Posted on by Fraser Cain

Is There Water on the Moon?

The first object in the night sky most of us ever saw, the Moon remains a mystery. Haunted by poets, looked upon by youngsters in love, studied intensely by astronomers for four centuries, examined by geologists for the last 50 years, walked upon by twelve humans, this is Earth’s satellite.

And as we look towards the Moon with thoughts of setting up a permanent home there, one new question is paramount: does the Moon have water? Although none has been definitely detected, recent evidence suggests that it’s there.

Why should there be water on the Moon? Simply for the same reason that there’s water on Earth. A favorite theory is that water, either as water by itself or as its components of hydrogen and oxygen, was deposited on Earth during its early history–mostly during a period of “late heavy bombardment” 3.9 billion years ago–by the impacts of comets and asteroids. Because the Moon shares the same area of space as Earth, it should have received its share of water as well. However, since it has only a tiny fraction of Earth’s gravity, most of the Moon’s water supply should have evaporated and drifted off into space long ago. Most, but perhaps not all.

In ancient times, observers commonly thought the Moon had abundant water–in fact, the great lava plains like Mare Imbrium were called maria, or seas. But when Neil Armstrong and Buzz Aldrin landed on the Moon in 1969, they stepped out not into the water of the Sea of Tranquillity, but onto basaltic rock. No one was surprised by that–the idea of lunar maria had been replaced by lava plains decades earlier.

As preparations were underway in the mid 1960s for the Apollo program, questions about water on the Moon were barely on the radar screen. Geologists and astronomers were divided at the time as to whether the lunar surface was a result of volcanic forces from beneath, or cosmic forces from above. Grove Carl Gilbert in 1893 already had the answer. That famous geologist suggested that large asteroidal objects hit the Moon, forming its craters. Ralph Baldwin articulated the same idea in 1949, and Gene Shoemaker revived the idea again around 1960. Shoemaker, almost alone among geologists of his day, saw the Moon as a fertile subject for field geology. He saw the craters on the Moon as logical impact sites that were formed not gradually in eons, but explosively in seconds.

The Apollo flights confirmed that the dominant geological process on the Moon is impact-related. That discovery, in turn, ushered in a new question: Since Earth’s water was probably delivered largely by comets and asteroids, could this process have done the same for the Moon? And could some of that water still be there?

In 1994, the SDI-NASA Clementine spacecraft orbited the Moon and mapped its surface. In one experiment, Clementine beamed radio signals into shadowed craters near the Moon’s south pole. The reflections, received by antennas on Earth, seemed to come from icy material.

That makes sense. If there is water on the Moon, it’s probably hiding in the permanent shadows of deep, cold craters, safe from vaporizing sunlight, frozen solid.

So far so good, but… the Clementine data were not conclusive, and when astronomers tried to find ice in the same craters using the giant Arecibo radar in Puerto Rico, they couldn’t. Maybe Clementine was somehow wrong.

In 1998, NASA sent another spacecraft, Lunar Prospector, to check. Using a device called a neutron spectrometer, Lunar Prospector scanned the Moon’s surface for hydrogen-rich minerals. Once again, polar craters yielded an intriguing signal: neutron ratios indicated hydrogen. Could it be the “H” in H2O? Many researchers think so.

Lunar Prospector eventually sacrificed itself to the search. When the spacecraft’s primary mission was finished, NASA decided to crash Prospector near the Moon’s south pole, hoping to liberate a bit of its meager layer of water. Earth’s satellite might briefly become a comet as amounts of water vapor were released.

Lunar Prospector crashed, as planned, and several teams of researchers tried to detect that cloud, but without success. Either there was no water, or there was not enough water to be detected by Earth-based telescopes, or the telescopes were not looking in precisely the right place. In any event, no water was found from Prospector’s impact.

