Monster Sized, 55,000 Solar Mass First Stars Left no Blackhole

Certain primordial stars—those between 55,000 and 56,000 times the mass of our Sun, or solar masses—may have died unusually. In death, these objects—among the Universe’s first-generation of stars—would have exploded as supernovae and burned completely, leaving no remnant black hole behind.

Astrophysicists at the University of California, Santa Cruz (UCSC) and the University of Minnesota came to this conclusion after running a number of supercomputer simulations at the Department of Energy’s (DOE's) National Energy Research Scientific Computing Center (NERSC) and Minnesota Supercomputing Institute at the University of Minnesota. They relied extensively on CASTRO, a compressible astrophysics code developed at DOE's Lawrence Berkeley National Laboratory’s (Berkeley Lab’s) Computational Research Division (CRD). Their findings were recently published in Astrophysical Journal (ApJ).

First-generation stars are especially interesting because they produced the first heavy elements, or chemical elements other than hydrogen and helium. In death, they sent their chemical creations into outer space, paving the way for subsequent generations of stars, solar systems and galaxies. With a greater understanding of how these first stars died, scientists hope to glean some insights about how the Universe, as we know it today, came to be.

“We found that there is a narrow window where supermassive stars could explode completely instead of becoming a supermassive black hole—no one has ever found this mechanism before,” says Ke-Jung Chen, a postdoctoral researcher at UCSC and lead author of the ApJ paper. “Without NERSC resources, it would have taken us a lot longer to reach this result. From a user perspective, the facility is run very efficiently and it is an extremely convenient place to do science.”

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China's PandaX Facility is Looking for Dark Matter

The new PandaX facility, located deep underground in the southwestern Chinese province of Sichuan, hosts a large liquid-xenon detector designed to search for direct evidence of dark matter interactions with the nuclei of xenon and to observe 136Xe double-beta decay.

The detector's central vessel was designed to accommodate a staged target volume increase from an initial 120 kg (stage I) to 0.5 t (stage II) and ultimately to a multi-ton scale.

The technical design of the PandaX facility and detector is outlined in a new paper co-authored by Ji Xiangdong, of the Institute of Nuclear and Particle Physics, Astronomy and Cosmology at Shanghai Jiao Tong University, and published in the Beijing-based journal SCIENCE CHINA Physics, Mechanics & Astronomy.

While noting that cosmologists generally agree that 80 percent of the matter in the universe is made up of some form of "dark matter," these researchers also acknowledge that so far, no physicist has ever produced experimental data that provides convincing evidence for the existence and structure of dark matter.

"The standard model of particle physics, which has been very successful in explaining the properties of ordinary matter, can neither explain dark matter's existence nor its properties," Professor Ji and co-authors across China and the United States write in the new study. "Yet the discovery and identification of dark matter would have a profound impact on cosmology, astronomy, and particle physics."

"A leading dark matter candidate consistent with all astrophysical data is a weakly interacting massive particle (WIMP)," they add. "WIMPs could be studied in standard particle physics through either observations of ordinary matter particles produced through DM [dark matter] annihilations in the halo of the Milky Way, production of DM particles through high-energy collisions in accelerators such as the Large Hadron Collider, or WIMPs could be detected through their interactions with atomic nuclei in specially designed detectors."

Direct detection experiments are deployed in underground laboratories around the world. When WIMPs interact with nucleons in a detection medium, it is predicted they will recoil and generate kinetic motion of atoms (heat), ionization (free electrons) and scintillation (de-excitation of excited electrons).

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DOE & NSF Both Fund Dark Matter Experiments

For a change, U.S. particle physicists are savoring some good news about government funding. The Department of Energy (DOE) and the National Science Foundation (NSF) announced on Friday that they will try to fund two major experiments to detect particles of the mysterious dark matter whose gravity binds the galaxies instead of just one. The decision allays fears that the funding agencies could afford only one experiment to continue the search for so-called weakly interacting massive particles, or WIMPs. It also averts having to choose between the two leading WIMP-search teams in the United States.

