Posted on by Fraser Cain

Mini-Van Sized Rover for 2009

Image credit: NASA

Pathfinder was the size of a shoebox; the Mars Exploration Rovers are as big as golf-carts; but a future Martian rover could be as big as a mini-van. Engineers from Montana State University are helping to design the Mars Scientific Laboratory (MSL), which could make its way to the Red Planet by 2009. Unlike Spirit and Opportunity, which are solar powered, the MSL will have a nuclear reactor, so it will be able to remain operational on the surface for an entire Martian year (two years on Earth), and measure long-term climate changes.

If you think the Mars rovers are interesting, wait until you see a mini-van clambering over the planet’s red rocks and dusty lake beds.

The two golf-cart size rovers that are mesmerizing the country now are preparing the way for a 2009 mission to Mars called the Mars Scientific Laboratory, says William Hiscock, head of the physics department and director of the Montana Space Grant Consortium based at Montana State University-Bozeman. The 2009 mission will involve a rover, too, but that vehicle will be the size of a mini-van.

Lest anyone picture adventurous soccer parents doubling as astronauts, Hiscock said the upcoming rover, like the Spirit and Opportunity rovers, will be remotely controlled. It will be nuclear powered instead of solar powered.

Nuclear power is a good thing, because it means the rover won’t be disabled by dust covering the power source, Hiscock said. The current rovers are expected to run 90 days before they’re done in by conditions like dust or extreme temperature changes.

“Dust builds up on solar panels, decreasing the light getting in. The power fades away because of it,” Hiscock explained.

Roving around Mars is like being 100,000 feet above sea level on Earth, Hiscock added. So when day turns into night, temperatures can drop up to 200 degrees, only to surge again the next day.

“That puts a lot of thermal stress on electronics and wiring,” Hiscock said. “Eventually probably, something just breaks after going through so many cycles.”

The Sojourner rover that landed on Mars in 1997 and still sets on the planet was disabled by dust and extreme temperatures, Hiscock said. It weighed 23 pounds, which means the Spirit and Opportunity are almost big enough to roll over it. The two rovers each weigh about 400 pounds.

Michelle Larson, deputy director of the Montana Space Grant Consortium, said the larger size of the 2009 rover will give it the ability to survive longer than current and past rovers.

“Therefore, science experiments performed on the 2009 rover will be able to make long duration measurements to see how the environment changes in time,” Larson said. “The intent is to have the science instruments on the rover operating for an entire Martian year (which is approximately two Earth years).”

The 2009 mission will investigate the capacity of the Mars environment to sustain life, Larson said. Among other things, the mission will look for organic carbon compounds and features that might have resulted from biological processes. The mission will look at the geology and geochemistry of the landing area, investigate the role of water and other processes that may have been relevant to past living conditions. The mission will look at the effects of cosmic and solar radiation on the Martian surface.

Original Source: Montana State University News Release

Posted on by Fraser Cain

Martian Gravity To Be Tested on Mice

Image credit: MIT

Researchers from MIT are planning to test the effects of Martian gravity on mammals, by sending 15 mice into orbit for five weeks. The mice would be launched aboard a one-metre “spaceship”, which would be spun so that the force mimics the gravity on Mars. Scientist know that weightlessness causes health problems, including bone loss, but human travelers to Mars could stay for months or even years in a permanent outpost – it’s critical to know if the human body can handle it. If all goes well, the mission could launch in 2006.

Students and researchers at MIT are designing a space mission to learn about the effects of Mars-level gravity using pint-sized astronauts.

The 15 mouse-trounauts will orbit Earth for five weeks to help researchers learn how Martian gravity – about one-third that of Earth – will affect the mammalian body.

The goal of the Mars Gravity Biosatellite Program is to send the mice into near-Earth orbit inside a one-meter space ship simulating Mars’ gravity, then bring them back to Earth. It won’t be the first time mice have flown in space, but it will be the first time mammals of any kind have lived in partial gravity for an extended period. The spin of the spacecraft will create an effect on the mice equivalent to Mars’ gravity.

