“Today’s telescopes are detecting planets around distant stars, and NASA’s Kepler Telescope, launched in 2009, is a champion among them,” Nesvorny says. It finds planets by continuously monitoring the brightness of more than 150,000 stars, searching for brief periods of time, known as transits, when a star appears fainter because it is obscured by a planet passing in the foreground. But there’s a twist.

Image right: Using Kepler Telescope transit data of planet “b”, scientists predicted that a second planet “c” about the mass of Saturn orbits the distant star KOI-872. This research, led by Southwest Research Institute and the Harvard-Smithsonian Center for Astrophysics, is providing evidence of an orderly arrangement of planets orbiting KOI-872, not unlike our own solar system. (Image courtesy Southwest Research Institute)

“For a planet following a strictly Keplerian orbit around its host star, the spacing, timing and other properties of the observed transit light curve should be unchanging in time,” said Kipping of the Harvard Smithsonian Center for Astrophysics. “Several effects, however, can produce deviations from the Keplerian case so that the spacing of the transits is not strictly periodic.”

A hidden planet, for example, can distort the sequence of transits if it gravitationally pulls on the transiting planet and delays some transits relative to others.

As part of the Hunt for the Exomoons with Kepler (HEK) project, the team analyzed recently released Kepler data and identified systems with transiting planets that show transit variations indicative of hidden companions, such as unseen moons or planets. The team identified the Sun-like star known as KOI-872 (KOI stands for Kepler Objects of Interest) as exceptional in that it shows transits with remarkable time variations over two hours.

“It quickly became apparent to us that a large hidden object must be pulling on the transiting planet,” says Nesvorny. “To put this in context, if a bullet train arrives in a station two hours late, there must be a very good reason for that. The trick was to find what it is.”

Using Le Verrier’s perturbation theory to speed up time-consuming computer calculations of many possible configurations of planetary orbits, the HEK team showed that the observed variations can be best explained by an unseen planet about the mass of Saturn that orbits the host star every 57 days. According to the analysis, the planetary orbits are very nearly coplanar and circular, reminiscent of the orderly arrangement of orbits in our solar system.

The team’s claim will be put to the test by Kepler’s new observations, which will track dozens of new transits of KOI-872, comparing their timing to published predictions.

“Whilst the principal goal of the HEK project will continue to focus on searching for moons, this first planetary system discovered by HEK demonstrates the unexpected discoveries possible with transit analysis,” Kipping says.–Source: Southwest Research Institute

Article link: “The Detection and Characterization of a Nontransiting Planet by Transit Timing Variations” by Nesvorny, Kipping, Lars Buchhave (Niels Bohr Institute), Gaspar Bakos (Princeton University), Joel Hartman (Princeton University) and Allan Schmitt (Citizen Science), was published May 10 in the journal Science online, at the Science Express website.

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Two very different models explain the possible origin of Type Ia supernovae, and different studies support each model. New evidence shows that both models are correct – some of these supernovae are created one way and some the other.

Image above: The Tycho supernova remnant is the result of a Type Ia supernova explosion. The explosion was observed by Danish astronomer Tycho Brahe in 1572. More than 400 years later, the ejecta from that explosion has expanded to fill a bubble 55 light-years across. In this image, low-energy X-rays (red) show expanding debris from the supernova explosion and high energy X-rays (blue) show the blast wave – a shell of extremely energetic electrons. (Credit: X-ray: NASA/CXC/Rutgers/K.Eriksen et al.; Optical: DSS)

“Previous studies have produced conflicting results. The conflict disappears if both types of explosion are happening,” explained Smithsonian astronomer and Clay Fellow Ryan Foley (Harvard-Smithsonian Center for Astrophysics).

Type Ia supernovae are known to originate from white dwarfs – the dense cores of dead stars. White dwarfs are also called degenerate stars because they’re supported by quantum degeneracy pressure.

In the single-degenerate model for a supernova, a white dwarf gathers material from a companion star until it reaches a tipping point where a runaway nuclear reaction begins and the star explodes. In the double-degenerate model, two white dwarfs merge and explode. Single-degenerate systems should have gas from the companion star around the supernova, while the double-degenerate systems will lack that gas.

“Just like mineral water can be with or without gas, so can supernovae,” said Robert Kirshner, Clowes Professor of Astronomy at Harvard University and a co-author on the study.

