Research Rundown
Science Journal -- Spring 1997 -- Vol 14, No. 1
A new frog discovered in Cuba is the smallest in the Northern Hemisphere and is tied for the world record with the smallest frog in the Southern Hemisphere, say a team of biologists from Cuba and Penn State.
The one-centimeter-long frog also is the smallest of the tetrapods, a grouping that includes all animals with backbones except fishes, according to a paper published in the journal Copeia by Cuban scientist Alberto R. Estrada and Penn State Assistant Professor of Biology S. Blair Hedges.
Estrada discovered the tiny orange-striped black frog living under leaf litter and among the roots of ferns in a humid rainforest on the western slope of Cuba's Monte Iberia. Hedges and Estrada say it is a member of the genus Eleutherodactylus, which in print on this page is more than three times as long as the frog itself.
Hedges has teamed with Estrada and other Cuban scientists to find many new species of snakes, lizards, and frogs in Cuba's rainforests during the past several years, including a lizard tied for the record of world's tiniest. "You don't often find species that are the smallest, especially in a big group like tetrapods," he adds.
Cuban scientists restricted by that country's economic conditions typically have teamed up with foreign colleagues in order to carry on their work since the onset of severe economic hardships triggered by the fall of the Soviet Union. "The tropical forests in Cuba are even more fragile and more threatened than those in the Amazon of South America because they are so small?less than 10 percent of the island's land area?and they are now being cut down at an increasing rate, mainly for subsistence farming and cooking fuel," Hedges adds. "We still have an incomplete knowledge of the biodiversity on this planet, including areas like Cuba that are very close to the United States."
This research was sponsored by the National Science Foundation.
A color photo of the frog is available on the World Wide Web at :
<www.science.psu.edu/alert/FROG.htm>.
Barbara K. Kennedy
A discovery published in the journal Science has revealed the function of an enzyme thought to control such life-sustaining processes as the clotting of blood, the secretion of cell products, and the safe disposal of dead cells. "This research, plus additional work we have not yet published, indicates we may have found the first members of a previously unrecognized family of genes that code for these kinds of enzymes in all living cells," says Robert A. Schlegel, professor of biochemistry and molecular biology at Penn State.
Schlegel and his research team discovered that the enzyme's function is to control certain chemical reactions at the cell's surface. It moves one of the building blocks of the cell's double-layered protective membrane, a phospholipid molecule named phosphatidylserine (PS), from the outside to the inside layer of the membrane. When PS appears on the outside of the membrane, it serves as a foothold where other compounds can latch onto the cell, initiating reactions such as blood coagulation.
Schlegel and his colleagues determined that the enzyme patrols the cell membrane, flipping back to the inside any PS molecules that stray to the outside?unless they are needed for a particular reaction. Scientists call this enzyme "aminophospholipid translocase."
"Researchers have found aminophospholipid translocase activity in every type of tissue where they have looked for it," Schlegel says. "It is of enormous importance in blood cells. We suggest it may have a common function in all cells?to trigger the recognition of dying cells that should be removed before their disintegration can do any damage?but that remains to be proven."
In blood cells, the enzyme keeps PS on the inside most of the time "so your blood clots only when you are cut, not when it is circulating in your veins," Schlegel explains.
The enzyme also helps certain cells die gracefully at the appointed time without causing harmful inflammation?a process known as programmed cell death or apoptosis. "Apoptosis is one of the hottest topics in biology right now," Schlegel says. "It is a process involved in the development of adults from embryos and is very likely a process in such diseases as AIDS and cancer." The enzyme shuts off during apoptosis, allowing straying PS molecules to stay on the outside of the cell membrane, signaling macrophages?the garbage-disposal cells of the body?to surround and digest the dying cell, isolating it from the rest of the organism before it can do any damage.
The function of the enzyme had been a mystery since it was first identified along with similar enzymes in red blood cells 20 years ago. "Researchers had identified the function of all the other similar red-blood-cell enzymes over the years, but not this one's," Schlegel says. "It was the only one left whose function we did not know for sure." Scientists suspected the enzyme might be moving PS to the inside of the cell membrane?a function they termed "aminophospholipid translocase"?but they had not been able to prove it.
Schlegel and his colleagues approached the problem by first figuring out how to get enough of the enzyme to work with. "We are the first to isolate this enzyme in large enough quantities to determine its protein sequence and then to clone its gene," Schlegel says.