The mouse cages will be designed for comfort and protection with room for the little travelers to lope around for exercise in the simulated gravity of Mars.

“Astronauts living on space stations have encountered serious health problems such as bone loss due to their weightless environment [zero gravity],? the team said in a statement. “The first crew on Mars could experience similar effects; scientists do not yet know whether partial gravity is sufficient to prevent these health hazards. A crew of mice will provide the first answers.?

The multi-university group, led by MIT and involving the University of Washington at Seattle and the University of Queensland in Brisbane, Australia, is managed by MIT research affiliate Paul Wooster (MIT S.B. 2003).

The MIT team is providing overall systems engineering and project management, as well as designing and building the payload module, and planning the scientific experiments. Students and researchers from Washington are designing and building the spacecraft bus, which contains the power, propulsion and communications components. Re-entry and recovery systems are the responsibility of the Australian group.

The project is expected to cost about $15 million plus the cost of the launch. The teams have received more than $400,000 for building the spacecraft from a variety of sources including NASA, the three universities, and a number of private companies and individuals. The teams have also secured commitments to cover approximately half the cost of the $6 million launch.

The program is overseen by a program board composed of faculty from each of the universities and outside space experts, and supported by a broad network of advisors from the space field. Given appropriate funding, the mission could launch as early as mid-2006.

For more information on the Mars Gravity Biosatellite, visit http://www.marsgravity.org.

Original Source: MIT News Release

Posted on by Fraser Cain

Spirit Rolls Off the Lander

Image credit: NASA/JPL

NASA’s Spirit rover successfully rolled off the landing platform and out onto the Martian surface this morning, beginning its mission of exploration. The rover traveled 3 meters in 78 seconds, and it ended up about 80 centimetres away from the lander. Now that Spirit’s firmly on the ground, NASA scientists and engineers will make daily decisions about what science tasks it will perform, and where it will travel. Spirit’s twin rover, Opportunity, will arrive on Mars on January 25 to explore another region on the other side of the planet.

NASA’s Mars Exploration Rover Spirit successfully drove off its lander platform and onto the soil of Mars early today.

The robot’s first picture looking back at the now-empty lander and showing wheel tracks in the soil set off cheers from the robot’s flight team at NASA’s Jet Propulsion Laboratory, Pasadena, Calif.

“Spirit is now ready to start its mission of exploration and discovery. We have six wheels in the dirt,” said JPL Director Dr. Charles Elachi.

Since Spirit landed inside Mars’ Gusev Crater on Jan. 3 (PST and EST; Jan. 4 Universal Time), JPL engineers have put it through a careful sequence of unfolding, standing up, checking its surroundings and other steps leading up to today’s drive-off.

“It has taken an incredible effort by an incredible group of people,” said Mars Exploration Rover Project Manager Peter Theisinger of JPL.

The drive moved Spirit 3 meters (10 feet) in 78 seconds, ending with the back of the rover about 80 centimeters (2.6 feet) away from the foot of the egress ramp, said JPL’s Joel Krajewski, leader of the team that developed the sequence of events from landing to drive- off. The flight time sent the command for the drive-off at 12:21 a.m. PST today and received data confirming the event at 1:53 a.m. PST. The data showed that the rover completed the drive-off at 08:41 Universal Time (12:41 a.m. PST).

“There was a great sigh of relief from me,” said JPL’s Kevin Burke, lead mechanical engineer for the drive-off. “We are now on the surface of Mars.”

With the rover on the ground, an international team of scientists assembled at JPL will be making daily decisions about how to use the rover for examining rocks, soils and atmosphere with a suite of scientific instruments onboard.

“Now, we are the mission that we all envisioned three-and-a-half years ago, and that’s tremendously exciting,” said JPL’s Jennifer Trosper, mission manager.

JPL engineer Chris Lewicki, flight director, said “It’s as if we get to drive a nice sports car, but in the end we’re just the valets who bring it around to the front and give the keys to the science team.”

