Posted on by Brian Ventrudo

Star-Birth Myth Shattered

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An international team of astronomers has debunked a long-held belief about how stars are formed.

Since the 1950’s, astronomers believed groups of new-born stars obeyed the same rules of star formation, which meant the ratio of massive stars to lighter stars was pretty much the same from galaxy to galaxy.  For every star 20 times more massive than the Sun or larger, for example, there’d be 500 stars equal to or less than the mass of the Sun.

“This was a really useful idea. Unfortunately it seems not to be true,” said team research leader Dr. Gerhardt Meurer of Johns Hopkins University in Baltimore.

This mass distribution of newly-born stars is called the ‘initial mass function’, or IMF.  Most of the light we see from galaxies comes from the highest mass stars, while the total mass in stars is dominated by the lower mass stars which can’t be seen, so the IMF has implications in accurately determining the mass of galaxies.  By measuring the amount of light from a population of stars, and making some corrections for the stars’ ages, astronomers can use the IMF to estimate the total mass of that population of stars.

Results for different galaxies can be compared only if the IMF is the same everywhere, but Dr. Meurer’s team has shown this ratio of high-mass to low-mass newborn stars differs between galaxies.  Small ‘dwarf’ galaxies, for instance, form many more low-mass stars than expected.

To arrive at this finding, Dr. Meurer’s team used galaxies in the HIPASS Survey (HI Parkes All Sky Survey) done with the Parkes radio telescope near Sydney, Australia.  A radio survey was used because galaxies contain substantial amounts of neutral hydrogen gas, the raw material for forming stars, and the neutral hydrogen emits radio waves.

The team measured two tracers of star formation, ultraviolet and H-alpha emissions, in 103 of the survey galaxies using NASA’s GALEX satellite and the 1.5-m CTIO optical telescope in Chile.

Selecting galaxies on the basis of their neutral hydrogen gave a sample of galaxies of many different shapes and sizes, unbiased by their star formation history.

H-alpha emission traces the presence of very massive stars called O stars, the birth of a star with a mass more than 20 times that of the Sun.

The UV emission, traces both O stars and the less massive B stars — overall, stars more than three times the mass of the Sun.

Meurer’s team found the ratio of H-alpha to UV emission varied from galaxy to galaxy, implying the IMF also did, at least at its upper end.

“This is complicated work, and we’ve necessarily had to take into account many factors that affect the ratio of H-alpha to UV emission, such as the fact that B stars live much longer than O stars,” Dr. Meurer said.

Dr. Meurer’s team suggests the IMF seems to be sensitive to the physical conditions of the star-forming region, particularly gas pressure.  For instance, massive stars are most likely to form in high-pressure environments such as tightly bound star clusters.

The team’s results allow a better understanding of other recently observed phenomena that have been puzzling astronomers, such as variation of the ratio of H-alpha to ultraviolet light as a function of radius within some galaxies.  This now makes sense as the stellar mix varies as the pressure drops with radius, just like the pressure varies with altitude on the Earth.

The work confirms tentative suggestions made first by Veronique Buat and collaborators in France in 1987, and then a more substantial study last year by Eric Hoversteen and Karl Glazebrook working out of Johns Hopkins and Swinburne Universities that suggested the same result.

Source: CSIRO

Posted on by Nancy Atkinson

Fog on Titan? Help Review Mike Brown’s Paper

Fog on Titan. Credit: Mike Brown, et al.

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Titan is the only place in the solar system other than the earth that appears to have large quantities of liquid sitting on the surface. Granted, conditions on Titan are quite different than on Earth. For one thing, it’s a lot colder on Titan and the liquids there are various types of hydrocarbons. “Methane is to Titan what water is to the earth,” says astronomer Mike Brown (yes, that guy, of Pluto, Eris and Makemake fame.) But now Brown and his colleagues have discovered another similarity. Titan has fog. “All of those bright sparkly reddish white patches (shown in the image here) are fog banks hanging out at the surface in Titan’s late southern summer,” Brown wrote in his blog.

Wow.

But how does this happen? Fog only usually appears when 1.) there is liquid in the atmosphere (i.e., that means it must be “humid” on Titan) and 2.) the air temperature cools drastically. But Titan’s atmosphere is extremely thick, so it cools slowly. Plus the atmosphere is already really cold and making it colder would be difficult.