The researchers decided to work with cow adrenal cells because the enzyme is present in large quantities in organs like the adrenal gland that secrete compounds such as hormones. "Cow adrenal glands are big and readily available, so you have a lot of material to work with," Schlegel explains. "Plus, a procedure for isolating this enzyme from the adrenal gland already had been published."
After they successfully cloned the gene for the enzyme, they sent its nucleotide sequence to the worldwide gene databanks to see if it would match any of the millions of other genes that scientists have sequenced. The nucleotide sequence of the gene determines the amino-acid sequence of the enzyme that the gene specifies. "We got lucky," Schlegel says. The researchers discovered three highly similar genes in three very different organisms: yeast, the malaria parasite, and the nematode worm.
Better yet, another lab already had developed a mutant yeast strain that lacks the enzyme. "Yeast cells do many of the same things that mammal cells do," Schlegel comments. Schlegel and his team grew some of the mutant yeast and some normal yeast and used them both to test the function of the enzyme.
They attached a fluorescent tag to some PS phospholipids, put them on the surface of both normal and mutant yeast cells, and watched what happened. "The fluorescence on the surface stayed the same in the mutant yeast but it decreased substantially in the normal yeast," Schlegel says. "The normal yeast cells were able to move PS inside the cell membrane but the mutant yeast cells?the ones without the enzyme?could not, which proves that the enzyme is the aminophospholipid translocase," Schlegel explains.
The researchers then went one step further. They attached a fluorescent tag to another phospholipid building block of the cell wall and found that their enzyme did not move it at all, either in the mutant or in the normal yeast. Schlegel says this test confirmed that his first experiment was not just the result of some general defect in the mutant cells.
The scientists say their next goal is to breed mutant mice that do not have this enzyme so they can learn about its function in mammals and its role in diseases that affect mammalsÑincluding humans. "We suspect that this enzyme is one member of a whole family that controls a variety of important functions in all cells," Schlegel says. Because the function of an enzyme can affect how its gene is named, Schlegel says scientists probably will wait until they know what all the other members of this family of enzymes do before they give the new gene family a name.
Other members of the research team include Xiaojing Tang, currently a postdoctoral fellow at the Fred Hutchinson Cancer Center, Margaret S. Halleck, senior research associate at Penn State, and Patrick Williamson, professor of biology at Amherst College. This research was supported by Amherst College and Penn State.
Barbara K. Kennedy
The University of Texas and Penn State butted heads during the Fiesta Bowl, but the two schools are putting their heads together off the field to build the largest and most powerful optical telescope in the continental United States.
With the Hobby-Eberly Telescope, astronomers will be able to see a football that is twice as far away as the moon.
The brand-new William P. Hobby-Robert E. Eberly Telescope is being built by a partnership involving The University of Texas at Austin and Penn State, along with Stanford University and the German universities of Göttingen and Munich.
The telescope is one of the largest in the world, but its $13.5-million cost is one-fifth of others in its class because of its innovative design features. For example, its 11-meter mirror will be made up of 91 identical pieces that can be cost-effectively produced in quantity.
The universities are using the telescope to train the next generation of scientific leaders. For example, the first scientific instrument installed on the telescope was designed and built by two Penn State students and their professor.
Texas and Penn State astronomers and their students are planning to use the Hobby-Eberly Telescope to search for planets around other stars and to reveal other mysteries about the universe.
The concept for the telescope's novel design was invented by Penn State astronomers Lawrence W. Ramsey and Daniel W. Weedman.
The Hobby-Eberly Telescope took its first look at the universe on December 10, 1996Ña milestone event known as "first-light."
The telescope is named for former Texas Lieutenant-Governor Bill Hobby and for Robert Eberly, a Penn State benefactor.
Astronomers in Australia, South Africa, Chile, and Germany are discussing the possibility of building a telescope of the cost-saving Hobby-Eberly Telescope design in the southern hemisphere.
The Hobby-Eberly Telescope will be commissioned in late 1997 at the McDonald Observatory in a remote area of western Texas known for having the darkest skies in North America.
Photographs of the telescope are available on the Web at
<http://www.astro.psu.edu/het/>.
Barbara K. Kennedy
Scientists have discovered some of the techniques cells use to control their genes?including processes important in leukemia and other cancers?according to a research paper published in the journal Science. The research demonstrates, for the first time, that high-powered, promiscuous proteins roam throughout a cell's nucleus, temporarily joining with other molecules to find and turn on specific genes by permanently untangling the tightly knotted structures that prevent them from functioning.