Foley and his colleagues studied 23 Type Ia supernovae to look for signatures of gas around the supernovae, which should be present only in single-degenerate systems. They found that the more powerful explosions tended to come from “gassy” systems, or systems with outflows of gas. However, only a fraction of supernovae show evidence for outflows. The remainder seem to come from double-degenerate systems.

“There are definitely two kinds of environments – with and without outflows of gas. Both are found around Type Ia supernovae,” Foley said.

This finding has important implications for measurements of dark energy and the expanding universe. If two different mechanisms are at work in Type Ia supernovae, then the two types must be considered separately when calculating cosmic distances and expansion rates.

“It’s like measuring the universe with a mix of yardsticks and meter sticks – you’ll get about the same answer, but not quite. To get an accurate answer, you need to separate the yardsticks from the meter sticks,” Foley explained.

This study raises an interesting question – if two different mechanisms create Type Ia supernovae, why are they homogeneous enough to serve as standard candles?

“How can supernovae coming from different systems look so similar? I don’t have the answer for that,” said Foley.

The paper describing this research will appear in the Astrophysical Journal and is available online.

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“Black holes, like sharks, suffer from a popular misconception that they are perpetual killing machines,” said Ryan Chornock of the Harvard-Smithsonian Center for Astrophysics. “Actually, they’re quiet for most of their lives. Occasionally a star wanders too close, and that’s when a feeding frenzy begins.”

Image right: These images, taken with NASA’s Galaxy Evolution Explorer and the Pan-STARRS1 telescope in Hawaii, show a galaxy that brightened suddenly, caused by a flare from its nucleus. The top left image, taken in 2009, shows the galaxy before the flare, when it wasn’t visible in ultraviolet light. In the top right image, taken on June 23, 2010, the galaxy had become 350 times brighter in ultraviolet light. The bottom left image, shows the galaxy (the bright dot in the center) in 2009 before the flare’s appearance. The bottom right image, taken from June to August 2010, shows the flare from the galaxy nucleus.  (Credit: NASA, S. Gezari (JHU), A. Rest (STScI), and R. Chornock (Harvard-Smithsonian CfA)

Chornock and his colleagues, led by Suvi Gezari of Johns Hopkins University, reported their discovery of a feeding supermassive black hole in the May 3 issue of the journal Nature.

If a star passes too close to a black hole, tidal forces can rip it apart.

Its constituent gases then swirl in toward the black hole. Friction heats the gases and causes them to glow. By searching for newly glowing supermassive black holes, astronomers can spot them in the midst of a feast.

The team discovered just such a glow on May 31, 2010 using the Pan-STARRS1 telescope on Mount Haleakala in Hawaii. The flare brightened to a peak on July 12th before fading away over the course of a year.

Image left: This computer-simulated image shows gas from a tidally shredded star falling into a black hole. Some of the gas also is being ejected at high speeds into space. Credit: NASA, S. Gezari (JHU), and J. Guillochon (UC Santa Cruz)

“We observed the demise of a star and its digestion by the black hole in real time,” said Harvard co-author Edo Berger.

The glow came from a previously dormant supermassive black hole at the center of a galaxy 2.7 billion light-years away. The black hole contains as much mass as 3 million suns, making it about the same size as the Milky Way’s central black hole.

Follow-up observations with the MMT Observatory in Arizona showed that the black hole was consuming large amounts of helium. Therefore, the shredded star likely was the core of a red giant star. The lack of hydrogen showed that the star lost its outer atmosphere on a previous pass by the black hole.

“This star barely survived one encounter with the black hole, only to meet its unfortunate end in round two,” said Chornock.

The discovery demonstrates the sleuthing power of the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS), which was designed to locate all kinds of transient phenomena in the night sky.

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Researchers used Chandra to discover a new ultraluminous X-ray source, or ULX. These objects give off more X-rays than most binary systems, in which a companion star orbits the remains of a collapsed star. These collapsed stars form either a dense core called a neutron star or a black hole. The extra X-ray emission suggests ULXs contain black holes that might be much more massive than the ones found elsewhere in our galaxy.

