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Findings
September/October 2006

Black hole studies
by Bruce Fellman

You can’t observe what’s going on inside a black hole, but Yale astrophysicist Meg Urry and an international research team have been able to learn by proxy about the inner workings of one of the strangest places in the universe. Using NASA’s three orbiting telescopes, Urry and her colleagues examined a jet of glowing material that begins near the edge of a black hole and extends far out into space. A few percent of all black holes have these jets. “The jet’s characteristics enable us to investigate what you can’t see, touch, taste, or feel,” says Urry, the Israel Munson Professor of Physics and Astronomy.

Her study’s findings, which appear in the September issue of the Astrophysical Journal, have also helped scientists to choose between two competing theories about the jets. The result, ironically enough, appears to be the rejection of a hypothesis first developed by Urry and her collaborators.

The researchers looked at images taken by the Hubble, Chandra, and Spitzer telescopes of a dim point of light in the constellation Virgo. This object, known as 3C273, has fascinated and perplexed astronomers since the discovery in 1963 that it is not a star at all. Called a quasar (shorthand for “quasi-stellar radio source”) the object is roughly the size of our solar system and mind-bogglingly distant—about two billion light-years away. Quasars are the brightest things in the heavens; each can beam out more light than all the stars in a hundred giant galaxies.

The power source for all this light is a supermassive black hole surrounded by vast amounts of matter—a loosely organized galaxy, perhaps. Some of this material is continually being dragged into the black hole, says Urry. “But before it falls in, it heats up and glows. So, unlike a star, which generates light by nuclear fusion, a quasar uses gravity as its power source.”

A few percent of the 100,000 known quasars also send jets of energy into space. Scientists reasoned that these jets were composed of highly energized electrons traveling through a magnetic field, generating light by a process known as synchrotron radiation. But Urry was troubled by both the time and distance over which any light-emitting particles had to remain highly energetic. The jet in 3C273 is at least 100,000 light-years long—about as long end-to-end as the entire Milky Way galaxy.

“Highly energized particles should lose all their energy instantly and disappear,” says Urry. “But they’re living for thousands of years. Something was weird.”

Perhaps, she suggested, the particles weren’t that energetic in the first place. Urry hypothesized that the jet was made of relatively low-energy electrons, and its light and other kinds of energy came about as the charged particles crashed into dense fields of photons—the cosmic background radiation left over from the beginnings of the universe.

But when Urry and her colleagues examined x-ray (Chandra), optical (Hubble), and infrared (Spitzer) images of the jet, they concluded that low-energy electrons were not the answer. “Our explanation is looking bad,” she says. “The data we’ve collected is best explained by synchrotron radiation from highly energized particles.”

Urry is still trying to understand why the particles are so long-lived, where they’re coming from, and how they’re continually accelerated. “Black holes are way better at particle acceleration than any of the machines we’ve conceived of on Earth,” says Urry. “Our work only tells us what black holes are doing. We don’t know how they’re doing it.”

A secret to staying slim
by Elizabeth Svoboda '03

There may be a thinness gene after all. Associate professor of pharmacology Anton Bennett and his team found that mice bred without the gene-regulating enzyme MKP-1 remain resistant to obesity regardless of how much high-fat food they consume.

Bennett stumbled on MKP-1’s weight-control properties by accident. He acquired a strain of MKP-1-deficient mice from a major pharmaceutical company after it discovered the enzyme was not an ideal target for cancer drugs. Bennett decided to find out whether mice with their MKP-1 knocked out had any other unique attributes.

“A grad student noticed that the knockout mice were smaller than the wild types,” says Bennett. “That gave us the idea to see if MKP-1 was involved in obesity.” His experiments, published recently in the journal Cell Metabolism, showed that mice without the enzyme gained weight much more slowly than their normal counterparts, even on a very fatty diet. The knockout mice also maintained blood-glucose levels in a normal range, which was surprising given that underweight animals usually show a decreased tolerance for glucose in the bloodstream.

Bennett suspects that MKP-1 may serve as a brake on genes that kick metabolism into high gear. “When MKP-1 is absent, that regulatory control is lost, and metabolism speeds up.” An anti-obesity drug that would suppress MKP-1 in humans, Bennett stresses, is still years away.

The origin of the thinking brain
by Trey Popp '97

Thirty days after conception, the human embryo is about as long as a comma, its limbs are no more than microscopic ridges, and the nascent brain is little more than a hollow tube. Scientists have been uncertain precisely how this seemingly simple neural structure gives rise to the various areas of the brain, especially the cerebral cortex—the part often deemed responsible for our most “human” characteristics. But in a recent paper, researchers from the Yale School of Medicine and Oxford University describe their discovery of a new class of nerve cells that appear earlier in neural development than anyone had imagined and may play a critical role in the creation of the “thinking” part of the brain. The paper was published in the journal Nature Neuroscience in July.

The cerebral cortex, which makes up about 40 percent of our brain’s total weight, directs higher-order processes like communication and reasoning. It has achieved its fullest flowering in humans, but the processes that gave rise to its large size remain a mystery. Yale neurobiologist Pasko Rakic and his colleagues suspect that the “predecessor cells” they discovered may be key to solving this puzzle.