Spirit was launched from Cape Canaveral Air Force Station, Fla., on June 10, 2003. Now that it is on Mars, its task is to spend the rest of its mission exploring for clues in rocks and soil about whether the past environment in Gusev Crater was ever watery and suitable to sustain life. Spirit’s twin Mars Exploration Rover, Opportunity, will reach Mars on Jan. 25 (EST and Universal Time; 9:05 p.m., Jan. 24, PST) to begin a similar examination of a site on the opposite side of the planet.

JPL, a division of the California Institute of Technology in Pasadena, manages the Mars Exploration Rover project for NASA’s Office of Space Science, Washington, D.C. Images and additional information about the project are available from JPL at http://marsrovers.jpl.nasa.gov and from Cornell University, Ithaca, N.Y., at http://athena.cornell.edu.

Posted on by Fraser Cain

Spitzer Image of the Tarantula Nebula

Image credit: NASA/JPL

The latest image from the Spitzer Space Telescope is of often-photographed Tarantula Nebula. Spitzer, however, is able to pierce through the dust and material that surrounds the nebula to take a good look inside this active star-forming region. This new photograph has turned up previously hidden stars inside the nebula, as well as empty cavities of space around them – their powerful radiation blows all the dust away. Images like this will help astronomers understand the environments that form stars and get a better sense of where our own Solar System came from.

A dusty stellar nursery shines brightly in a new image from NASA’s Spitzer Space Telescope, formerly known as the Space Infrared Telescope Facility. Spitzer’s heat-sensing “infrared eyes” have pierced the veiled core of the Tarantula Nebula to provide an unprecedented peek at massive newborn stars.

The new image is available online at http://www.spitzer.caltech.edu and http://photojournal.jpl.nasa.gov/catalog/PIA05062.

“We can now see the details of what’s going on inside this active star-forming region,” said Dr. Bernhard Brandl, principal investigator for the latest observations and an astronomer at both Cornell University, Ithaca, N.Y., and the University of Leiden, the Netherlands.

Launched on August 25, 2003, from Cape Canaveral Air Force Station, Florida, the Spitzer Space Telescope is the fourth of NASA’s Great Observatories, a program that also includes Compton Gamma Ray Observatory, the Chandra X-ray Observatory and the Hubble Space Telescope. Spitzer’s state-of-the-art infrared detectors can sense the infrared radiation, or heat, from the farthest, coldest and dustiest objects in the universe.

One such dusty object is the Tarantula Nebula. Located in the southern constellation of Dorado, in a nearby galaxy called the Large Magellanic Cloud, this glowing cloud of gas and dust is one of the most dynamic star-forming regions in our local group of galaxies. It harbors some of the most massive stars in the universe, up to 100 times more massive than our own Sun, and is the only nebula outside our galaxy visible to the naked eye.

While other telescopes have highlighted the nebula’s spidery filaments and its star-studded core, none was capable of fully penetrating its dust-enshrouded pockets of younger stars.

The new Spitzer image shows, for the first time, a more complete picture of this huge stellar nursery, including previously hidden stars. The image also captures in stunning detail a hollow cavity around the stars, where intense radiation has blown away cosmic dust.

“You can see a hole in the cloud as if a giant hair dryer blew away all the gas and dust,” said Brandl.

By studying this portrait of a family of stars, astronomers can piece together how stars in general, including those like our Sun, form.

JPL manages the Spitzer Space Telescope mission for NASA’s Office of Space Science, Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology in Pasadena. JPL is a division of Caltech.

Additional information about the Spitzer Space Telescope is available at http://www.spitzer.caltech.edu.

Original Source: NASA/JPL News Release

Posted on by Fraser Cain

Star Mimics a Black Hole

Image credit: Chandra

Astronomers using the Australia Telescope Compact Array have found a rapidly spinning neutron star which is spitting out jets of material at nearly the speed of light. Jets like this have only been seen previously coming out of black holes, and this discovery challenges the theory that only the environment around a black hole can be so energetic. The astronomers studied Circinus X-1, an object located about 20,000 light years away, which is a bright source of X-rays. They know it’s a neutron star, but it also has these unusual characteristics.

