- Wednesday’s Near-Earth Asteroid Caught on Film
- Supernova Wind Solves Galaxy Formation Mystery
- First Direct Measurement of an Exoplanet’s Light Spectrum
Posted: 13 Jan 2010 05:27 PM PST
The rock, between 30 and 50 feet across, was not in danger of striking the planet and probably would have burned up in the atmosphere before hitting Earth's surface, if it had headed our way. The asteroid, dubbed 2010 AL30 was first spotted and announced Monday. It is the closest encounter Earth will have with any known object until 2024.
In 2029 an asteroid known as Apophis will come three times closer than Wednesday's asteroid did. Though the chances it will hit Earth are just one in 250,000, it is the subject of a lot of discussion, and Russia has announced it is making plans to deflect it.
Images: E. Guido and G. Sostero
Posted: 13 Jan 2010 01:52 PM PST
After years of struggling to understand how to properly assemble a galaxy, astronomers have discovered that the answer is blowin' in the wind. The supernova wind, that is.
New computer simulations show that winds generated by supernovas, which are the explosions of massive stars, can push stars out from the center of a dwarf galaxy. This simulation of supernova winds redistributes both ordinary matter and invisible dark matter in a way that almost perfectly matches observations of the way matter is distributed in actual dwarf galaxies. Fabio Governato of the University of Washington in Seattle and his colleagues describe their simulations in the Jan. 14 Nature.
Previous attempts to model galaxy formation based on the highly successful theory of cold dark matter — which states that invisible material must account for 85 percent of the mass of the universe — have done "an awesome job" of explaining such global properties as where, when and how many galaxies should form, notes Governato. But the models have failed to reproduce some of the key features of individual galaxies.
In particular, those simulations have produced galaxies whose centers are stuffed with too much dark matter and that are surrounded by a spherical distribution of stars that actual dwarf galaxies don't possess. Dwarf galaxies, which are low-mass bodies with relatively uniform distributions of stars, are the most common type of galaxy in the neighborhood of the Milky Way.
Most of these earlier models included either a simplistic description of star formation or neglected star formation altogether. "Our simulations achieve the necessary resolution to follow the formation of individual star forming regions — dense clouds of gas containing the equivalent of 100,000 suns," says Governato. Star formation is concentrated in the center of a galaxy, and because massive stars live for only a short time, they go supernova in the same region where they were born. As a result, supernova winds are also concentrated in galaxy centers.
Governato's team showed that the supernova winds are intense enough to push both stars and star-forming clouds out of a dwarf galaxy's core. Dark matter responds to gravity but is impervious to the winds. As the stars exit the core, the dark matter there feels a smaller gravitational tug and expands outward.
In one fell swoop, the model's successful simulation of supernova winds not only reduces the density of the dark matter at the core but also does away with the spherical distribution of stars around the core, matching the properties of actual dwarf galaxies, Governato says.
Other studies have shown that supernova winds influenced the assembly of faraway dwarf galaxies that hark from the early universe, which had a chemical composition much simpler than today's, notes Till Sawala of the Max Planck Institute for Astrophysics in Garching, Germany. But the new simulations are the first to successfully apply supernova winds to the formation of nearby dwarfs, Sawala adds.
Successful simulations of supernova winds can help in understanding star formation because supernovas explode close to where massive stars are born. At the same time, Simon White, director of the institute, notes that it's unclear exactly how the particular star-forming recipe used by Governato and his colleagues differs from those of other teams and why it's achieved such a good match with observations.
In another study, which is in press for the Monthly Notices of the Royal Astronomical Society, Sawala, White and their colleagues examine the effect of supernova winds in dwarf galaxies that are much smaller than those modeled by Governato and his colleagues. The researchers show that supernova winds in those "ultra-dwarf" galaxies hamper star formation so much that the tiny galaxies are barely visible. The finding could explain another long-standing discrepancy: Dark matter theory predicts a much higher abundance of tiny satellite galaxies around the Milky Way than has been observed. Perhaps the galaxies are really there but have too few stars to be detected.
Images: Governato et al./Nature 2010
Posted: 13 Jan 2010 10:27 AM PST
As astronomers begin detecting planets that are more and more like Earth, their task will be to determine if the planets are capable of supporting life. Now, the first direct observation of the light spectrum emitted by an exoplanet shows how they might do this.
Using the Very Large Telescope in the Chilean desert, astronomers were able to see the infrared spectrum of the exoplanet HR 8799c, 129 light-years away from Earth. Though this planet is a gaseous planet larger than Jupiter and not habitable, scientists could use the same technique to find the telltale atmospheric signals of gases like water vapor and nitrogen on Earth-like planets by measuring variations in the color of the planet's light.
"The spectrum of a planet is like a fingerprint. It provides key information about the chemical elements in the planet's atmosphere," astronomer Markus Janson of the University of Toronto, who led the work, said in a press release. "With this information, we can better understand how the planet formed and, in the future, we might even be able to find telltale signs of the presence of life."
At the same time, the difficulty of observing a planet much larger, brighter and much farther away from its star than any Earth-like planet shows just how far we have to go before we'll be able to detect if there are smaller, life-ready planets closer to their stars.
"It's just that this is hundreds of times easier because the planet is at a temperature of 1,000 degrees [Celsius, about 1,800 degrees Fahrenheit], so it's radiating like crazy in the infrared," said Greg Laughlin, an exoplanet astronomer at University of California, Santa Cruz, who was not involved with the research. "It's 38 times farther from its parent star than the Earth is from the sun."
The infrared light emitted by the planet is particularly strong at a wavelength of about four microns. That's a part of the spectrum where its star is not as bright, providing a sweet spot for planetary observations.
Even though this situation is especially good for using the light-detection method, the new study can be seen as a proof-of-concept for the technique of screening out starlight to see a planet's comparatively meager radiations.
"Here they are able to use adaptive optics get rid of the starlight and get the planetary light directly," Laughlin said, calling it an "encouraging milestone."
The planet itself is an interesting object, unlike anything in our solar system. It is glowing from the heat of its creation, not just by reflection of its star. At 10 times the mass of Jupiter, it nearly reached the threshold to become a brown dwarf star. Instead, it's a smoldering planet, perfectly suited for exoplanetary observation.
The work, which will be published in Astrophysical Journal, stretches our current telescopes and data processing to the limit.
"The Very Large Telescope is one of the premier telescopes in the world, absolutely awesome equipment, and it is able to barely nose in and get true spectra of exoplanets in this very fortunate situation," Laughlin said.
Other techniques have been used to peer into the atmospheres of some other exoplanets. In those cases, astronomers look at the light coming from a star both during and after a planet crosses its face. By taking the difference between the two, they can determine some things about the composition of the planet's atmosphere by how the light changes when passing through it.
The exciting thing about exoplanetary research right now is that there is a profusion of techniques and ideas about how to get from our current observations to the detection and study of an Earth-like planet.
"Even though it is a gigantic leap, it is something that is a matter of technology," Laughlin affirmed. "The planets are there, the physics is there, the roadmap is there. We just need to improve our technology."
Images: ESO/M. Janson
Citation: "Spatially resolved spectroscopy of the exoplanet HR 8799 c", by M. Janson et al. in Astrophysical Journal.
|You are subscribed to email updates from Johnus Morphopalus's Facebook notes |
To stop receiving these emails, you may unsubscribe now.
|Email delivery powered by Google|
|Google Inc., 20 West Kinzie, Chicago IL USA 60610|