Posted on by Nancy Atkinson

25% of Sun-Like Stars Could Host Earth-Sized Worlds

Artists impression of a distant solar system. Credit: ESO

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A five-year survey of nearby solar-mass stars has provided astronomers with an estimate of how many stars of this type could have Earth-size planets. Andrew Howard and Geoffrey Marcy from the University of California Berkeley studied 166 G and K stars within 80 light-years of Earth, determining the number, mass and orbital distance of any of the stars’ planets. Since Earth-sized worlds have not yet been found, they extrapolated the number of that size of planets, based on the fraction of stars that host Neptune to super-Earth sized planets. Their findings are encouraging, since it means planets the size of Neptune and smaller are probably much more common than gas-giant planets, like Jupiter. But what they found also conflict with current models of planet formation and migration.


“Of about 100 typical sun-like stars, one or two have planets the size of Jupiter, roughly six have a planet the size of Neptune, and about 12 have super-Earths between three and 10 Earth masses,” said Howard. “If we extrapolate down to Earth-size planets – between one-half and two times the mass of Earth – we predict that you’d find about 23 for every 100 stars.”

“This is the first estimate based on actual measurements of the fraction of stars that have Earth-size planets,” said Marcy. Previous studies have estimated the proportion of Jupiter and Saturn-size exoplanets, but never down to as small as this study, and the astronomers say this enabled them to estimate the Earth-size planets.

“What this means,” Howard added, “is that, as NASA develops new techniques over the next decade to find truly Earth-size planets, it won’t have to look too far.”

Using the 10-meter Keck telescopes in Hawaii, the astronomers measured the small wobble of each star from the tug of orbiting planets. For systems with multiple planets, teasing out the radial velocity signature of each planet is very complex, since each signature is extremely small. The more times a star is observed, the better the data. Current techniques allow detection of planets massive enough and near enough to their stars to cause a wobble of about 1 meter per second. That means they saw only massive, Jupiter-like gas giants up to three times the mass of Jupiter (1,000 times Earth’s mass) orbiting as far as one-quarter of an astronomical unit (AU) from the star, or smaller, closer super-Earths and Neptune-like planets (15-30 times the mass of the earth). An AU is 93 million miles, the average distance between the earth and the sun.

Histogram of stellar masses for Eta-Earth stars. Credit: Howard, et al.

Only 22 of the stars had detectable planets – 33 planets in all – within this range of masses and orbital distances. After accounting statistically for the fact that some stars were observed more often than others, the researchers estimated that about 1.6 percent of the sun-like stars in their sample had Jupiter-size planets and 12 percent had super-Earths (3-10 Earth masses). If the trend of increasing numbers of smaller planets continues, they concluded, 23 percent of the stars would have Earth-size planets.

Based on these statistics, Howard and Marcy, — who is also member of NASA’s Kepler mission to survey 156,000 faint stars in search of transiting planets — estimate that the telescope will detect 120-260 “plausibly terrestrial worlds” orbiting some 10,000 nearby G and K dwarf stars with orbital periods less than 50 days.

“One of astronomy’s goals is to find ‘eta-Earth,’ the fraction of sun-like stars that have an earth,” Howard said. “This is a first estimate, and the real number could be one in eight instead of one in four. But it’s not one in 100, which is glorious news.”

They were able to only detect close-in planets, so they say there could be even more Earth-size planets at greater distances, including within the habitable zone — or Goldilocks zone — located at a distance form the star where conditions are not too hot or too cold to allow the presence of liquid water.

But the researchers note that their results conflict with current models of planet formation and migration, where it is thought that nascent planets spiral inward towards the sun because of interactions with the gas in the disk. Such models predict a “planet desert” in the inner region of solar systems. But that’s where all the planets are being found.

“Just where we see the most planets, models predict we would find no cacti at all,” Marcy said. “These results will transform astronomers’ views of how planets form.”

Howard and Marcy report their results in the Oct. 29 issue of the journal Science.