Scientists using CSIRO’s Australia TelescopeCompact Array, a radio synthesis telescope in New South Wales, Australia, have seen a neutron star spitting out a jet of matter at very close to the speed of light. This is the first time such a fast jet has been seen from anything other than a black hole.

The discovery, reported in this week’s issue of Nature, challenges the idea that only black holes can create the conditions needed to accelerate jets of particles to extreme speeds.

“Making jets is a fundamental cosmic process, but one that is still not well understood even after decades of work,” says team leader Dr. Rob Fender of the University of Amsterdam.

“What we’ve seen should help us understand how much larger objects, such as massive black holes, can produce jets that we can see half-way across the Universe.”

The scientists, from The Netherlands, the UK and Australia, studied Circinus X-1, a bright and variable source of cosmic X-rays, over a three-year period.

Circinus X-1 lies inside our Galaxy, about 20 000 light-years from Earth, in the constellation Circinus near the Southern Cross.

It consists of two stars: a ‘regular’ star, probably about 3 to 5 times the mass of our Sun, and a small compact companion.

“We know that the companion’s a neutron star from the kind of X-ray bursts it’s been seen to give off,” says team member Dr. Helen Johnston of the University of Sydney.

“Those X-ray bursts are a sign of a star that has a surface. A black hole doesn’t have a surface. So the companion must be a neutron star.”

A neutron star is a compressed, very dense ball of matter formed when a giant star explodes after its nuclear fuel runs out. In the hierarchy of extreme objects in the Universe, it is just one step away from a black hole.

The two stars in Circinus X-1 interact, with the neutron star’s gravity pulling matter off the larger star onto the neutron star’s surface.

This ‘accretion’ process generates X-rays. The strength of the X-ray emission varies with time, showing that the two stars of Circinus X-1 travel around each other in a very elongated orbit with a 17 day period.

“At their point of closest approach, the two stars are almost touching,” says Dr. Johnston.

Since the 1970s astronomers have known that Circinus X-1 produces radio waves as well as X-rays. A large ‘nebula’ of radio emission lies around the X-ray source. Within the nebula lies the new-found jet of radio-emitting material.

Jets are believed to emerge, not from black holes themselves, but from their ‘accretion disk’ – the belt of dismembered stars and gas that a black hole drags in towards it.

In Circinus X-1 it’s likely that the accretion disk varies with the 17-day cycle, being at its most intense when the stars are at their closest point in the orbit.

The jet from Circinus X-1 is travelling at 99.8% of the speed of light. This is the fastest outflow seen from any object in our Galaxy, and matches that of the fastest jets being shot out of other complete galaxies. In those galaxies, the jets come from supermassive black holes, millions or billions of times the mass of the Sun, that lie at the centres of the galaxies.

Whatever process accelerates jets to near the speed of light, it does not rely on the special properties of a black hole.

“The key process must be one common to both black holes and neutron stars, such as accretion flow,” says Dr. Kinwah Wu of Unversity College London, UK.

Original Source: CSIRO News Release

Posted on by Fraser Cain

First a Crater, then Head for the Hills

Image credit: NASA/JPL

NASA’s Spirit Rover has completed its pivoting maneuver atop its landing platform, and it’s nearly ready to roll out onto the Martian surface. Mission scientists have decided that the rover’s first target will be a relatively nearby 200-metre wide impact crater, which is approximately 250 metres northeast of the landing site. A crater like this is a convenient hole in the ground which allows the rover to look back into Martian history to see if there are sedimentary layers; a sure indication that there was standing water in the past. After studying the crater, Spirit will make for a set of hills approximately 3 kilometres away; although, that could be outside its range.

NASA’s Spirit has begun pivoting atop its lander platform on Mars, and the robot’s human partners have announced plans to send it toward a crater, then toward some hills, during the mission.