In 2008, NASA plans to send a new spacecraft to the Moon: the Lunar Reconnaissance Orbiter (LRO), bristling with advanced sensors that can sense water in at least four different ways. Scientists are hopeful that LRO can decide the question of Moon water once and for all.

Our interest is not just scientific. If we are indeed to build a base on the Moon, the presence of water already there would offer a tremendous advantage in building and running it. It’s been 35 years since we first set foot on the Moon. Now ambitious eyes once again look toward our satellite not just as a place to visit, but as a place to live.

Original Source: Science@NASA

Posted on by Fraser Cain

Perfect Liquid Hints at Early Universe

Physicists working to re-create the matter that existed at the birth of the universe expected something like a gas and ended up with the “perfect” liquid, four teams of researchers reported at an April 18 meeting of the American Physical Society. One of the teams is led by MIT.

“These truly stunning findings have led us to conclude that we are seeing something completely new–an unexpected form of matter–which is opening new avenues of thought about the fundamental properties of matter and the conditions that existed just after [the Big Bang],” said Raymond Orbach, director of the U.S. Department of Energy’s Office of Science, the primary supporter of the research.

Unlike ordinary liquids, in which individual molecules move about randomly, the new matter seems to move in a pattern that exhibits a high degree of coordination among the particles–something like a school of fish that responds as one entity while moving through a changing environment. That fluid motion is nearly “perfect,” as defined by the equations of hydrodynamics.

Picture a stream of honey, then a stream of water. “Water flows much more easily than honey, and the new liquid we’ve created seems to flow much more easily than water,” said Wit Busza, leader of the MIT team and the Francis Friedman Professor of Physics. Other MIT faculty involved in the work are Professor Bolek Wyslouch and Associate Professor Gunther Roland, both of physics.

Busza notes that the results don’t rule out that a gas-like form of matter existed at some point in the young universe, but the data do suggest “something different, and maybe even more interesting, at the lower energy densities created at RHIC (Relativistic Heavy Ion Collider).”

The research has also led to several other surprises. For example, “there is an elegance we see in the data that is not reflected in our theoretical understanding–yet,” said Roland.

Birth of the universe
About ten millionths of a second after the Big Bang, physicists believe that the universe was composed of a gas of weakly interacting objects, quarks and gluons that would ultimately clump together to form atomic nuclei and matter as we know it.

So, over the last 25 years, scientists have been working to re-create that gas, or quark-gluon plasma, by building ever-larger atom smashers. “The idea is to accelerate nuclei to nearly the speed of light, then have them crash head-on,” Busza said. “Under those conditions the plasma is expected to form.” The current results were achieved at the Relativistic Heavy Ion Collider located at the DOE’s Brookhaven National Laboratory.

RHIC accelerates gold nuclei in a circular tube some 2 kilometers in diameter. In four places the nuclei collide, and around those sites teams of scientists have built detectors to collect the data. The four instruments–STAR, PHENIX, PHOBOS and BRAHMS–vary in their approaches to tracking and analyzing particles’ behavior. The work reported at the APS meeting summarizes the first three years of RHIC results from all four devices. Papers from each team will also be published simultaneously in an upcoming issue of the journal Nuclear Physics A.

MIT is the lead institution for PHOBOS, a collaboration between the United States, Poland and Taiwan. “We are very small,” said Busza, who developed the concept for the device. “STAR and PHENIX each cost about $100 million and have some 400 staff. We cost less than $10 million and have about 50 people,” he said. (BRAHMS is also small.)

Nevertheless, the PHOBOS team got the first physics results from three of the five RHIC experimental runs and tied for first on a fourth. (The fifth run is still being analyzed.)

For one of those runs, the team collected the data, analyzed them and submitted a paper on the work all within five weeks. “That’s unheard of in high-energy physics,” said Busza, who credits Roland with the fast turnaround. “He was the person who managed the extraction of the physics from the data.”