Sources: UC Berkeley, Science

Posted on by Nancy Atkinson

New Water-Related Discovery from Hibernating Spirit Rover

A mosaic of images shows the soil in front of the Mars Exploration Rover Spirit. Bright-toned soil was freshly exposed by the rover's left-front wheel. The inset show a magnified view of the nearby rectangles within the mosaic, showing the differences between undisturbed and disturbed soil. Credit: NASA/JPL-Caltech/Cornell University

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She may be down, but she’s not out – out of the discovery department, anyway. Data from the Spirit Mars rover – currently in hibernation – shows evidence that water, perhaps as snow melt, trickled into the subsurface fairly recently and may be doing so on a continuing basis.

The area where Spirit became stuck in sandy soil in April of 2009 was churned up by her spinning wheels as engineers at the Jet Propulsion Laboratory attempted to drive her out of a veritable sand trap. This wheel-churning brought subsurface soil layers — which include the water soluble mineral ferric sulfate — up to the surface. Under a thin covering of windblown sand and dust, relatively insoluble minerals such as hematite, silica and gypsum are concentrated near the surface and more-soluble ferric sulfates have higher concentrations below that layer. This pattern suggests water has moved downward through the soil, dissolving and carrying the ferric sulfates.

In combination with another recent discovery — that underground aquifers may have fed ancient seas on Mars — shows a water cycle likely was present in the past on the Red Planet, and may even be present today.

The deputy principal investigator for the Spirit and Opportunity rover, Ray Arvidson and his team say that thin films of water may have entered the ground from frost or snow. (The Phoenix lander saw evidence of current snowfall.) The seepage could have happened during cyclical climate changes in periods when Mars tilted farther on its axis.

“The lack of exposures at the surface indicates the preferential dissolution of ferric sulfates must be a relatively recent and ongoing process since wind has been systematically stripping soil and altering landscapes in the region Spirit has been examining,” said Arvidson.

This isn’t the first time that Spirit’s wheels have churned up interesting stuff. Back in 2008, researchers said Spirit’s bum front wheel uncovered signs minerals that are found in hot springs, similar to what is at Yellowstone National Park on Earth, and similar hot springs may have once bubbled or steamed on Mars.

But there’s been no word from the rover since March 22, 2010, after she went into cold-induced hibernation. Because Spirit was stuck, the rover drivers could not get her in the best position to receive maximum sunlight.

“With insufficient solar energy during the winter, Spirit goes into a deep-sleep hibernation mode where all rover systems are turned off, including the radio and survival heaters,” said John Callas, project manager for Spirit and Opportunity. “All available solar array energy goes into charging the batteries and keeping the mission clock running.”

While she was stuck and still awake, researchers took advantage and examined in great detail soil layers the wheels had exposed, and also neighboring surfaces, making comparisons between the two. While trying to drive back out of her predicament, Spirit made 13 inches of progress in its last 10 backward drives before energy levels fell too low. Those drives exposed a new area of soil for possible examination if Spirit does awaken and if its robotic arm is still usable.

However, it is thought that the aging Spirit rover experienced the coldest temperatures ever, and it may not survive. Everyone is still holding out hope that the rover may yet make contact through one of the orbiting spacecraft and the Deep Space Network.

If Spirit does get back to work, the top priority is a multi-month study that can be done without driving the rover. The study would measure the rotation of Mars through the Doppler signature of the stationary rover’s radio signal with enough precision to gain new information about the planet’s core.

Meanwhile, over on the other side of Mars, the rover Opportunity has been making steady progress toward a large crater, Endeavour, which is now approximately 8 kilometers (5 miles) away.

The newest findings were published in the Journal of Geophysical Research.

Source: JPL

Posted on by Nicholos Wethington

Researchers Discover 2nd Largest Impact Crater in Australia

The Cooper Basin hides an impact crater that was recently discovered by geothermal energy researchers. The crater may be the second largest discovered in Australia. Image Credit: Southern Australia Dept. of Transport, Energy and Infrastructure

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Geothermal energy researchers from the University of Queensland in Australia have identified what may be the second largest meteorite impact crater in Australia. Dr. Tonguç Uysal of the University of Queensland and Dr. Andrew Glikson of Australian National University identified rock structures that appear to have formed because of the shock of a meteorite impact. Their discovery was made while doing geothermal energy research in the Cooper Basin, which lies on the border between Queensland and South Australia.