Determining exactly where the spacecraft landed, in the context of images taken from orbit, has given planners a useful map of the vicinity. After Spirit drives off its lander and examines nearby soil and rocks, the scientists and engineers managing it from NASA’s Jet Propulsion Laboratory, Pasadena, Calif., intend to tell it to head for a crater that is about 250 meters (about 270 yards) northeast of the lander.

“We’ll be careful as we approach. No one has ever driven up to a martian crater before,” said Dr. Steve Squyres of Cornell University, Ithaca, N.Y., principal investigator for the science instruments on Spirit and on its twin Mars Exploration Rover, Opportunity.

The impact that dug the crater about 200 meters (about 220 yards) wide probably flung rocks from as deep as 20 to 30 meters (22 to 33 yards) onto the surrounding surface, where Spirit may find them and examine them. “It will provide a window into the subsurface of Mars,” Squyres said.

Craters come in all sizes. The main scientific goal for Spirit is to determine whether the Connecticut-sized Gusev Crater ever contained a lake. Taking advantage of the nearby unnamed crater for access to buried deposits will add to what Spirit can learn from surface materials near the lander. After that, if all goes well, the rover will head toward a range of hills about 3 kilometers (2 miles) away for a look at rocks that sit higher than the landing neighborhood’s surface. That distance is about five times as far as NASA’s mission- success criteria for how far either rover would drive. The highest hills in the group rise about 100 meters (110 yards) above the plain.

“I cannot tell you we’re going to reach those hills,” Squyres said. “We’re going to go toward them.” Getting closer would improve the detail resolved by Spirit’s panoramic camera and by the infrared instrument used for identifying minerals from a distance.

First, though, comes drive-off. Overnight Monday to Tuesday, Spirit began rolling. It backed up 25 centimeters (10 inches), turned its wheels and pivoted 45 degrees.

“The engineering team is just elated that we’re driving,” said JPL’s Chris Lewicki, flight director. “We’ve cut loose our ties and we’re ready to rove.” After two more pivots, for a total clockwise turn of 115 degrees, Spirit will be ready for driving onto the martian surface very early Thursday morning, according to latest plans.

Engineers and scientists have determined where on the martian surface the lander came to rest. NASA’s Mars Odyssey orbiter was used in a technique similar to satellite-based global positioning systems on Earth to estimate the location of the landing site, said JPL’s Joe Guinn of the rover mission’s navigation team. Other researchers correlated features seen on the horizon in Spirit’s panoramic views with hills and craters identifiable in images taken by Mars Global Surveyor and Odyssey. “We’ve got a tremendous vista here with all kinds of features on the horizon,” said JPL’s Dr. Tim Parker, landing site-mapping geologist.

The spacecraft came to rest only about 250 to 300 meters (270 to 330 yards) southeast of its first impact. Transverse rockets successful slowed horizontal motion seconds before impact, said JPL’s Rob Manning, who headed development of the entry, descent and landing system. The spacecraft, encased in airbags, was just 8.5 meters (27.9 feet) off the ground when its bridle was cut for the final freefall to the surface. It first bounced about 8.4 meters (27.6 feet) high, then bounced 27 more times before stopping.

Analysis of Spirit’s landing may aid in minor adjustments for Opportunity, on track for landing on the opposite side of Mars on Jan. 25 (Universal Time and EST; 9:05 p.m. Jan. 24, PST).

JPL, a division of the California Institute of Technology in Pasadena, manages the Mars Exploration Rover project for NASA’s Office of Space Science, Washington. For more information about NASA and the Mars mission on the Internet, visit http://www.nasa.gov. Additional information about the rover project is available from NASA’s JPL at http://marsrovers.jpl.nasa.gov and from Cornell University at http://athena.cornell.edu.

Original Source: NASA/JPL News Release

Posted on by Fraser Cain

Bush: Human Beings are Heading Into the Cosmos

Image credit: Whitehouse.gov

As predicted for several months, US President George W. Bush announced his plan for the future human exploration of space. Bush was joined by NASA administrator Sean O’Keefe and the press briefing was introduced by the commander of Expedition 8, Michael Foale – currently aboard the International Space Station.