“If you were to turn the sun totally off,” said Brown, “Titan’s atmosphere would still take something like 100 years to cool down. And even the coldest parts of the surface are much too warm to ever cause fog to condense.”

So what is going on there?

To get the humidity in Titan’s atmosphere, Brown said the liquid methane must be evaporating.
“Evaporating methane means it must have rained,” he wrote. “Rain means streams and pools and erosion and geology. Fog means that Titan has a currently active methane hydrological cycle doing who knows what on Titan.”

Plus, the only one way to make the fog stick around on the ground for any amount of time is have both humidity and cool air. And the only way to cool the air on Titan is have it in contact with something cold: like a pool of evaporating liquid methane.

Brown said the fog doesn’t appear to be around the just the dark areas near the south pole that likely are hydrocarbon lakes. “It looks like it might be more or less everywhere at the south pole. My guess is that the southern summer polar rainy season that we have witnessed over the past few years has deposited small pools of liquid methane all over the pole. It’s slowly evaporating back into the atmosphere where it will eventually drift to the northern pole where, I think, we can expect another stormy summer season. Stay tuned. Northern summer solstice is in 2016.”

And here comes the fun part (as if fog on Titan wasn’t fun enough!) Brown is looking for a little citizen science help. You can read the paper on this by Brown and his colleagues here. Most peer review is done by one person, and brown would like a few more eyes to see this paper to look for any flaws, and to see if their arguments make sense and are convincing.

Brown says: “I thought I would try an experiment of my own here. It goes like this: feel free to provide a review of my paper! I know this is not for everyone. Send it directly to me or comment here (at his blog). I will take serious comments as seriously as those of the official reviewer and will incorporate changes into the final version of the paper before it is published.

Please, though, serious reviewers only.

Source: Mike Brown’s Blog

Posted on by Nancy Atkinson

Researchers Say Sun Cycle Alters Earth’s Climate

The sunspot cycle from 1995 to the present. The jagged curve traces actual sunspot counts. Smooth curves are fits to the data and one forecaster's predictions of future activity. Credit: David Hathaway, NASA/MSFC

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If the energy from the sun varies by only 0.1 percent during the 11-year solar cycle, could such a small variation drive major changes in weather patterns on Earth? Yes, say researchers from the National Center for Atmospheric Research (NCAR) who used more than a century of weather observations and three powerful computer models in their study. They found subtle connections between solar cycle, the stratosphere, and the tropical Pacific Ocean that work in sync to generate periodic weather patterns that affect much of the globe. Scientists say this will help in predicting the intensity of certain climate phenomena, such as the Indian monsoon and tropical Pacific rainfall, years in advance.

“The Sun, the stratosphere, and the oceans are connected in ways that can influence events such as winter rainfall in North America,” says NCAR scientist Gerald Meehl, the lead author. “Understanding the role of the solar cycle can provide added insight as scientists work toward predicting regional weather patterns for the next couple of decades.”

The new study looked at the connection between the Sun’s impact on two seemingly unrelated regions. Chemicals in the stratosphere and sea surface temperatures in the Pacific Ocean respond during solar maximum in a way that amplifies the Sun’s influence on some aspects of air movement. This can intensify winds and rainfall, change sea surface temperatures and cloud cover over certain tropical and subtropical regions, and ultimately influence global weather.

The team first confirmed an earlier theory, that the slight increase in solar energy during the peak production of sunspots is absorbed by stratospheric ozone. The energy warms the air in the stratosphere over the tropics, where sunlight is most intense, while also stimulating the production of additional ozone there that absorbs even more solar energy. Since the stratosphere warms unevenly, with the most pronounced warming occurring at lower latitudes, stratospheric winds are altered and, through a chain of interconnected processes, end up strengthening tropical precipitation.

At the same time, the increased sunlight at solar maximum causes a slight warming of ocean surface waters across the subtropical Pacific, where Sun-blocking clouds are normally scarce. That small amount of extra heat leads to more evaporation, producing additional water vapor. In turn, the moisture is carried by trade winds to the normally rainy areas of the western tropical Pacific, fueling heavier rains and reinforcing the effects of the stratospheric mechanism.