The meteorite that caused the impact was likely 8 to 12 km in diameter (5 to 7.5 miles), Dr. Glikson said in an interview. It is also possible that a cluster of smaller meteorites impacted the region, so further testing is needed to pin down the exact nature of the impactor. The impact likely occurred over 300 million years ago, and the shock of the impact altered rock in a zone 80 km (50 miles) in diameter.

Dr. Glikson said, “Dr Uysal is studying the geochemistry and isotopes of granites from the basement below the Cooper Basin and observed potential shock lamella in the quartz grains.” Distinctive features of a shock due to a violent event such as a volcanic eruption, meteorite impact or earthquake are preserved in the rock surrounding such an event. In the case of the Cooper Basin impact, “penetrative intracrystalline planar deformation features” – essentially microscopic lines oriented in the same direction – were discovered in quartz grains. Additionally, the magnetic orientation of some of the rocks is slightly altered, further evidence of an impact event.

The impact structure itself may extend 10,000 square kilometers ( 3,850 square miles) and 524 meters (1,700 feet) deep, though Dr. Glikson said that further studies of the area include, “Studies of the geophysical structure of the basement below the Cooper Basin aimed at defining the impact structure.”

There is significant interest in the Cooper Basin as a source of geothermal energy, and there are several oil and gas companies currently mining the region, which is an important on-shore repository of petroleum. The impact event is likely the reason why this region is such a hotspot for geothermal activity.

“Large impacts result in a hydrothermal cell (boiling of ground water) which effect redistribution and re-concentration of K [potassium], Th [thorium] and U [uranium] upwards in the crust, hence elevated generation of heat from crustal zones enriched in the radiogenic elements,” Dr. Glikson explained.

The recent discovery of this impact crater makes it the second largest in Australia, second only to the Woodleigh impact structure (120 km in diameter), which was produced by an asteroid 6 to 12 km (4 to 8 miles) across, about 360 million years ago.

Dr. Glikson and Dr. Uysal will be presenting their findings at the upcoming Australian Geothermal Energy Conference in Adelaide, which runs from the 16th – 19th of November. They also plan to have their results published in a peer-reviewed journal, Dr. Glikson said. You can read a preliminary abstract of their conference paper here.

Source: Queensland University press release, conference paper abstract, interview with Dr. Andrew Glikson

Posted on by Nancy Atkinson

Time Traveler Caught on Film?

Screen grab of Clarke's zoom in of the Charlie Chaplin film 'The Circus.'

There’s a video making the rounds and creating buzz on the internet and we thought we might as well join in. Filmmaker George Clarke from Ireland is a Charlie Chaplin fan, and saw something unusual in a 1928 Chaplin movie called “The Circus.” In a crowd scene at the opening of the movie there appears to be a woman (or a man in drag) talking on a cell phone as she walks in front of Grauman’s Chinese Theatre. In the video above, Clarke goes on about it for awhile, but at about 2:40 in, you can see the footage. This person has all the mannerisms of someone walking down the street and talking on a cell phone.

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I’ve been checking around the web and no one seems to be able to come up with a good explanation, although there are lots of questions, such as, how could she be using a cell phone in 1928 since there were no cell phone towers or satellites at that time? Across the internet there are discussions of “Back to the Future”- like Walkie Talkies, alien homing devices, and pretty much everything else you can think of. My favorite discussion comes from the Washington Post, which claims this person is the worst time traveler ever, and the only reason no one has noticed this person before is “Because this may be the first time in history that someone has watched the DVD extras of “The Circus.” Forget the DVD extras! People didn’t even watch “The Circus” when it came out!”