Image right: On the left is an optical image of M83 from the Very Large Telescope in Chile. On the right is a composite image showing X-ray data from Chandra in pink and optical data from the Hubble Space Telescope in blue and yellow. The ULX is located near the bottom of the composite image. (Left image – Optical: ESO/VLT; Close-up – X-ray: NASA/CXC/Curtin University/R. Soria et al., Optical: NASA/STScI/Middlebury College/F. Winkler et al.)

The companion stars to ULXs, when identified, are usually young, massive stars, implying their black holes are also young. The latest research, however, provides direct evidence that ULXs can contain much older black holes and some sources may have been misidentified as young ones.

The intriguing new ULX is located in M83, a spiral galaxy about 15 million light years from Earth, discovered in 2010 with Chandra. Astronomers compared this data with Chandra images from 2000 and 2001, which showed the source had increased in X-ray brightness by at least 3,000 times and has since become the brightest X-ray source in M83.

“The flaring up of this ULX took us by surprise and was a sure sign we had discovered something new about the way black holes grow,” said Roberto Soria of Curtin University in Australia, who led the new study. The dramatic jump in X-ray brightness, according to the researchers, likely occurred because of a sudden increase in the amount of material falling into the black hole.

In 2011, Soria and his colleagues used optical images from the Gemini Observatory and NASA’s Hubble Space Telescope to discover a bright blue source at the position of the X-ray source. The object had not been previously observed in a Magellan Telescope image taken in April 2009 or a Hubble image obtained in August 2009. The lack of a blue source in the earlier images indicates the black hole’s companion star is fainter, redder and has a much lower mass than most of the companions that previously have been directly linked to ULXs. The bright, blue optical emission seen in 2011 must have been caused by a dramatic accumulation of more material from the companion star.

The companion to the black hole in M83 is likely a red giant star at least 500 million years old, with a mass less than four times the sun’s.

Another ULX containing a volatile, old black hole recently was discovered in the Andromeda galaxy by Amanpreet Kaur, from Clemson University, and colleagues and published in the February 2012 issue of Astronomy and Astrophysics. Matthew Middleton and colleagues from the University of Durham reported more information in the March 2012 issue of the Monthly Notices of the Royal Astronomical Society. They used data from Chandra, XMM-Newton and HST to show the ULX is highly variable and its companion is an old, red star.

A paper describing these results will appear in the May 10th issue of The Astrophysical Journal.

NASA’s Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program for NASA’s Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory controls Chandra’s science and flight operations from Cambridge, Mass.

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The top 10 IRAC images the team selected are (click to view):

• A “space tornado”
• The Orion Nebula
• The Helix Nebula
• The Trifid Nebula
• The “Mountains of Creation”
• A young star cluster
• Our Milky Way galaxy
• The Whirlpool galaxy
• The Sombrero galaxy
• The young, distant universe
• (Full Gallery)

Image right: This “tornado,” designated Herbig-Haro 49/50, is shaped by a cosmic jet packing a powerful punch as it plows through clouds of interstellar gas and dust. (Credit: NASA / JPL-Caltech / J. Bally, University of Colorado)

“IRAC continues to be an amazing camera, still producing important discoveries and spectacular new images of the infrared universe,” said principal investigator Giovanni Fazio of the Harvard-Smithsonian Center for Astrophysics.

The warm-mission images particularly highlight the continuing capabilities of Spitzer. Indeed, NASA’s Senior Review Panel has recommended extending the Spitzer warm mission through 2015. They specifically commended the Spitzer team for telescope improvements that have made it a powerful instrument for science, especially in exoplanet studies.

Left: In this image of the nearby Sombrero Galaxy, IRAC clearly sees a dramatic disk of warm dust (red) caused by star formation around the central bulge (blue). The Sombrero is located 28 million light-years away in the constellation Virgo.
(Credit: NASA / JPL-Caltech / R. Kennicutt, Univ. of Arizona)

IRAC is sensitive to infrared light—light beyond the red end of the visible spectrum. It can image nebulae of cold dust, peer inside obscured dust clouds where new stars are forming, and detect faint emissions from very distant galaxies.

During its 1,000-day undertaking, IRAC used its two shortest-wavelength infrared sensors. However, some of the images featured today include data collected during the cold mission, when all four of its infrared sensors could function.