Under the new plan, the United States would complete its work on the International Space Station by 2010, which is being developed by 15 countries, and then retire the space shuttle fleet. In tandem with this, NASA will develop a new program of human space exploration which will eventually return humans to the Moon.

As predicted for several months, US President George W. Bush announced his plan for the future human exploration of space. Bush was joined by NASA administrator Sean O’Keefe and the press briefing was introduced by the commander of Expedition 8, Michael Foale – currently aboard the International Space Station.

Under the new plan, the United States would complete its work on the International Space Station by 2010, which is being developed by 15 countries, and then retire the space shuttle fleet. In tandem with this, NASA will develop a new program of human space exploration which will eventually return humans to the Moon.

The first robotic explorers would reach the Moon in 2008; human explorers would follow by 2015-2020. Although Bush was expected to announce a permanent lunar base, no details were given. Bush hinted, but didn’t provide any details about follow-on human missions to Mars.

The plans call for a new kind of spacecraft, called the Crew Exploration Vehicle; a general purpose spacecraft which would be capable of servicing the International Space Station and reaching locations beyond low-Earth orbit, such as the Moon, asteroids, and the Lagrange points (stable places in space which are balanced between the gravity of two objects, such as the Earth and Moon).

NASA has said that this new vehicle will be dramatically different from the Orbital Space Plane, which NASA was developing as a replacement spacecraft to travel to and from the International Space Station. NASA had originally intended to award contracts for the OSP in 2004, which would eventually cost $15 billion US.

In order to finance this new plan, the president will be asking Congress in February to provide NASA with an additional $1 billion US in 2005, spread out over five years. Additional funds for the program would come from reorganizing NASA’s existing projects, like retiring the space shuttle by the end of the decade.

Maintaining and launching the space shuttle costs approximately $4 billion a year and the International Space Station costs $1 billion a year. It’s not clear what effect winding down the shuttle will have on the thousands of workers and contractors employed by the program; although, Bush did say that it would be “with existing programs and personnel.”

Bush called this new initiative a “journey, not a race”, and encouraged international partners to join the United States in exploring the solar system with human beings.

He said that the next step will be the formation of a special commission to “explore the vision I have outlined today”. This commission, led by former Air Force Secretary Peter Aldridge, will deliver a report to President Bush within four months.

More background on the new space initiative is available here.

Posted on by Fraser Cain

More Radio Shows to Listen To

A mentioned a few months ago that I always tune a couple of science radio programs through the Internet: CBC’s Quirks and Quarks, and NPR’s Talk of the Nation Science Friday. Since then, I’ve turned up a few more shows to listen to on a regular basis. One is PlanetEarthRadio.com, which has dedicated streams just for space and astronomy. Another is the science programs on BBC Radio 4 which have been nicely archived for your listening pleasure. And Australia’s ABC has The Science Show.

My new favorite, however, is The Space Show, hosted by Dr. David Livingston. Each program is a 90-minute interview with a space scientist or advocate. I’m astonished and jealous at the caliber of guests Dr. Livingston has been able to get to interview. Give it a listen.

Do you have any other suggestions for radio shows to listen to? Send them in… I’m all ears.

Fraser Cain
Publisher
Universe Today

Posted on by Fraser Cain

Binary Systems Could Create Most Nebulae

Image credit: Hubble

New research from the National Optical Astronomy Observatory may help to explain the formation and shape of many planetary nebulae. The culprit might just be binary star systems, where two stars orbit a common centre of gravity. Astronomers believe that planetary nebulae are caused when white dwarf stars slough off their outer layers, but they couldn’t explain how the nebulae could form jets of material or unusual lobes and prominences. A second star orbiting the dying white dwarf could whip up the outer layers into the strange shapes astronomers see.

Near the end of its lifetime, a star like the Sun ejects its outer layers into space, producing a hazy cloud of material called a planetary nebula. The complex shapes and dazzling colors of planetary nebulae make them some of the most popular objects in the night sky, for both amateur observing and scientific study.