"This research concerns a central process in gene regulation?how energy-driven teams of molecules function as chromosome-remodeling machines that unlock the cell's genetic codes," says Jerry L. Workman, associate professor of molecular and cell biology and the leader of the research group at Penn State.
A chromosome, the gene-containing structure in a cell's nucleus, is one, long, rope-like molecule of DNA tangled up with proteins and intricately knotted, twisted, and looped into a densely packed structure. Genes are sections of DNA that contain a cell's genetic codes. "All cells contain the same genes but each cell turns on only the particular genes it needs," Workman explains.
A gene "turns on" when a transcription enzyme attaches to it and copies its genetic code, which it then uses to make the cell's proteins and other molecules. The chromosome's dense packaging effectively locks up all the genes by tying them into knots, leaving no place for the transcription enzyme to attach.
The research reveals that a high-powered protein complex apparently untangles a knotted-up gene while other molecules called transcription activators slip in and securely attach themselves to a binding site on the gene. "A transcription activator helps the transcription enzyme bind exactly where it should to start copying a specific gene," Workman explains. The combination of the temporary disruption caused by the powerful protein complex and the binding action of the transcription activator results in the permanent smoothing out of the previously knotted gene, clearing enough space for the transcription enzyme to attach.
"We have demonstrated that a permanent structural change occurs only at the specific site where the transcription activator attaches," Workman says. "We also demonstrated that the cell's energy-driven protein complexes, which are far outnumbered by the genes that have to be turned on, work as roving catalysts throughout the chromosome, helping to turn on many genes rather than remaining attached to a single one."
Workman explains that the protein complex gets the extra power it needs from the cell's energy molecule, adenosine triphosphate (ATP), to wrench open the tangled DNA knots. "Proteins that need to function like machines inside the cell typically break off a phosphate from an ATP molecule, using the energy released to fuel their work," Workman explains.
Workman and his colleagues set up a test involving the smallest knot in the chromosome tangle, a structure consisting of a core of protein molecules known as histones wrapped around with a double loop of DNA. They first made a long string of this knotted DNA, then treated it with an enzyme that cuts only between the knots. They then separated the DNA fragments by size, using a technique called gel electrophoresis that produces a fuzzy image of alternating black and white bands stacked one on top of the other. "The white bands tell you where the knots are and the black bands show you where the DNA was cut," Workman explains.
They next attached purified transcription activators to one of the DNA knots, then added an ATP-powered protein complex and ran the gel test again. This time the resulting picture was even fuzzier, with dramatically less contrast between the black and white areas. "We lost the apparent positions of the knots, which tells us that the protein complex was disrupting them all in some way," Workman says.
Workman and his colleagues then added more knotted strings of DNA to their test-tube mixture to give the powerful protein complex someplace else to go, as they suspected it does in a living cell. "The protein complex apparently moved off our knotted string of DNA because the positions of all the original knots reappeared on the next gel?except for the one with transcription activators attached to it," Workman explains. "That knot appears to have been untangled permanently." The catalytic action of the roving, ATP-powered protein complex had never before been shown in a molecule that regulates transcription, Workman says.
"This research gives us new information about the process that controls gene expression, an important factor in diseases like cancer that involve uncontrolled cell growth that can result from defects in a cell's gene-expression system," Workman says. "It demonstrates that access to the genes within the chromosome structure is a very dynamic process that is powered by energy sources within the cell."
Workman says his research also provides an alternative to the long-standing theory that genes can be turned on only as chromosomes duplicate prior to cell division, when they get pulled apart and their DNA knots untangle briefly. "This study shows that a cell can turn on the genes it needs even after they have been tightly knotted up inside chromosomes," he adds.
This research is supported by the United States National Institutes of Health, the European Molecular Biology Organization, the Medical Research Council of Canada, and the Leukemia Society. Its authors include Penn State Postdoctoral Fellow Thomas A. Owen-Hughes, Penn State Graduate Student Rhea T. Utley, Penn State Postdoctoral Fellow Jacques Cote, University of Massachusetts Associate Professor of Biochemistry Craig L. Peterson, and Workman. Peterson and Workman are Leukemia Society Scholars.
Barbara K. Kennedy
Standard Model of Galaxy Formation
Challenged by New Observations
Many of the galaxies in the universe could have formed very differently from the process now widely accepted by astronomers, according to a paper published in The Astrophysical Journal. The study concludes that a large fraction of dwarf galaxies?the most plentiful galaxies in the universeÑcould form not by the stately gravitational accumulation of matter but by the raucous rearrangement of tidal debris from clashes between giant galaxies.