Many additional images from Spitzer can be found online at http://www.spitzer.caltech.edu/

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Smithsonian astronomers have joined their colleagues from other observatories in a daring new venture: to photograph the giant black hole at the heart of our Milky Way galaxy. Their bold effort will require nothing less than an Earth-sized telescope, which has been named the Event Horizon Telescope or EHT. (The event horizon is a black hole’s boundary or outer edge – the point of no return.)

“For the first time, we intend to take a picture of a black hole, or more precisely its shadow,” says Jonathan Weintroub of the Smithsonian Astrophysical Observatory (SAO). SAO is a key part of the international collaboration working to create the EHT.

Image above: This simulation shows what the Milky Way’s central black hole may look like to the Event Horizon Telescope. Powerful gravitational forces bend light around the black hole, leaving a silhouette against a glowing background. Credit: A. Loeb & A. Broderick (CfA)

They’ve targeted the Milky Way’s central black hole because it covers the largest apparent area of the sky. Physically, it spans about 7 million miles (12 million km). That may sound large, but it’s located 26,000 light-years from Earth, or 150,000 trillion miles. It appears the size of a poppy seed in Los Angeles as seen from Boston. As a result, observers will need extremely high resolution to tease out any details.

Another challenge is that the galactic center is cloaked in gas and dust and crowded with stars. Almost no visible light from this region makes it to Earth. Radio waves can penetrate the gloom, so the Event Horizon Telescope will focus on the radio spectrum. These radio waves are naturally occurring, coming from both hot gas and free-flying electrons surrounding the black hole.

The black hole feeds on gas and dust swirling around it like water draining from a bathtub. As that material spirals inward, friction heats it and causes it to shine. The black hole is silhouetted against that glowing background.

The black hole’s gravity also bends light passing nearby – an effect known as gravitational lensing. As a result, theorists calculate that the Event Horizon Telescope will show a bright, circular outline with the black hole’s shadow at the center.

To get this iconic photo, a worldwide network of radio telescopes must link together in a technique called “interferometry.” In essence, interferometry provides the same resolution (although not the same light-gathering power) as a single telescope thousands of miles across. The Smithsonian’s Submillimeter Array, located atop Mauna Kea in Hawaii, will join this network.

“The Submillimeter Array will be a vitally important component of the Event Horizon Telescope,” Weintroub says. “Its location, collecting area and sensitivity all will contribute to the success of this effort.”

He emphasizes that the project will be a gradual process as more facilities link together. Initially, researchers will measure only the most basic information about the black hole – its size. As they gather more data, glowing “hot spots” may emerge from the black hole’s swirling accretion disk. Eventually, the full picture of the black hole’s environment will be unveiled.

The Event Horizon Telescope ultimately may link observatories in Hawaii, Arizona, California, Mexico, Chile, Europe, and Antarctica. Its best performance will come when the Atacama Large Millimeter/Submillimeter Array (ALMA), now under construction in Chile, joins the network.

“We are poised to catch a wave as ALMA comes online,” Weintroub says. “Once its capabilities are added to this project, we expect to get some amazing results. By the end of the decade, we should have the first-ever close-up photo of a black hole.”–By Christine Pulliam

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Using new calculations and previous observations of our own Milky Way and other galaxies, “we found black holes grow enormously as a result of sucking in captured binary star partners,” says University of Utah physics and astronomy professor Ben Bromley, lead author of the study, published April 2 in “Astrophysical Journal Letters.”

Bromley conducted the study with astronomers Scott Kenyon, Margaret Geller and Warren Brown, all of the Harvard-Smithsonian Center for Astrophysics.

“Black holes are very efficient eating machines,” says Kenyon. “They can double their mass in less than a billion years. That may seem long by human standards, but over the history of the Galaxy it’s pretty fast.”

A binary pair of stars orbiting each other “is essentially a single object much bigger than the size of the individual stars, so it is going to interact with the black hole more efficiently,” Bromley explains. “The binary doesn’t have to get nearly as close for one of the stars to get ripped away and captured.”

To prove the theory will require more powerful telescopes to find three key signs: large numbers of small stars captured near supermassive black holes, more observations of stars being “shredded” by gravity from black holes, and large numbers of “hypervelocity stars” that are flung from galaxies at more than 1 million mph when their binary partners are captured.

Black holes are objects in space so dense that not even light can escape their gravity, although powerful jets of light and energy can be emitted from a black hole’s vicinity as gas and stars are sucked into it.