New research suggests that many if not most of the stellar corpses at the centers of these wildly varied cosmic objects have companion stars, a surprising finding that will influence how astronomers explain their origins.

Astronomers used the Wisconsin-Indiana-Yale-NOAO 3.5-meter telescope at the National Science Foundation?s Kitt Peak National Observatory to take radial velocity measurements of 11 central stars of planetary nebulae (PNe), looking for the telltale, repeatable wobble that indicates the presence of a companion’s gravitational influence. This technique is also used to search for extrasolar planets around nearby stars. Ten of the 11 central stars of the PNe in the recent study showed clear evidence for radial velocity oscillations.

?If our current results are confirmed with further observations, we could be at the start of a revolution in the study of the origin of planetary nebulae,? says Howard Bond of the Space Telescope Science Institute in Baltimore, the principal investigator of the results presented today in Atlanta at the 203rd meeting of the American Astronomical Society. ?If these nebulae arise from binary stars, it implies a very different origin for these systems than what most astronomers had thought.?

It might be expected that nebulae ejected from spherical stars would be spherical, but many years of telescope observations show this not to be the case. In fact, most PNe are either elliptical or have pronounced lobes, often accompanied by jet-like structures.

There is general agreement that in order to eject gas with these observed morphologies, single stars would have to rotate rather rapidly or have reasonably strong magnetic fields, which themselves are the product of stellar rotation. However, the stars that most commonly eject PNe are large, bloated giants, indisposed to fast rotation.

?The most direct way to spin up these vast, fluffy stars is by the action of an orbiting companion. In extreme cases, as a red giant star gradually increases in size, it may actually swallow a companion star, which would then spiral down inside the giant and eventually eject its outer layers,? explains Orsola De Marco, an astronomer at the American Museum of Natural History (AMNH) in New York and the lead author of the publication reporting the first results of this project. ?Despite this, the mainstream astronomical view remains rooted in single star theories for the evolution of planetary nebulae, supported by the small percentage of planetary nebulae central stars that that were previously known to be binaries. However, our new research threatens to turn this viewpoint on its head.?

Astronomers currently believe that the majority of stars?those that begin with no more than eight times the mass of our Sun?end their lives by ejecting a planetary nebula and becoming a cosmic ember called a white dwarf. However, the new results from the WIYN telescope suggest that the story may be more complicated, in that an interaction with a companion star may be required to produce most planetary nebulae.

?We need more data to determine the exact periods of the binary central stars, since this is the only way to be sure of their binarity and eliminate other possible physical sources that could simulate the stellar wobble,? De Marco says. ?We are reasonably sure that these variations are due to binarity, but determination of their precise periods is the only way to be sure. We must also increase the size of our sample.?

Among the objects observed in this initial study are Abell 78, NGC 6891, NGC 6210, and IC 4593. The new radial velocity measurements were taken by the WIYN Hydra spectrographic instrument.

A previously released Hubble Space Telescope image of NGC 6210 is available at: http://hubblesite.org/newscenter/newsdesk/archive/releases/1998/36/image/a

Co-authors of this work are Dianne Harmer of the National Optical Astronomy Observatory (NOAO) in Tucson, AZ, and Andrew Fleming of Michigan Technological University in Houghton, MI, an NSF Research Experiences for Undergraduates (REU) student at AMNH during the summer of 2003.

These results (Abstract 127.03 in the AAS meeting program) will be discussed in an oral session that begins at 10:00 a.m. on Thursday, January 8, in Regency VI. This research has been accepted for publication in the February 1, 2004, issue of Astrophysical Journal Letters.

Images of other planetary nebulae taken by Kitt Peak telescopes are available in the NOAO Image Gallery at:

http://www.noao.edu/image_gallery/planetary_nebulae.html
and
http://www.noao.edu/outreach/aop/observers/pn.html.

The Wisconsin-Indiana-Yale-NOAO (WIYN) 3.5-meter telescope is located at Kitt Peak National Observatory, 55 miles southwest of Tucson, AZ. Kitt Peak National Observatory is part of the National Optical Astronomy Observatory, which is operated by the Association of Universities for Research in Astronomy (AURA), Inc., under a cooperative agreement with the National Science Foundation (NSF).