"We have the opportunity right now for the U.S. experiments to push further in sensitivity and possibly make a discovery," says Richard Gaitskell, a physicist at Brown University and a member of the team developing a WIMP detector called LZ, one of the two leading projects. "There's a real commitment from the community and the funding agencies." Blas Cabrera, a physicist at Stanford University in Palo Alto, California, and spokesman for the rival SuperCDMS experiment, says that having to pick only one team “would have been a grave mistake."

For decades, astronomers and astrophysicists have reasoned that some sort of otherwise unobservable dark matter provides most of the gravity that keeps the galaxies from flying apart. Physicists hope to identify that stuff by detecting particles of it floating around us. For example, dark matter could consist of WIMPs, hypothetical particles that would barely interact with ordinary matter and weigh much more than protons.

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Beyond Extraordinary Claim: Gravitational Constant is Variable (& its a solution to the faint sun paradox!)

Can a variable gravitational constant resolve the Faint Young Sun Paradox ?

Authors:

Sahni et al

Abstract:

Solar models suggest that four billion years ago the young Sun was about 75% fainter than it is today, rendering Earth's oceans frozen and lifeless. However, there is ample geophysical evidence that Earth had a liquid ocean teeming with life 4 Gyr ago. Since L⊙∝G7M5⊙, the Sun's luminosity L⊙ is exceedingly sensitive to small changes in the gravitational constant G. We show that a percent-level increase in G in the past would have prevented Earth's oceans from freezing, resolving the faint young Sun paradox. Such small changes in G are consistent with observational bounds on ΔG/G. Since LSNIa∝G−3/2, an increase in G leads to fainter supernovae, creating tension between standard candle and standard ruler probes of dark energy. Precisely such a tension has recently been reported by the Planck team.

Habitable Zone is Governed by Complex Rules of the Parent Stars

Habitable Zone Dependence on Stellar Parameter Uncertainties

Authors:

Kane et al

Abstract:

An important property of exoplanetary systems is the extent of the Habitable Zone (HZ), defined as that region where water can exist in a liquid state on the surface of a planet with sufficient atmospheric pressure. Both ground and space-based observations have revealed a plethora of confirmed exoplanets and exoplanetary candidates, most notably from the Kepler mission using the transit detection technique. Many of these detected planets lie within the predicted HZ of their host star. However, as is the case with the derived properties of the planets themselves, the HZ boundaries depend on how well we understand the host star. Here we quantify the uncertainties of HZ boundaries on the parameter uncertainties of the host star. We examine the distribution of stellar parameter uncertainties from confirmed exoplanet hosts and Kepler candidate hosts and translate these into HZ boundary uncertainties. We apply this to several known systems with a HZ planet to determine the uncertainty in their HZ status.

SCR 1848–6855 System has a Rare Cool White Dwarf Only 75 Light-years Away

THE SOLAR NEIGHBORHOOD. XXXI. DISCOVERY OF AN UNUSUAL RED+WHITE DWARF BINARY AT ~25 pc VIA ASTROMETRY AND UV IMAGING

Authors:

Jao et al

Abstract:

We report the discovery of a nearby M5.0V dwarf at 24.6 pc, SCR 1848–6855, that is orbited by an unusual companion causing an astrometric perturbation of more than 200 mas. This is by far the largest perturbation found to date among more than 700 targets observed during our long-term astrometry/photometry program at the CTIO 0.9 m telescope. We present here a suite of astrometric, photometric, and spectroscopic observations of this high proper motion (~1.''3 yr–1) system in an effort to reveal the nature of this unusual binary. The measured near-UV and optical U band fluxes exceed those expected for comparable M5.0V stars, and excess flux is also detected in the spectral range 4000-7000 Å. The elusive companion has been detected in HST-STIS+MAMA images at 1820 Å and 2700 Å, and our analysis shows that it is probably a rare, cool, white dwarf with T = 4600-5500 K. Given the long-term astrometric coverage, the prospects for an accurate mass determination are excellent, although as yet we can only provide limits on the unusual companion's mass.

