UC Santa Cruz Tip Sheet May 1996
Research news and feature ideas, issued periodically by the UCSC Public Information Office. For more information, contact Robert Irion at (408) 459-2495 or irion@ua.ucsc.edu
Astrophysics I
A model for the birth and strange life of the first new planet orbiting a "normal" star
Delight zipped around planet Earth last October when astronomers discovered signs of a new planet in the cosmos, orbiting a star much like our own Sun. But fantasies about life on this distant body went up in flames when the details became clear: The planet is so close to its star that temperatures on its sunny side soar to about 2,000 degrees.
Indeed, the planet's existence seemed so marginal that it strained credulity. Its size--about as big as Jupiter--implies that it is mostly made of gas, yet its blast-furnace orbit surely would have boiled off such an atmosphere. Further, astronomers had thought that large planets develop only in colder parts of the gaseous disks that swathe baby stars. A few suggested the evidence might point to something else entirely--remnants of a brown dwarf, or even vibrations of the star itself.
To paraphrase former vice presidential candidate James Stockdale, the key questions about the planet were: What is it? How did it get there? Now, a UCSC-led team thinks it has the answers.
In the April 18 issue of Nature, the researchers propose that the planet, called 51 Pegasi B, is indeed a gas giant that coalesced at a more reasonable distance from its star, perhaps 100 times further away than it is today. Then, in a million-year gravitational tug-of-war among the star, the planet, and gas and dust in the rest of the disk, the planet spiraled slowly but relentlessly toward the star. Finally, inward and outward forces on the planet's orbit canceled each other out just before the star would have consumed the planet.
"We have said for years that planets can migrate toward their stars early in a solar system's history," says astrophysicist Douglas Lin. "The new part of the theory is that this migration could stop. It is possible that 51 Pegasi B is the last of a series of planets, all but one of which have perished in their parent star." Contact: Douglas Lin--(408) 459-2732 or lin@ucolick.org
Astrophysics II
Computer models of galaxy collisions yield puzzling results about dark-matter halos
When galaxies collide, the results can be strikingly beautiful or deadly dull. Some pairs of galaxies fling sweeping arcs of stars into space; others just merge into shapeless blobs. The difference, it turns out, is a matter of some gravity.
Gravity dictates the overall shapes of galaxies during a collision, as well as the path of each star. However, the key forces come not from the stars themselves, but from invisible "halos" of dark matter theorized by astronomers to surround every galaxy. These halos can create deep gravitational pits, making it less likely that stars will escape a collision to form graceful luminous arcs.
That delicate dance of physics allowed a UCSC team to use a supercomputer model of colliding galaxies as a novel way to probe how much dark matter is out there. When the researchers compared their results to images of real galaxies caught in the act of colliding, they unveiled a puzzle.
The model's collisions created dramatic "tidal tails" of stars only when the mass of each galaxy's dark-matter halo was fairly low. The simulated tidal tails became pathetically short and stubby as the team raised the dark-matter ratio.
Here's the dilemma: Popular theories of the evolution of the universe predict that galaxies should have huge cocoons of dark matter. However, several galaxy pairs have hurled tremendous tails of stars into space. This implies--according to the computer model- -that the dark-matter halos around those particular galaxies are wimpy, not massive. The team's report, led by postdoctoral researcher John Dubinski, appears in the May 10 issue of the Astrophysical Journal. Contact: John Dubinski--(408) 459-5246 or dubinski@ucolick.org
Geology
Coastal sleuths track the restless migration of sand off the California shoreline
The beaches may look stable, but our sandy shores are driven relentlessly down the coast by waves and currents. Led by geologist Gary Griggs, a UCSC team is clarifying the big picture of sand movement just offshore.
Sand grains, it seems, travel along certain submarine routes, like cars following highways. Darting among treacherous coves in nimble research boats, the team has mapped major thoroughfares and parking lots for sand along the central California coast.
