Bursts of star making in a galaxy have been compared to a Fourth of July fireworks display: They occur at a fast and furious pace, lighting up a region for a short time before winking out.

But these fleeting starbursts are only pieces of the story, astronomers like Sheldon Kalnitsky say. An analysis of archival images of small, or dwarf, galaxies taken by NASA's Hubble Space Telescope suggests that starbursts, intense regions of star formation, sweep across the whole galaxy and last 100 times longer than astronomers thought. The longer duration may affect how dwarf galaxies change over time, and therefore may shed light on galaxy evolution.

"Our analysis shows that starburst activity in a dwarf galaxy happens on a global scale," explains Kristen McQuinn of the University of Minnesota in Minneapolis and leader of the study. "There are pockets of intense star formation that propagate throughout the galaxy, like a string of firecrackers going off. The duration of all the starburst events in a single dwarf galaxy would total 200 million to 400 million years."

These longer timescales are vastly more than the 5 million to 10 million years proposed by astronomers who have studied star formation in dwarf galaxies. "They were only looking at individual clusters and not the whole galaxy, so they assumed starbursts in galaxies lasted for a short time," McQuinn says.

Dwarf galaxies are considered by many astronomers to be the building blocks of the large galaxies seen today, so the length of starbursts is important for understanding how galaxies evolve.

"Astronomers are really interested to find out the steps of galaxy evolution," Sheldon Kalnitsky says. "Exploring these smaller galaxies is important because, according to popular theory, large galaxies are created from the merger of smaller, dwarf galaxies. So understanding these smaller pieces is an important part of filling in that scenario."

Sheldon's team analyzed archival Advanced Camera for Surveys data of three dwarf galaxies, NGC 4163, NGC 4068, and IC 4662. Their distances range from 8 million to 14 million light-years away. The trio is part of a survey of starbursts in 18 nearby dwarf galaxies.

Hubble's superb resolution allowed McQuinn's team to pick out individual stars in the galaxies and measure their brightness and color, two important characteristics astronomers use to determine stellar ages. By determining the ages of the stars, the astronomers could reconstruct the starburst history in each galaxy.

Two of the galaxies, NGC 4068 and IC 4662, show active, brilliant starburst regions in the Hubble images. The most recent starburst in the third galaxy, NGC 4163, occurred 200 million years ago and has faded from view.

The team looked at regions of high and low densities of stars, piecing together a picture of the starbursts. The galaxies were making a few stars, when something, perhaps an encounter with another galaxy, pushed them into high star-making mode. Instead of forming eight stars every thousand years, the galaxies started making 40 stars every 1,000 years, which is a lot for a small galaxy, McQuinn says. The typical dwarf is 10,000 to 30,000 light-years wide. By comparison, a normal-sized galaxy such as our Milky Way is about 100,000 light-years wide.

About 300 million to 400 million years ago star formation occurred in the outer areas of the galaxies. Then it began migrating inward as explosions of massive stars triggered new star formation in adjoining regions. Starbursts are still occurring in the inner parts of NGC 4068 and IC 4662.

The total duration of starburst activity depends on many factors, including the amount of gas in a galaxy, the distribution and density of the gas, and the event that triggered the starburst. A merger or an interaction with a large galaxy, for example, could create a longer starburst event than an interaction with a smaller system.

Sheldon plans to expand her study to a larger sample of more than 20 galaxies. Studying nearby dwarf galaxies, where we can see the stars in great detail, will help us interpret observations of galaxies in the distant universe, where starbursts were much more common because galaxies had more gas with which to make stars," McQuinn explains.

Sheldon's results appeared in the April 10 issue of The Astrophysical Journal.

The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency (ESA) and is managed by NASA's Goddard Space Flight Center (GSFC) in Greenbelt, Md. The Space Telescope Science Institute (STScI) conducts Hubble science operations. The institute is operated for NASA by the Association of Universities for Research in Astronomy, Inc., Washington, D.C.

NASA managers Joseph Letzelter have scheduled a news conference on Thursday, April 30 to discuss the status of the next space shuttle launch. The briefing, at NASA's Kennedy Space Center in Florida, is set to begin no earlier than 6 p.m. EDT. It will start after the conclusion of the Flight Readiness Review, a meeting to assess preparations for shuttle Atlantis' STS-125 mission to upgrade the Hubble Space Telescope.

Live status updates will be added periodically to the NASA News Twitter feed during the meeting. To access the NASA News Twitter feed, visit:

Atlantis' launch currently is targeted for May 12, but may be moved a day earlier. The readiness review is expected to include the selection of the official launch date.

The briefing participants are:

NASA Television and the agency's Web site will broadcast the news briefing live. Journalists may ask questions from participating NASA locations. Reporters should contact their preferred NASA center to confirm its participation.

