| | | | 
Lawrence Berkeley National Lab | | Watching the Stars.
At the heart of the Sudbury Neutrino Observatory in Canada is a large
spherical vessel of water surrounded by 9500 photodetectors. It's one
of a handful of facilities worldwide that could glimpse a proto-neutron
star or witness the birth of a black hole. (Click image for larger
version.)
| | | | Astronomers
go to mountaintop observatories to get a good look at the sky, but the
best view might be over a mile underground inside neutrino detectors.
Neutrinos--neutral particles that regularly fly through the Earth
undetected--may provide astronomers with information that light cannot.
A paper in the 4 June PRL predicts that neutrinos
from proto-neutron stars might reveal the existence of exotic quark
matter inside these stars. It also shows that the presence of such
matter could lead to the birth of a black hole, an event the authors
believe could be detected from neutrino observations. When
a star explodes in a supernova, it leaves behind a dense core, called a
proto-neutron star, which contains an equal number of protons and
neutrons. The impulse from the supernova quickly converts the protons
into neutrons--a process that releases many energetic neutrinos.
Seconds after the explosion, the conversion is complete: The
proto-neutron star has become a neutron star--a cold, dead star made
primarily of neutrons. By the time the light and dust from the
supernova dissipate, the proto-neutron star is gone. "Observing
the neutrinos is the only way we can observe the proto-neutron star,"
says James Lattimer of the State University of New York (SUNY) at Stony
Brook. In 1987, detectors around the world recorded nearly twenty
neutrinos from a proto-neutron star in the heart of a supernova.
Neutrinos like these, Lattimer says, could provide information about
the life of such a star. In their paper, the SUNY team calculates the
neutrino energy that would be detected for proto-neutron stars made of
three proposed forms of "quark matter": matter in which quarks become
unglued from each other, matter filled with baryons containing strange
quarks, and matter filled with kaon particles, which also contain
strange quarks. In each case, the group describes a signature neutrino
signal that could be detected at facilities like the new Sudbury
Neutrino Observatory in Canada or Super-Kamiokande in Japan. The
team also shows that these detectors could watch black holes form.
Their calculations reveal that the presence of quark matter could
"soften" the proto-neutron star, making it easier to compress. In
certain cases, the team believes that this softening could cause the
proto-neutron star to collapse under its own gravity into a black hole.
If that happened, detectors on earth would see a sudden cessation of
neutrinos from the star. "You could catch the [black hole's formation]
during the time it's happening, and that's important," says Madappa
Prakash, the head of the SUNY group. "It's like catching a thief in the
act." The
new neutrino detectors will have "unprecedented sensitivity," says Adam
Burrows of the University of Arizona in Tucson. Burrows believes that
the SUNY team's calculations will help these detectors analyze neutrino
data from the next supernova. But until such an event occurs, he adds,
it will be impossible to tell exactly what a proto-neutron star looks
like. --Geoff Brumfiel | Evolution of Proto-Neutron Stars with Quarks
José
A. Pons, Andrew W. Steiner, Madappa Prakash, and James M. Lattimer
Phys. Rev. Lett. 86, 5223 (4 June 2001) | | | |
