Hypothesized Formation of the First Stars

Scientists are simulating how the very first stars in our universe were born. This diagram shows a still from one such simulation. The cube on the right is a blown up region at the center of the box on the left.

The stars we see today formed out of collapsing clouds of gas and dust. In the very early universe, however, the stars had fewer ingredients available. There wasn't any dust yet, or heavy elements, both of which help cool the gas in a cloud so that it can collapse. Instead, the very first stars formed from nothing but hydrogen and helium gas. Astronomers theorize that, in order to overcome their lack of cooling ingredients, these stars would have needed more mass to form. The first stars were thought to have been more massive than even the most massive stars observed today.

At the very center of each box shown here is the forming star - the star itself is too small to see at this scale. The red areas show hot gas with temperatures as high as 50,000 Kelvin (90,000 degrees Fahrenheit), heated by, and surrounding, the forming star. Blue shows much cooler gas, with the darkest blue showing the densest portions of cool gas, shaped like a disk surrounding the seedling star.

As the star pulls matter from the disk onto it, it grows more massive. Meanwhile, some gas -- shown in the red areas -- is so hot that it expands and escapes. Eventually, large amounts of the surrounding gas become too hot and escape. At this point, the star stops growing -- it has finished "baking."

Scientists at NASA's Jet Propulsion Laboratory, Pasadena, California, have used these simulations to show that the first stars, during their formation, had a greater impact on surrounding gas than previously thought. The higher gas temperatures would have caused the stars to stop growing sooner. As a result, the first stars were not likely hundreds of times the mass of the Sun, but only tens of times its mass.

None of these first stars still exist today. After a few million years they exploded in fiery supernovae, spewing heavier elements cooked in their interiors out into the surrounding gas.

For technical details and videos visit http://www-tap.scphys.kyoto-u.ac.jp/~hosokawa/firststarstop_e.html.

Photo credit: NASA/JPL-Caltech/Kyoto University

Earth and Moon by Voyager 1

This picture of a crescent-shaped Earth and Moon -- the first of its kind ever taken by a spacecraft -- was recorded September 18, 1977, by NASA's Voyager 1 when it was 7.25 million miles (11.66 million kilometers) from Earth. The Moon is at the top of the picture and beyond the Earth as viewed by Voyager. In the picture are eastern Asia, the western Pacific Ocean and part of the Arctic. Voyager 1 was directly above Mt. Everest (on the night side of the planet at 25 degrees North latitude) when the picture was taken. The photo was made from three images taken through color filters, then processed by the Jet Propulsion Laboratory's Image Processing Lab. Because the Earth is many times brighter than the Moon, the Moon was artificially brightened by a factor of three relative to the Earth by computer enhancement so that both bodies would show clearly in the print. Voyager 2 was launched August 20, 1977, followed by Voyager 1 on September 5, 1977, en route to encounters at Jupiter in 1979 and Saturn in 1980 and 1981.

Photo credit: NASA/JPL

Backward Black Hole Shoots Powerful Jets

This artist's concept shows a galaxy with a supermassive black hole at its core. The black hole is shooting out jets of radio waves.

New research led by theoretical astrophysicist David Garofalo of NASA's Jet Propulsion Laboratory in Pasadena, California, suggests supermassive black holes that spin backwards might produce more ferocious jets of gas. The results have broad implications for how galaxies change over time.

Black holes are immense distortions of space and time with gravity that is so great, even light itself cannot escape. Astronomers have known for more than a decade that all galaxies, including our own Milky Way, are anchored by tremendous, so-called supermassive black holes, containing billions of suns' worth of mass. The black holes are surrounded and nourished by disks of gas and dust, called accretion disks. Powerful jets stream out from below and above the disks like lasers, and fierce winds blow off from the disks themselves. The black holes can spin either in the same direction as the disks, called prograde black holes, or against the flow -- the retrograde black holes.

Scientists say that the backward black holes shoot more powerful jets because there's more space between the black hole and the inner edge of the orbiting disk. This gap provides more room for the build-up of magnetic fields, which fuel the jets, an idea known as the Reynold's conjecture after the theoretical astrophysicist Chris Reynolds of the University of Maryland, College Park.