The top-down influence of the stratosphere and the bottom-up influence of the ocean work together to intensify this loop and strengthen the trade winds. As more sunshine hits drier areas, these changes reinforce each other, leading to less clouds in the subtropics, allowing even more sunlight to reach the surface, and producing a positive feedback loop that further magnifies the climate response.

These stratospheric and ocean responses during solar maximum keep the equatorial eastern Pacific even cooler and drier than usual, producing conditions similar to a La Nina event. However, the cooling of about 1-2 degrees Fahrenheit is focused farther east than in a typical La Nina, is only about half as strong, and is associated with different wind patterns in the stratosphere.

Earth’s response to the solar cycle continues for a year or two following peak sunspot activity. The La Nina-like pattern triggered by the solar maximum tends to evolve into a pattern similar to El Nino as slow-moving currents replace the cool water over the eastern tropical Pacific with warmer water. The ocean response is only about half as strong as with El Nino and the lagged warmth is not as consistent as the La Nina-like pattern that occurs during peaks in the solar cycle.

Solar maximum could potentially enhance a true La Nina event or dampen a true El Nino event. The La Nina of 1988-89 occurred near the peak of solar maximum. That La Nina became unusually strong and was associated with significant changes in weather patterns, such as an unusually mild and dry winter in the southwestern United States.

The Indian monsoon, Pacific sea surface temperatures and precipitation, and other regional climate patterns are largely driven by rising and sinking air in Earth’s tropics and subtropics. Therefore the new study could help scientists use solar-cycle predictions to estimate how that circulation, and the regional climate patterns related to it, might vary over the next decade or two.

The team used three different computer models to look at all the variables and each came up with the same result, that even a small variablilty in the sun’s energy could have profound effects on Earth.

“With the help of increased computing power and improved models, as well as observational discoveries, we are uncovering more of how the mechanisms combine to connect solar variability to our weather and climate,” Meehl says.

The team’s research was published in the Journal Science.

Posted on by Fraser Cain

The Universe DVD Giveaway

In case you haven’t heard, Season 4 of the History Channel’s “The Universe” has begun. To help celebrate, they’ve generously offered to give away two sweet prizes related to the show. One person will get “The Universe Collector’s Set“, which contains Season 1, Season 2, and the 2 specials. And another person will get to choose between Season 1 on Bluray, or Season 2 on DVD.

To enter the giveaway, just email [email protected] with the Subject Line: “Universe DVD Giveaway“. I’ll collect all the entries and pick two randomly as winners. Then I’ll delete all the emails.

The deadline to enter is Monday, August 31st, 2009 at 12:00 noon (Pacific Time).

And if you want to check out The Universe now, you can buy full episodes on iTunes, order DVDs from the History Channel, and even watch it on the television. The next episode, “It Fell From Space” airs on September 1, 2009

Posted on by Nancy Atkinson

LookUP to Find Astronomical Objects

Sky map of Epsilon Aurigae

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Have you heard about LookUP? Stuart Lowe from the Jodrell Bank Centre for Astrophysics created this web tool to provide quick access to information about the the position and other details of specific astronomical objects. Instead of having to go search through an astronomical database, all you have to do is type in the name of the object (this doesn’t apply for spacecraft) and LookUP contacts the relevant astronomical databases for you and provides info such as right ascension and declination. There’s also mobile version, an application for iPhones, and a widget for your desktop. The newest tool will thrill all the astronomy Twitterers out there. Rob Simpson from Orbiting Frog fame created a Twitter account for LookUP. All you do is send a tweet to it with the name of your object, and it will send you the info and a link with for further information. For example, I wanted to know where Asteroid Apophis was, and LookUp Tweeted back: Apophis is at RA 10:35:13.594 dec 07:37:40.210 More info http://bit.ly/1aVqzG (that is valid for the time I sent the Tweet.) Check it out; it’s all very quick and easy and wonderful for all you stargazers out there.

LookUP

Posted on by Nancy Atkinson

How Close Was That Lightning to the Shuttle?

