Baby Jupiters Must Gain Weight Fast

The planet Jupiter gained weight in a hurry during its infancy. It had to, since the material from which it formed probably disappeared in just a few million years, according to a new study of planet formation around young stars.

  Smithsonian astronomers examined the 5 million-year-old star cluster NGC 2362 with NASA's Spitzer Space Telescope, which can detect the signatures of actively forming planets in infrared light. They found that all stars with the mass of the Sun or greater have lost their protoplanetary (planet-forming) disks. Only a few stars less massive than the Sun retain their protoplanetary disks. These disks provide the raw material for forming gas giants like Jupiter. Therefore, gas giants have to form in less than 5 million years or they probably won't form at all.

"Even though astronomers have detected hundreds of Jupiter-mass planets around other stars, our results suggest that such planets must form extremely fast. Whatever process is responsible for forming Jupiters has to be incredibly efficient," said lead researcher Thayne Currie of the Harvard-Smithsonian Center for Astrophysics. Currie presented the team's findings at a meeting of the American Astronomical Society in Long Beach, Calif.

Even though nearly all gas giant-forming disks in NGC 2362 have disappeared, several stars in the cluster have "debris disks," which indicates that smaller rocky or icy bodies such as Earth, Mars, or Pluto may still be forming.

"The Earth got going sooner, but Jupiter finished first, thanks to a big growth spurt," explained co-author Scott Kenyon.

Kenyon added that while Earth took about 20 to 30 million years to reach its final mass, Jupiter was fully grown in only 2 to 3 million years.

Previous studies indicated that protoplanetary disks disappear within 10 million years. The new findings put even tighter constraints on the time available to create gas giant planets around stars of various masses.

Possible Abnormality In Fundamental Building Block Of Einstein's Theory Of Relativity

Physicists at Indiana University have developed a promising new way to identify a possible abnormality in a fundamental building block of Einstein's theory of relativity known as "Lorentz invariance." If confirmed, the abnormality would disprove the basic tenet that the laws of physics remain the same for any two objects traveling at a constant speed or rotated relative to one another.

     IU distinguished physics professor Alan Kostelecky and graduate student Jay Tasson take on the long-held notion of the exact symmetry promulgated in Einstein's 1905 theory and show in a paper to be published in Physical Review Letters that there may be unexpected violations of Lorentz invariance that can be detected in specialized experiments.

"It is surprising and delightful that comparatively large relativity violations could still be awaiting discovery despite a century of precision testing," said Kostelecky. "Discovering them would be like finding a camel in a haystack instead of a needle."

If the findings help reveal the first evidence of Lorentz violations, it would prove relativity is not exact. Space-time would not look the same in all directions and there would be measurable relativity violations, however minuscule.

The violations can be understood as preferred directions in empty space-time caused by a mesh-like vacuum of background fields. These would be separate from the entirety of known particles and forces, which are explained by a theory called the Standard Model that includes Einstein's theory of relativity.

The background fields are predicted by a generalization of this theory called the Standard Model Extension, developed by Kostelecky to describe all hypothetical relativity violations.

Hard to detect, each background field offers its own universal standard for determining whether or not an object is moving, or in which direction it is going. If a field interacts with certain particles, then the behavior of those particles changes and can reveal the relativity violations caused by the field. Gravity distorts the fields, and this produces particle behaviors that can reveal otherwise hidden violations.

The new violations change the gravitational properties of objects depending on their motion and composition. Objects on the Earth are always moving differently in different seasons because the Earth revolves around the Sun, so apples could fall faster in some seasons than others. Also, different objects like apples and oranges may fall differently.

"No dedicated experiment has yet sought a seasonal variation of the rate of an object's fall in the Earth's gravity," said Kostelecky. "Since Newton's time over 300 years ago, apples have been assumed to fall at the same rate in the summer and the winter."

Spotting these minute variances is another matter as the differences in rate of fall would be tiny because gravity is a weak force. The new paper catalogues possible experiments that could detect the effects. Among them are ones studying gravitational properties of matter on the Earth and in space.

The Standard Model Extension predicts that a particle and an antiparticle would interact differently with the background fields, which means matter and antimatter would feel gravity differently. So, an apple and an anti-apple could fall at different rates, too.

"The gravitational properties of antimatter remain largely unexplored," said Kostelecky. "If an apple and an anti-apple were dropped simultaneously from the leaning Tower of Pisa, nobody knows whether they would hit the ground at the same or different times."