What’s next?
Although the larger RHIC detectors will continue to collect data, PHOBOS has been retired. “From a cost-benefit perspective, we feel we’ve extracted as much knowledge as we can from such a small experiment,” Busza said.

So the team is now looking to the future. The members hope to continue their studies at RHIC’s successor, the Large Hadron Collider (LHC) being built in Europe. That facility will have 30 times the collision energy of RHIC, which will bring the scientists that much closer to the conditions at the birth of the universe. “At LHC we’ll test what we think we learned from RHIC,” Busza said. “We also expect new surprises, perhaps even bigger surprises,” he concluded.

MIT research staff currently involved in PHOBOS are Maarten Ballintijn, Piotr Kulinich, Christof Roland, George Stephans, Robin Verdier, Gerrit vanNieuwenhuizen and Constantin Loizides. Six graduate students are also on the team; the research has already resulted in five theses, with two on the way.

Original Source: MIT News Release

Posted on by Fraser Cain

Audio Feedback?

I’ve just wrapped up my fifth audio interview for Universe Today, and I was hoping to get some feedback from listeners. My goal with this is to focus on specific breaking research and chat with the researchers – it’s very minimalist, though, not a lot of rambling about the weather here at the Cain Cottage in Courtenay. I’ve been having a fun time, and should be able to produce 2-3 of these a week. So, give me any feedback. Who do you want to interviews with? I’m not crazy about the audio quality, and I’ve got my eyes on some new equipment that should improve things greatly.

If you like longer, more in-depth radio interviews, I highly recommend the Space Show, hosted by Dr. David Livingston, which spends 1+ hours talking to a single guest about a range of topics – no subscription link, yet. I can’t believe the quality of guests he’s had on the show in the past, especially this guy. Another great audio show is Slacker Astronomy. They tend to focus on a single topic, and explain it more comprehensively – with silly humour.

I’ve become a huge fan of Podcasting in the last few months (although, I despise the term… we seem to be stuck with it). I love being subscribed to various audio programs, so they just show up on my computer whenever they’ve been updated. It helps to have a portable audio player, but you can just play shows from your computer too; the point is that you’re subscribed. You can download the free subscription software here, and then start subscribing to various Podcast feeds. Here’s what I’m subscribed to: Quirks and Quarks (feed), In Our Time (feed), Reith Lectures (feed). Got any you like? Drop me an email with your suggestions.

Fraser Cain
Publisher
Universe Today

Posted on by Fraser Cain

Low Oxygen Accelerated the Great Dying

The biggest mass extinction in Earth history some 251 million years ago was preceded by elevated extinction rates before the main event and was followed by a delayed recovery that lasted for millions of years. New research by two University of Washington scientists suggests that a sharp decline in atmospheric oxygen levels was likely a major reason for both the elevated extinction rates and the very slow recovery.

Earth’s land at the time was still massed in a supercontinent called Pangea, and most of the land above sea level became uninhabitable because low oxygen made breathing too difficult for most organisms to survive, said Raymond Huey, a UW biology professor.

What’s more, in many cases nearby populations of the same species were cut off from each other because even low-altitude passes had insufficient oxygen to allow animals to cross from one valley to the next. That population fragmentation likely increased the extinction rate and slowed recovery following the mass extinction, Huey said.

“Biologists have previously thought about the physiological consequences of low oxygen levels during the late Permian period, but not about these biogeographical ones,” he said.

Atmospheric oxygen content, about 21 percent today, was a very rich 30 percent in the early Permian period. However, previous carbon-cycle modeling by Robert Berner at Yale University has calculated that atmospheric oxygen began plummeting soon after, reaching about 16 percent at the end of the Permian and bottoming out at less than 12 percent about 10 million years into the Triassic period.

“Oxygen dropped from its highest level to its lowest level ever in only 20 million years, which is quite rapid, and animals that once were able to cross mountain passes quite easily suddenly had their movements severely restricted,” Huey said.

