Anne Minard, Author at Universe Today

April 1, 2009December 24, 2015 by Anne Minard

Astrophysics Satellite Detects Dark Matter Clue?

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An international collaboration of astronomers is reporting an unusual spike of atmospheric particles that could be a long-sought signature of dark matter.

The orbiting PAMELA satellite, an astro physics mission operated by Italy, Russia, Germany and Sweden, has detected a glut of positrons — antimatter counterparts to electrons — in the energy range theorized to be associated with the decay of dark matter. The results appear in this week’s issue of the journal Nature.

Dark matter is the unseen substance that accounts for most of the mass of our universe, and the presence of which can be inferred from gravitational effects on visible matter. When dark matter particles are annihilated after contact with anti-matter, they should yield a variety of subatomic particles, including electrons and positrons.

Antiparticles account for a small fraction of cosmic rays and are also known to be produced in interactions between cosmic-ray nuclei and atoms in the interstellar medium, which is referred to as a ‘secondary source.”

Previous statistically limited measurements of the ratio of positron and electron fluxes have been interpreted as evidence for a primary source for the positrons, as has an increase in the total electron-positron flux at energies between 300 and 600 GeV. Primary sources could include pulsars, microquasars or dark matter annihilation.

Lead study author Oscar Adriani, an astrophysics researcher at the University of Florence in Italy, and his colleagues are reporting a positron to electron ratio that systematically increases in a way that could indicate dark matter annihilation.

The new paper reports a measurement of the positron fraction in the energy range 1.5–100GeV.

“We find that the positron fraction increases sharply over much of that range, in a way that appears to be completely inconsistent with secondary sources,” the authors wrote in the Nature paper. “We therefore conclude that a primary source, be it an astrophysical object or dark matter annihilation, is necessary.” Another feasible source for the anitmatter particles, besides dark matter annihilation, could be a pulsar, they note.

PAMELA, which stands for a Payload for Antimatter Matter Exploration and Light Nuclei Astrophysics, was launched in June 2006 and initially slated to last three years. Mission scientists now say it will continue to collect data until at least December 2009, which will help pin down whether the positrons are coming from dark matter anihilation or a single, nearby source.

Source: Nature (there is also an arXiv/astro-ph version here)

April 1, 2009December 24, 2015 by Anne Minard

New Study: Some Massive Galaxies Were Practically Born That Way

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New research is casting doubt on the prevailing view that the heaviest galaxies in the universe started out small and gained mass by devouring other matter that ventured too close.

Peering at galaxies two-thirds of the way back in time to the Big Bang, an international team of astronomers is suggesting that some of the giants we see today were just as massive in that earlier age as they are now.

The new findings were released today in the journal Nature.

Lead author Chris Collins, an astronomer at the United Kindgdom’s Liverpool John Moores University, and his colleagues made their discovery using one of the largest optical telescopes in the World, called Subaru (named after the Japanese word for the Pleiades star cluster), located on the Island of Hawaii and owned by the National Observatory of Japan.

They focused on brightest cluster galaxies (BCGs), located at the centers of galaxy clusters. The massive galaxies constitute a separate population from bright elliptical galaxies, and both their predictability and extreme luminosity have motivated their use as standard candles for cosmology, the authors point out.

Analysing the light from these remote galaxies, the astronomers effectively weighed them and found that despite feeding on a constant diet of small galaxies, the heaviest galaxies have not increased their weight over the last 9 billion years. In a universe whose age is 13.7 billion years old, these results spark a debate as to how these galaxies put on so much weight in the first few billion years after the Big Bang.

“Current predictions using simulations run on super computers suggest that at such a young age these galaxies should be only 20 percent of their final weight, so to find galaxies so large suggests that galaxy formation is a much more rapid process than we previously thought,” Collins said, “and perhaps the theories are missing some important physics.”

John Stott, Collin’s colleague at LJMU and a co-author on the paper, said the team was “surprised to find that the largest and brightest galaxies in the Universe have remained essentially unchanged for the last 9 billion years, having grown rapidly soon after the Big Bang.”

One possibility being considered is that the galaxies formed by the collapse of an already massive cloud at the dawn of the universe.