It doesn’t appear this is a movie set, just film from taken out front of a real location. Anyway, its a weird video and there’s lots of discussion out there, but what are your thoughts?

Via SciBlogs

Posted on by Nancy Atkinson

Where In The Universe #123

After a small hiatus, it’s time once again for another Where In The Universe Challenge. Test your visual knowledge of the cosmos by naming where in the Universe this image was taken and give yourself extra points if you can name the spacecraft/telescope responsible for this picture. Post your guesses in the comments section, and check back on later at this same post to find the answer. To make this challenge fun for everyone, please don’t include links or extensive explanations with your answer. Good luck!

UPDATE: The answer has been posted below.

This is an image of NGC 6240 that contains X-ray data from Chandra (shown in red, orange, and yellow) combined with an optical image from the Hubble Space Telescope. In 2002, the discovery of two merging black holes was announced based on Chandra data in this galaxy. The two black holes are a mere 3,000 light years apart and are seen as the bright point-like sources in the middle of the image.

For more information about this image, see the Chandra website.

Posted on by Jason Rhian

Former Shuttle Astronaut Reflects on Discovery’s Final Mission

Discovery returns to Earth with the crew of STS-29. Robert Springer was a member of this crew and recently sat down and gave his thoughts about the end of the shuttle era. Photo Credit: NASA

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As he looks back over the years, former shuttle astronaut Robert Springer remembers the shuttle era very clearly. He flew on Atlantis – and Discovery. With the final flight of Discovery only a few days away, he took time out of his busy schedule to reminisce about his time ‘riding rockets.’

“Great memories,” Springer said, “I’m really proud of the opportunity I had and the chance to serve my country, and so it was was special — very special.”

Springer received his aviator’s wings in 1966 with the United States Marine Corps. He flew F-4 Phantoms in Vietnam where he also served as an advisor to the South Korean Marine Corps. Springer would fly some 300 combat missions in F-4s and an additional 250 combat missions in O-1 Bird Dogs, UH-1 “Hueys.” Springer would eventually attend navy Fighter Weapons School – known more commonly as “TOPGUN.” Springer has been awarded numerous awards including the Navy Distinguished Flying Cross and the Bronze Star.

He was selected to become an astronaut in 1980, completing training one a year later in 1981. He served on the support crew for STS-3 working on various aspects of the “Canadarm” remote manipulator system. Between 1984 and 1985 he served as CAPCOM on seven shuttle flights. After waiting nine years he flew his first mission in 1989 aboard Discovery on STS-29.

Crew portrait with Springer in the middle of the top row. Image Credit: NASA

STS-29 was a highly-successful mission that deployed a Tracking and Data Relay Satellite (TDRS) and conducted numerous experiments while on orbit. A year later in 1990 Springer again left Earth for the black sky on STS-38. This mission was aboard Atlantis and was a classified Department of Defense mission. It was the first mission to land at Kennedy Space Center in Florida since 1985. Of the two missions, Springer remembers STS-38 with a bit of a smile.

“My first flight on STS-29 was shortly after the first Return-to-Flight in 1988 and while the media attention was nice, once is enough,” Springer said. “So for STS-38 we were completely cut off from the press – it was fantastic! I just felt kind of bad for the new guys on that flight as they missed that aspect of a shuttle mission.”

When speaking with Springer, you can see the smile fade somewhat when the subject turns to the final flight of Discovery, arguably the most historic of the surviving orbiters.

“It’s going to be a little tough, realizing that this will be the last time that Discovery will be going into space,” Springer said while looking out at Launch Complex 39a. “You know that someday that the program is going to come to an end, but to actually have that take place and come to fruition, while exciting to see it launch – it will be sad.”

He fondly recollected his experience on board Discovery as one of the most amazing experiences in a career that has witnessed some of the most powerful experiences in American history.

“The flight overall was fantastic, it was so incredibly intense,” Springer said with a smile. “We were one of the first flights after the Challenger accident. While we normally plan for a 16 hour day during missions, we were so busy it ended up being an 18 hour day. Whenever we had a free minute we would hog the windows and stare out into space until you couldn’t fight it anymore and you’d drift off to sleep – and around the shuttle cabin.”

