would
continue, leaving behind either a "nucleon star" or a
black hole. (Science, 13 August 1993.)
Regards,
Padi Boyd,
for the Ask a High-Energy Astronomer team
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