MORE ABOUT LEAD IMAGE: The image shows the central 1.5 x 1.5 arc min of the cluster corresponding to 0.75 Mpc at this distance. The clusters X-ray emission is used to pinpoint the location of the brightest galaxy in the cluster as shown by the green contours which represent the X-ray intensity as measured by the XMM-Newton X-ray satellite.

Source: LJMU’s Astrophysics Research Institute

March 31, 2009April 26, 2016 by Anne Minard

New Bill Would Extend Shuttle Life, but NASA Doesn’t Need the Time

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The Senate Budget Committee has given the green light to fund NASA’s shuttle program past the end of 2010, when the program is set to retire.

But NASA isn’t asking for an extension.

Florida Sen. Bill Nelson requested the $2.5 billion provision, which was included in the broader five-year spending plan that passed committee Monday afternoon. His office argues that launching nine missions in 18 months puts too much pressure on the agency, and could compromise safety.

NASA is preparing to launch the shuttle Atlantis on May 12 for a servicing mission of the Hubble Space Telescope, and the eight remaining missions are dedicated to completing the International Space Station.

“We are confident that we can fly out the shuttle manifest before the end of 2010,” said John Yembrick, a spokesman out of NASA’s Washington headquarters.

Nelson’s office isn’t as optimistic.

“Given that there are roughly only 18 months but nine flights left, we have a concern that may be unrealistic,” said Dan McLaughlin, a spokesman for Nelson’s office. He cited the Challenger and Columbia accidents, where “the investigation board in both cases identified scheduling pressure as a contributing factor to those accidents.”

orion — Artist's rendering of the next-generation Orion crew exploration vehicle docked to a lunar lander in lunar orbit. (Obsolete configuration.) Credit: Lockheed Martin Corp.

In the past, NASA has been “overly optimistic about schedules for shuttle missions,” McLaughlin said. But in reality, the agency has gotten four or five launches off the ground in each of the past several years. “It doesn’t take but a bad hurricane season and the best laid plans can fall apart. Could NASA do it? Yeah. But a lot of things would have to go right.”

The $2.5 billion provision, if it passes the full Senate and House, would alleviate the pressure, Nelson thinks, by opening up the possibility for additional funding in 2011 — and allow NASA to proceed with safety as a first concern. The measure would soften a firm line both the Bush and Obama administrations have taken on retiring the program by the end of 2010.

The Budget Committee’s decision sends a strong signal that the shuttle shouldn’t be retired on a date-certain, but only when all the missions are completed, Nelson reportedly said immediately after the Thursday vote.

ares-collage1 — Concept of Ares I, left, the crew launch vehicle and Ares V, the cargo launch vehicle. Credit: NASA/Marshall Space Flight Center

Meanwhile, NASA is looking forward to the next generation of launch vehicles, Orion (above, concept credit Lockheed Martin Corp.) and the Ares series. The vehicles are designed to return people to the moon — and perhaps even Mars — to live and explore. The first Ares test flight is planned for later this year.

The gap between the planned shuttle retirement in 2010, and the availability of the next generation launch vehicles, will be five years. During that time the United States is likely to partner with Russia to use Soyuz launch vehicles for low-orbit work and as the space station’s docked emergency vehicle — which is part of the astronauts’ escape plan in the event of debris hits or other dangers aboard the ISS.

It is also possible that commercial vehicles could rise to the challenge before 2015, NASA’s Yembrick said. NASA has awarded two contracts to companies that will deliver cargo to the space station after the retirement of the space shuttle: Orbital Sciences Corp. of Dulles, Virginia, and Space Exploration Technologies (SpaceX) of Hawthorne, California.

“Once they’ve proven that they can successfully deliver cargo, we also may one day look at purchasing crew services,” Yembrick said. “We don’t want to speculate when that may occur.”

Sources: Spaceref, interviews with Dan McLaughlin and John Yembrick.

March 31, 2009December 24, 2015 by Anne Minard

Fresh Mars Impact Craters Blast Ice Onto Surface

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Fresh impact craters on Mars have revealed more evidence of stable ice that’s been hiding just beneath the surface all along, say scientists working on images sent back by the HiRISE camera aboard NASA’s Mars Reconnaissance Orbiter.

The craters appeared sometime between January and September of last year, in areas that had been previously imaged without them prior to January 2008. The impacts served as “natural probes” to excavate evidence that gets to a long-standing question about ice on Mars: where is it stable, and where is it residual, in the process of sublimating away?

