Distant Star's Sound Waves Reveal Cycle Similar to the Sun's

In a bid to unlock longstanding mysteries of the Sun, including the impacts on Earth of its 11-year cycle, an international team of scientists has successfully probed a distant star. By monitoring the star's sound waves, the team has observed a magnetic cycle analogous to the Sun's solar cycle.

The study, conducted by scientists at the National Center for Atmospheric Research (NCAR) and colleagues in France and Spain, is being published in Science.

The scientists studied a star known as HD49933, which is located 100 light years from Earth in the constellation Monoceros, the Unicorn, just east of Orion. The team examined the star's acoustic fluctuations, using a technique called "stellar seismology." They detected the signature of "starspots," areas of intense magnetic activity on the surface that are similar to sunspots. While scientists have previously observed these magnetic cycles in other stars, this was the first time they have discovered such a cycle using stellar seismology.

"Essentially, the star is ringing like a bell," says NCAR scientist Travis Metcalfe, a co-author of the new study. "As it moves through its starspot cycle, the tone and volume of the ringing changes in a very specific pattern, moving to higher tones with lower volume at the peak of its magnetic cycle."

"We've discovered a magnetic activity cycle in this star, similar to what we see with the Sun," says co-author and NCAR scientist Savita Mathur. "This technique of listening to the stars will allow us to examine potentially hundreds of stars."

The team hopes to assess the potential for other stars in our galaxy to host planets, including some perhaps capable of sustaining life.

"Understanding the activity of stars harboring planets is necessary because magnetic conditions on the star's surface could influence the habitable zone, where life could develop," says CEA-Saclay scientist Rafael Garcia, the study's lead author.

Studying many stars with stellar seismology could help scientists better understand how magnetic activity cycles can differ from star to star, as well as the processes behind such cycles. The work could especially shed light on the magnetic processes that go on within the Sun, furthering our understanding of its influence on Earth's climate. It may also lead to better predictions of the solar cycle and resulting geomagnetic storms that can cause major disruption to power grids and communication networks.

In addition to NCAR, the team's scientists are from France's Center for Nuclear Studies of Saclay (CEA-Saclay), Paris/Meudon Observatory (OPM), the University of Toulouse, and Spain's Institute of Astrophysics of the Canaries (IAC). The research was funded by the National Science Foundation, which is NCAR's sponsor, the CEA, the French Stellar Physics National Research Plan, and the Spanish National Research Plan.

Classifying stars

The scientists examined 187 days of data captured by the international Convection Rotation and Planetary Transits (CoRoT) space mission.

Launched on December 27, 2006, CoRoT was developed and is operated by the French National Center for Space Studies (CNES) with contributions from Austria, Belgium, Brazil, Germany, Spain, and the European Space Agency. CoRoT is equipped with a 27-centimeter (11-inch) diameter telescope and a 4-CCD (charge-coupled device) camera sensitive to tiny variations in the light intensity from stars.

The study authors found that HD49933 is much bigger and hotter than the Sun, and its magnetic cycle is much shorter. Whereas past surveys of stars have found cycles similar to the 11-year cycle of the Sun, this star has a cycle of less than a year.

This short cycle is important to scientists because it may enable them to observe an entire cycle more quickly, thereby gleaning more information about magnetic patterns than if they could only observe part of a longer cycle.

The scientists plan to expand their observations by using other stars observed by CoRoT as well as data from NASA's Kepler mission, launched in March 2009. Kepler is seeking Earth-sized planets to survey. The mission will provide continuous data over three to five years from hundreds of stars that could be hosting planets.

"If it turns out that a short magnetic cycle is common in stars, then we will potentially observe a large number of full cycles during Kepler's mission," says Metcalfe. "The more stars and complete magnetic cycles we have to observe, the more we can place the Sun into context and explore the impacts of magnetic activity on possible planets hosted by these stars."

The team has spent the past six months exploring the structure and dynamics of HD49933 and classifying its size. They will next verify their observations using ground-based telescopes to confirm the magnetic activity of the star. When the star reemerges from behind the Sun in September, they hope to measure the full length of the cycle. The CoRoT mission was designed to collect up to 150 days of continuous data at a time, which was not enough to determine the exact length of the star's cycle.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by National Center for Atmospheric Research/University Corporation for Atmospheric Research.

