Dark matter powered the first stars, physicists speculate
The first stars to form in the early universe may have been “dark stars” fueled by an altogether different engine than those visible in the night sky now, according to a team of physicists that includes U-M professor Katherine Freese.
Ordinary stars like the sun burn brightly because they are fueled by nuclear fusion in their core that converts hydrogen to helium. But these theoretical dark stars would have run on dark matter particles colliding and annihilating each other.
Dark matter is a substance astronomers have not observed directly, but they deduce it exists because they detect its gravitational effects on visible matter. The prevailing theory is that the visible parts of the universe make up just 15 percent of its total matter.
Freese and her colleagues analyzed the young universe through the lens of the dark matter theory.
“We asked: Well, what about this enormous reservoir of dark matter? What does it do and what does it mean for star formation,” says Freese, a professor in the Department of Physics who studies particle astrophysics. She is an author of a paper on this research to be published in the January edition of Physical Review Letters.
The findings dramatically alter the current theoretical framework for the formation of the first stars, the paper says.
The universe is estimated to be 15 billion years old, with the first stars having formed when the cosmos was just 150 million years old.
They are thought to have formed inside clouds of dark matter, when hydrogen and helium gases cooled to a temperature at which nuclear fusion could begin. Conventional theory says dark matter didn’t affect this process except to provide the gravity to bring the gases together.
Freese and her colleagues believe otherwise. They say the dark matter concentrations were high enough for the particles in the dark matter clouds to collide with each other, destroying themselves and, more importantly, keeping the burgeoning star too hot to collapse to a high enough density for fusion to begin.
The paper is called “Dark matter and the first stars: A new phase of stellar evolution.” Freese also is associate director of the Michigan Center for Theoretical Physics.
Protein protects brain against compound in lead poisoning
Scientists have discovered that a protein known as PEPT2 protects the brains of mice from a naturally occurring but potentially toxic compound present in lead poisoning and in a class of liver diseases that can cause serious neurological complications.
Scientists at U-M found that when dosed with the compound called 5-aminolevulinic acid (5-ALA), mice without the PEPT2 protein died sooner, had neuromuscular dysfunction and had up to 30 times higher concentrations of the toxic compound in their cerebrospinal fluid than did mice with the PEPT2.
PEPT2 is part of a class of membrane proteins called transporter proteins. The research focuses on understanding how these proteins work so that eventually, transporter proteins can be used to deliver different compounds to or from areas of the body in order to help fight diseases such as cancer.
“The findings suggest that the PEPT2 protein could work the same way in humans,” says David Smith, professor and chair of pharmaceutical sciences. “If that is the case, then PEPT2 may have relevance as a secondary genetic modifier of conditions such as acute hepatic porphyrias and lead poisoning, and in drug transport at the blood-brain barrier.
“We are looking at how to use the body’s own machinery to get the compounds to where we want them to go.”
Naturally occurring in the body, the acid is involved in forming a substance called heme, which is a component of hemoglobin as well as many important enzymes. If there is an accumulation or an overproduction of 5-ALA in the body, however, it can become toxic. High concentrations of 5-ALA are present in people who have lead poisoning or hepatic porphyrias.
Smith’s co-authors on the paper, which appears in the December issue of the Journal of Neurochemistry, include Yongjun Hu, Hong Shen, pharmaceutical sciences and Upjohn Center for Clinical Pharmacology; and Richard Keep, departments of neurosurgery and molecular and integrative physiology.
— Laura Bailey, News Service
Connection found between hospital volume, infant mortality in heart patients
A new U-M study suggests that there may be a way to give babies born with severe heart defects a better chance at living: Get them to the hospitals that are the most experienced at handling such cases.
In the first national study of this issue, a team of researchers found that infants with specific complex heart defects are much less likely to die before leaving the hospital if they are treated at the centers that treat the largest numbers of these patients. This relationship between hospital volume and mortality has been seen in adult heart operations, but the new study suggests it holds true for infants as well. The study is published online in the journal Pediatric Cardiology.
“A generation ago, we were just happy when these patients lived, but that’s not good enough anymore,” says lead author Dr. Jennifer Hirsch, a pediatric cardiac surgeon and member of the Michigan Congenital Heart Center.
Hirsch and her colleagues based their study on data from the 2003 Kids’ Inpatient Database, a national database sponsored by the Agency for Healthcare Research and Quality that includes information on children hospitalized in 36 states.
They analyzed data for two of the most severe congenital heart defects: transposition of the great arteries (TGA), in which the major blood vessels leading between the heart and lungs are switched, and hypoplastic left heart syndrome (HLHS), in which the left side of the heart does not develop properly.
Both defects are lethal if not treated within a few weeks of birth, with operations called the arterial switch operation for TGA and the Norwood procedure for HLHS. Infants may need additional operations later in life, but these initial open-heart procedures are critical for their survival.
The study shows that an infant’s risk of dying in the hospital during or after their operation varied greatly depending on the number of each procedure performed that year at the hospital.
In addition to Hirsch, the paper’s authors are pediatric heart surgeon Dr. Richard Ohye, James Gurney and Janet Donohue, of the Child Health Evaluation and Research Unit. More information on the Michigan Congenital Heart Center is at www.med.umich.edu/cvc/mchc.
— Kara Gavin, UMHS Public Relations
Mixed results: Combining scaffold ingredients yields surprising nanoporous structure
With a novel twist on existing techniques used to create porous crystals, U-M researchers have developed a new, high-capacity material that may be useful in storing hydrogen, methane and carbon dioxide.
The work builds on a worldwide research effort in the area of porous coordination polymers with high surface areas. Omar Yaghi, a former U-M professor and pioneer in this area, coined the term metal-organic frameworks (MOFs) for these materials, which can be described as scaffolds made up of metal hubs linked together with struts of organic compounds. MOFs typically are made by combining one type of metal with one type of organic linker, but Matzger’s team tried a new strategy: mixing two types of linkers with one metal (zinc).
The result was not a mixture of two types of MOFs, as might be expected, but an entirely new material, dubbed UMCM-1 (U-M Crystalline Material-1), whose structure differs dramatically from that of all known MOFs.
The UMCM-1 structure is made up of six, microporous cage-like structures surrounding a hexagonal channel. The channel, categorized as a mesopore (a pore in the two- to 50-nanometer range), “is like a highway connecting all the microporous cages,” a feature that might expedite filling the micropores, says Matzger, an associate professor of chemistry. Researchers have been tinkering with porous materials, trying to improve their capacities, in hopes of finding ways to compactly store large amounts of hydrogen, methane, carbon dioxide and other economically and environmentally important gases.
The mixed-linker approach “exponentially increases the possibilities” for making new, porous materials, Matzger says. In addition, because it allows for mixing a less-expensive linker with a more expensive one, it could lead to substantial cost savings.
Matzger’s coauthors on the paper are postdoctoral researcher Kyoungmoo Koh and research scientist Antek Wong-Foy. The researchers received funding from the U.S. Department of Energy.
Their latest results were published online Dec. 4 in the journal Angewandte Chemie.
— Nancy Ross-Flanigan, News Service
