Astronomers using the National Science Foundation’s 140 Foot Radio
Telescope in Green Bank, W.Va., were able to infer the amount of matter
created by the Big Bang, and confirmed that it accounts for only a small
portion of the effects of gravity observed in the Universe. The
scientists were able to make these conclusions by determining the
abundance of the rare element helium-3 (helium with only one neutron and
two protons in its nucleus) in the Milky Way Galaxy.

“Moments after the Big Bang, protons and neutrons began to combine to
form helium-3 and other basic elements,” said Robert Rood of the
University of Virginia. “By accurately measuring the abundance of this
primordial element in our Galaxy today, we were able infer just how much
matter was created when the Universe was only a few minutes old.” Rood
and his colleagues, Thomas Bania from Boston University and Dana Balser
from the National Radio Astronomy Observatory (NRAO), report their
findings in the January 3 edition of the scientific journal Nature.

Rood began searching for helium-3 in the Milky Way Galaxy in 1978. At
that time, scientists believed that stars like our Sun synthesized
helium-3 in their nuclear furnaces. Surprisingly, Rood’s observations
indicated that there was far less of this element in the Galaxy than the
current models predicted. “If stars were indeed producing helium-3, as
scientists believed, then we should have detected this element in much
greater concentrations,” he said.

This unexpected discovery prompted Rood and his colleagues to broaden
their search, and to look throughout the Milky Way for signs of stellar
production of helium-3. Over the course of two decades, the researchers
discovered that regardless of where they looked – whether in the areas
of sparse star formation like the outer edges of the Galaxy, or in areas
of intense star formation near center of the Galaxy – the relative
abundance of helium-3 remained constant. By concurrently measuring the
amount hydrogen (also created by the Big Bang) in the same areas, the
scientists were able to determine the relative abundance of helium-3.

“Since stellar processes appear to have little or no impact on the
amount of helium-3 in the Galaxy, we were able to deduce two very
important things,” said Bania. “First, since our current models predict
stellar production of helium-3, then we will need to rethink our
understanding of the internal workings of stars like our Sun. Second,
since helium-3 has not been created or destroyed in our Galaxy in any
appreciable amounts, then what we detected is most likely equal to the
abundance of primordial helium-3 created by the Big Bang.”

The scientists were able to use this discovery to calculate how much
“normal” matter was created during the Big Bang. (Normal matter is
anything made of baryons, subatomic particles that include neutrons and
protons.) The researchers made these calculations by taking what they
know of the composition of the Universe today, and essentially running
time in reverse. In this case, the ratio of helium-3 to hydrogen gives
the ratio of baryons to photons (the density of radiation) just after
the Big Bang. By using the rate of expansion of the Universe, given by
the Hubble Constant, the scientists could then infer just how much
normal matter was produced during the Big Bang.

“Our findings for helium-3 in fact support other studies that also
constrain the amount of matter in the Universe,” said Balser. “Taken
together, these studies show that the matter that makes up stars,
planets, and the visible Universe can only account for a small fraction
of what we observe as the effects gravity in the Universe.”

Dark matter, which can be both baryonic (dead stars, rocks, etc.) and
non-baryonic, and other as-yet-unidentified forces appear to be the
primary sources of the gravity that holds galaxies, and the larger
structures of the Universe together. “The fact that most of the matter
in the Universe is non-baryonic, that is to say not made of any particle
we’ve ever seen on Earth, is a very exciting concept,” commented Rood.

The astronomers conducted their research using measurements at a
frequency of 8.665 GHz (3.46 cm), which is emitted naturally by ionized

The 140 Foot Radio Telescope at the NRAO in Green Bank now is
decommissioned after a long and highly productive career. “Though the
140 Foot Telescope enabled us to make remarkable observations,”
commented Rood, “we anticipate that the new Robert C. Byrd Green Bank
Telescope will greatly increase our ability to continue this research.”

The National Radio Astronomy Observatory is a facility of the National
Science Foundation, operated under cooperative agreement by Associated
Universities, Inc.

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Robert Rood

Phone: (434) 924-4886


Thomas Bania

Phone: (617) 353-3652


Dana Balser

Phone: (304) 456-2204