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Journal Reference:

1. Rafael A. García, Savita Mathur, David Salabert, Jérôme Ballot, Clara Régulo, Travis S. Metcalfe, and Annie Baglin.CoRoT Reveals a Magnetic Activity Cycle in a Sun-Like Star. Science, 2010; 329 (5995): 1032 DOI:10.1126/science.1191064

Earth and Moon Formed Later Than Previously Thought?

Earth and Moon Formed Later Than Previously Thought, New Research Suggests

Astronomers have theorized that the planet Earth and the Moon were created as the result of a giant collision between two planets the size of Mars and Venus. Until now, the collision was thought to have happened when the solar system was 30 million years old, or approximately 4,537 million years ago. But new research shows that Earth and the Moon must have formed much later -- perhaps up to 150 million years after the formation of the solar system.

The research results have been published in the scientific journal Earth and Planetary Science Letters.

"We have determined the ages of the Earth and the Moon using tungsten isotopes, which can reveal whether the iron cores and their stone surfaces have been mixed together during the collision," explains Tais W. Dahl, who did the research as his thesis project in geophysics at the Niels Bohr Institute at the University of Copenhagen in collaboration with professor David J. Stevenson from the California Institute of Technology (Caltech).

Turbulent collisions

The planets in the solar system are thought to have been created by collisions between small dwarf planets orbiting the newborn Sun. In the collisions, the small planets melted together and formed larger and larger planets. Earth and the Moon are believed to be the result of a gigantic collision between two planets the size of Mars and Venus. The two planets collided at a time when both had a core of metal (iron) and a surrounding mantle of silicates (rock). But when did it happen and how did it happen? The collision took place in less than 24 hours and the temperature of the Earth was so high (7000º C), that both rock and metal must have melted in the turbulent collision. But were the stone mass and iron mass also mixed together?

Until recently it was believed that the rock and iron mixed completely during the planet formation and so the conclusion was that the Moon was formed when the solar system was 30 million years old or approximately 4,537 million years ago. But new research shows something completely different.

Dating with radioactive elements

The age of Earth and the Moon can be dated by examining the presence of certain elements in Earth's mantle. Hafnium-182 is a radioactive substance, which decays and is converted into the isotope tungsten-182. The two elements have markedly different chemical properties and while the tungsten isotopes prefer to bond with metal, hafnium prefers to bond to silicates, i.e. rock.

It takes 50-60 million years for all hafnium to decay and be converted into tungsten, and during the Moon forming collision nearly all the metal sank into Earth's core. But did all the tungsten go into the core?

"We have studied to what degree metal and rock mix together during the planet forming collisions. Using dynamic model calculations of the turbulent mixing of the liquid rock and iron masses we have found that tungsten isotopes from the Earth's early formation remain in the rocky mantle," explains Dahl.

The new studies imply that the moon forming collision occurred after all of the hafnium had decayed completely into tungsten.

"Our results show that metal core and rock are unable to emulsify in these collisions between planets that are greater than 10 kilometres in diameter and therefore that most of the Earth's iron core (80-99 %) did not remove tungsten from the rocky material in the mantle during formation," explains Dahl.

The result of the research means that Earth and the Moon must have been formed much later than previously thought -- that is to say not 30 million years after the formation of the solar system 4,567 million years ago but perhaps up to 150 million years after the formation of the solar system.

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Journal Reference:

1. Tais W. Dahl, David J. Stevenson. Turbulent mixing of metal and silicate during planet accretion -- And interpretation of the Hf-W chronometer. Earth and Planetary Science Letters, 2010; 295 (1-2): 177 DOI: 10.1016/j.epsl.2010.03.038

Black Hole Found to Be Much Closer to Earth Than Previously Thought

An international team of astronomers has accurately measured the distance from Earth to a black hole for the first time.

(Credit: Image courtesy of SRON Netherlands Institute for Space Research

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An international team of astronomers has accurately measured the distance from Earth to a black hole for the first time. Without needing to rely on mathematical models the astronomers came up with a distance of 7800 light years, much closer than had been assumed until now. The researchers achieved this breakthrough by measuring the radio emissions from the black hole and its associated dying star.

Due to the much lower error margin (<6%),>

Story Source:
Adapted from materials provided by SRON Netherlands Institute for Space Research, via AlphaGalileo.