Small black holes result from the collapse of individual stars. But the centers of most galaxies, including our own Milky Way, are occupied by what are popularly known as “supermassive” black holes that contain mass ranging from 1 million to 10 billion stars the size of our sun.

Astrophysicists long have debated how supermassive black holes grew during the 14 billion years since the universe began in a great expansion of matter and energy named the Big Bang. One side believes black holes grow larger mainly by sucking in vast amounts of gas; the other side says they grow primarily by capturing and sucking in stars.

The new theory about binary stars – a pair of stars that orbit each other – arose from Bromley’s earlier research to explain hypervelocity stars, which have been observed leaving our Milky Way galaxy at speeds ranging from 1.1 million to 1.8 million mph, compared with the roughly 350,000 mph speed of most stars.

“The hypervelocity stars we see come from binary stars that stray close to the galaxy’s massive black hole,” he says. “The hole peels off one binary partner, while the other partner – the hypervelocity star – gets flung out in a gravitational slingshot.”

“We put the numbers together for observed hypervelocity stars and other evidence, and found that the rate of binary encounters [with our galaxy's supermassive black hole] would mean most of the mass of the galaxy’s black hole came from binary stars,” Bromley says. “We estimated these interactions for supermassive black holes in other galaxies and found that they too can grow to billions of solar masses in this way.”

Bromley refers to the process of a supermassive black hole capturing stars from binary pairs as “filling the bathtub.” Once the tub – the area near the black hole – is occupied by a cluster of captured stars, they go “down the drain” into the black hole over millions of years. The study shows the “tub” fills at about the same rate it drains, meaning stars captured by a supermassive black hole eventually are swallowed.–Source: University of Utah

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An artist’s illustration on the left shows a simplified picture of the inner layers of the star that formed Cas A just before it exploded, with the predominant concentrations of different elements represented by different colors: iron in the core (blue), overlaid by sulfur and silicon (green), then magnesium, neon and oxygen (red). The image from NASA’s Chandra X-ray Observatory on the right uses the same color scheme to show the distribution of iron, sulfur and magnesium in the supernova remnant. The data show that the distributions of sulfur and silicon are similar, as are the distributions of magnesium and neon. Oxygen, which according to theoretical models is the most abundant element in the remnant, is difficult to detect because the X-ray emission characteristic of oxygen ions is strongly absorbed by gas in along the line of sight to Cas A, and because almost all the oxygen ions have had all their electrons stripped away.

A comparison of the illustration and the Chandra element map (right) shows clearly that most of the iron, which according to theoretical models of the pre-supernova was originally on the inside of the star, is now located near the outer edges of the remnant. Surprisingly, there is no evidence from X-ray (Chandra) or infrared (Spitzer Space Telescope) observations for iron near the center of the remnant, where it was formed. Also, much of the silicon and sulfur, as well as the magnesium, is now found toward the outer edges of the still-expanding debris. The distribution of the elements indicates that a strong instability in the explosion process somehow turned the star inside out.

This latest work, which builds on earlier Chandra observations, represents the most detailed study ever made of X-ray emitting debris in Cas A, or any other supernova remnant resulting from the explosion of a massive star. It is based on a million seconds of Chandra observing time. Tallying up what they see in the Chandra data, astronomers estimate that the total amount of X-ray emitting debris has a mass just over three times that of the Sun. This debris was found to contain about 0.13 times the mass of the Sun in iron, 0.03 in sulfur and only 0.01 in magnesium.

The researchers found clumps of almost pure iron, indicating that this material must have been produced by nuclear reactions near the center of the pre-supernova star, where the neutron star was formed. That such pure iron should exist was anticipated because another signature of this type of nuclear reaction is the formation of the radioactive nucleus titanium-44, or Ti-44. Emission from Ti-44, which is unstable with a half-life of 63 years, has been detected in Cas A with several high-energy observatories including the Compton Gamma Ray Observatory, BeppoSAX, and the International Gamma-Ray Astrophysics Laboratory (INTEGRAL).

These results appeared in the February 20th issue of The Astrophysical Journal in a paper by Una Hwang of Goddard Space Flight Center and Johns Hopkins University, and (John) Martin Laming of the Naval Research Laboratory. NASA’s Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program for NASA’s Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory controls Chandra’s science and flight operations from Cambridge, Mass.

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