The Reddest Brown Dwarf of Them all

The extremely red L dwarf ULAS J222711−004547 - dominated by dust

Authors:

Marocco et al

Abstract:

We report the discovery of a peculiar L dwarf from the UKIDSS LAS, ULAS J222711-004547. The very red infrared photometry (MKO J-K = 2.79±0.06, WISE W1-W2 = 0.65±0.05) of ULAS J222711-004547 makes it one of the reddest brown dwarfs discovered so far. We obtained a moderate resolution spectrum of this target, and classify it as L7pec, confirming its very red nature. Comparison to theoretical models suggests that the object could be a low-gravity L dwarf with a solar or higher than solar metallicity. Nonetheless, the match of such fits to the spectrum is rather poor and this and other peculiar red L dwarfs pose new challenges for the modeling of ultracool atmospheres. We determined the proper motion of ULAS J222711-004547 using the data available in the literature, and we find that its kinematics do not suggest membership of any of the known young associations. We show that applying a simple de-reddening curve to its spectrum allows it to resemble the spectra of the L7 spectroscopic standards. Given the negligible interstellar reddening of the field containing our target, we conclude that the reddening of the spectrum is mostly due to an excess of dust in the photosphere of the target. De-reddening the spectrum using extinction curves for different dust species gives surprisingly good results and suggests a characteristic grain size of ∼0.5 μm. We show that by increasing the optical depth, the same extinction curves allow the spectrum of ULAS J222711-004547 to resemble the spectra of unusually blue L dwarfs and slightly metal-poor L dwarfs. Grains of similar size yield very good fits when de-reddening other unusually red L dwarfs in the L5 to L7.5 range. These results suggest that the diversity in near infrared colours and spectra seen in late-L dwarfs could be due to differences in the optical thickness of the dust cloud deck.

How Common are Gas Giants Around Red Dwarf Stars?

THE TRENDS HIGH-CONTRAST IMAGING SURVEY. IV. THE OCCURRENCE RATE OF GIANT PLANETS AROUND M DWARFS

Authors:

Montet et al

Abstract:

Doppler-based planet surveys have discovered numerous giant planets but are incomplete beyond several AU. At larger star-planet separations, direct planet detection through high-contrast imaging has proven successful, but this technique is sensitive only to young planets and characterization relies upon theoretical evolution models. Here we demonstrate that radial velocity measurements and high-contrast imaging can be combined to overcome these issues. The presence of widely separated companions can be deduced by identifying an acceleration (long-term trend) in the radial velocity of a star. By obtaining high spatial resolution follow-up imaging observations, we rule out scenarios in which such accelerations are caused by stellar binary companions with high statistical confidence. We report results from an analysis of Doppler measurements of a sample of 111 M-dwarf stars with a median of 29 radial velocity observations over a median time baseline of 11.8 yr. By targeting stars that exhibit a radial velocity acceleration ("trend") with adaptive optics imaging, we determine that 6.5% ± 3.0% of M-dwarf stars host one or more massive companions with 1 less than m/MJ less than 13 and 0 less than a less than 20 AU. These results are lower than analyses of the planet occurrence rate around higher-mass stars. We find the giant planet occurrence rate is described by a double power law in stellar mass M and metallicity F ≡ [Fe/H] such that $f(M,F) = 0.039^{+0.056}_{-0.028} M^{0.8^{+1.1}_{-0.9}} 10^{(3.8 \pm 1.2)F}$. Our results are consistent with gravitational microlensing measurements of the planet occurrence rate; this study represents the first model-independent comparison with microlensing observations.

Exoplanets Around NN Serpentis May be First Observations of Secondary Planetary Formation

Second generation planet formation in NN Serpentis?