Study leader Shane Byrne, of the University of Arizona’s Lunar and Planetary Laboratory, presented the new set of images last week, at the Lunar and Planetary Science Conference in Texas.

Computer models agree that Mars contains stable high-latitude ice, but researchers have encountered difficulty deciding the quantity and geographical boundary of the ice, partly because they can’t see it beneath the surface and partly because pinning down an indirect measure of sub-surface ice — a long-term, global average water vapor concentration in the atmosphere — has proved challenging.

mars-ejecta2 — Credit: NASA/JPL/University of Arizona

The new craters are a significant clue, because they hit not in the high latitudes where planetary scientists are fairly certain about stable ice, but in the mid-latitudes where the ice’s reach is unclear.

“Here we report on natural probes of the Martian subsurface which have ‘detected’ ice in this critical mid-latitude zone,” wrote Byrne and his co-authors.

“In five such cases (with latitudes spanning 43.3° to 55.6° N), these impacts have excavated bright material which in High Resolution Imaging Science Experiment (HiRISE) data have a brightness and color consistent with water ice.”

Each of the five new craters is a few meters in diameter, several decimeters deep and with associated bright material a few meters across, the authors report. Four of them showed no spectral evidence of water ice. But one proved a jackpot.

“Spectra from this site show clear water ice absorption features at 1.25, 1.5 and 2 ?m,” the team reported. Exposed surface ice is not expected to be stable at the latitudes, and the team has already noticed shrinkage and fading.

Based on atmospheric water vapor data, even stable underground ice isn’t expected to be widespread at the mid-latitudes where the reservoir was found: “Thus the ground ice exposed here is probably in the process of retreat from a previously larger extent,” the authors wrote.

Source: LPSC proceedings

March 26, 2009December 24, 2015 by Anne Minard

New Views of Spring on Mars

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New high-resolution images taken last month of Mars’ south polar region are revealing signs of spring that are decidedly Martian.

The image above features a spider trough network left behind as seasonal dry ice caps have sublimated away in the warmer temperatures. It’s part of a new series of images released this week by the University of Arizona’s High Resolution Imaging Experiment, or HiRISE, aboard NASA’s Mars Reconnaissance Orbiter.

See more information and photos below.

The gas beneath the ice cap can flow in the same places year after year, eroding troughs in the surface of the planet.

“What happens on Mars, we think, is that as the seasonal ice cap thins from the bottom, gas underneath the cap builds up pressure,” said HiRISE deputy principal investigator Candice J. Hansen-Koharcheck of the NASA Jet Propulsion Laboratory in Pasadena, California.

“And where gas under the ice finds a weak spot or a crack, it will flow out of the opening, often carrying a little dust from the surface below.”

The next HiRISE image shows how dust that has been carried to the surface by gas jetting through the ice cap is blown about by prevailing winds before settling in fan-shaped deposits atop the ice cap. Varying orientations suggest that as the ice layer thins, a set of gas jets becomes active, they die down, then further away another set starts up at a later time with a different prevailing wind direction.

co2-jets — NASA/JPL/University of Arizona

Many jets appear to be active at the same time since numerous fans are all deposited in the same direction: this next, closer image is an example of such an occurrence.

co2-jets-closeup — Credit: NASA/JPL/University of Arizona

This southern hemisphere crater has gullies on its north and northeast walls. Gullies are proposed to be carved by liquid water originating from the subsurface or melting ice/snow on the surface.

Dark dunes are visible on the crater floor. Lighter, smaller dunes rim the south side of the crater floor. The entire scene, pictured below, has a pitted texture, suggesting that ground ice was once present in this region. When ground ice sublimates (goes from a solid directly to a gas), it leaves behind empty spaces in the soil that turn into pits as the remaining overlying soil collapses to fill them.

The full set of new HiRISE Mars images is here. Check out all the downloadable formats and sizes, with some even designed to fit an iPhone screen!

Source: Lori Stiles, at the University of Arizona

March 25, 2009March 24, 2012 by Anne Minard

Don’t ‘Supermassive’ Me: Black Holes Regulate Their Own Mass

Stellar-mass black holes, between 7 and 25 times the Sun’s mass, are called “micro-quasars” when they spawn powerful jets of particles and radiation, miniature versions of those seen in quasars. Stellar-mass black holes are on the small end of the scale opposite supermassive black holes, including those in quasars, which weigh millions to billions of times the mass of the Sun.