Most sand near Santa Cruz comes from the north, swept by the oblique attack of waves in a process called littoral drift. Griggs estimates some 300,000 cubic yards pass by every year, about one dump truck full every 17 minutes. But beaches are interrupted by rocky headlands--roadblocks for migrating sand. To learn how sand moves around such obstacles, researcher James Tait had to map the submarine geography.
Tait's team discovered large offshore areas devoid of sand. Most sediment collects in submerged stream valleys carved out by rivers when the sea level was lower, some 10,000 to 20,000 years ago. Tait suspects these valleys trap sediment until storms churn the water enough to carry sand over the ancient river banks.
To investigate sand pathways by computer, Tait developed a mathematical tool with help from a seismologist. They tested the method in Monterey Bay, which contains a complex blend of sand from along the coast and several rivers. Tait's method sorted the mix for thousands of samples, indicating how much sand came from each source. Contact: Gary Griggs--(408) 459-5006 or griggs@cats.ucsc.edu
(Writer: Erik Stokstad)
Chemistry
Chemist's research on synthesizing organic compounds is patently rewarding
Holding a patent, says chemist Bakthan Singaram, is like playing Lotto: It could make you rich, but don't bank on it. Instead, Singaram reaps his rewards by devising new chemical processes to overcome some thorny challenges. In the end, his work may help a host of industries, from drug companies to makers of computer chips.
Singaram's team holds a patent on a better way to make a family of chemical compounds called "beta-amino alcohols," used by doctors to treat tuberculosis, heart disease, and other ailments. When chemists make beta-amino alcohols in the lab, they get 50-50 mixtures of "left-handed" and "right-handed" versions. The two types of molecules are mirror images of each other, but the human body can use only one of them. For some drugs, the mirror image of the bioactive form can trigger serious side effects.
The group has patented a method to make either left-handed or right-handed beta-amino alcohols in essentially pure form. The method draws upon turpentine oils from pine trees and boron compounds related to those used in mild laundry detergents. "The materials are environmentally friendly, relatively cheap, and recyclable," says Singaram.
Another patent, still pending, also holds great promise. Singaram and others worked on a safe way to make a gas called silane. Under carefully controlled conditions, silane will decompose into hydrogen gas and a layer of ultrapure silicon--desirable for computer chips. However, silane has the nasty habit of exploding when it contacts air. The new method lets workers make small amounts of nearly pure silane and then "scrub" the rest of the gas before it becomes a hazard. Contact: Bakthan Singaram--(408) 459-3154 or singaram@chemistry.ucsc.edu
Astronomy
The "Great Circle Camera" scans sky sharply and swiftly
A clever new camera is sharpening our views of space. Created in part by astronomer Dennis Zaritsky, the Great Circle Camera also lets astronomers fiddle less with their telescopes and spend more time stargazing.
The best way to photograph a large swath of sky, says Zaritsky, is simply to "park the telescope and let the sky drift by." But until now, that method, called a drift scan, only worked well near the equator. Telescopes pointing anywhere else take blurry images of stars during a drift scan, because the stars follow curved paths on the sky. Zaritsky's camera corrects the distortion by precisely rotating while the telescope itself stays still.
The drift scan can be at least twice as efficient as another common technique, in which astronomers aim their telescope at a particular object and follow along as it travels through the night sky. That works fine for a single star or galaxy, but surveying wider reaches of the sky becomes burdensome.
Zaritsky began using the Great Circle Camera two years ago in Chile for the first complete four-color survey of the Large Magellanic Cloud (LMC). Visible only from the Southern Hemisphere, the LMC is one of the nearest galaxies to our own--and it covers a substantial portion of the sky, making it an ideal target for a drift scan. "The LMC is our best chance for really understanding an entire galaxy," says Zaritsky. A detailed map of its stars, he says, will shed light on how the galaxy has evolved over billions of years. Contact: Dennis Zaritsky--(408) 459-5170 or dennis@ucolick.org
(Writer: Erik Stokstad)
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