He calculated that when the oxygen level hit 16 percent, breathing at sea level would have been like trying to breathe at the summit of a 9,200-foot mountain today. By the early Triassic period, sea-level oxygen content of less than 12 percent would have been the same as it is today in the thin air at 17,400 feet, higher than any permanent human habitation. That means even animals at sea level would have been oxygen challenged.

Huey and UW paleontologist Peter Ward are authors of a paper detailing the work, published in the April 15 edition of the journal Science. The work was supported by grants from the National Science Foundation and the National Aeronautics and Space Administration’s Astrobiology Institute.

Not only was atmospheric oxygen content dropping at the end of the Permian, the scientists said, but carbon dioxide levels were rising, leading to global climate warming.

“Declining oxygen and warming temperatures would have been doubly stressful for late Permian animals,” Huey said. “As the climate warms, body temperatures and metabolic rates go up. That means oxygen demand is going up, so animals would face an increased oxygen demand and a reduced supply. It would be like forcing athletes to exercise more but giving them less food. They’d be in trouble.”

Ward was lead author of a paper published in Science earlier this year presenting evidence that extinction rates of land vertebrates were elevated throughout the late Permian, likely because of climate change, and culminated in a mass extinction at the end of the Permian. The event, often called “the Great Dying,” was the greatest mass extinction in Earth’s history, killing 90 percent of all marine life and nearly three-quarters of land plants and animals.

Ward said paleontologists had previously assumed that Pangea was not just a supercontinent but also a “superhighway” on which species would have encountered few roadblocks while moving from one place to another.

However, it appears the greatly reduced oxygen actually created impassable barriers that affected the ability of animals to move and survive, he said.

“If this is true, then I think we have to go back and look at oxygen and its role in evolution and how different species developed,” Ward said. “You can go without food for a couple of weeks. You can go without water for a few days. How long can you go without oxygen, a couple of minutes? There’s nothing with a greater evolutionary effect than oxygen.”

Original Source: UW News Release

Posted on by Fraser Cain

The Search for the Mountain of Eternal Sunlight

ESA?s SMART-1 mission to the Moon has been monitoring the illumination of lunar poles since the beginning of 2005, about two months before arriving at its final science orbit.

Ever since, the AMIE on-board camera has been taking images which are even able to show polar areas in low illumination conditions. Images like these will help identify if peaks of eternal light exist at the poles.

SMART-1 took views of the North Polar Region from a distance of 5000 km during a pause in the spiralling descent to the science orbit. One can see highland terrains, very highly cratered due to their old age. The rims of the large craters project very long shadows even on surrounding features. SMART-1 is monitoring the polar shadows cast during the Moon rotation, and their seasonal variations, to look for places with long-lasting illumination.

The image shows a 275 km area close to the North pole (upper left corner) observed by SMART-1 on 29 December 2004 from a distance of 5500 km. This shows a heavily cratered highland terrain, and is used to monitor illumination of polar areas, and long shadows cast by large crater rims.

SMART-1 also observated a North polar area 250 km wide on 19 January 2005 (close to North winter solstice) from a distance of 5000 km. The illuminated part of crater rim is very close to the North pole and is a candidate for a peak of eternal sunlight.

?This shows the ability of SMART-1 and its camera to image even for low light levels at the poles and prospect for sites for future exploration?, says AMIE camera Principal Investigator Jean-Luc Josset, (SPACE-X, Switzerland).

?If we can confirm peaks of eternal light?, adds Bernard Foing, SMART-1 Project Scientist, ?these could be a key locations for possible future lunar outposts?.

The existence of peaks of eternal light at the poles, that is areas that remain eternally illuminated regardless of seasonal variations, was first predicted in the second half of the nineteenth century by the astronomer Camille Flammarion. Even if for most of the Moon the length of the day does not vary perceptibly during the course of seasons, this is not the case over the poles, where illumination can vary extensively during the course of the year. The less favourable illumination conditions occur around the northern winter solstice, around 24 January. There are areas at the bottom of near-polar craters that do not see direct sunshine, where ice might potentially be trapped. Also there are areas at higher elevation on the rim of polar craters that see the Sun more than half of the time. Eventually, there may be areas that are always illuminated by sunlight.