The research is one of the most systematic studies ever done of dwarf galaxies in compact groups, according to Jane C. Charlton, assistant professor of astronomy and astrophysics at Penn State, who authored the paper along with Sally D. Hunsberger, a Penn State graduate student in astronomy and astrophysics, and Dennis Zaritsky, assistant professor of astronomy and astrophysics at the University of California at Santa Cruz.
The researchers used the 60-inch telescope at the Mount Palomar Observatory to study 42 groups of galaxies known as Hickson compact groups, one of the rarest and densest environments in the universe and one in which galaxy collisions occur frequently. In these groups, a few galaxies are packed together as tightly as in the high-velocity centers of giant galaxy clusters, but they move slowly enough to interact as they brush past each other. "This combination is conducive to the formation of tidal tails," the researchers say, referring to the filmy wisps that the passing galaxies draw away from one another.
"Initially, we just wanted to see how many dwarf galaxies we could find in compact groups, but then we noticed a lot of interesting tidal debris in seven of them," Charlton says. "We took a closer look at the tidal features and detected 47 areas that appear to be dwarf galaxies." They speculate that some of the dwarfs found elsewhere throughout the compact groups originally formed in the tidal debris, while others formed by normal gravitational accretion.
Dwarf galaxies, roughly 100 million times the mass of our sun, are tiny compared to giant galaxies such as the Milky Way, which is about 100 billion solar masses. Astronomers had found numerous dwarf galaxies in all environments, including dense galaxy clusters and looser groups of "field" galaxies.
"Dwarfs usually are spread out in giant clusters, not located near the galaxies," Charlton says. Astronomers had assumed that the dwarfs in clusters formed by gravitational accretion, but the new discovery makes Charlton suspect that a large fraction of all the dwarfs in the universe initially formed in tidal debris from galaxy collisions, later to be flung away from the site of their birth.
"Because tidal tails are observed in all environments, this formation mechanism could have more general implications," the researchers assert. "If up to 50 percent of them form in tidal debris in compact groups, then maybe up to 50 percent of them form in tidal debris everywhere," Charlton says.
In order to estimate how many dwarfs form in tidal debris, the researchers first considered how many dwarfs are spread throughout their set of 42 compact groups, then compared that number with how many dwarfs they found in the tidal tails. They then estimated how many dwarfs would be made in tidal debris throughout the full lifetime of each group. "It is a little tricky," Charlton comments. "There are many factors that go into the estimate, but we always tried to err on the conservative side. Our most conservative estimate is that at least one-third and perhaps more than one-half of dwarf galaxies in the compact groups are formed in tidal debris."
Charlton says the key to estimating what fraction of all dwarf galaxies form in this way is how often mergers occur everywhere throughout the universe. "If you accept the prevailing theory that elliptical galaxies form via the merger of two spiral galaxies, then the fraction of all galaxies that are elliptical will give you an approximation of how many mergers there have been," she explains. Charlton adds up a number of clues to make her estimate. More than 50 percent of the galaxies in the center of large clusters are elliptical, indicating a larger merger rate there than anywhere else in the universe. This observation suggests that lots of dwarf-forming mergers took place in the past life of a cluster. "A larger rate should lead to a larger number of dwarfs per giant and that is, in fact, what we observe in these regions," Charlton says. "Today, mergers occur less frequently in clusters because the velocities there are so large, but velocities weren't as large when the clusters were first forming, so many or most of the dwarfs we see could have formed in tidal debris long ago," she explains. Astronomers also see mergers going on today in field environments such as the Local Group, in which the Milky Way resides, as well as in compact groups. So, Charlton concludes, "a large fraction of dwarf galaxies are likely to form in tidal debris all over the universe."
Another clue, Hunsberger adds, is that the relationship between the surface brightness and the radius of the core region takes different forms for giant galaxies and dwarf galaxies. "It is hard to imagine that galaxies with these very different properties arise from the same formation mechanism," she says.
In order to test their theories, the astronomers have been granted time on the Hubble Space Telescope within the next year to get a clearer look at the objects they suspect are dwarf galaxies in the compact groups.
"It will be interesting to compare the different properties of the dwarfs inside and outside the tidal tails," Charlton says. The research could help to improve the models astronomers use to understand how structures form in the universe. "Maybe we will find two populations of dwarf galaxies with different properties from each other, perhaps because they formed in two very different ways," she adds.
The research was supported by Penn State and the California Space Institute.
Barbara K. Kennedy
Recent identification of Jupiter-like planets around distant stars has raised hopes of extraterrestrial life outside our solar system, but not on the gas giants themselves.
