Om nom nom: black hole dismembers and eats a large planet

Computer simulation of a black hole stripping material off a brown dwarf or large planet, shown at the lower right. The material flowing onto the black hole produces a burst of gamma rays and X-rays.

ESA

Black holes have a fearsome reputation that's only partly justified. The maw of a black hole is indeed a potentially destructive thing, but most matter—including gas stripped from nearby stars—is not destined to end inside the black hole. Instead, a lot of it ends orbiting the black hole, and the energy that's released by the material that is getting swallowed blasts a lot of material back out into space. So, black holes don't simply devour every object that comes near them.

All of this makes a new observation particularly interesting. Astronomers M. Nikołajuk and R. Walter caught a black hole in the act of destroying and consuming part of a large planet or small brown dwarf. This event involved a supermassive black hole located in a relatively nearby galaxy, and emitted a burst of intense X-ray light that fluctuated over a short time span, then faded. The flare and its aftermath behaved as expected if the black hole disrupted an object at least 14 times Jupiter's mass, then consumed about 10 percent of the gas that once was part of the object.

In 2011, astronomers using the INTEGRAL (INTErnational Gamma-Ray Astrophysics Laboratory) gamma ray telescope discovered a strong source of emissions coming from the galaxy NGC 4845. Follow-up observations using INTEGRAL along with other gamma- and X-ray telescopes confirmed the flare was located within the central region of the galaxy, where the supermassive black hole resides.

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Possible habitable zone planet is a mere 12 light years away

An artist's conception of the potential planet.

PHL at the University of Arecibo

Most of the exoplanets we've discovered thus far have been found because they're easy to spot—Jupiter-sized giants orbiting close in to their host stars. But the Kepler mission has been providing a huge catalog of exoplanets and with it we've obtained a very different perspective, finding that planets in general are common and most of them are far smaller than the gas giants first identified. This new perspective has raised the prospect that we can identify some orbiting nearby stars, following identification with direct observations searching for signs that the planet's atmosphere is shaped by life.

More recently, astronomers have started making progress towards identifying planetary candidates that are close enough that we could eventually image them with an orbiting telescope. Just in October, astronomers announced that there was a hint of a signal from an exoplanet in the light from one of the closest stars, Centauri B. Today, the astronomers have released a paper that suggests there are several planets around the nearby star Tau Ceti, and one of them is likely to be within the star's habitable zone.

It's important to note that the signals of the planets are buried deep in a variety of optical noise, both from the telescopes and instruments, and from the star itself. Further observations are going to be needed to confirm that the signals appear consistently. But this work certainly suggests those follow-up observations are going to be a high priority.

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If it forms like a star but looks like a planet…

http://www.eurekalert.org/multimedia/pub/49723.php?from=226003

You may have seen headlines earlier this week about a planet found wandering alone, without a star to orbit. Although that aspect of the new planetary find seems to have grabbed the headlines, it's actually one of the least interesting features of the new find. The body in question awkwardly straddles the border between near-stars called brown dwarfs and giant super-Jupiter class planets, and its features suggest it may have formed through a process identical to one that creates stars. The alternative—that it was ejected from a system of planets that formed orbiting a star—would suggest interstellar space is teeming with rogue planets.

Rogue planets, those that aren't gravitationally bound to a star, have been identified previously through surveys looking for a phenomenon called "microlensing." This occurs when the planet acts as a gravitational lens, briefly brightening a star in the background as the planet passes between the star and Earth. A survey of microlensing objects identified a number of possible planets that mapped to points in space where there were no stars in the neighborhood.

But in this case, the authors managed to directly image one relatively nearby (less than 140 light years away). It happened while they were looking for something else: brown dwarfs. These bodies are large enough to have ignited deuterium fusion (over 13 times the mass of Jupiter), but not large enough to have kicked off sustained fusion of hydrogen. Anything below the brown dwarf cutoff is considered a planet (with the largest of these gas giants typically termed "super Jupiters").

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Old data reveals Super-Earth lurking in a nearby star’s habitable zone

UPR Arecibo

A reanalysis of old data obtained by an Earth-based observatory has found what seems to be the signal of a large planet, somewhere between the mass of Earth and Neptune, orbiting a dwarf star about 42 light years from Earth. It's part of a crowded system of six planets, but appears to be the only one of them that's in the host star's habitable zone. And, according to the people who have identified it, the planet should be close enough to Earth to be imaged directly by some of the observatories currently in the planning stages.

The star in question is HD 40307, which is only about three-quarters the mass of the Sun, and quite a bit dimmer. The star has been targeted for observations using the HARPS, the same instrument that recently spotted the signal of an exoplanet in the Alpha Centauri system. The instrument looks for periodic changes in the light emitted by the star. These arise from Doppler shifts caused by its orbiting planets, which periodically pull the star in different directions.