Original Source: ESA News Release

Posted on by Fraser Cain

Problem with Opportunity’s Front Wheel

The terrain that Opportunity is crossing has been steadily getting more wavy. After a long drive southward from “Voyager” crater, Opportunity’s right-front steering motor stalled out on sol 433 during an end-of-drive turn. While performing tests to help the team diagnose the condition of that motor, the rover also continued to make remote-sensing observations. Testing in sol 435 did show motion in the steering motor, but analysis is still underway. The rover resumed normal science and driving operations on sol 436, but with restrictions on use of the right-front steering motor. It drove 30 meters on sol 437. Opportunity and Spirit are capable of driving with one or more steering motors disabled, though turns would be less precise. The latest revision in flight software on both rovers, uploaded in February, gives them improved capabilities for dealing with exactly this type of condition. It gives them upgraded ability to repeatedly evaluate how well they are following the intended course during a drive, and to adjust the steering autonomously if appropriate.

Original Source: NASA/JPL News Release

Posted on by Fraser Cain

Ghostly Supernova Remnant

This image, made by combining 150 hours of archived Chandra data, shows the remnant of a supernova explosion. The central bright cloud of high-energy electrons is surrounded by a distinctive shell of hot gas.

The shell is due to a shock wave generated as the material ejected by the supernova plows into interstellar matter. The shock wave heats gas to millions of degrees, producing X-rays in the process.

Although many supernovas leave behind bright shells, others do not. This supernova remnant, identified as G21.5-0.9 by radio astronomers 30 years ago, was considered to be one that had no shell until it was revealed by Chandra.

The absence of a detectable shell around this and similar supernova remnants had led astronomers to speculate that another, weaker type of explosion had occurred. Now this hypothesis seems unlikely, and it is probable that the explosion of every massive star sends a strong shock wave rumbling through interstellar space.

Some supernova shells are faint because of the lack of material around the star before it explodes. Rapid mass loss from the star before the explosion could have cleared out the region.

By examining the properties of the shell with an X-ray telescope, astronomers can work back to deduce the age (a few thousand years), and energy of the explosion, as well as information about the state of the star a million years before it exploded. The star that produced this supernova shell is thought to have been at least 10 times as massive as the Sun.

Original Source: Chandra News Release

Posted on by Fraser Cain

Ancient Impact Craters Reveal Mars’ First Equator

Since the time billions of years ago when Mars was formed, it has never been a spherically symmetric planet, nor is it composed of similar materials throughout, say scientists who have studied the planet. Since its formation, it has changed its shape, for example, through the development of the Tharsis bulge, an eight kilometer [five mile] high feature that covers one-sixth of the Martian surface, and through volcanic activity. As a result of these and other factors, its polar axis has not been stable relative to surface features and is known to have wandered through the eons as Mars rotated around it and revolved around the Sun.

Now, a Canadian researcher has calculated the location of Mars’ ancient poles, based upon the location of five giant impact basins on the planet’s surface. Jafar Arkani-Hamed of McGill University in Montreal, Quebec, has determined that these five basins, named Argyre, Hellas, Isidis, Thaumasia, and Utopia, all lie along the arc of a great circle. This suggests that the projectiles that caused the basins originated with a single source and that the impacts trace the Martian equator at the time of impact, which was prior to the development of the Tharsis bulge, he says.