"While gas giants probably will not support life, the moons orbiting these planets might meet the requirements necessary to sustain life," says Darren Williams, graduate student in astronomy and astrophysics at Penn State. In a recent issue of the journal Nature, Williams, James F. Kasting, professor of geosciences, and Richard Wade, associate professor of astronomy and astrophysics, outline these requirements.
"First, the gas giant must orbit its star within the habitable zoneóthe zone around a star where the solar flux allows liquid water to exist," Williams says. "If the orbit is too distant, water freezes. If it is too close, high temperatures cause the hydrogen in water to be lost to space. "
The researchers examined the known gas giants to see if they fell into their star's habitable zone. "Only 16 Cyg Bb and 47 Uma B come near to being in the habitable zone," says Williams. "Also, moons around gas giants must be able to sustain an atmosphere for billions of years and must also be close enough to their planet to have a stable orbit."
A moon's mass, the ionizing radiation it receives, the solar flux, and the magnetic effects of the gas giant all play a part in trying to remove the atmosphere.
If a moon is too small, heating will cause the molecules of oxygen and nitrogen in the atmosphere to attain escape velocity?the speed at which the moon's gravity will no longer hold them?and disappear into space. To retain oxygen and nitrogen, the moon must be at least 0.07 the size of the Earth. But stellar heating is not the only consideration. When ionized atomic nitrogen recombines with electrons, it may also be lost to space. A moon must be at least 0.12 the mass of Earth to keep from losing appreciable amounts of nitrogen by this process.
Another way to lose atmosphere is through the action of the gas giant's magnetosphere?the area in which the planet's magnetic field operates. Moons in the magnetosphere lose atmosphere because of bombardment by trapped energetic charged particles. A planet with its own magnetic field is protected from this effect, but, until recently, it was thought small bodies, like moons, did not have magnetic fields. "The Galileo spacecraft's recent identification of a magnetosphere around Ganymede, which is only 0.03 the mass of Earth, suggests that some moons may not be affected by their planet's magnetosphere," says Williams. "We also know that Saturn's moon Titan travels in and out of the magnetosphere, but still has a dense nitrogen atmosphere. This may not be the problem it was once thought."
To retain an atmosphere, moons must first form an atmosphere. Moons around extra solar gas giants might have received their water through bombardment by icy comets or carbonaceous asteroids, but research in our own solar system suggests that moons orbiting Jupiter-size planets have trouble retaining volatiles from comets.
If, however, moons originated in the outer part of stellar nebula, they may have incorporated large amounts of water. These moons may have so much water that when in the habitable zone, they are oceanic with little dry land. Between these watery moons and those devoid of water are inner moons like Jupiter's Europa which have a good balance of rock and water and are most likely to be Earth-like.
In the long term, habitable moons must also be able to compensate for the increasing brightness of their suns through time. An increase in carbon dioxide, from volcanic activity, can cause greenhouse warming which compensates for a fainter sun. As the moon ages?and the star becomes brighter?rock weathering continues to remove carbon dioxide from the atmosphere, but a decrease in geologic activity reduces the amounts of carbon dioxide replaced by geologic activity which, in turn, decreases greenhouse warming. Normally, for a planet to retain internal heat and remain geologically active for 4.5 billion years, it must be at least 0.23 the mass of Earth or just over twice the mass of Mars. This would be a large, planet-sized moon.
Moons close enough to gas giants, however, may be warmed by tidal heating?the gravitation pull on the moon of the gas giant. These moons would support tectonic activity or at least individual volcanoes.
Williams is not the first to suggest moons of gas giants as likely locations for extraterrestrial life. In the popular film "Return of the Jedi," the Ewoks race through a terrestrial-looking landscape on the Forest Moon of Endor, in pursuit of the minions of Darth Vader, while the planet orbits a gas giant similar to Jupiter.
The planets 47 Uma B and 16 Cyg Bb are not perfect subjects for habitable moons. 47 Uma B lies just outside the habitable zone and 16 Cyg Bb has an orbit that is so eccentric it traverses the entire habitable zone dipping inside and outside the acceptable orbit. While these are not perfect, there seems to be sufficient flexibility and variety of factors to suggest that given a large enough gas giant with large enough moons, life could evolve and persist.
