Author: Nancy Atkinson

[/caption]

Globular clusters are gravitationally bound, dense concentrations of stars. There can be hundreds of thousands of stars in a cluster, and they are so close together that it’s hard to distinguish globular clusters outside of our galaxy from stars within our own galaxy just using ground-based telescopes: in other words, these big bunches of far away stars can look like a single, nearby star. But astronomers recently used the Hubble Space Telescope’s sharp eyes to identify, incredibly, over 11,000 globular clusters in the Virgo cluster of galaxies. And in doing so, they also noticed something interesting about where the globulars are located. Globular clusters don’t seem to form uniformly from galaxy to galaxy; instead they like to be where the action is near the center of galaxy clusters. The globulars are also more prevalent in dwarf galaxies near the center of the cluster of galaxies.

Hubble’s Advanced Camera for Surveys resolved the star clusters in 100 galaxies of various sizes, shapes, and brightnesses, even in faint, dwarf galaxies. Comprised of over 2,000 galaxies, the Virgo cluster is the nearest large galaxy cluster to Earth, located about 54 million light-years away.
Astronomers have long known that the giant elliptical galaxy at the cluster’s center, M87, hosts a larger-than-predicted population of globular star clusters. The origin of so many globulars has been a long-standing mystery.

“Our study shows that the efficiency of star cluster formation depends on the environment,” said Patrick Cote of the Herzberg Institute of Astrophysics in Victoria, British Columbia. “Dwarf galaxies closest to Virgo’s crowded center contained more globular clusters than those farther away.”

The team found a bounty of globular clusters in most dwarf galaxies within 3 million light-years of the cluster’s center, where the giant elliptical galaxy M87 resides. The number of globulars in these dwarfs ranged from a few dozen to several dozen, but these numbers were surprisingly high for the low masses of the galaxies they inhabited. By contrast, dwarfs in the outskirts of the cluster had fewer globulars. Many of M87’s star clusters may have been snatched from smaller galaxies that ventured too close to it.

“We found few or no globular clusters in galaxies within 130,000 light-years from M87, suggesting the giant galaxy stripped the smaller ones of their star clusters,” explained Eric Peng of Peking University in Beijing, China, and lead author of the Hubble study. “These smaller galaxies are contributing to the buildup of M87.”

Hubble’s “eye” is so sharp that it was able to pick out the fuzzy globular clusters from stars in our galaxy and from faraway galaxies in the background. “With Hubble we were able to identify and study about 90 percent of the globular clusters in all our observed fields,” Peng said. “This was crucial for dwarf galaxies that have only a handful of star clusters.”

Evidence of M87’s galactic cannibalism comes from an analysis of the globular clusters’ composition. “In M87 there are three times as many globulars deficient in heavy elements, such as iron, than globulars rich in those elements,” Peng said. “This suggests that many of these ‘metal-poor’ star clusters may have been stolen from nearby dwarf galaxies, which also contain globulars deficient in heavy elements.”

Studying globular star clusters is critical to understanding the early, intense star-forming episodes that mark galaxy formation. They are known to reside in all but the faintest of galaxies.

“Star formation near the core of Virgo is very intense and occurs in a small volume over a short amount of time,” Peng noted. “It may be more rapid and more efficient than star formation in the outskirts. The high star-formation rate may be driven by the gravitational collapse of dark matter, an invisible form of matter, which is denser and collapses sooner near the cluster’s center. M87 sits at the center of a large concentration of dark matter, and all of these globulars near the center probably formed early in the history of the Virgo cluster.”

The fewer number of globular clusters in dwarf galaxies farther away from the center may be due to the masses of the star clusters that formed, Peng said. “Star formation farther away from the central region was not as robust, which may have produced only less massive star clusters that dissipated over time,” he explained.

Original News Source: HubbleSite Press Release

[/caption]
Scientists from the Phoenix lander are analyzing conflicting results from soil samples delivered to two science instruments on the Mars lander. Two different samples analyzed by the spacecraft’s Wet Chemistry Lab both suggested one of the soil constituents may be perchlorate, a highly oxidizing substance that is considered toxic. But results from the TEGA instrument, (Thermal and Evolved-Gas Analyzer) downloaded from the lander over the weekend indicated no evidence of perchlorate. These findings may may have prompted the reports of “provocative” science results recently. Today, Phoenix officials said any reports of the spacecraft finding life were unfounded, and over the weekend, the Phoenix spacecraft itself said, via Twitter, that reports of White House briefings were not true. NASA will hold a media teleconference on Tuesday, Aug. 5, at 2 p.m. EDT, to discuss the recent science activities. A press release from the Phoenix team today said, “Confirmation of the presence of perchlorate and supporting data is important prior to scientific peer review and subsequent public announcements.”

Scientists said that while the conflicting results are unexpected, they are working hard to understand the soil chemistry and mineralogy in the Mars northern arctic region.

“This is surprising since an earlier TEGA measurement of surface materials was consistent with but not conclusive of the presence of perchlorate,” said Peter Smith, Phoenix’s principal investigator at the University of Arizona, Tucson. “We are committed to following a rigorous scientific process. While we have not completed our process on these soil samples, we have very interesting intermediate results,” said Smith, “Initial MECA analyses suggested Earth-like soil. Further analysis has revealed un-Earthlike aspects of the soil chemistry.”

The team also is working to totally exonerate any possibility of the perchlorate readings being influenced by terrestrial sources which may have migrated from the spacecraft, either into samples or into the instrumentation. One type of perchlorate, ammonium perchlorate, is sometimes used as an oxidizer in rocket fuel.