Writing in the Journal of Geophysical Research (Planets), Arkani-Hamed calculates that the source of the five projectiles was an asteroid that had been circling the Sun in the same plane as Mars and most of the other planets. At one point, it passed close to the planet, until the force of Martian gravity surpassed the tensile strength of the asteroid, at which point it fragmented. The five large fragments would have remained in the same plane, that of Mars’ then-equator. They hit in different spots around the Martian globe, due to Mars’ rotation on its then-axis and the differing lengths of time the fragments took before impacting on Mars.

Arkani-Hamed describes the locations of the resulting basins, only three of which are well preserved. The two others have been detected by analysis of Martian gravitational anomalies. The great circle they describe on the Martian surface has its center at latitude -30 and longitude 175. By realigning the map of Mars with that spot as the south pole, the great circle marks the ancient equator.

Arkani-Hamed estimates that the mass of the asteroid captured by Mars was about one percent of that of Earth’s Moon. Its diameter was in the range of 800 to 1,000 kilometers [500 to 600 miles], depending upon its density, which cannot be determined.

The significance of Arkani-Hamed’s findings, if borne out by further research, is that the extent of presumed underground water on Mars would have to be reassessed. “The region near the present equator was at the pole when running water most likely existed,” he said in a statement. “As surface water diminished, the polar caps remained the main source of water that most likely penetrated to deeper strata and has remained as permafrost, underlain by a thick groundwater reservoir. This is important for future manned missions to Mars.”

Original Source: AGU News Release

Posted on by Fraser Cain

Fundamental Aspect of the Universe has Remained Unchanged

A fundamental number that affects the color of light emitted by atoms as well as all chemical interactions has not changed in more than 7 billion years, according to observations by a team of astronomers charting the evolution of galaxies and the universe.

The results are being reported today (Monday, April 18) at the annual meeting of the American Physical Society (APS) by astronomer Jeffrey Newman, a Hubble Fellow at Lawrence Berkeley National Laboratory representing DEEP2, a collaboration led by the University of California, Berkeley, and UC Santa Cruz. Newman is presenting the data and an update on the DEEP2 project at a 1 p.m. EDT press conference at the Marriott Waterside Hotel in Tampa, Fla.

The fine structure constant, one of a handful of pure numbers that occupy a central role in physics, pops up in nearly all equations involving electricity and magnetism, including those describing the emission of electromagnetic waves – light – by atoms. Despite its fundamental nature, however, some theorists have suggested that it changes subtly as the universe ages, reflecting a change in the attraction between the atomic nucleus and the electrons buzzing around it.

Over the past few years, a group of Australian astronomers has reported that the constant has increased over the lifetime of the universe by about one part in 100,000, based on its measurements of the absorption of light from distant quasars as the light passes through galaxies closer to us. Other astronomers, however, have found no such change using the same technique.

The new observations by the DEEP2 survey team use a more direct method to provide an independent measure of the constant, and show no change within one part in 30,000.

“The fine structure constant sets the strength of the electromagnetic force, which affects how atoms hold together and the energy levels within an atom. At some level, it is helping set the scale of all ordinary matter made up of atoms,” Newman said. “This null result means theorists don’t need to find an explanation for why it would change so much.”

The fine structure constant, designated by the Greek letter alpha, is a ratio of other “constants” of nature that, in some theories, could change over cosmic time. Equal to the square of the charge of the electron divided by the speed of light times Planck’s constant, alpha would change, according to one recent theory, only if the speed of light changed over time. Some theories of dark energy or grand unification, in particular those that involve many extra dimensions beyond the four of space and time with which we are familiar, predict a gradual evolution of the fine structure constant, Newman said.

DEEP2 is a five-year survey of galaxies more than 7-to-8-billion-light years distant whose light has been stretched out or redshifted to nearly double its original wavelength by the expansion of the universe. Though the collaborative project, supported by the National Science Foundation, was not designed to look for variation in the fine structure constant, it became clear that a subset of the 40,000 galaxies so far observed would serve that purpose.

