Researchers find a planet they can’t see

A new planet was detected via its gravitational influence on a hot Jupiter-class planet.

NASA

The Kepler mission has only been taking data for two years. In that time, its rate of discovery has been staggering: over 2,300 planet candidates, with another 61 confirmed planets. Those numbers are even more impressive if you consider that Kepler can only detect planets around a small fraction of the stars that it's observing.

Kepler works by watching for the shadow cast when a planet passes between its host star and the Earth. That means the plane of a planet's orbit has to be aligned so that it passes between us and the star. If the orbital plane is tilted, we won't be able to detect it with this method.

But now, researchers have demonstrated that it's possible to spot a few objects that Kepler can't otherwise see directly. While searching for hints of moons orbiting exoplanets, they found that one of the planets spotted by Kepler was being tugged around by another planet—one that orbited in a slightly different plane, and was otherwise undetectable using this method.

Researchers find a planet they can’t see

A new planet was detected via its gravitational influence on a hot Jupiter-class planet.

NASA

Black holes throttle star formation

An active galactic nucleus, powered by a black hole.

NASA

What sets the limits on a galaxy's size? It might be the supermassive black hole sitting in its core. Many observations indicate the mass of the central black hole in a galaxy is correlated with the mass of the central region of the galaxy itself.

A widely accepted model states that galaxies and the supermassive black hole share an evolutionary relationship. During the early days, when a galaxy is young, the raw ingredients for both star formation and black hole growth are common. However, as the black hole becomes active through consuming gas, the matter it's drawing in blasts the star-forming medium away through powerful winds, slowing the birth rates of new stars.

While this model is clear, direct evidence for it has been lacking: the black holes drive processes that shine very brightly, dominating the light coming from star formation in most wavelengths. Nevertheless, researchers used the Chandra Deep Field North (CDF-N) X-ray survey and the submillimeter instrument on the Herschel Space Observatory to measure both the star formation rate and black hole activity. As M. J. Page et al. report in Nature, they found rates of star birth in galaxies slowed down once the central black hole became active. This result provides strong support for the shared evolution of galaxies and the black holes at their hearts.

Black holes throttle star formation

An active galactic nucleus, powered by a black hole.

NASA

Researchers spot planet-eating white dwarfs

Planets as small as Earth are hard to spot orbiting other stars; obtaining good data about their chemical composition is well beyond the abilities of our current instruments. However, a new study of four white dwarfs provides hints about the fate of planets like our own. It's not an especially happy one, as the astronomers found that the chemical composition of debris on the white dwarfs closely matches that of Earth.

These observations, which will be published in the Monthly Notices of the Royal Astronomical Society, focused on four "polluted" white dwarfs, which have traces of elements not usually seen in this type of star. B. T. Gänsicke et al. studied their ultraviolet spectrum using the Hubble Space Telescope, and determined they contained excessive amounts of silicon, aluminum, iron, and other elements, with abundances similar to those found on Earth. These results indicate that rocky debris has crashed onto the white dwarfs—debris that may possibly be from the destruction of a planet similar in composition to Earth.

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Researchers spot planet-eating white dwarfs

Artist's depiction of chunks of a planet falling onto a white dwarf. Astronomers have observed the chemical signature of these rocky remains.

Photograph by © Mark A. Garlick / space-art.co.uk / University of Warwick

White dwarfs are the cores of lower-mass stars that have run out of nuclear fuel and shed their outer layers. Our Sun falls into this mass category and will eventually experience that fate, so white dwarf systems provide potentially interesting glimpses into the evolution of the Solar System. White dwarfs are very compact: while their masses are still comparable to the Sun's, their sizes are closer to Earth's.

A burp of light from a black hole reveals that it ate a star

The easiest way to spot a supermassive black hole (SMBH) is when it expels a huge jet of matter in one of the most energetic displays in the Universe. While astronomers have spotted these huge black holes at the centers of most galaxies, not all are active—meaning the jet isn't there, and the SMBH is hiding. However, even inactive black holes may give themselves away if we can spot them eating stars: the disruption of a star by gravitational forces can produce a burst of light.

As reported in Nature, the Pan-STARRS1 (PS1) galaxy survey spotted a burst of intense ultraviolet and visible light from the center of a galaxy with no known SMBH. S. Gezari et al. performed a spectral analysis on the flare, and determined it to be consistent with the destruction of a red giant star with a helium-rich core. The likely culprit for the star's disruption is a black hole with a mass between 2.7 and 2.9 million times that of our Sun.

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Black hole eats star, burps light

Ultraviolet (top row) and visible light (bottom) images of a flare in a galaxy, created when a black hole possibly ate a star.

Photograph by NASA, S. Gezari (The Johns Hopkins University, Baltimore, Md.), and A. Rest (Space Telescope Science Institute, Baltimore, Md.)

Gravity will tear us apart

Saturn may have snagged Pluto’s cousin, turned it into a moon

Saturn's moon Phoebe might be a planetesimal—a remnant of the rocky building blocks of the planets in our Solar System. A new study by Julie C. Castillo-Rogez et al. from Cassini spacecraft data indicates that Phoebe dates back to the very earliest days of the Solar System. Based on surface features and evidence that the moon is significantly more dense than the larger Saturnian satellites, the astronomers argue that Phoebe likely formed much farther from the Sun then fell inward, where it was snagged by Saturn's gravity.

Using detailed observations from Cassini and Earth-based telescopes, in combination with detailed computer simulations, Castillo-Rogez et al. determined that Phoebe began as a spherical body. Based upon the density and comparison with bodies of similar size, Phoebe may have a rocky core surrounded by a porous icy shell. The layered structure grants Phoebe kinship with the planets and the planet-like asteroid Vesta, as well as the larger Kuiper Belt objects such as Pluto. Phoebe's physical properties, as well as its odd orbital characteristics, led the authors to conclude that the moon formed in the Kuiper Belt region, making it a cousin to Pluto.

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Why do stars seem to "know" what type of galaxy they will inhabit?

When they form, do stars "know" what kind of galaxy they will inhabit? Obviously that question is too anthropomorphic—stars have no minds. Nevertheless, fundamental differences appear to exist in the populations of stars in spiral galaxies (like the Milky Way) and those in elliptical galaxies. Not only that, different elliptical galaxies also differ from each other, as determined by the motion of stars and the ratio of mass to light, which is a measure of the relative amounts of stars and dark matter.

Using a sample of 260 nearby elliptical galaxies from the ATLAS^3D project, astronomers Michele Cappellari et al. constructed a two-dimensional map of stellar positions and motion. Through this study and an analysis of the particular types of stars (as determined by their spectra), the researchers were able to determine the number of stars in different mass ranges, something known as the initial mass function (IMF, not to be confused with the International Monetary Fund).

They determined that the IMF varies a lot from galaxy to galaxy, meaning that the formation of stars must depend on the detailed history of a galaxy's life—in contrast to earlier predictions.

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