Posted: 29 Nov 2010 02:24 PM PST
A century of comet data suggests a dark, Jupiter-sized object is lurking at the solar system's outer edge and hurling chunks of ice and dust toward Earth.
"We've accumulated 10 years' more data, double the comets we viewed to test this hypothesis," said planetary scientist John Matese of the University of Louisiana. "Only now should we be able to falsify or verify that you could have a Jupiter-mass object out there."
In 1999, Matese and colleague Daniel Whitmire suggested the sun has a hidden companion that boots icy bodies from the Oort Cloud, a spherical haze of comets at the solar system's fringes, into the inner solar system where we can see them.
In a new analysis of observations dating back to 1898, Matese and Whitmire confirm their original idea: About 20 percent of the comets visible from Earth were sent by a dark, distant planet.
This idea was a reaction to an earlier notion that a dim brown-dwarf or red-dwarf star, ominously dubbed Nemesis, has pummeled the Earth with deadly comet showers every 30 million years or so. Later research suggested that mass extinctions on Earth don't line up with the Nemesis predictions, so many astronomers now think that object doesn't exist.
"But we began to ask, what kind of an object could you hope to infer from the present data that we are seeing?" Matese said. "What could possibly tickle [comets'] orbits and make them come very close to the sun so we could see them?"
Rather than a malevolent death star, a smaller and more benign companion called Tyche (Nemesis' good sister in Greek mythology) could send comets streaming from the Oort Cloud toward Earth.
The cosmic snowballs that form the hearts of comets generally hang out in the Oort Cloud until their orbits are nudged by some outside force. This push could come from one of three things, Matese said. The constant gravitational pull of the Milky Way's disk can drag comets out of their icy homes and into the inner solar system. A passing star can shake comets loose from the Oort Cloud as it zips by. Or a large companion like Nemesis or Tyche can pull comets out of their comfort zones.
Computational models show that comets in each of these scenarios, when their apparent origins are mapped in space, make a characteristic pattern in the sky.
"We looked at the patterns and asked, 'Is there additional evidence of a pattern that might be associated with a passing star or with a bound object?'" Matese said.
After examining the orbits of more than 100 comets in the Minor Planet Center database, the researchers concluded that 80 percent of comets born in the Oort Cloud were pushed out by the galaxy's gravity. The remaining 20 percent, however, needed a nudge from a distant object about 1.4 times the mass of Jupiter.
"Something smaller than Jovian mass wouldn't be strong enough to do the deed," Matese said. "Something more massive, like a brown dwarf, would give a much stronger signal than the 20 percent we assert."
There's one problem, however. The pattern only works for comets that come from the spherical outer Oort Cloud, which extends from about 0.3 to 0.8 light-years from the sun. Comets from the flatter, more doughnut-shaped inner Oort Cloud don't create the same distinctive pattern.
"That's troubling," Matese said. "It requires an entirely new dynamical explanation for how inner Oort Cloud comets are made observable."
That the same weird pattern from 1999 is still there today "definitely makes it a stronger case than past papers," said planetary scientist Nathan Kaib of the Canadian Institute for Theoretical Astrophysics, who was not involved in the new work. But he would still like to see more data.
"I think this whole issue will be resolved in the next five to 10 years, because there's surveys coming on line … that will dwarf the comet sample we have today," he said. "Whether these types of asymmetries in the directions that comets are coming from actually do exist or not will definitely be hammered out by those surveys."
We may not have to wait that long, Matese said. An object like Tyche could be seen directly by WISE, NASA's infrared space telescope.
"We anticipate that this WISE is going to falsify or verify our conjecture," he said. "We just have to be patient."
Images: 1) Comet Sliding Spring, a visitor from the Oort Cloud, was captured by WISE in January 2010. Credit: NASA/JPL-Caltech/UCLA
Posted: 29 Nov 2010 12:20 PM PST
Most cosmologists trace the birth of the universe to the Big Bang 13.7 billion years ago. But a new analysis of the relic radiation generated by that explosive event suggests the universe got its start eons earlier and has cycled through myriad episodes of birth and death, with the Big Bang merely the most recent in a series of starting guns.
That startling notion, proposed by theoretical physicist Roger Penrose of the University of Oxford in England and Vahe Gurzadyan of the Yerevan Physics Institute and Yerevan State University in Armenia, goes against the standard theory of cosmology known as inflation.
The researchers base their findings on circular patterns they discovered in the cosmic microwave background, the ubiquitous microwave glow left over from the Big Bang. The circular features indicate that the cosmos itself circles through epochs of endings and beginnings, Penrose and Gurzadyan assert. The researchers describe their controversial findings in an article posted at arXiv.org on November 17.
The circular features are regions where tiny temperature variations in the otherwise uniform microwave background are smaller than average. Those features, Penrose said, cannot be explained by the highly successful inflation theory, which posits that the infant cosmos underwent an enormous growth spurt, ballooning from something on the scale of an atom to the size of a grapefruit during the universe's first tiny fraction of a second. Inflation would either erase such patterns or could not easily generate them.
"The existence of large-scale coherent features in the microwave background of this form would appear to contradict the inflationary model and would be a very distinctive signature of Penrose's model" of a cyclic universe, comments cosmologist David Spergel of Princeton University. But, he adds, "The paper does not provide enough detail about the analysis to assess the reality of these circles."
Penrose interprets the circles as providing a look back, past the glass wall of the most recent Big Bang, into the universe's previous episode, or "aeon," as he calls it. The circles, he suggests, were generated by collisions between supermassive black holes that occurred during this earlier aeon. The colliding black holes would have created a cacophony of gravitational waves — ripples in spacetime due to the acceleration of the giant masses. Those waves would have been spherical and uniformly distributed.
According to the detailed mathematics worked out by Penrose, when the uniform distribution of gravitational waves from the previous aeon entered the current aeon, they were converted into a pulse of energy. The pulse provided a uniform kick to the allotment of dark matter, the invisible material that accounts for more than 80 percent of the mass of the cosmos.
"The dark matter material along the burst therefore has this uniform character," says Penrose. "This is what is seen as a circle in our cosmic microwave background sky, and it should look like a fairly uniform circle."
Each circle has a lower-than-average variation in temperature, which is just what he and Gurzadyan found when they analyzed data from NASA's orbiting Wilkinson Microwave Anisotropy Probe, or WMAP, which scanned the entire sky for nine years, and the balloon-borne BOOMERANG experiment, which studied microwave background over a smaller fraction of the heavens.
Because the team found similar circular features with two different detectors, Penrose says it's unlikely he and his colleagues are being fooled by instrumental noise or other artifacts.
But Spergel says he is concerned that the team has not accounted for variations in the noise level of WMAP data acquired over different parts of the sky. WMAP examined different sky regions for different amounts of time. Maps of the microwave background generated from those regions studied the longest would have lower noise and smaller recorded variations in the temperature of the microwave glow. Those lower-noise maps could artificially produce the circles that Penrose and Gurzadyan ascribe to their model of a cyclic universe, Spergel says.
A new, more detailed map of the cosmic microwave background, now being conducted by the European Space Agency's Planck mission, could provide a more definitive test of the theory, Penrose says.
Image: Dark circles indicate regions in space where the cosmic microwave background has temperature variations that are lower than average. The features hint that the universe was born long before the Big Bang 13.7 billion years ago and had undergone myriad cycles of birth and death before that time. arXiv/V.G. Gurzadyan and R. Penrose
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