“In this gigantic survey, it turns out that a small fraction of the data seems to be perfect for answering the question Jeff’s asking,” said DEEP2 principal investigator Marc Davis, professor of astronomy and of physics at UC Berkeley. “This survey is really general purpose and will serve a million uses.”

Several years ago, astronomer John Bahcall of the Institute for Advanced Study pointed out that, in the search for variations in the fine structure constant, measuring emission lines from distant galaxies would be more direct and less error-prone that measuring absorption lines. Newman quickly realized that DEEP2 galaxies containing oxygen emission lines were perfectly suited to provide a precise measure of any change.

“When the contradictory results from absorption lines starting showing up, I had the idea that, since we have all these high redshift galaxies, maybe we can do something not with absorption lines, but with emission lines within our sample,” Newman said. “Emission lines would be very slightly different if the fine structure constant changed.”

The DEEP2 data allowed Newman and his colleagues to measure the wavelength of emission lines of ionized oxygen (OIII, that is, oxygen that has lost two electrons) to a precision of better than 0.01 Angstroms out of 5,000 Angstroms. An Angstrom, about the width of a hydrogen atom, is equivalent to 10 nanometers.

“This is a precision surpassed only by people trying to look for planets,” he said, referring to detection of faint wobbles in stars due to planets tugging on the star.

The DEEP2 team compared the wavelengths of two OIII emission lines for 300 individual galaxies at various distances or redshifts, ranging from a redshift of about 0.4 (approximately 4 billion years ago) to 0.8 (about 7 billion years ago). The measured fine structure constant was no different from today’s value, which is approximately 1/137. There also was no upward or downward trend in the value of alpha over this 4-billion-year time period.

“Our null result is not the most precise measurement, but another method (looking at absorption lines) that gives more precise results involves systematic errors that cause different people using the method to come up with different results,” Newman said.

Newman also announced at the APS meeting the public release of the first season of data (2002) from the DEEP2 survey, which represents 10 percent of the 50,000 distant galaxies the team hopes to survey. DEEP2 uses the DEIMOS spectrograph on the Keck II telescope in Hawaii to record redshift, brightness and color spectrum of these distant galaxies, primarily to compare galaxy clustering then versus now. The survey, now more than 80 percent complete, should finish observations this summer, with full data release by 2007.

“This is really a unique data set for constraining both how galaxies have evolved and how the universe has evolved over time,” Newman said. “The Sloan Digital Sky Survey is making measurements out to about redshift 0.2, looking back the last 2-3 billion years. We really start at redshift 0.7 and peak at 0.8 or 0.9, equivalent to 7-8 billion years ago, a time when the universe was half as old as it is today.”

The survey also has completed measurements that could shed light on the nature of dark energy – a mysterious energy that permeates the universe and seems to be causing the universe’s expansion to accelerate. The team now is modeling various theories of dark energy to compare theoretical predictions with the new DEEP2 measurements.

As Davis explained it, the amount of dark energy, now estimated to be 70 percent of all the energy in the universe, determines the evolution of galaxies and clusters of galaxies. By counting the number of small groups and massive clusters of galaxies in a distant volume of space as a function of their redshift and mass, it is possible to measure the amount by which the universe has expanded to the present day, which depends on the nature of dark energy.

“Basically, you count the clusters and ask, ‘Are there a lot, or a few?'” Davis said. “That’s all it amounts to. If there are very few clusters, that means the universe expanded quite a ways. And if there are a lot of clusters the universe didn’t expand as much.”

Davis currently is comparing DEEP2 measurements with predictions of the simplest dark energy theory, but hopes to collaborate with other theoreticians to test more exotic dark energy theories.

“What they are really trying to get at is how the dark energy density is changing as the universe is expanding,” said UC Berkeley theoretical physicist Martin White, a professor of astronomy and of physics who has worked with Davis. “If the dark energy density is Einstein’s cosmological constant, then the theoretical prediction is that it doesn’t change. The holy grail now is to get some evidence that it’s not the cosmological constant, that it is in fact changing.”