Image credit: NASA/JPL-Caltech

Note: For more information, see Backwards Black Holes Might Make Bigger Jets.

Jupiter Loses a Stripe

In a development that has transformed the appearance of the solar system's largest planet, one of Jupiter's two main cloud belts has completely disappeared.

"This is a big event," says planetary scientist Glenn Orton of NASA's Jet Propulsion Lab. "We're monitoring the situation closely and do not yet fully understand what's going on."

Known as the South Equatorial Belt (SEB), the brown cloudy band is twice as wide as Earth and more than twenty times as long. The loss of such an enormous "stripe" can be seen with ease halfway across the solar system.

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Orton thinks the belt is not actually gone, but may be just hiding underneath some higher clouds.

"It's possible," he hypothesizes, "that some 'ammonia cirrus' has formed on top of the SEB, hiding the SEB from view." On Earth, white wispy cirrus clouds are made of ice crystals. On Jupiter, the same sort of clouds can form, but the crystals are made of ammonia (NH3) instead of water (H20).

What would trigger such a broad outbreak of "ammonia cirrus"? Orton suspects that changes in global wind patterns have brought ammonia-rich material into the clear, cold zone above the SEB, setting the stage for formation of the high-altitude, icy clouds.

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This isn't the first time the SEB has faded out.

"The SEB fades at irregular intervals, most recently in 1973-75, 1989-90, 1993, 2007, 2010," says John Rogers, director of the British Astronomical Association's Jupiter Section. "The 2007 fading was terminated rather early, but in the other years the SEB was almost absent, as at present."

The return of the SEB can be dramatic.

"We can look forward to a spectacular outburst of storms and vortices when the 'SEB Revival' begins," says Rogers. "It always begins at a single point, and a disturbance spreads out rapidly around the planet from there, often becoming spectacular even for amateurs eyeballing the planet through medium-sized telescopes. However we can't predict when or where it will start. On historical precedent it could be any time in the next 2 years. We hope it will be in the next few months so that everyone can get a good view.

Photo credit: Anthony Wesley

NASA: New Radar Maps of the Moon's South Pole

Above: This movie is a simulation of the amount of solar illumination in the south polar region of moon over a solar day generated using high resolution topography. (Credit: NASA)

NASA has obtained new high-resolution radar maps of the Moon's south pole--a region the space agency is considering as a landing site when astronauts return to the Moon in the years ahead.

"We now know the south pole has peaks as high as Mt. McKinley and crater floors four times deeper than the Grand Canyon," says Doug Cooke, deputy associate administrator for the Exploration Systems Mission Directorate at NASA Headquarters. "These data will be an invaluable tool for advance planning of lunar missions."

Scientists at NASA's Jet Propulsion Laboratory collected the data using the Goldstone Solar System Radar located in California's Mojave Desert. Three times in 2006, JPL scientists targeted the moon's south polar region using Goldstone's 70-meter radar dish. The antenna, three-quarters the size of a football field, sent a 500-kilowatt strong, 90-minute long radar stream 231,800 miles to the Moon. The radar illuminated the rough-hewn lunar surface over an area measuring about 400 by 250 miles. Signals were reflected back to two of Goldstone's 34-meter antennas on Earth. Scientists have been analyzing the echoes ever since, and the data were released by NASA for the first time this week.

NASA is eying the Moon's south polar region as a possible site for future outposts. The location has many advantages; for one thing, there is evidence of water frozen in deep dark south polar craters. Water can be split into oxygen to breathe and hydrogen to burn as rocket fuel--or astronauts could simply drink it. Planners are also looking for "peaks of eternal light." Tall polar mountains where the sun never sets might be a good place for a solar power station.

These are the highest-resolution maps to date. The best images, previously, were generated by the Clementine spacecraft, which could resolve lunar terrain features near the south pole at 1 kilometer per pixel. The JPL radar maps are 50 times more detailed.

As wonderful as they are, however, these images will pale in comparison to next-generation photos from NASA's Lunar Reconnaissance Orbiter. The spacecraft is scheduled to launch in late 2008 and its camera will beam back photos of the moon with details as small as 1 meter.