A'ndrea Elyse Messer
The first planets beyond the Solar System were discovered by Alex Wolszczan, distinguished professor of astronomy and astrophysics, in 1991. Contrary to the common expectation that the extrasolar planets would be first detected around a solar-type star, Wolszczan's planets circle a billion year old, rapidly spinning neutron star called a millisecond pulsar. The three terrestrial mass planets around the pulsar PSR B1257+12 orbit their central star with the periods of 25.3, 66.5 and 98.2 days at the respective distances of 0.19, 0.36 and 0.47 astronomical units.
Although the initial evidence for pulsar planets based on high precision pulse timing measurements was strong, their existence was inferred indirectly from the systematic variations in pulse arrival times and required confirmation. Fortunately, because the ratio of orbital periods of the two outer planets is close to 3:2, this "near-resonance" condition enhances their mutual gravitational interaction to the point that it can be detected with the pulse timing method. The predicted effect of these perturbations on planetary orbits was identified by Wolszczan in 1994, after three years of timing observations of PSR B1257+12 with the 305-meter Arecibo radiotelescope. This result provided the final confirmation that the periodic variations seen in the arrival times of pulses from PSR B1257+12 are indeed caused by orbiting planets.
The three planets around PSR B1257+12 remain the only known system of terrestrial mass bodies orbiting a star other than the sun. The recent spectacular detections of Jupiter-mass planets around solar-type stars provide further evidence that extrasolar planetary systems exist in a variety of forms that would be difficult to anticipate on the basis of our present knowledge of the solar system alone.
An extraordinary precision of the pulsar timing makes it a particularly suitable method in the studies of planetary perturbations and in the searches for terrestrial-mass or even asteroid-mass planets outside the solar system. Since the optical methods of planetary detection are currently not capable of such precision, the investigations of pulsar planets will remain a unique source of information on low-mass planets and on planetary dynamics in the foreseeable future.
A search for more planets around PSR B1257+12 and other millisecond pulsars continues at Arecibo Observatory with a new, remotely controlled pulsar detector (the Penn State Pulsar Machine) built by Wolszczan and his collaborators. Another recently completed version of this system, designed for medium-size radio telescopes, has been attached to a 32-meter dish of the Torun Radio Astronomy Observatory in Poland to begin a long-term search for planets around hundreds of known pulsars.
Alexander Wolszczan
Donald Schneider, associate professor of astronomy and astrophysics, is a member of one of the two research groups that recently released dramatic images of quasars obtained with the Hubble Space Telescope. The images, which show that quasars live in a remarkable variety of galaxies including many that are violently colliding, suggest that there may be a variety of mechanisms for igniting these most energetic objects in the universe.
The researchers note that the quasars studied do not appear to have obviously damaged the galaxies in which they live. This observation could mean that quasars are relatively short-lived phenomena that many galaxies, including the Milky Way, experienced long ago.
Though a number of the images show collisions between pairs of galaxies which could trigger the birth of quasars, some pictures reveal apparently normal, undisturbed galaxies containing quasars. "We were amazed by the beauty and clarity of the Hubble images, as well as the diversity of quasar environments," says Schneider. "The new data indicate that the source of the quasar phenomenon is considerably more complex than previously believed."
Discovered only 33 years ago, quasars are among the most baffling objects in the universe because of their small size and prodigious energy output. Quasars are not much bigger than our solar system but pour out 100 to 1,000 times as much light as an entire galaxy containing a hundred billion stars.
A super-massive black hole, gobbling up stars, gas, and dust, is theorized to be the "engine" powering a quasar. Most astronomers agree an active black hole is the only credible possibility that explains how quasars can be so compact, variable, and powerful. Nevertheless, definitive evidence has been elusive because quasars are so bright that they mask any details of the "environment" where they live. Both astronomy teams agree that Hubble images show conclusively:
¥That most quasars lie at the cores of luminous galaxies, both spiral and elliptical. Though underlying galaxies were suggested in ground-based quasar observations, astronomers had to wait for Hubble's capabilities to show the host galaxies clearly enough for astronomers to begin to classify their shapes.
¥Interactions between galaxies, either through direct collisions or near encounters, can be important in "turning on" a quasar by dumping fuel onto a black hole. However some quasars look unperturbed, so there may be other, more subtle, mechanisms for feeding the black hole. "Some of the galaxies we observed don't appear to know they have a quasar in their cores," says John Bahcall of the Institute for Advanced Study in Princeton, New Jersey, who collaborated with Schneider. "This may be a very important clue, since it was a completely unexpected result."
¥Quasars that do not emit much of their luminosity in radio waves often are found in elliptical galaxies, not always in spiral galaxies, as previously believed.
