How Green is My Universe?

The Australian 2dF Galaxy Redshift Survey, conducted from the 3.9-meter Anglo-Australian Observatory, is one of those large-scale, fundamental astronomy projects destined to produce results for decades to come. With its goal of obtaining high-quality spectra and redshifts for 250,000 galaxies, to a range of billions of light years from Earth, the survey has the potential of uncovering answers to fundamental questions in Cosmology.

You could spend years sifting through this survey data to determine truths about the Universe. But, is it possible to condense all that information into one succinct observation or truth that anyone on the street would immediately understand? Astronomers at John Hopkins University may have just done that.

The Cosmic Spectrum: Line graph of the intensity of all the optical energy in the measured Universe, by wavelength. Inset graphic: The Cosmic Spectrum in color -- intensity of a color is proportional to its intensity in the universe. The wavelengths of some of the elements responsible for these colors are indicated. Illustration here and below from Johns Hopkins University, "The Cosmic Spectrum and the Color of the Universe" web page by Karl Glazebrook & Ivan Baldry

Using methods that calculate the eye's response to different wavelengths of light, all the visible light spectra of the 2dF survey was combined. As a result, we now have the answer to a fundamental truth about the Universe that anyone will instantly understand. Yet, the question this truth answers is so basic that most of the population of the planet has never thought of it. Without any more suspense, the answer is "green" and the question is: "What color is the Universe?"

"The color is quite close to the standard shade of pale turqoise, although it's a few percent greener," says Karl Glazebrook, an assistant professor of astronomy at Johns Hopkins and one of the authors of a paper on the subject. His co-author, Ivan Baldry, a postdoctoral fellow at Hopkins, vouches for the veracity of the work: "We believe that the 2dF survey is large enough, reaching out several billion light years, to make this a truly representative sample."

Cosmic Spectrum as it would appear on a paint chip at a house paint store.

So, this is the color one would experience if all available light in the Universe were viewable at once. What makes the Universe green? Envy? Bad sushi? Glazebrook points out that, "from one perspective, it's surprising that it turns out to be greenish, because there are no green stars." But he points out that the answer is found in "the large numbers of old red stars and young blue stars in the universe that gives us the green."

The Universe was not always the lovely green it is today. Young blue stars dominated early in its lifetime, the current "green period" can be attributed to cosmic evolution to middle-age. In old-age the stellar population of the Universe will consist of many old red stars.

More information:
Johns Hopkins University; Jan. 10, 2002; Press Release: "Astronomers Determine Color of The Universe"

Iron Sun

We all learned in "Astronomy 101" that the Solar System formed from the coalescence of hydrogen and heavier material. Contracting under gravity, the central part of this "solar nebular" grew dense enough in hydrogen to start a fusion reaction, while material orbiting the center clumped into planetesimals and planets. The concentration of heavy elements -- especially iron -- is the give-away that the solar nebula was populated with material seeded by supernova explosions in prior generations of suns. In "Astronomy 101," this theory for the formation of the Solar System is the only one mentioned, with ongoing research being done to workout the details.

One researcher, Dr. Oliver Manuel, has been looking into these details for 40-years. He has studied "strange xenon" -- a xenon isotope released into the Universe when supernovas explode. In 1972, Manual co-authored a paper that indicated primitive meteorites contained a mix of strange and normal xenon. Subsequently, he and another researcher found that ancient helium in meteorites is only found in association with strange xenon. Dr. Manuel explains this by asserting that strange xenon is found in the helium-rich, outer layers of a supernova, and normal xenon inhabits the interior, where helium is absent due to it being converted into heavier elements by fusion.

Based on those strange xenon studies, Dr. Manuel has been advocating his own Solar System formation theory since 1975, and he's been trying to prove it ever since. (Anyone that got an 'A' in "Astronomy 101" must now brace themselves.) Dr. Manuel believes a spinning supernova exploded some five billion years ago. Debris from the explosion coalesced around the exploded core to form the Sun. Planets and other bodies in the Solar System were formed from supernova debris. In Dr. Manuel's view, the Sun should have an iron core that generates most of its heat, with hydrogen fusion taking place around it. In opposition to the standard view that the Sun is mostly hydrogen with a smattering of helium and other elements, Dr. Manuel believes that iron is the Sun's most abundant element.

In Dr. Manuel's theory, the gas giant outer planets are dominated by hydrogen, helium, and light elements because they were formed from material in the outer part of the supernova. Dr. Manuel believes the detection of strange xenon in Jupiter's helium-rich atmosphere, by the Galileo spacecraft, bolsters this claim. Earth and the rocky inner planets contain iron, other heavy elements, and no strange xenon because they formed out of material form the supernova's interior.

"We think that the solar system came from a single star, and the sun formed on a collapsed supernova core," says Manuel, who was scheduled to present a paper on the topic at the American Astronomical Society meeting in Washington, D.C. this month.

More information:
SpaceDaily.com; Jan 11, 2002; Solar Science: "Scientist Claims Sun Is Already An Iron Monger"

Scorched Earth

Dr. Robert Smith concludes that an event billions of years from now "is the ultimate justification for developing an International Space Station." The University of Sussex astronomer is referring to the eventual demise of life on Earth, as the Sun enters its final phase of life.

The textbooks tell us that one day the Sun will burn up the hydrogen fuel at its core. Without the outward pressure of hydrogen fusion the core will shrink, while hydrogen fusion continues in a shell outside the core. Eventually, the core will heat up as it shrinks: this heat will swell the hydrogen shell to an enormous size: the Sun will enter the red supergiant phase. Current textbooks say the Earth will be vaporized in 7.5-billion years, as the bloated Sun engulfs our planet.

Dr. Smith and his team took a new look at this scenario with the latest data and now believe the textbooks are wrong. Taking into account the mass loss of the aging Sun and decreased gravity, "the orbit of the Earth would increase beyond the Sun's outer atmosphere by a small but crucial margin at all phases of the Sun's evolution - allowing our planet to continue," says Smith.

His reckoning is that the surface of the Earth will become inhospitable in 5.7-billion years -- some 200-million years later than previously thought. Is there a way for people to escape the demise of Earth? Mars and the outer planets will still be there, but planet-hopping can only buy time as there will come periods when no planet will be safe for life. Dr. Smith suggests we get used to the idea of building "survival capsules" to wait it out -- hence the Space Station is the first step in that direction.

More information:
University of Sussex; Jan. 8,2002; Press Release: "Good News: How The Earth Will Survive When The Sun Becomes A Supergiant"