Posted on by Nancy Atkinson

Buckyballs Could Be Plentiful in the Universe

An infrared photo of the Small Magellanic Cloud taken by Spitzer is shown here in this artist's illustration, with two callouts. The middle callout shows a magnified view of an example of a planetary nebula, and the right callout shows an even further magnified depiction of buckyballs, which consist of 60 carbon atoms arranged like soccer balls. Image credit: NASA/JPL-Caltech

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Earlier this year, astronomers using the Spitzer Space Telescope announced they had found – for the first time — carbon molecules, known as “buckyballs,” in space. They were detected in one planetary nebula, and even though they were predicted to be rather prevalent out in space, no one was really sure. Until now. They’ve now been found in the space between stars, and around four more planetary nebulae, with one dying star in a nearby galaxy holding a staggering quantity of buckyballs — the equivalent mass of 15 times that of Earth’s Moon.

“It turns out that buckyballs are much more common and abundant in the universe than initially thought,” said astronomer Letizia Stanghellini of the National Optical Astronomy Observatory in Tucson, Ariz. “Spitzer had recently found them in one specific location, but now we see them in other environments. This has implications for the chemistry of life. It’s possible that buckyballs from outer space provided seeds for life on Earth.”

Buckyballs are soccer-ball-shaped molecules that were first observed in a laboratory 25 years ago, and are named for their resemblance to architect Buckminster Fuller’s geodesic domes, which have interlocking circles on the surface of a partial sphere. Also known as C60, and Fullerenes, they are the third major form of pure carbon; graphite and diamond are the other two. They have been thought to be common in space since they have been found in meteorites, and also in more everyday materials such as soot.

While two different studies announced today confirm that buckyballs could be widespread in space, they are turning up in places where astronomers thought they couldn’t exist. So, obviously we don’t have these molecules fully figured out yet.

All the planetary nebulae in which buckyballs have been detected are rich in hydrogen. This goes against what researchers thought for decades — they had assumed that, as is the case with making buckyballs in the lab, hydrogen could not be present. The hydrogen, they theorized, would contaminate the carbon, causing it to form chains and other structures rather than the spheres, which contain no hydrogen at all.

“We now know that fullerenes and hydrogen coexist in planetary nebulae, which is really important for telling us how they form in space,” said Anibal García-Hernández from the Instituto de Astrofísica de Canarias, Spain, lead author, working with Stanghellini on a paper appearing online Oct. 28 in the Astrophysical Journal Letters.

Using Spitzer, this team found the buckyballs around three dying sun-like stars, called planetary nebulae, in the our own Milky Way galaxy, plus in another planetary nebula the Small Magellanic Cloud, a nearby galaxy. This was particularly exciting to the researchers, because, in contrast to the planetary nebulae in the Milky Way, the distance to this galaxy is known. Knowing the distance to the source of the buckyballs meant that the astronomers could calculate their quantity — two percent of Earth’s mass, or the equivalent mass of 15 times that of Earth’s Moon.

Planetary nebulae are made of material shed from the dying stars.

Another Spitzer study about the discovery of buckyballs in space was also recently published in the Astrophysical Journal Letters, (October 10, 2010) and was led by Kris Sellgren of Ohio State University, Columbus. This study found that buckyballs are also present in the space between stars, but not too far away from young solar systems.

They were found among two nebulae; NGC 2023, located near the well-known Horsehead Nebula in the constellation of Orion, and the second, NGC 7023, known as the Iris Nebula, in the constellation Cepheus.
These are the largest molecules ever discovered floating between the stars. Astronomers aren’t sure yet if these cosmic balls formed in a nearby planetary nebula and wandered away, or if they perhaps can spring up in interstellar space.

“It’s exciting to find buckyballs in between stars that are still forming their solar systems, just a comet’s throw away,” Sellgren said. “This could be the link between fullerenes in space and fullerenes in meteorites.”
Since carbon is the key building block for life as we know it, their perhaps prevalent existence in space is intriguing.