The scientists studied human embryos that had been aborted between 31 and 51 days after fertilization. The predecessor neurons were in place at the earliest stage they examined—a full two weeks before neurons had ever been found in human embryos. One of the interesting things about these nerve cells is that, although they were observed in the part of the embryo that develops into the cerebral cortex, they are apparently generated elsewhere. “We think these cells come from lower parts of the brain, which are evolutionarily older, and then migrate tangentially and give information,” says Rakic. The function and lifespan of these distinctive cells, which have not been found in any other species to date, are unknown.

The discovery is so basic that Nature Neuroscience initially wavered over publishing it, says neurobiologist Annette Markus, an associate editor at the journal. “We usually expect there to be some idea of what the function of things are, not just a plain description,” she explains. “But this description was particularly beautiful.”

Rakic is now looking for evidence of these early neurons in mouse and macaque monkey embryos. If they turn up in a species suitable for laboratory experiments, he speculates that further research might eventually reveal the causes of some cognitive disorders. “There are some disorders that appear postnatally, but their origin is before birth, in early gene expression,” he says. “Development is sequential. Every step has to be completed before the next. But if one of the early steps is wrong, then subsequent steps are a little off, and in the end things might not line up perfectly.” With the discovery of the first neurons in the cerebral cortex, scientists may be able to focus one step closer to the very beginning. 

Pregnant? Avoid “keepsake” ultrasounds
by Bruce Fellman

Sonograms have become a routine part of prenatal car e, but a study by neurobiologist Pasko Rakic and colleagues demonstrates a potential risk in commercial ultrasound. When the researchers exposed fetal mice to more than a half hour of ultrasound during a critical time in embryonic development, they found that a “small but statistically significant number” of mouse brain cells did not migrate to their proper place in the brain. The results appear in the August 22 issue of the Proceedings of the National Academy of Sciences.

Rakic is currently investigating what effects ultrasound might have on the brain development of non-human primates. He and other scientists recommend that pregnant women continue to have medically necessary prenatal tests. “Ultrasound has been shown to be very beneficial in the medical context,” says Rakic, who is quick to point out significant differences between the procedures his team used and those recommended by physicians' groups. (Each fetal mouse was exposed to 30 minutes or more of continuous ultrasound; human fetuses receive a fraction of that amount during a typical exam.) “Instead, our study warns against the non-medical use of ultrasound in, for example, prenatal ultrasound videos.”

A bear market in investment smarts
by Marc Wortman

For anyone who wants to make money, the first rule is : don’t throw it away. But when it comes to the stock market, apparently even Harvard College and Wharton MBA students haven’t absorbed that piece of common sense.

The students were test subjects for new research on investors' understanding of the fees charged by mutual funds. Those fees vary widely: even among S&P 500 index funds—whose portfolios are identical—the most expensive funds charge as much as 28 times more than the cheapest funds. Many studies have shown that more-expensive mutual funds offer worse returns. “So why are people willing to pay high fees?” asks James J. Choi, an assistant professor of finance at the School of Management.

Choi and two Harvard colleagues asked their test subjects to allocate $10,000 across four S&P 500 index funds with varying fees. For the study, the latest version of which was published in the National Bureau of Economic Research Working Paper Series in July, the researchers varied the amount of information they provided about the fees and portfolio returns. Subjects in the control group, who received only the funds' prospectuses, largely ignored the fees and instead chose funds with high past returns—a mistake that would cost a real-world investor money. Other subjects, who received both the prospectuses and a fee summary sheet, chose lower-cost portfolios, implying that control subjects had a hard time finding the fees in the prospectuses. “If Harvard undergrads and Wharton MBA students are this bad at understanding the impact of fund fees,” says Choi, “then the typical American investor is probably even worse off.”  

Noted

In the August Social Policy Report, psychology professor Joseph L. Mahoney and his colleagues showed that “organized activities do not dominate American young people’s free time. “ In fact, the researchers found that 40 percent of children don’t participate in organized activities at all, and they suggested that more should join in. Their analysis of data from national surveys demonstrated that involvement was correlated with academic success, less substance abuse, and a better relationship with parents.

Want to know if someone is anti-Semitic? For the August Journal of Conflict Resolution, management professor Edward H. Kaplan and policy analyst Charles A. Small analyzed a 2004 survey of 5,000 citizens of ten European countries and found that people with extreme anti-Israel sentiment are roughly six times more likely to harbor anti-Semitic views than those with more moderate views.

In August’s Conservation Biology, Mark C. Urban, a graduate student at the environment school, showed that roads can make it easier for wildlife diseases to spread. Urban studied the rates at which resident snails at various distances from a wilderness highway in Alaska were infected by parasites. Infection occurred only in ponds within 1,000 feet from the road.

Exercising too little and market practices that encourage overeating are the major causes of obesity, professor of psychiatry Carlos M. Grilo and his colleagues write in the June 27 online issue of the International Journal of Obesity. But they also list ten other important yet often overlooked factors that research has shown can contribute to excessive weight gain. Among them: inadequate sleep, chemical contaminants that disrupt endocrine function, and medications such as antidepressants and birth control pills.

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