Lightning strikes close to the launchpad at Kennedy Space Center on August 25, 2009. Credit: NASA, Ben Cooper. Click the image for access to a larger version.

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If you’re wondering why the first launch attempt for space shuttle Discovery was scrubbed early Tuesday morning, here’s your answer. Yikes! But what a gorgeous picture! And of course, the second launch attempt early Wednesday morning was called off when instrumentation for an 8-inch fill and drain valve on the shuttle’s external tank indicated the valve had failed to close. But yesterday, the valve functioned correctly five times during launch pad tests, NASA said. That means NASA will likely go ahead with a launch attempt at 04:22 GMT (12:22 a.m. ET) on Friday. But the anomaly remains unexplained, so it will be up to the mission management team to decide if the shuttle can fly as is, or if engineers need to know more about the issue. The decision won’t be made, however until the MMT meets Thursday afternoon, just hours before the scheduled liftoff time. As the saying goes, there’s a million parts on the shuttle and if only one is not working….

UPDATE: Launch now is targeted for no earlier than 11:59 p.m. Friday, Aug. 28, to allow engineers more time to develop plans for resolving the issue with the valve.

See below for a close-up of the lightning shot, to see how close it actually came to the shuttle.

Lightining strikes close to Discovery on the launchpad on Aug. 25, 2009. Credit: NASA/Ben Cooper. Click image for access to larger version.
Lightining strikes close to Discovery on the launchpad on Aug. 25, 2009. Credit: NASA/Ben Cooper. Click image for access to larger version.

Discovery’s 13-day mission will deliver more than 7 tons of supplies, science racks and equipment, as well as additional environmental hardware to sustain six crew members on the International Space Station. The equipment includes a freezer to store research samples, a new sleeping compartment and the COLBERT treadmill. The mission is the 128th in the Space Shuttle Program, the 37th flight of Discovery and the 30th station assembly flight.

Hat Tip to absolutespacegrl on Twitter!

Posted on by Nancy Atkinson

Mars Reconnissance Orbiter Goes Into Safe Mode Again

Artists concept of the Mars Reconnaisance Orbiter. Credit: NASA/JPL

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NASA’s Mars Reconnaissance Orbiter put itself into a safe mode Wednesday morning, Aug. 26, for the fourth time this year. While in safe mode, the spacecraft can communicate normally with Earth, but aborts its scheduled activities, and awaits further instructions from ground controllers. “We hope to gain a better understanding of what is triggering these events and then have the spacecraft safely resume its study of Mars by next week,” said MRO Project Manager Jim Erickson.

Engineers have begun the process of diagnosing the problem prior to restoring the orbiter to normal science operations, a process expected to take several days. They will watch for engineering data from the spacecraft that might aid in identifying the cause of event and possibly of previous ones.

A possible cause for the frequent anomalies is cosmic ray hits. But the spacecraft has reacted differently with the various safe mode entries. The orbiter spontaneously rebooted its computer Wednesday, as it did in February and June, but did not switch to a redundant computer, as it did in early August.

To help in investigating a root cause of the three previous anomalies, engineers had programmed the spacecraft to frequently record engineering data onto non-volatile memory. That could give an improved record of spacecraft events leading up to the reboot.

MRO has been in Mars orbit since 2006, and has returned more data than all other current and past Mars missions combined.

Source: JPL

Posted on by John Carl Villanueva

Charge of Electron

Charge of Electron
Simplified Scheme of Millikan’s Oil-drop Experiment

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The charge of the electron is equivalent to the magnitude of the elementary charge (e) but bearing a negative sign. Since the value of the elementary charge is roughly 1.602 x 10-19 coulombs (C), then the charge of the electron is -1.602 x 10-19 C.

When expressed in atomic units, the elementary charge takes the value of unity; i.e., e = 1. Thus, the electron’s charge can be denoted by -e. Although the proton is much more massive than the electron, it only has a charge of e. Hence, neutral atoms always bear the same number of protons and electrons.

JJ Thomson is the undisputed discoverer of the electron. However, despite all those experiments he performed on it, he could only manage to obtain the electron’s charge to mass ratio. The distinction of being the first to measure the electron’s charge goes to Robert Millikan through his oil-drop experiment in 1909.