The micro-quasars’ jets may be part of a secret weapon for keeping their petite figures, according to new research.

Continue reading “Don’t ‘Supermassive’ Me: Black Holes Regulate Their Own Mass”

March 25, 2009December 24, 2015 by Anne Minard

Calling All Amateur Astronomers: Help Comb Arecibo Data for Gems

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Einstein@Home is one of the world’s largest public computing projects, with more than 200,000 people donating time on their own computers to mine gravitational wave data for the tell-tale signs of pulsars.

Now, Einstein@Home will begin searching Arecibo radio data to find binary systems consisting of the most extreme objects in the universe: a spinning neutron star orbiting another neutron star or a black hole.

And the project needs even more public participation.

Today, Bruce Allen, director of the Einstein@Home project, and Jim Cordes, of Cornell University, announced that the Einstein@Home project is beginning to analyze data taken by the PALFA Consortium at the Arecibo Observatory in Puerto Rico. PALFA is the Pulsar Arecibo L-band Feed Array Consortium, an ongoing search effort.

The Arecibo Observatory is the largest single-aperture radio telescope on the planet and is used for studies of pulsars, galaxies, solar system objects, and the Earth’s atmosphere.

Current searches of radio data lose sensitivity for orbital periods shorter than about 50 minutes. But the enormous computational capabilities of the Einstein@Home project (equivalent to tens of thousands of computers) make it possible to detect pulsars in binary systems with orbital periods as short as 11 minutes. The project is based at the University of Wisconsin in Milwaukee and the Albert Einstein Institute in Germany.

“Discovery of a pulsar orbiting a neutron star or black hole, with a sub-hour orbital period, would provide tremendous opportunities to test General Relativity and to estimate how often such binaries merge,” said Cordes.

The mergers of such systems are among the rarest and most spectacular events in the universe. They emit bursts of gravitational waves that current detectors might be able to detect, and they are also thought to emit bursts of gamma rays just before the merged stars collapse to form a black hole.

“While our long-term goal is to detect gravitational waves, in the shorter term we hope to discover at least a few new radio pulsars per year, which should be a lot of fun for Einstein@Home participants and should also be very interesting for astronomers,” Allen added. “We expect that most of the project’s participants will be eager to do both types of searches.”

Einstein@Home participants will automatically receive work for both the radio and gravitational-wave searches.

The large data sets from the Arecibo survey are archived and processed initially at Cornell and other PALFA institutions. For the Einstein@Home project, data are sent to the Albert Einstein Institute in Hannover via high-bandwidth Internet links, pre-processed and then distributed to computers around the world. The results are returned to AEI, Cornell, and UWM for further investigation.

You can join the Einstein@Home effort here.

LEAD IMAGE: Artist’s rendering of a neutron star. Credit: Space Telescope Science Institute.

Source: LIGO Scientific Collaboration Research Group

March 23, 2009December 24, 2015 by Anne Minard

Moonshadows on Saturn’s Rings Are Harbingers of Spring

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Moonshadows on Saturn’s rings are foretelling the planet’s equinox, when the sun will be exactly aligned with the planet’s equator and rings — and then will shift north from the southern hemisphere, kickstarting northern spring.

NASA’s Cassini spacecraft has captured, for the first time, the tell-tale moonshadows – sort of like groundhogs on Earth.

moonshadow2 — Click to play the short movie. Credit: NASA/JPL/Space Science Institute

The image above is a still from a movie, from Cassini’s hour-long observation of the shadow of the small moon Epimetheus.

Like Earth and most of the other planets, Saturn’s spin axis is tilted relative to its motion around the sun. So the sun, seen from Saturn, cycles from the southern hemisphere to the north and back again. A full sweep of seasonal changes on Saturn and its rings and moons takes a Saturnian year, equal to 29.5 Earth years. Thus, about every 15 Earth years, or half-Saturn-year, the sun passes through the plane containing the planet’s rings.