Now that more is known about the environments in which quasars exist, the teams emphasize astronomers must address even larger puzzles. Do most quasars flare up for a brief period of a galaxy's life (100 million years or less)? If so, then many galaxies could be "burned out" quasars. If, alternatively, quasars are long-lived, it implies that they are more rare and that a few extremely massive black holes formed very early in the history of the universe.
Astronomers also need to address a "chicken and egg" problem about the birth of quasars. Did the massive black holes form first and the galaxies later formed around them? Or did galaxies precede black holes, which quickly grew in their cores through stellar collision and merger?
Advanced instruments planned for Hubble should also help pin down more details. The Near Infrared Camera and Multi-Object Spectrometer (NICMOS) to be installed in 1997, and the Advanced Camera, to be installed in 1999, will have coronagraphic devices which will block out the glare of a quasar, allowing astronomers to see closer into a galaxy's nucleus. By viewing galactic structures in infrared light, the NICMOS should be able to provide important new details about the host galaxies of quasars.
NASA/Schneider
The apparent shrinking of the gender gap in salaries is due less to improvement in women's wages than to a decline in the wages of many men due to structural changes in the labor force. "Furthermore, the growing income inequality among men is being reflected also among women," says Martina Morris, associate professor of sociology and statistics. "While a small number of women have moved into high-income brackets, most have not. Successful women appear to have short coat tails."
Morris is coauthor of the paper, "Women's Gains or Men's Losses? A Closer Look at the Shrinking Gender Gap in Earnings," published in the American Journal of Sociology. Her coauthors are Annette Bernhardt, senior research associate with the Institute on Education and the Economy, Teachers College, Columbia University, and Mark S. Hancock, associate professor of statistics at Penn State.
"For American women who work outside the home, the 1980s brought good news," Morris says. "After years of stagnation, their economic standing in the labor market finally began to improve."
The typical working woman earned about 60 cents on the male dollar throughout much of the post-World War II period, a wage gap that remained unchanged despite progress on working women's issues in social, political and legal domains.
"During the 1980s, this gap finally began to narrow, and by the end of the decade wage gap estimates ranged from 65 to 72 cents on the dollar," Morris notes. "Many pundits attributed women's progress to more education, more years of work experience and greater career commitment. But other factors were also at work during this period."
America's shift to a post-industrial, service-based economy was generating a striking increase in earnings inequality for American workers. Men, whose earnings depended more on manufacturing's "family wage," experienced this disparity in earnings much more than women. Thus, a number of complex shifts affected both men's and women's earnings and influenced trends in the gender wage gap, says Morris.
"In the end, however, we find that rising inequality in men's wages, rather than improvement in women's wages, played the dominant role and in fact women's gains were often really men's losses in disguise," Morris adds. In addition, the few inroads that women made into higher income categories can be traced to the growing polarization in their own earnings?a small group of women who are pulling away into the upper tier, rather than a general improvement among all women's wages.
"Women's recent economic gains can thus be interpreted in part as an act of ventriloquism," Morris says. "The worsening of men's earnings both improved women's relative standing in the wage hierarchy and camouflaged the effects of growing inequality in women's earnings."
The researchers used Current Population Survey data from 1967 to 1987.
Paul Blaum
Potassium and nickel have, for the first time, bonded with each other to form a compound, according to research published recently in the journal Science. Using pressures as high as those deep within the Earth to form the new potassium/nickel compound, Penn State Assistant Professor of ChemistryJohn V. Badding and his colleagues demonstrated that pressurized potassium functions like a new element with chemical properties like a transition metal. The research could further scientific understanding of fundamental chemistry as well as the chemistry and composition of the Earth's core.
"Alkali elements like potassium don't form compounds with transition elements like nickel at normal pressure because their size and electronic structure are so incompatible," Badding explains. By making the potassium/nickel compound, the researchers demonstrated that pressurized potassium functions chemically like a new member of the transition-element family.
The chemists produced the compound by first compressing potassium and nickel powder in a diamond-anvil cell to 310 thousand times normal atmospheric pressure (31 Gpa), then heating it with a laser to about 4,000 degrees F (2,500 K). They confirmed the formation of the resulting compound with a powerful single-wavelength X-ray-diffraction device.
Potassium buckles under these pressures, collapsing by a factor of 5. Its single outermost valence electron, which controls bonding, deforms from the spherical "s" orbital shape typical of the alkali elements to the smaller-volume, four-leaf-clover-pattern, "d" orbital characteristic of the transition elements.
