Contact: Richard Boyd
Boyd.10@osu.edu
614-292-2875
Ohio State University
COLUMBUS, Ohio – The next time a distant supernova glitters
in the night sky, scientists may be able to solve a mystery about
subatomic particles here on Earth.
An Ohio State University astrophysicist and his colleagues have
devised a way to use the speed of material streaming outward
from a supernova to measure the mass of an elusive subatomic
particle known as the neutrino.
Knowing the mass of this particle may help scientists better
understand nuclear reactions inside stars, as well as the so-called
missing dark matter of the universe, said Richard Boyd, professor
of physics and astronomy at Ohio State.
Scientists currently believe
that three types of neutrinos
exist, each with a different
mass some ten thousand times
less than the mass of an
electron, Boyd explained.
If so, then heavier neutrinos
ejected from a supernova will
take longer to reach Earth
than lighter neutrinos, Boyd
and his coauthors wrote in a
recent issue of Physical
Review Letters.
Boyd’s collaborators include John Beacom, formerly a
postdoctoral researcher at the California Institute of Technology
and now a research fellow at Fermi National Accelerator
Laboratory; and Anthony Mezzacappa, head of the Supernova
Theory Group at Oak Ridge National Laboratory.
Boyd described neutrinos as the key to scientists’ understanding
of the nuclear reactions that take place in stars. According to
current theories, millions of neutrinos should be radiating out of
our sun, or other stars, every second.
“If we don’t know the mass of neutrinos, then we can’t use that
information to test our theories,” Boyd said. “These extremely
small masses are hard to measure here on Earth, but if we could
measure the differences in flight time of neutrinos from a
supernova, we could improve our measurements a million times
over.”
Neutrinos are the most penetrating subatomic particles known,
Boyd said. They pass easily through stars, the Earth — and very
often through solid lead. Scientists have built giant underground
water tanks to catch neutrinos that pass through.
While many neutrino-induced events have been observed, no one
has succeeded in measuring the masses of neutrinos, despite
decades of effort. At the same time, scientists have been working
to explain certain gravitational effects that indicate much of the
mass of the universe may be made of unseen, or “dark,” matter.
If neutrinos exist in the numbers scientists expect, even with a tiny
mass, then they make an ideal candidate for dark matter, because
they are both abundant and nearly invisible.
The researchers’ new technique for measuring neutrino mass
hinges on the idea that about half of the supernovas that occur in
the future — at least, the ones we can observe from Earth — will
spawn black holes.
Only a small portion of stars end their lives in supernovas —
cataclysmic explosions so bright that the star may temporarily
outshine its home galaxy. While only a handful of supernovas
have been recorded in the Milky Way Galaxy since the early 17th
century, all have occurred close to Earth. This suggests that most
galactic supernovas are hidden from astronomers’ view. But they
would not be at all hidden from the supernova neutrino detectors,
Boyd said.
Boyd explained that as an exploding star collapsed to form a
black hole, the star could release 99 percent of its final energy in
the form of neutrinos. The very last neutrinos released would all
have to leave the star at the same time — just before the black
hole formed.
Like the crack of a starting pistol before a race, the instant when
a black hole forms could give researchers a definite starting point
for timing a neutrino’s journey from a supernova to Earth.
As the neutrinos raced to Earth, heavier neutrinos should fall
behind lighter neutrinos, if only by a second or two in tens of
thousands of years of travel, Boyd said.
“It’s a very small time shift, but one we can measure,” he added.
“And it would allow us the most precise way we’ve ever had of
detecting the masses of neutrinos.”
Boyd estimates that Earth will witness at least a few supernovas
in the next hundred years.
Ohio State is one of a team of institutions collaborating on the
design of a new detector, the Observatory for Multiflavor
Neutrinos from Supernovae (OMNIS). The word “multiflavor”
refers to scientists’ dubbing of the three different types of
neutrinos as different “flavors” of the particle.
If OMNIS secures the funding it plans to request from the
National Science Foundation (NSF) and the Department of
Energy, the member institutions will construct a lead and iron
detector in a salt mine in New Mexico. Today’s detectors can
only detect one type of neutrino, but the OMNIS detector will be
able to detect the other two, Boyd said.
Scientists expect all three types of neutrinos to be emitted from a
supernova. The challenge is to determine which type has been
detected, Boyd said. OMNIS will be able to detect the two
types other detectors would see only very faintly.
Boyd’s part of the collaboration was funded by the NSF.
Mezzacappa received support from Oak Ridge National
Laboratory, managed by the non-profit company UT-Battelle,
LLC, for the U.S. Department of Energy. Beacom’s work was
funded by the California Institute of Technology.
Contact: Richard Boyd, Boyd.10@osu.edu, 614-292-2875;
Written by Pam Frost Gorder, Gorder.1@osu.edu, 614-292-9475