Authors:

Völschow et al

Abstract:

In this paper, we study the general impact of stellar mass-ejection events in planetary orbits in post-common envelope binaries with circumbinary planets like those around NN Serpentis. We discuss a set of simple equations that determine upper and lower limits for orbital expansion and investigate the effect of initial eccentricity. We deduce the range of possible semi-major axes and initial eccentricity values of the planets prior to the common-envelope event. In addition to spherically-symmetric mass-ejection events, we consider planetary dynamics under the influence of an expanding disk. In order to have survived, we suggest that the present planets in NN Ser must have had semi-major axes >∼10 AU and high eccentricity values which is in conflict with current observations. Consequently, we argue that these planets were not formed together with their hosting stellar system, but rather originated from the fraction of matter of the envelope that remained bound to the binary. According to the cooling age of the white dwarf primary of 106 yr, the planets around NN Ser might be the youngest known so far and open up a wide range of further study of second generation planet formation.

Kepler-410b: a hot Neptune in an Eccentric Orbit

What asteroseismology can do for exoplanets: Kepler-410A b is a Small Neptune around a bright star, in an eccentric orbit consistent with low obliquity

Authors:

Van Eylen et al

Abstract:

We confirm the Kepler planet candidate Kepler-410b (KOI-42b) as a Neptune sized exoplanet on a 17.8 day, eccentric orbit around the bright (Kp = 9.4) star Kepler-410A. This is the third brightest confirmed planet host star in the Kepler field and one of the brightest hosts of all currently known transiting exoplanets. Kepler-410 consists of a blend between the fast rotating planet host star (Kepler-410A) and a fainter star (Kepler-410B), which has complicated the confirmation of the planetary candidate. Employing asteroseismology, using constraints from the transit light curve, adaptive optics and speckle images, and Spitzer transit observations, we demonstrate that the candidate can only be an exoplanet orbiting Kepler-410A. Via asteroseismology we determine the following stellar and planetary parameters with high precision; M⋆=1.214±0.033 M⊙, R⋆=1.352±0.010 R⊙, Age = 2.76±0.54 Gyr, planetary radius (2.838±0.054 R⊕), and orbital eccentricity (0.17+0.07−0.06). In addition, rotational splitting of the pulsation modes allows for a measurement of Kepler-410A's inclination and rotation rate. Our measurement of an inclination of 82.5+7.5−2.5 [∘] indicates a low obliquity in this system. Transit timing variations indicate the presence of at least one additional (non-transiting) planet in the system.

Kepler-91b: A Dying Exoplanet With 55 Million Years Left to Live (at most)

Kepler-91b: a planet at the end of its life. Planet and giant host star properties via light-curve variations

Authors:

Lillo-Box et al

Abstract:

The evolution of planetary systems is intimately linked to the evolution of their host star. Our understanding of the whole planetary evolution process is based on the large planet diversity observed so far. To date, only few tens of planets have been discovered orbiting stars ascending the Red Giant Branch. Although several theories have been proposed, the question of how planets die remains open due to the small number statistics. In this work we study the giant star Kepler-91 (KOI-2133) in order to determine the nature of a transiting companion. This system was detected by the Kepler Space Telescope. However, its planetary confirmation is needed. We confirm the planetary nature of the object transiting the star Kepler-91 by deriving a mass of Mp=0.88+0.17−0.33 MJup and a planetary radius of Rp=1.384+0.011−0.054 RJup. Asteroseismic analysis produces a stellar radius of R⋆=6.30±0.16 R⊙ and a mass of M⋆=1.31±0.10 M⊙. We find that its eccentric orbit (e=0.066+0.013−0.017) is just 1.32+0.07−0.22 R⋆ away from the stellar atmosphere at the pericenter. Kepler-91b could be the previous stage of the planet engulfment, recently detected for BD+48 740. Our estimations show that Kepler-91b will be swallowed by its host star in less than 55 Myr. Among the confirmed planets around giant stars, this is the planetary-mass body closest to its host star. At pericenter passage, the star subtends an angle of 48∘, covering around 10% of the sky as seen from the planet. The planetary atmosphere seems to be inflated probably due to the high stellar irradiation.

