deuterium_galactic_000628 Call it a gentle rain from near the beginning of time.
Scientists who used a radio telescope to study a gargantuan gas cloud said they made the first definitive measurements of deuterium -- a heavy form of hydrogen -- near the center of our Milky Way Galaxy.
Moreover, they found more deuterium there than they expected -- indicating the deuterium comes from primordial gas that is raining into the galaxy, the researchers argued. "This is evidence that very old gas is constantly flowing into the Milky Way," said astronomer Donald Lubowich of the American Institute of Physics and Hofstra University.
"It could be from the birth of the universe or the birth of the galaxy. I can't distinguish between the two. I do know it's coming from material that's 10 billion to 12 billion years old," he said. Lubowich is an author of the study, published in the June 29 issue of the journal Nature.
Many researchers have argued all deuterium was made within a few minutes of the
Big Bang that formed the universe 13 billion to 15 billion years ago. Elements heavier than carbon were made inside stars 1 billion to 2 billion years later, Lubowich said. Deuterium-to-hydrogen ratios in gas left over from the Big Bang reveal the density of ordinary matter in the early universe. Most deuterium is burned in stars and becomes helium. Lubowich said his measurements were consistent with deuterium levels that would be expected if only a fraction of the universe was made of ordinary matter, with the rest made of yet-unidentified "dark matter" and "dark energy." He also said the study also shows the Milky Way has far too little deuterium to ever have been a super-bright galaxy known as a quasar.
Finding deuterium near the galactic center "is a real tour de force," said Michael Turner, University of Chicago astrophysics chairman. "It's only been measured in a few places."
The study "supports the view that
deuterium was only made in the Big Bang," said Turner.However, Princeton University physicist James Peebles and astronomer Edward Jenkins questioned how Lubowich could be sure most of the deuterium he measured was primordial.
Lubowich said that if the deuterium was produced by stars, elements also made by stars would be present in much higher levels than have been measured.
If the deuterium was an unburned leftover from dead stars, the researchers should have found one part deuterium for every trillion parts of hydrogen. Instead, they found 1.7 parts per million -- far more than expected, indicating primordial deuterium is raining in from intergalactic space or the edges of the Milky Way, Lubowich said.
Dark matters
The argument that very little matter is ordinary matter is based on deuterium abundance. Deuterium-hydrogen ratios found at the galactic center are consistent with estimates that ordinary matter constitutes only 3 percent to 5 percent of the "critical density" needed for the universe ultimately to collapse under its own gravity, Italian astronomer Francesca Matteucci said in a commentary accompanying the study.
That implies most matter is mysterious "
dark matter," and also that ordinary and dark matter together provide "only one third of the critical density needed to close the universe," she said.That, in turn, suggests the universe is "open" and will expand forever, she said by e-mail from Trieste, Italy. Turner, however, said that ignores recent evidence that the universe is "flat," which makes it essentially impossible to determine if the universe will collapse or expand forever.
Lubowich conducted the study with researchers Jay Pasachoff of Williams College, Thomas Balonek of Colgate University, Tom Millar of Manchester University and a few students. They used the National Radio Astronomy Observatory (NRAO) Millimeter Wave Telescope at Kitt Peak, Arizona to detect microwave frequencies emitted by the different rotation rates of hydrogen and deuterium in cyanide gas molecules.
The gases were in the Sagittarius A gas cloud roughly 32 light-years from the center of the 100,000-light-year-wide Milky Way. Earth is 25,000 light-years from the center. (A light-year is 5.88 trillion miles, or 9.5 trillion kilometers).
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