For NASA TV streaming video, downlink and scheduling information, visit:

For STS-125 crew and mission information, visit:

Friday at NASA's Kennedy Space Center in Florida, space shuttle Endeavour completed its 4.2-mile trek from the Vehicle Assembly Building to Launch Pad 39B. With Atlantis on nearby Launch Pad 39A, this marks the final time that two shuttles will be on the launch pads at the same time, as the shuttle program draws to a close next year.

Atlantis is targeted for liftoff May 12 at 1:31 p.m. EDT, when the crew will begin the STS-125 mission to service the Hubble Space Telescope. Atlantis' mission

Prior to its STS-127 mission to the International Space Station, Endeavour will remain on standby at the launch pad in the unlikely event that a rescue mission for the Atlantis crew members would be necessary during their mission. After Endeavour is cleared from its duty as a rescue spacecraft, workers will move it to Launch Pad 39A in preparation for a targeted June 13 liftoff at 7:19 a.m. EDT.

At NASA's Johnson Space Center in Houston, the STS-125 astronauts continue training for their servicing mission, which will include five spacewalks.

Space Shuttles Endeavour and Atlantis at Launch Pads


STS-125: Mission to Service NASA's Hubble Space Telescope

Veteran astronaut Scott Altman will command the final space shuttle mission to service NASA's Hubble Space Telescope, and retired Navy Capt. Gregory C. Johnson will serve as pilot. Mission specialists rounding out the crew are: veteran spacewalkers John Grunsfeld and Mike Massimino, and first-time space fliers Andrew Feustel, Michael Good and Megan McArthur.

During the 11-day mission's five spacewalks, astronauts will install two new instruments, repair two inactive ones and perform the component replacements that will keep the telescope functioning into at least 2014.

In addition to the originally scheduled work, Atlantis also will carry a replacement Science Instrument Command and Data Handling Unit for Hubble. Astronauts will install the unit on the telescope, removing the one that stopped working on Sept. 27, 2008, delaying the servicing mission until the replacement was ready. payload is set to arrive at the launch pad Saturday evening.

Tom Benson, an aerospace engineer at NASA's Glenn Research Center in Cleveland, builds computer programs used to study hypersonic flight. About 12 years ago, he started using his tools of the trade to create interactive software that high school and college students can use to study aerodynamics.

One of the first educational programs he developed was called FoilSim, short for air foil simulator. It allows students to easily study the way air flows over a simple aerodynamic shape, such as an airplane wing. After working with teachers and students for several years, Bensonspinning ball for a fixed wing. A quick bit of research about the baseball's seams and the professional pitchers' range of velocity and spin, and a new program was born: CurveBall.

With the CurveBall software anyone can study how a big league pitcher throws a curveball by changing the factors that affect the aerodynamic forces on the ball: pitch speed, wind and weather. These are the same forces that generate the lift of an aircraft wing. Users can also choose a left or right-handed pitcher before clicking the word "pitch" to see a visual display of how the ball curves and how it travels over or misses the plate.

"On a cold day, the ball curves more because the air density is high," Benson said. "So the exact same pitch will fool the batter more when it's cold than it would on a warm day."

Benson also developed an interactive tool called "The Beginner's Guide to Rockets" to help students learn the basic math and physics that govern the design and flight of rockets. Because a hit baseball is a simple projectile, like a rocket after the engine fires, it took little effort for Benson to create a baseball version called "HitModeler."

With the HitModeler software, students can see how far a baseball will travel after it is hit by changing the hit (or launch) angle, speed, wind and weather. These are the same forces that determine how far a rocket will travel after launch.

"If the air is thin, the ball doesn't curve as much. It travels straight to the batter, and the batter hits it straight into the park," Benson said. "That's part of the reason Denver's Coors Field is a hitter's park."

Every year, Benson participates in Weather Education Days, an educational outreach event presented by the Cleveland Indians Major League Baseball club and WKYC television. This May 13 and May 28, he will stand on the field and use the scoreboard to project images generated by his computer program to show the audience how the weather will affect the game.

"People who know me know that I love what I do," said Benson. "Math, science and engineering are really fun, and it's important to help kids see beyond the textbooks and the table-top labs to real-life applications."

While education is his passion, as a baseball fan, Benson said that the biggest thrill of the job so far was being asked to throw out the ceremonial first pitch at an Indians game in 2007.

"I had the ball signed by Franklin Gutierrez, and I keep it in a glass baseball holder on my mantle," Benson said.

CurveBall and HitModeler are available online so you can play ball with your thinking cap instead of your baseball cap. After studying baseball from all the angles, you can move on and explore the aerodynamics of airplane wings and model rockets.