Polarization is VERY Important When Using Microlensing to Find Exoplanets

Exoplanetary searches with gravitational microlensing: polarization issues

Authors:

Zakharov et al

Abstract:

There are different methods for finding exoplanets such as radial spectral shifts, astrometrical measurements, transits, timing etc. Gravitational microlensing (including pixel-lensing) is among the most promising techniques with the potentiality of detecting Earth-like planets at distances about a few astronomical units from their host star or near the so-called snow line with a temperature in the range 0−1000 C on a solid surface of an exoplanet. We emphasize the importance of polarization measurements which can help to resolve degeneracies in theoretical models. In particular, the polarization angle could give additional information about the relative position of the lens with respect to the source.

Examining Local Stellar and Near Stellar Objects for the Hydrogen Burning Limit

The Solar Neighborhood XXXII. The Hydrogen Burning Limit

Authors:

Dietrich et al

Abstract:

We construct a Hertzsprung-Russell diagram for the stellar/substellar boundary based on a sample of 63 objects ranging in spectral type from M6V to L4. We report newly observed VRI photometry for all 63 objects and new trigonometric parallaxes for 37 objects. The remaining 26 objects have trigonometric parallaxes from the literature. We combine our optical photometry and trigonometric parallaxes with 2MASS and WISE photometry and employ a novel SED fitting algorithm to determine effective temperatures, bolometric luminosities, and radii. Our uncertainties range from ~20K to ~150K in temperature, ~0.01 to ~0.06 in log(L/Ls}) and 3% to 10% in radius. We check our methodology by comparing our calculated radii to radii directly measured via long baseline optical interferometry. We find evidence for the local minimum in the radius-temperature and radius-luminosity trends that signals the end of the stellar main sequence and the start of the brown dwarf sequence at T ~ 2075K, log(L/Ls)~ -3.9, and (R/Rs) ~ 0.086. The existence of this local minimum is predicted by evolutionary models, but at temperatures ~400K cooler. The minimum radius happens near the locus of 2MASS J0523-1403, an L2.5 dwarf with V-K=9.42. We make qualitative arguments as to why the effects of the recent revision in solar abundances accounts for the discrepancy between our findings and the evolutionary models. We also report new color-absolute magnitude relations for optical and infrared colors useful for estimating photometric distances. We study the optical variability of all 63 targets and find an overall variability fraction of 36^{+9}_{-7}% at a threshold of 15 milli-magnitudes in the I band, in agreement with previous studies.

Carbon/Oxygen Ratios in Exoplanet 55 Cancri System

CARBON AND OXYGEN ABUNDANCES IN COOL METAL-RICH EXOPLANET HOSTS: A CASE STUDY OF THE C/O RATIO OF 55 CANCRI*

Authors:

Johanna K. Teske, Katia Cunha, Simon C. Schuler, Caitlin A. Griffith, and Verne V. Smith

Abstract:

The super-Earth exoplanet 55 Cnc e, the smallest member of a five-planet system, has recently been observed to transit its host star. The radius estimates from transit observations, coupled with spectroscopic determinations of mass, provide constraints on its interior composition. The composition of exoplanetary interiors and atmospheres are particularly sensitive to elemental C/O ratio, which to first order can be estimated from the host stars. Results from a recent spectroscopic study analyzing the 6300 Å [O I] line and two C I lines suggest that 55 Cnc has a carbon-rich composition (C/O = 1.12 ± 0.09). However, oxygen abundances derived using the 6300 Å [O I] line are highly sensitive to a Ni I blend, particularly in metal-rich stars such as 55 Cnc ([Fe/H] =0.34 ± 0.18). Here, we further investigate 55 Cnc's composition by deriving the carbon and oxygen abundances from these and additional C and O absorption features. We find that the measured C/O ratio depends on the oxygen lines used. The C/O ratio that we derive based on the 6300 Å [O I] line alone is consistent with the previous value. Yet, our investigation of additional abundance indicators results in a mean C/O ratio of 0.78 ± 0.08. The lower C/O ratio of 55 Cnc determined here may place this system at the sensitive boundary between protoplanetary disk compositions giving rise to planets with high (greater than 0.8) versus low ( less than 0.8) C/O ratios. This study illustrates the caution that must applied when determining planet host star C/O ratios, particularly in cool, metal-rich stars.