“When surprising results are found, we want to review and assure our extensive pre-launch contamination control processes covered this potential,” said Barry Goldstein, Phoenix project manager at NASA’s Jet Propulsion Laboratory.

An article on AviationWeek.com reported August 1 that the US president had been briefed on findings from Phoenix, and NASA would be ready to reveal the findings in mid-August. An article on Universe Today was based on that report. Today, Aviation Week & Space Technology stands by its report, saying that “the new information involves the “potential for life” on Mars. That potential can either be positive or negative, and the new data indicate the new soil tests are at best inconclusive, according to the information being released on the soil chemistry experiment.”

Phoenix’s Wet Chemistry Lab is part of the Microscopy, Electrochemistry, and Conductivity Analyzer, or MECA instrument which studies soluble chemicals in the soil by mixing a soil sample with a water-based solution with several reagents brought from Earth. The inner surface of each cell’s beaker has 26 sensors that give information about the acidity or alkalinity and concentrations of elements such as chloride or perchlorate. The beaker also can detect concentrations of magnesium, calcium and potassium, which form salts that are soluble in water.

The TEGA instrument has tiny ovens that heat soil samples, and analyzers that “sniff” vapors released from substances in a sample.

Original News Source: Phoenix News

[/caption]
What were the first stars like that formed shortly after the Big Bang? We don’t know much about the conditions of the early universe 13 billion years ago, but a new computer simulation provides the most detailed picture yet of the first stars and how they came into existence. The composition of the early universe was quite different from that of today, said Dr. Naoki Yoshida, Nagoya University in Nagoya, Japan and Dr. Lars Hernquist at the Harvard-Smithsonian Center for Astrophysics in Cambridge, MA. An article that will be published to the August 1 journal Science describes their findings from the computer model that simulates the early days of the universe, the “cosmic dark ages,” where the physics governing the universe were somewhat simpler. The astronomers believe small, simple protostars formed, which eventually became massive, but short-lived stars.

According to their simulations, gravity acted on minute density variations in matter, gases, and the mysterious “dark matter” of the universe after the Big Bang in order to form the early stages of a star called a protostar. With a mass of just one percent of our Sun, Dr. Yoshida’s simulation also shows that the protostar would likely evolve into a massive star capable of synthesizing heavy elements, not just in later generations of stars, but soon after the Big Bang. These stars would have been up to one hundred times as massive as our Sun and would have burned for no more than one million years. “This general picture of star formation, and the ability to compare how stellar objects form in different time periods and regions of the universe, will eventually allow investigation in the origins of life and planets,” said Hernquist.

“The abundance of elements in the Universe has increased as stars have accumulated,” he says, “and the formation and destruction of stars continues to spread these elements further across the Universe. So when you think about it, all of the elements in our bodies originally formed from nuclear reactions in the centers of stars, long ago.”

The goal of their research is to be able to figure out how the primordial stars formed, as well as predicting the mass and properties of the first stars of the universe. The researchers hope to eventually extend this simulation to the point of nuclear reaction initiation – when a stellar object becomes a true star. But that’s the point where the physics becomes much more complicated, and the researchers say they’ll need more computational resources to simulate that process.

Original news source: Harvard Smithsonian Center for Astrophysics

[/caption]
A team of astronomers has found what they say is the clearest detection to date of dark energy in the universe. Scientists at the University of Hawaii compared an existing database of galaxies with a map of the cosmic microwave background radiation (CMB), and were able to detect dark energy’s effect on vast cosmic structures such as superclusters of galaxies, where there is a high concentration of galaxies, and supervoids, areas in space with a small number of galaxies. “We were able to image dark energy in action, as it stretches huge supervoids and superclusters of galaxies,” said Dr. István Szapudi said, from U of Hawaii’s Institute for Astronomy.

The discovery in 1998 that the universe was actually speeding up in its expansion was a surprise to astronomers. Dark energy refers to the fact that something must fill the vast reaches of mostly empty space in the Universe in order to be able to make space accelerate in its expansion. Dark energy works against the tendency of gravity to pull galaxies together and so causes the universe’s expansion to speed up.But the nature of dark energy and why it exists is one of the biggest puzzles of modern science.

The team from the University of Hawaii made the discovery by measuring the subtle imprints that superclusters and supervoids leave in microwaves that pass through them. Superclusters and supervoids are the largest structures in the universe.

“When a microwave enters a supercluster, it gains some gravitational energy, and therefore vibrates slightly faster,” explained Szapudi. “Later, as it leaves the supercluster, it should lose exactly the same amount of energy. But if dark energy causes the universe to stretch out at a faster rate, the supercluster flattens out in the half-billion years it takes the microwave to cross it. Thus, the wave gets to keep some of the energy it gained as it entered the supercluster.”

“Dark energy sort of gives microwaves a memory of where they’ve been recently,” postdoctoral scientist Mark Neyrinck said.

“With this method, for the first time we can actually see what supervoids and superclusters do to microwaves passing through them,” said graduate student Benjamin Granett.

The signal is difficult to detect, since ripples in the primordial CMB are larger than the imprints of individual superclusters and supervoids. To extract a signal, the team averaged together patches of the CMB map around the 50 largest supervoids and the 50 largest superclusters that they detected in extremely bright galaxies drawn from the Sloan Digital Sky Survey, a project that mapped the distribution of galaxies over a quarter of the sky.

The astronomers say there is only a one in 200,000 chance that the evidence they detected would occur by chance.

Original News Source: U of Hawaii press release