"A single d-electron is an extraordinary valence configuration that we just don't find in any of the other elements," Badding says. When potassium's outermost electron transforms to the d-orbital state, potassium sheds its alkali character and starts behaving like a transition element, making its bonding with nickel possible.
"Nickel's electron configuration changes much more slowly under pressure because it is relatively incompressible, so nickel stays in its primarily d-electron configuration while potassium changes completely," Badding explains.
Strictly speaking, an element is defined by the number of protons in its nucleus, but chemists also associate a certain electronic structure and characteristic chemistry with certain groups of elements. "I think you can argue that when you change the chemistry of potassium from that of an alkali-like s-electron element to that of a transition-metal-like d-electron element, you've pretty much got a new element," Badding says.
The research may help geophysicists understand the composition of the Earth's core, which contains primarily iron or an iron/nickel alloy plus some unknown lighter element or elements. "Our research shows it is possible that potassium could be incorporated as a compound into Earth's core," Badding says. The research also could help to explain the source of heat in the core, which could result from the radioactive decay of potassium that might be present there. "Our next step is to make potassium/iron compounds," Badding adds.
"We are fascinated now by the interesting chemistry of pressurized potassium and intrigued by its geophysical implications, as well as by a variety of other chemical situations in which alkali elements in a d-electron state could have interesting or important chemistry," Badding says. "The formation of the compound cesium difluoride, which would involve bonding to electrons in a noble-gas configuration octet, should be favored under high pressure. Also, the availability of the d-electron bonding state of the alkali metals should allow new chemistry with many of the nonmetallic elements," he explains.
Other members of the research team include Graduate Student Laura J. Parker and Postdoctoral Fellow Toshiyuki Atou, now a research associate at Tohoku University in Japan. This research was sponsored by the National Science Foundation, the Petroleum Research Fund of the American Chemical Society, and the David and Lucille Packard Foundation.
Barbara K. Kennedy
Gene Study Shows Modern Orders of
Birds and Mammals
Lived Before Dinosaur Extinction
A large gene study suggests that modern orders of birds and mammals evolved when the continents were separating 100 million years ago?much earlier than previous estimates based on fossil studies, which link the evolutionary event to mass extinctions 65 million years ago.
"We have substantial evidence that these modern groups of animals originated well before the extinction of the dinosaurs," says Blair Hedges, assistant professor of biology at Penn State, whose research was published recently in the journal Nature.
In the largest genetic study of its kind, the researchers analyzed 79 genes from species representing six orders of mammals and seven orders of birds. Those species included primarily human, mouse, cow, chicken, pigeon, duck, and ostrich. "We analyzed a large amount of data?all the relevant information for these species now available in the world's genetic databases," Hedges says. "The widespread use of genetic model organisms for medical research is the reason why so many gene sequences are available," he explains.
By comparing individual genes in pairs of species, the researchers found that about half the genes in their study had accumulated mutations at a fairly constant rate relative to one another during their evolution, so they could use each mutation as a "tick" in a kind of molecular clock. The scientists calibrated their molecular clock to an evolutionary event well established by fossil studies. "A clock isn't any good unless it is calibrated to a time that everyone else agrees on," Hedges explains, "and just about everyone agrees that the reptilian ancestors of birds and mammals appeared about 310 million years ago." Using this date as a secure calibration point?and the mutation rate for each of the constant-rate genes as a timing device?the researchers were able to determine how long ago each order originated.
"After averaging the time estimates for all the constant-rate genes, we traced back the origin of the orders to about 100 million years ago," Hedges explains. Most previous studies of this type involved only one or just a few genes, Hedges says, and lack the statistical power and accuracy of this study.
"These results are unexpected," Hedges says, "because very few fossils resembling modern orders of birds and mammals have been found in rocks dating before 65 million years ago and paleontologists are in dispute over whether some of these specimens are of modern or ancient orders." The researchers speculate that these animals might not have been very abundant before 65 million years ago because the dinosaurs were so dominant then. "If there were not very many of them, we might not ever find the small proportion that became fossilized," Hedges says. "Our research is showing that the fossil record of the orders of mammals and birds apparently is very biased."
Hedges says scientists might some day be able to better determine when each order originated and on which continent it arose if they had gene sequences for more orders of mammals and birds plus more fossil discoveries.
In addition to Hedges, the research team includes Patrick H. Parker, a Penn State graduate student in biology, Charles G. Sibley, Yale University professor emeritus of biology, and Sudhir Kumar, a Penn State graduate student in biology.
This research was supported, in part, by the National Institutes of Health and the National Science Foundation.
Barbara K. Kennedy