The Millikan Oil-Drop Experiment

Here’s the basic idea. If you know the density and dimensions (thus subsequently the volume) of a substance, it’s going to be easy to calculate its mass and the force that gravity exerts on it, a.k.a. weight. If you recall, weight is just m x g.

Now let’s assume these substances to be charged oil drops. If you subject these drops to gravity alone, they’ll fall freely. However, if they are allowed to fall in a uniform electric field, their trajectory will be altered depending on the direction and magnitude of the field.

If the forces due to the field are directed opposite to gravity, the downward velocity of the particles may decrease. At some point, when the upward force is equal to the downward force, the velocities may even go down to zero and the particles will stay in mid-air.

At this specific instance, if we know the magnitude of the electric field (in N/C, units defining the force per unit charge) and the weight of each particle, we can calculate the force of the electric field on a single particle and finally derive the charge.

Thus, a basic Millikan Oil-Drop Experiment setup will include an enclosure containing falling charged oil drops, a device to measure their radii, an adjustable uniform electric field, and a meter to determine the field’s magnitude.

By repeating the experiment on a large number of oil drops, Millikan and his colleague, Harvey Fletcher, obtained electron charge values within 1% of the currently accepted one.

We have some articles in Universe Today that are related to the charge of the electron. Here are two of them:

Physics World also has some more:

Tired eyes? Let your ears help you learn for a change. Here are some episodes from Astronomy Cast that just might suit your taste:

Sources:
Wikipedia
GSU Hyperphysics
University of Alaska-Fairbanks

Posted on by Nancy Atkinson

Mars Kicking Spirit When She’s Down

This full-circle view from the panoramic camera (Pancam) on NASA's Mars Exploration Rover Spirit shows the terrain surrounding the location called "Troy," where Spirit became embedded in soft soil during the spring of 2009. Credit: NASA/JPL

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The Spirit rover has been stuck in loose soil on Mars for several months now, and just as the rover team is preparing to execute maneuvers to attempt to free Spirit, a dust storm hits. Is Mars an unforgiving planet or what? The amount of electricity generated by the solar panels on Spirit has been declining for the past several Martian days, or sols, because of the storm, and Spirit’s daily activities have been trimmed. Those watching over the rover are keeping an eye on weather reports from observations by NASA’s Mars Reconnaissance Orbiter. While the rover team at JPL are keeping their “spirits” up, a recent image from the rover indicates Spirit herself might be getting frustrated with her string of bad luck:

Get me out of here! Credit: NASA/JPL, image enhancement by Stuart Atkinson
Get me out of here! Credit: NASA/JPL, image enhancement by Stuart Atkinson

Thanks to Stuart Atkinson from Cumbrian Sky for his image spoof!

Spirit’s solar panels generated 392 watt-hours during the mission’s Sol 2006 (Aug. 24, 2009), down from 744 watt-hours five sols earlier, but still generous compared with the 240 watt-hours per sol that was typical before a series of panel-cleaning events about four months ago.

“We expect that power will improve again as this storm passes, but we will continue to watch this vigilantly,” said JPL’s John Callas, project manager for Spirit and its twin, Opportunity. “Spirit remains power positive with healthy energy margins and charged batteries. The weather prediction from the Mars Color Imager team is that the storm is abating, but skies will remain dusty over Spirit for the next few sols.”

Recent images from the Mars Color Imager camera on Mars Reconnaissance Orbiter showed this regional storm becoming less extensive Monday even as it shifted southward so that its southern edge covered the Gusev Crater area where Spirit is working. Malin Space Science Systems in San Diego, which operates that camera, provides frequent weather updates to the rover team. Check out weekly weather reports here.

Meanwhile, in JPL’s In-Situ Instrument Laboratory, the rover team is continuing testing of strategies for getting Spirit out of a patch of soft soil where it is embedded on Mars. On Sol 2005 (Aug. 23, 2009) Spirit used its panoramic camera to examine the nature of how soil at the site has stuck to the rover’s middle wheels. The team has also used Spirit’s rock abrasion tool as a penetrometer to measure physical properties of the soil around Spirit by pressing into the soil with three different levels of force. The team is aiming to start sending drive commands to Spirit in September.

Source: JPL