Original Source: UC Berkeley

Posted on by Fraser Cain

Audio: Oldest Star Discovered

Image credit: ANU
Listen to the interview: Oldest Star Discovered (2.5 mb)

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Fraser Cain: How old is this star that you’ve found?

Anna Frebel: Well, that’s a bit of a problem because we cannot actually place an exact age on the star. You would need to measure radioactive elements in the star and if you said already that the star if very primitive, it is mint condition, so we don’t see any radioactive elements and hence we can only make a good guess on how old it is.

Fraser: How does it look different from our own sun?

Frebel: It’s very different from our Sun. We found the star because it had very low iron as compared to the Sun and this is also the reason why we think it is the oldest star because it has the lowest iron ever observed, and not only the iron, but also many other elements; carbon and nitrogen are very low as compared to the Sun.

Fraser: Why does our Sun have larger amounts of iron and this one doesn’t?

Frebel: If you consider the chemical evolution of the galaxy, and the entire universe, and you might know that after the Big Bang, the universe started out only with hydrogen and helium, and a little bit of lithium, and all the time, the heavy elements were synthesized in the stars themselves, now, certain elements such as carbon, nitrogen, oxygen and iron were synthesized during the lifetime of stars, but other elements, especially the heavy ones, were produced in supernova explosions; the death of a big star. So over time, the stars got enriched more and more in heavy elements; the Sun is not very old by astronomical standards, hence it has much more heavy elements than the star 183027, which was what we found.

Fraser: So you are saying that normal stars like our Sun have been through the wash cycle several times, and they have had their matter recycled through several stars, and that’s why they have some of the higher elements in them. How can a star remain untouched from such a long period?

Frebel: Well the density of stars in some areas is rather low and others, it’s higher; this star is a field halo star, so it’s in an area of our galaxy which is not very populated, so it’s just been sitting there for many, many, many years, and because it’s a low mass star, it is still very unevolved, so it’s just waiting there for us to find it.

Fraser: What kind of star is it, because I understand that our Sun is several billion years old, but definitely not the age of the universe, so what kind of star is it that it could be as old as the Big Bang?

Frebel: The star is a low mass star, it’s a bit lighter than the Sun and that means that it evolved very very slowly. I mean the Sun, well, it’s still in its teenage years, so it hasn’t burned much. High mass stars burn very very fast, and they explode quickly as a supernova enriching the surrounding gas; the interstellar medium with heavy elements, but this star, because it is so low in mass has just been sitting there and burning its hydrogen slowly and we think the hydrogen has just finished burning. So helium should be the next stage.

Fraser: How early on do you think it actually formed? How long after the Big Bang?

Frebel: Well, we have 2 scenarios; one would be that it formed in the second generation of stars and the first generation formed within one billion years after the Big Bang. So that star should have formed very quickly, probably about one billion years after the Big Bang. And the second theory which we cannot exclude, although I personally don’t favor it, is that the star indeed is a first star itself, meaning that it formed as one of the very, very first stars in the universe and presumably that happened then within the first billion years.

Fraser: Do you think that there are many of these types of stars in the Milky Way?

Frebel: Good question; probably not because they are very old and hence they are very rare because it seems that there is a certain type of these low mass stars which are actually able to survive that long and astronomers have been searching for these types of stars for the last 30-40 years and so far, we’ve only found 2 in huge efforts, so we are really looking for the needle in the haystack I would say.

Fraser: In the last couple of years, I have been covering the fires at Mount Stromlo. How is the observatory doing?

Frebel: It’s doing very well. We haven’t been affected from a science point of view. We have been very much productive since the fires. The reconstruction has now started; we are getting an new advanced, technological instrumentation building so we have a lot of noise here, but that also means things are progressing. Everyone is doing very well and we’ve, I think psychologically, we’ve put the fires way behind us.