“Now that there are buckyballs confirmed in the interstellar medium and in circumstellar space, it’s likely that chemists will get more interested in the astrobiological implications of these fascinating molecules,” Sellgren said.

Sources: JPL, NOAO,, CalTech/Spitzer

, Earlier detection of Buckyballs in Space — NASA

Posted on by Nancy Atkinson

Most Intense Storm in History Cuts Across the US — As Seen from Space

Visible satellite image of the October 26, 2010 superstorm taken at 5:32pm EDT. Image credit: NASA/GSFC.

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Yowza! – Here’s a satellite image of a storm of record-breaking proportions. On October 26, 2010, the strongest storm ever recorded in the Midwest spawned 24 tornadoes, 282 reports of damaging winds, violent thunderstorms, and torrential rains. The mega-storm reached peak intensity late yesterday afternoon over Minnesota, resulting in the lowest barometric pressure readings ever recorded in the continental United States (except for from hurricanes and nor’easters affecting the Atlantic seaboard.) The storm continues today (Oct. 27) with more tornado watches posted for Mississippi, Alabama, and Georgia, a blizzard warning for North Dakota, high wind warnings for most of the upper Midwest, and near-hurricane force winds on Lake Superior.

Read more about this super-storm on Weather Underground, but see below for what extremely low air pressure means.

Air pressure is one of the most important factors which determines what the weather is like. A mass of low pressure is an area of air that is rising. As it rises, it expands and cools. Cooler air cannot hold as much water as warmer air, so as the air rises the water will condense and form clouds. This is why an area of low pressure will often be accompanied by clouds and rain — which is what occurred on October 26 — lots of clouds and lots of rain and even snow.

But winds were even a bigger factor in this superstorm. Our atmosphere really doesn’t like big differences in air pressure, so where areas of low pressure meet up with areas of high pressure, winds blow in an attempt to combat the differences in the air pressure. The larger the difference in pressure the stronger the winds will blow. So, the extreme low pressure readings yesterday meant the winds were really howling — and they were. In my neighborhood in Illinois, we had a fairly study flagpole get bent from the winds. But that was nothing compared to the hurricane-like winds other places experienced: for example, Grand Marais, Minnesota — near the Great Lakes and near the area of the lowest air pressure readings — had sustained winds of 43 mph gusting to 59 mph, lasting for over 7 hours. Today, that region is still getting pummeled by winds and snow.

You can see the link to Weather Underground above to see what other weather extremes were experienced during this storm.

Posted on by Mark Thompson

Super Star Smashes into the Record Books.

Pulses from neutron star (rear) are slowed as they pass near foreground white dwarf. This effect allowed astronomers to measure masses of the system. CREDIT: Bill Saxton, NRAO/AUI/NSF

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The discovery of a super massive neutron star has thrown our understanding of stellar evolution into turmoil. The new star, called PSR J1614-2230 contains twice the mass of the Sun but compressed down into a star that is smaller than the Earth (you could fit over a million Earth’s inside the Sun by comparison). It is estimated a thimbleful of material from the star could weigh more than 500 million tons — that equates to about a million airliners. The study has cast serious doubt over how matter reacts under extreme densities.

The study by a team of astronomers using the National Radio Astronomy Observatory in New Mexico focussed its attention on the star which is about 3,000 light years away (the distance light can travel in 3,000 years at a speed of 300,000 km per second). The stellar corpse whose life ended long ago is now rotating at an incredible speed, completing 317 rotations every second. Its emitting an intense beam of energy from its polar regions which just happens to point in the direction of us here on Earth. We can detect this radiation beam as it flashes on and off like a celestial lighthouse. This type of neutron star is classed a pulsar.

