Ultraviolet Spotlight on Plump Stars in Tiny Galaxies

Astronomers using NASA's Galaxy Evolution Explorer may be closer to knowing why some of the most massive stellar explosions ever observed occur in the tiniest of galaxies.

"It's like finding a sumo wrestler in a little 'Smart Car,'" said Don Neill, a member of NASA's Galaxy Evolution Explorer team at the California Institute of Technology in Pasadena, and lead author of a new study published in the Astrophysical Journal.

"The most powerful explosions of massive stars are happening in extremely low-mass galaxies. New data are revealing that the stars that start out massive in these little galaxies stay massive until they explode, while in larger galaxies they are whittled away as they age, and are less massive when they explode," said Neill.

Over the past few years, astronomers using data from the Palomar Transient Factory, a sky survey based at the ground-based Palomar Observatory near San Diego, have discovered a surprising number of exceptionally bright stellar explosions in so-called dwarf galaxies up to 1,000 times smaller than our Milky Way galaxy. Stellar explosions, called supernovae, occur when massive stars -- some up to 100 times the mass of our sun -- end their lives.

The Palomar observations may explain a mystery first pointed out by Neil deGrasse Tyson and John Scalo when they were at the University of Austin Texas (Tyson is now the director of the Hayden Planetarium in New York, N.Y.). They noted that supernovae were occurring where there seemed to be no galaxies at all, and they even proposed that dwarf galaxies were the culprits, as the Palomar data now indicate.

Now, astronomers are using ultraviolet data from the Galaxy Evolution Explorer to further examine the dwarf galaxies. Newly formed stars tend to radiate copious amounts of ultraviolet light, so the Galaxy Evolution Explorer, which has scanned much of the sky in ultraviolet light, is the ideal tool for measuring the rate of star birth in galaxies.

The results show that the little galaxies are low in mass, as suspected, and have low rates of star formation. In other words, the petite galaxies are not producing that many huge stars.

"Even in these little galaxies where the explosions are happening, the big guys are rare," said co-author Michael Rich of UCLA, who is a member of the mission team.

In addition, the new study helps explain why massive stars in little galaxies undergo even more powerful explosions than stars of a similar heft in larger galaxies like our Milky Way. The reason is that low-mass galaxies tend to have fewer heavy atoms, such as carbon and oxygen, than their larger counterparts. These small galaxies are younger, and thus their stars have had less time to enrich the environment with heavy atoms.

Every Day is Earth Day at NASA

Earth Day, April 22, is the annual celebration of the environment and a time to assess the work still needed to protect the natural gifts of our planet. It affirms that environmental awareness is part of our consciousness and that the idea of protecting the environment has moved into the mainstream.

NASA's Earth Science Mission seeks to understand Earth's systems and their responses to natural and anthropogenic (human-made) changes. A fleet of satellites in NASA's Earth Observing System gives scientists the global, long-term measurements they need to connect the atmosphere (air), lithosphere (land), hydrosphere (water), cryosphere (snow/ice), and biosphere (life) as a single system.

NASA works with many other partners from government, industry, academia, and international space agencies on the 17 satellite missions that make up the EOS series. Each of these satellites gathers a unique set of measurements for studying Earth. These measurements are used to improve weather forecasts, understand natural disasters, manage agriculture and forests, and predict how climate will change.

Geomagnetic wind in evolution

A G1-class geomagnetic storm is in progress, flashed by a high-speed solar wind river which is buffeting Earth's magnetic field. Lofty latitude sky watchers should be attentive for auroras.

What is a geomagnetic wind?

The Earth's magnetosphere is created by our attractive field and protects us from most of the particles the sun emits. When a CME or high-speed stream arrives at Earth it buffets the magnetosphere. If the new solar magnetic field is directed southward it interacts strongly with the oppositely leaning magnetic field of the Earth. The Earth's magnetic field is then peeled open like an onion allowing energetic solar wind particles to stream down the field lines to hit the atmosphere over the poles. At the Earth's surface a magnetic storm is seen as a fast drop in the Earth's magnetic ground strength. This decrease lasts about 6 to 12 hours, after which the attractive field gradually recovers over a period of several days.

What's causing the poles to warm faster than the rest of Earth?

The poles are warming faster than other parts of the Earth – a fact that has been widely accepted for years. But what is causing the accelerated warming?

Research aimed at answering that question has been done before, but a recent study by Patrick Taylor, a scientist at NASA's Langley Research Center in Hampton, Va., suggests a new reason.

Taylor's research shows the Earth's poles are warming faster than the rest of the planet because of energy in the atmosphere that is carried to the poles through large weather systems.


Decades of NASA data show the Earth is warming. According to NASA's Goddard Institute for Space Studies in Manhattan, the Earth has warmed about 1.44 degrees Fahrenheit during the last 40 years. But the poles are warming even faster; the Arctic has warmed by more than 3.5 degrees Fahrenheit during the same time period.

"It was previously thought that amplified polar warming was caused by melting ice, lowering surface albedo," Taylor said.

Albedo is the amount of sun’s energy that is reflected off the Earth’s surface and back into space, rather than absorbed. The more reflective the surface – such as ice – the more energy is reflected and the cooler the temperature. When ice melts, less energy is reflected and temperature increases.

"Surface albedo at the poles, however, is lowest in the summer, which is when we see the weakest temperature response. More recent research suggests that other atmospheric processes are at work," Taylor said.

For this study, Taylor used Clouds and the Earth's Radiant Energy System (CERES) satellite data, and a climate model that assumes carbon emissions will be reduced slightly below "business as usual."

His results suggest that summertime changes in clouds reflect a lot of the sun's energy, offsetting the low surface albedo, and that it must be something else that determines the amount of warming.

"The total warming at the poles is due to changes in clouds, water vapor, surface albedo and atmospheric temperature," he said. "But there is greater warming in the winter than in the summer and that is caused by energy transport," he said.

Taylor's research shows that the seasonality of the polar warming is largely a result of energy in the atmosphere that is being transported to the poles through large weather systems.

The importance of energy transport in the warming of the poles suggests more study is needed on the interactions between large weather systems and more local changes, involving clouds, water vapor, surface albedo and atmospheric temperature, in order to better understand climate sensitivity.

"We hope to learn more about the processes involved in atmospheric processes in order to better understand what climate models are telling us," Taylor said.

Pretty in Pink

Inside the Plasma Spray-Physical Vapor Deposition, or PS-PVD, ceramic powder is introduced into the plasma flame, which vaporizes it and then condenses it to form the ceramic coating.

The PS-PVD rig at NASA's Glenn Research Center uses new technology to create super thin ceramic coatings, which are being developed to protect high efficiency engines. The coatings created in the PS-PVD rig are thinner and more complex than those previously available.

The PS-PVD rig uses a system of vacuum pumps and a blower to remove air from the chamber, reducing the pressure inside to fraction of normal atmospheric pressure. The plasma flame is extremely hot and reaches 10,000 degrees Celsius. Ceramic powder is introduced from the torch into the plasma flame. The plasma vaporizes the ceramic powder, which then condenses 5 feet away from the torch onto the component to form the ceramic coating.

Plasma--not a gas, liquid or solid--is the fourth state of matter and often behaves like a gas, except that it conducts electricity and is affected by magnetic fields. On an astronomical scale, plasma is common. The sun is composed of plasma, fire is plasma, fluorescent and neon lights contain plasma. NASA’s PS-PVD rig is one of only two such facilities in the country and one of four in the world.