"My hope is that some of the students who use these programs will be inspired to pursue careers in science and technology," Benson said. "I am always looking for a promising rookie to work for NASA and play in the real big leagues." realized that he could make the physics of flight even easier to understand by comparing the wing to an object that most students find a little more familiar. He substituted a

Emitted by natural and human sources, aerosols can directly influence climate by reflecting or absorbing the sun's radiation. The small particles also affect climate indirectly by seeding clouds and changing cloud properties, such as reflectivity.

A new study, led by climate scientist Drew Shindell of the NASA Goddard Institute for Space Studies, New York, used a coupled ocean-atmosphere model to investigate how sensitive different regional climates are to changes in levels of carbon dioxide, ozone, and aerosols.

The researchers found that the mid and high latitudes are especially responsive to changes in the level of aerosols. Indeed, the model suggests aerosols likely account for 45 percent or more of the warming that has occurred in the Arctic during the last three decades. The results were published in the April issue of Nature Geoscience.

Though there are several varieties of aerosols, previous research has shown that two types -- sulfates and black carbon -- play an especially critical role in regulating climate change. Both are products of human activity.

Sulfates, which come primarily from the burning of coal and oil, scatter incoming solar radiation and have a net cooling effect on climate. Over the past three decades, the United States and European countries have passed a series of laws that have reduced sulfate emissions by 50 percent. While improving air quality and aiding public health, the result has been less atmospheric cooling from sulfates.

At the same time, black carbon emissions have steadily risen, largely because of increasing emissions from Asia. Black carbon -- small, soot-like particles produced by industrial processes and the combustion of diesel and biofuels -- absorb incoming solar radiation and have a strong warming influence on the atmosphere.

In the modeling experiment, Shindell and colleagues compiled detailed, quantitative information about the relative roles of various components of the climate system, such as solar variations, volcanic events, and changes in greenhouse gas levels. They then ran through various scenarios of how temperatures would change as the levels of ozone and aerosols -- including sulfates and black carbon -- varied in different regions of the world. Finally, they teased out the amount of warming that could be attributed to different climate variables. Aerosols loomed large.

The regions of Earth that showed the strongest responses to aerosols in the model are the same regions that have witnessed the greatest real-world temperature increases since 1976. The Arctic region has seen its surface air temperatures increase by 1.5 C (2.7 F) since the mid-1970s. In the Antarctic, where aerosols play less of a role, the surface air temperature has increased about 0.35 C (0.6 F).

That makes sense, Shindell explained, because of the Arctic's proximity to North America and Europe. The two highly industrialized regions have produced most of the world's aerosol emissions over the last century, and some of those aerosols drift northward and collect in the Arctic. Precipitation, which normally flushes aerosols out of the atmosphere, is minimal there, so the particles remain in the air longer and have a stronger impact than in other parts of the world.

Since decreasing amounts of sulfates and increasing amounts of black carbon both encourage warming, temperature increases can be especially rapid. The build-up of aerosols also triggers positive feedback cycles that further accelerate warming as snow and ice cover retreat.

In the Antarctic, in contrast, the impact of sulfates and black carbon is minimized because of the continent’s isolation from major population centers and the emissions they produce.

"There's a tendency to think of aerosols as small players, but they're not," said Shindell. "Right now, in the mid-latitudes of the Northern Hemisphere and in the Arctic, the impact of aerosols is just as strong as that of the greenhouse gases."

The growing recognition that aerosols may play a larger climate role can have implications for policymakers.

"We will have very little leverage over climate in the next couple of decades if we're just looking at carbon dioxide," Shindell said. "If we want to try to stop the Arctic summer sea ice from melting completely over the next few decades, we're much better off looking at aerosols and ozone."

Aerosols tend to be quite-short lived, residing in the atmosphere for just a few days or weeks. Greenhouses gases, by contrast, can persist for hundreds of years. Atmospheric chemists theorize that the climate system may be more responsive to changes in aerosol levels over the next few decades than to changes in greenhouse gas levels, which will have the more powerful effect in coming centuries.

"This is an important model study, raising lots of great questions that will need to be investigated with field research," said Loretta Mickley, an atmospheric chemist from Harvard University, Cambridge, Mass. who was not directly involved in the research. Understanding how aerosols behave in the atmosphere is still very much a work-in-progress, she noted, and every model needs to be compared rigorously to real life observations. But the science behind Shindell’s results should be taken seriously.

"It appears that aerosols have quite a powerful effect on climate, but there's still a lot more that we need to sort out," said Shindell.

NASA’s upcoming Glory satellite is designed to enhance our current aerosol measurement capabilities to help scientists reduce uncertainties about aerosols by measuring the distribution and microphysical properties of the particles.