During these times, the shadows of the planet’s rings fall in the equatorial region on the planet. And the shadows of Saturn’s moons external to the rings, especially those whose orbits are inclined with respect to the equator, begin to intersect the planet’s rings. When this occurs, the equinox period has essentially begun, and any vertical protuberances within the rings, including small embedded moons and narrow vertical warps in the rings, will also cast shadows on the rings. At exactly the moment of equinox, the shadows of the rings on the planet will be confined to a thin line around Saturn’s equator and the rings themselves will go dark, being illuminated only on their edge. The next equinox on Saturn, when the sun will pass from south to north, is Aug. 11, 2009.

Because of these unique illumination circumstances, Cassini imaging scientists have been eager to observe the planet and its rings around the time of equinox. Cassini’s first extended mission, which began on July 1, 2008, was intended to gather observations during this time. Hence its name: Cassini Equinox Mission.

More than just pretty pictures, the observations could reveal any deviations across the rings from a perfectly flat wafer-like disk. Saturn’s ring system is wide, spanning hundreds of thousands of miles or kilometers. But the main inner rings (called A, B and C) are perhaps only 10 meters (30 feet) thick, and they are sometimes obscured from view inside thicker outer rings.

“We hope that such images will help us measure any vertical warping in the A and B rings,” said John Weiss, an imaging team associate from the Space Science Institute in Boulder, Colorado. “Because we know how big the moons are, and where they are in their orbits around Saturn when they cast these shadows, we have all the information we need to infer any substantial vertical structure that might be present.”

On Jan. 8, Epimetheus, a small moon 113 kilometers (70 miles) across, was the first moon observed casting a shadow onto the outer edge of the A ring. Next Pan, 30 kilometers (20 miles) across and orbiting within the rings, was caught casting a shadow on the A ring on Feb. 12. Eventually, more moons will cast shadows on the rings and all shadows will grow longer as exact equinox approaches.

Source: Cassini Imaging Central Laboratory for Operations (CICLOPS)

March 23, 2009December 24, 2015 by Anne Minard

Why Space Hates Our Bones (and what we can do about it)

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Think it might be fun to live in space? Better ask your bones.

Earth’s space agencies have tackled some of the major obstacles to living in space, with pressurized spacesuits that offset the deadly vacuum and deflect incoming solar and cosmic rays. But in the absence of gravity, astronauts aboard the International Space Station are still losing up to 10 times more bone mass than most Earth-bound post-menopausal women.

In an attempt to address this bone loss, University of Washington researchers found 22 volunteers for a study using bed rest as an analog of spaceflight. The current crop of volunteers are halfway through their commitment to remain in bed, in a six-degree, head-down tilt position for 84 days. The study subjects are still sane, and already, results are promising.

subject — Photo courtesy of Peter Cavanagh, University of Washington

Surprisingly, it’s not necessarily students who are answering the call. Volunteers must be at least 22 years old, so the results apply to the age range of people most likely to be astronauts.

The head-down tilt mimics many of the physiological adaptations astronauts experience during spaceflight, such as bodily fluid shifts toward the head. The bed rest confinement mimics the complete “unloading” of the musculoskeletal system that astronauts feel as they float through space due to the lack of gravity, which accelerates bone loss.

Study leader Peter Cavanagh, a University of Washington professor of orthopaedics and sports medicine, said the volunteers have to be raised to a standing position at the end of their terms very slowly, “because they are very likely to faint” until the heart regains its ability to push blood to the brain. Sometimes, he said, volunteers feel pain in the bottoms of their feet when they finally put them down, and have trouble navigating corners while walking.

“They feel sort of generally weak,” Cavanagh said. “We put them through two weeks of rehab, and we buy them a membership at the health club for another month.”

In that respect, the study volunteers’ experience is similar to that of astronauts returning from long bouts in space. But for half the study subjects, there is a key difference — it’s in their stride.

Half of the study participants perform individually prescribed intermittent treadmill exercise similar to workouts by astronauts in space – but with one important difference: they are pulled towards the treadmill surface by a harness applying greater force than what the research team has previously measured during walking and running on the International Space Station treadmill.

The results from the first half of the study are “extremely promising,” Cavanagh said. Of the five study subjects so far who have been assigned to the exercise group, bone loss in four of them has been prevented in important skeletal regions by the treadmill exercise countermeasure, while the six non-exercising control subject participants all lost bone mass.