The HARPS team had already analyzed data from HD 40307, and determined that there were three planets apparent in the data obtained by the instrument. But now, an international team of researchers has gone back and reanalyzed the data using a number of different methods. Their work suggests there are at least six planets in the system.

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Exoplanet found right next door in Alpha Centauri

An artist's conception of the newly discovered planet.

ESO/L. Calçada

Today, planet hunters announced evidence there's a planet orbiting one of our closest stellar neighbors. One of the three stars of the α Centauri star system shows the sort of periodic changes in brightness that are a hallmark of the presence of an orbiting planet. And, even though the new world would be far too hot to support liquid water, the astronomers who discovered it point out small planets tend to form in groups. Odds are good that there are additional planets lurking further out from the host star.

Rapid advances in planet-hunting have led to an ever-increasing catalog of exoplanets, but most of these orbit distant stars. In contrast, the a Centauri system "is a household name," as Greg Laughlin of UC Santa Cruz put it. Just over four light years from Earth, the system includes two bright stars, Centauri A and B orbiting each other with an 80 year period, along with a red dwarf called Proxima Centauri. Centauri B has a Sun-like mass, but is quite a bit dimmer.

The planet was detected using the radial velocity method. As a massive body orbits its host star, it exerts a gravitational pull on it, pulling the star in slightly different directions as its position shifts. These create a small acceleration in the star itself, usually on the order of a few meters per second. That, in turn, shows up in the light emitted by the star as Doppler shifts in the light it emits, which vary with the orbital period of the planet.

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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

Tatooine-like planets may be common

Exoplanets—planets in star systems other than our own—have been found in orbit around single stars, with a lone exception: Kepler-16b is circumbinary, having two host stars in close orbit. Now, researchers working with data from the Kepler space-based observatory have identified two more promising exoplanet candidates orbiting binary stars, known as Kepler-34b and Kepler-35b. While the planets most likely are gas giants, the host stars in Kepler-34b are more Sun-like than the Kepler-16 system. These observations indicate that giant exoplanets orbiting two stars may be fairly common, occurring in perhaps one percent of close binaries.

In some ways, our Sun is unusual: stars with similar masses are more commonly found in binary systems. Lower-mass stars are more often found on their own and, since they are also less luminous than the Sun, it has been easier for astronomers to detect planets orbiting them. Finding circumbinary planets is plagued by two major difficulties: both the gravitational pull by the exoplanet and the amount of light it blocks if it passes between us and its hosts are tiny in comparison with the effect the two stars have on each other.

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Remains of gas giants, swallowed by red giant star, now orbit as small planets

There may come a day when exoplanet discoveries start to bore me, but we're not there yet. A day after the Kepler team announced the identification of Earth-sized planets orbiting a distant star, they're back with the description of a truly bizarre planetary system. In its past, KIC 05807616 expanded out to red giant size, swallowing two gas giants in the process. The cores of these planets continued to orbit, reemerging once the star shrunk again. Meanwhile, their impact on the star may have caused it to become an unusually hot form of dwarf star.

The star in question, KIC 05807616, has a rather interesting description: "a seemingly isolated pulsating hot B subdwarf." These have a somewhat unusual history. Normally, stars near the mass of our sun expand out as red giants, but then contract as they switch from fusing hydrogen to fusing the helium that has built up at their cores. Hot B dwarfs occur when something happens during the red giant phase that removes all the star's hydrogen, leaving nothing but a helium fusing core behind. KIC 05807616 has been in this stage for less than 20 million years, and in addition to its high temperatures, undergoes regular fluctuations, hence the "pulsating" part of that description.

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Kepler team spots Earth-sized planets orbiting sun-like star

Just two weeks after the confirmation of a planet that's within the habitable zone of a distant star, the Kepler team is back with the discovery of two Earth-sized planets orbiting in what is now a five-planet system (three other planets orbiting the star, Kepler-20, had been spotted earlier). Although these planets are much too hot to support liquid water, one of them (Kepler-20e) is the smallest exoplanet yet detected.

Kepler-20 was already a busy star system, with three small planets orbiting close in to the star: Kepler-20b is about twice the size of Earth and orbits once every 3.7 days; Kepler-20c is three times Earth's radius and orbits every 11 days; and Kepler-20d is 2.75 Earth radii with an orbit of 77.6 days. If that seems somewhat tightly packed, the new finds actually jam a couple more planets within the orbit of Kepler-20d. Kepler-20e has an orbit of six days, while Kepler-20f takes 19.6 days to orbit its host star.

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