Original Source: NOAO News Release

Posted on by Fraser Cain

New Method for Finding Exploding White Dwarf Stars

Image credit: SDSS

Researchers at the University of Washington have developed a new method for studying unusual astronomical pairings: pre-cataclysmic variables – a white dwarf and red dwarf tightly orbiting one another. Before this new method, only 100 of these objects had been discovered, but this new method has turned up another 400 in data from the Sloan Digital Sky Survey. When the two stars get close enough, material from the red dwarf streams onto the white dwarf and deposits on the surface. This heats up the white dwarf and can cause it to explode as a supernova.

Until recently, astrophysicists studying exotic star systems pairing a white dwarf and a red dwarf in very close proximity didn’t have much to go on.

Just five years ago, scientists knew of fewer than 100 such systems, called pre-cataclysmic variables. But today a team of University of Washington astronomers said that, with data from the Sloan Digital Sky Survey (SDSS), the number has now grown to nearly 500.

That is significant because researchers are now able to study white dwarf and red dwarf stars at different stages of their life cycles, giving scientists the ability to compare them and develop an understanding of how the systems evolve and change over the course of billions of years, possibly becoming supernovas.

“We’ve never had the opportunity to study a variety of these systems in detail before now,” said Nicole Silvestri, a University of Washington astronomy researcher. Using this large sample from the SDSS, Silvestri and her colleagues believe they can begin to answer some of the long-standing questions in astronomy about pre-cataclysmic variables and their eventual end products, cataclysmic variable systems.

Silvestri is lead author of a poster presentation on the findings presented today (January 6, 2004) at the American Astronomical Society’s annual meeting in Atlanta. Co-authors of the project are Suzanne Hawley and Paula Szkody of the University of Washington’s Astronomy Department. The National Science Foundation supported the research.

Pre-cataclysmic variable systems pair a red dwarf star about one-tenth the size of our sun and a dense remnant of a star, called a white dwarf, in close orbit around each other. When the two stars are close enough, orbiting one another in less than four hours, the gravity of the denser white dwarf is able to pull material off of the less dense red dwarf. Material from the red dwarf forms a disk around the white dwarf that eventually accumulates on the surface of the white dwarf. (Variability refers to the changing amount of light coming from the stars as they orbit each other).

As the white dwarf gains mass, many small explosions, called cataclysmic events, occur on the surface of the white dwarf. If the white dwarf gravity gets to a critical point, it can collapse catastrophically. This heats up the white dwarf tremendously and may cause it to explode as a supernova.

Pre-cataclysmic variables found so far in the SDSS data have orbital periods of between four and 12 hours and are not close enough to have begun transferring material between the stars.

Silvestri said the evolution of a pre-cataclysmic variable to a cataclysmic variable takes billions of years and studying just one system as it evolves would be impossible. But with nearly 500 pre-cataclysmic variables to study, “A dataset of this size will allow us to take snapshots in time of the evolution of the system,” she said. “This will allow the researchers to study how properties of each star change as the pair draw closer to each other, something that until now, has never been investigated.”

Silvestri and her colleagues are still at a loss to explain one oddity in the research. Thousands of isolated white dwarfs have been observed and hundreds of them have been found to be magnetic. And many white dwarfs in cataclysmic variables are magnetic. But not one of the white dwarfs observed in the pre-cataclysmic variable systems is magnetic.

“This makes the origin of magnetic cataclysmic variables (known as polars), which do contain magnetic white dwarfs, exceedingly mysterious,” added SDSS researcher Suzanne Hawley of the University of Washington.

“That’s a question we’re still trying to find an answer to,” Silvestri said. “How do you get a magnetic white dwarf in a cataclysmic variable if it doesn’t originate in one of these pairs that is evolving toward being a cataclysmic variable?” The University of Washington team, James Liebert of the University of Arizona and others are preparing a paper on that finding for the Astronomical Journal.

Original Source: SDSS News Release