“We have found that we can, on average, prevent bone loss in an important region of the hip with this intervention,” Cavanagh said. “No bed rest study ever before has accomplished this.”

Cavanagh said the study results will impact bone health in space by improving exercise prescriptions for astronauts on future space missions. Here on Earth, the work could help scientists understand how individualized exercise programs affect age- and gender-related osteoporosis.

As for the volunteers, the study leaders encourage them to “achieve something special,” Cavanagh said. “Some tried to learn Spanish. We had others who were preparing for exams, and doing things they would have difficulty doing if they led their life with the typical distractions.”

Cavanagh said the study subjects are kept busy with tests during the week, but the weekends can be difficult.

The volunteers make around $8 an hour, but they’re working 24 hours a day.

“One of my most satisfying moments,” Cavanagh said, “is handing them a $12,000 check at the end.”

Source: University of Washington and Peter Cavanagh

Added 3/24: See an interview with study participant Tabitha Garcia at author Anne Minard’s blog.

March 22, 2009December 24, 2015 by Anne Minard

Star Exploded Too Early, May Blow Apart Supernova Theory

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NASA’s Hubble Space Telescope has identified a star a million times brighter than the sun that exploded as a supernova in 2005 — well before it should have, according to current theories of stellar evolution.

The doomed star, estimated at about 100 times our sun’s mass, was not mature enough, according to theory, to have evolved a massive iron core of nuclear fusion ash. This is the supposed prerequisite for a core implosion that triggers a supernova blast.

“This might mean that we are fundamentally wrong about the evolution of massive stars, and that theories need revising,” says Avishay Gal-Yam of the Weizmann Institute of Science, in Rehovot, Israel. The finding appears in the online version of Nature Magazine.

The explosion, called supernova SN 2005gl, was seen in the barred-spiral galaxy NGC 266 on October 5, 2005. NGC 266 is about 200 million light years away, in the constellation Pisces.

The progenitor was so bright that it probably belonged to a class of stars called Luminous Blue Variables (LBVs), “because no other type of star is as intrinsically brilliant,” says Gal-Yam. But there’s a wrinkle: as an LBV-class star evolves, it sheds much of its mass through a violent stellar wind. Only at that point does it develop a large iron core and ultimately explodes as a core-collapse supernova.

“The progenitor identification shows that, at least in some cases, massive stars explode before losing most of their hydrogen envelope, suggesting that the evolution of the core and the evolution of the envelope are less coupled than previously thought, a finding which may require a revision of stellar evolution theory,” co-author Douglas Leonard, from California’s San Diego State University, said in a press release.

One possibility is that the progenitor to SN 2005gl was really a pair of stars — a binary system — that merged. This would have stoked nuclear reactions to brighten the star enormously, making it look more luminous and less evolved than it really was.

“This also leaves open the question that there may be other mechanisms for triggering supernova explosions,” says Gal-Yam. “We may be missing something very basic in understanding how a superluminous star goes through mass loss.”

Gal-Yam and Leonard located the progenitor in archival images of NGC 266 taken in 1997. They then used the Keck telescope to precisely locate the supernova on the outer arm of the galaxy. A follow-up observation with Hubble in 2007 unequivocally showed that the superluminous star was gone.

Extremely massive and luminous stars topping 100 solar masses, such as Eta Carinae in our own Milky Way Galaxy, are expected to lose their entire hydrogen envelopes prior to their ultimate explosions as supernovae.

“These observations demonstrate that many details in the evolution and fate of LBVs remain a mystery,” said Mario Livio, of the Space Telescope Science Institute in Baltimore. “We should continue to keep an eye on Eta Carinae – it may surprise us yet again.”

MOSAIC CAPTIONS: [Top Center] 2005 ground-based image of the supernova; [Bottom Left] 1997 Hubble archival visible-light image of the region of the galaxy where the supernova exploded, with white circle marking the progenitor star; [Bottom Center] Near-infrared light photo of the supernova explosion taken on Nov. 11, 2005, with the Keck telescope, with the blast centered on the position of the progenitor; [Bottom Right] Visible-light Hubble follow-up image taken on September 26, 2007. The progenitor star is gone. Credit: NASA, ESA, and A. Gal-Yam (Weizmann Institute of Science, Israel)

Source: HubbleSite