Artist impression of Pulsar
Artist impression of Pulsar

Rather fortuitously, the star is part of a binary star system and is orbited by a white dwarf star which completes one orbit in just nine days. Its through the measurements of the interaction of the two which gave astronomers the clue as to the pulsar’s mass. The orbit of the white dwarf takes it between the beam of radiation and us here on Earth so that the energy from the beam has to pass close by the companion star. By measuring the delay in the beam’s arrival caused by distortion of space-time in the proximity of the white dwarf, scientists can determine the mass of both objects. Its an effect called the Shapiro Delay and its simply luck that the orientation of the stars to the Earth allows the effect to be measured.

Dave Finley, Public Information Officer from NRAO told Universe Today ‘Pulsars are neutron stars, whose radiation beams emerge from the poles and sweep across the Earth.  The orientation of the poles (and thus of the beams) is a matter of chance. We just got very lucky with this system.’

The discovery which was made possible by the new ‘Green Bank Ultimate Pulsar Processing Instrument (GUPPI) was able to measure the pulses from the pulsar with incredible accuracy and thus come to the conclusion that the star weighed in at a hefty two times the mass of the Sun. Current theories suggested a mass of around one and a half solar masses were possible but this new discovery changes the understanding of the composition of such stars, even to the subatomic level.

Neutron stars or pulsars are extreme objects at the very edges of the conditions that matter can exist. They really test our knowledge of the physical Universe and slowly but surely, through dedicated work of teams of astronomers, we are not only learning more about the stars above our heads but more and more about matter in the Universe in which we live.

Mark Thompson is a writer and the astronomy presenter on the BBC One Show. See his website, The People’s Astronomer, and you can follow him on Twitter, @PeoplesAstro

Source: NRAO

Posted on by Jon Voisey

Where’s M31’s Thick Disc?

Within our own galaxy, the thick disc is a distinct population of stars that resides above and below the main (thin) disc. Its stars have a larger range of velocities, are generally older and more metal poor. While astronomers aren’t entirely sure how it formed (remnants of accretion of small galaxies or ejection from the thin disc), it’s certainly there and analogues have been observed in other galaxies, more than 10 megaparsecs away. If these thick discs are truly a product of mergers, then galaxies showing evidence of mergers in other regards should show the presence of this second population as well. Yet in the case of M31, the Andromeda galaxy, the closest major galaxy to our own, which is thought to have a rich merger history, traces of the thick disc have proved elusive. So where is it?


Part of the problem in finding this galactic component is the angle at which the galaxy is presented to us. The galaxies for which a thick disc component have been detected (aside from our own) all lie edge on. This makes the process of finding the thick component greatly simplified. Astronomers can use photometric systems designed for detecting different populations of stars (young vs. old) and observe the change in distribution. When galaxies are presented closer to face on, the projection of the thick component onto the thin makes the identification far more difficult. The Andromeda galaxy is somewhere in between these two extremes and makes an angle of 77° on the sky (where 90° is edge on).

Due to this difficulty, another method is necessary to search for this extended population. Since 2002, a team led by Michelle Collins of Cambridge university has been using the Keck II telescope to search for the expected disc. To do this, the team has been using spectroscopic observations of numerous red giant stars to determine if a specific sub-population can be found with thick disc characteristics. While a sub-population has been discovered before in M31, its velocity dispersion was too low, and the distribution was too closely tied to the classical thin disc to truly be considered the missing component. Instead, it is referred to as the “extended disc”.

But where others have failed, Collins’ team has prevailed. From her team’s study, a recent paper claims to have discovered the thick disc and with such a large sample, have made some interesting observations about its nature. The first is that M31’s thick disc is nearly three times as thick. Additionally, the average velocity of both the thin and thick discs are notably higher (thinM31 = 32.0 kms-1, thinMW = 20.0 kms-1; thickM31 = 45.7 kms-1, thickMW = 40.0 km-1). If the thick disc is indeed related to mergers, then this may indicate that M31 has undergone a more intensive period of recent interactions than our own galaxy. However, the team notes that, from their observations alone, they are unable to constrain the formation methods of this component. While other studies have shown that accretion and ejection each leave distinct fingerprints, the necessary components were not mapped in sufficient detail to distinguish between the two.