European Space Agency Selects Orbital Observatories for Next Major Space Missions

On 31 October, European Space Agency (ESA) director of science and robotic exploration, Alvaro Giménez, put forward the “hot and energetic Universe” and the “gravitational Universe” as the two themes that will shape the agency’s next large (L-class) projects —the €1-billion (US$1.4-billion) L2 and L3 missions, scheduled for launch in 2028 and 2034, respectively. ESA’s Science Programme Committee, composed of member-state representatives, will consider the recommendation and announce a decision at a meeting on 28–29 November. It would be rare for the committee not to endorse the science director’s advice.

The first of the themes is good news for Athena+ (the Advanced Telescope for High Energy Astrophysics), an X-ray observatory that would be the front runner in a formal call — planned for next year — for mission proposals to probe the hot and energetic aspects of the Universe. The observatory, which will carry a telescope and instruments to measure the energy of X-ray sources and image them with unprecedented precision, would study how hot gas evolves into galaxy clusters and how black holes grow. Luigi Piro, a member of the Athena+ instrument and optics working group at Italy’s National Institute for Astrophysics in Rome, says that half of all visible matter is in this ‘hot phase’, but is poorly understood. “We will now be able to tackle questions about how the Universe is actually working and what is the role of hot plasma and black holes in shaping the Universe,” he explains.

The second theme would focus on gravitational-wave astronomy, a field never before studied in space. The planned space-based mission eLISA (evolved Laser Interfero­meter Space Antenna) would detect the low-frequency gravitational waves that are thought to stretch the fabric of space-time. Gravitational waves have not been directly detected at ground-based observatories. eLISA would bounce lasers between three spacecraft at least one million kilometres apart, and spot a passing wave when it alters the precise positioning of one of the spacecraft.

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Blackhole Firewalls an Exciting Conumdrum for Physics

“The most exciting phrase to hear in science, the one that heralds new discoveries, is not ‘eureka!’ but ‘that's funny,’” Isaac Asimov once said. Well, something seriously funny is going on in theoretical physics these days. A recent conundrum about black holes is threatening to overturn some of the most basic tenets of physics, and many scientists are nothing but thrilled.

“To me it’s the best thing that’s happened in awhile,” says University of California, Berkeley, physicist Raphael Bousso of the so-called “black hole firewall paradox,” which concerns what happens at the boundary of a black hole. “This is a 9 on the Richter earthquake scale—it’s by far the most shocking and surprising thing that has happened in my career.” The quandary prompting such jubilation is an idea first put forward in July 2012, which was extended in a paper published October 21 in Physical Review Letters. Physicists have long assumed that space is smooth at a black hole’s event horizon—the point of no return where nothing that passes through can escape. A person crossing over that line shouldn’t immediately notice anything amiss, however, and neither should a distant observer watching that person. But physicists have also assumed that information can never be destroyed. The new work says those two ideas are mutually incompatible. “It’s a paradox because several things we believed were true can’t all be true,” says Joseph Polchinski of the Kavli Institute for Theoretical Physics and U.C. Santa Barbara, one of the main architects of the firewall idea.

Polchinski and his colleagues conclude that not only is space not smooth at a black hole horizon—at that point the laws of physics completely break down. Instead of an unobtrusive boundary, the scientists argue that there must actually be a sharp division they call a firewall. “The firewall is kind of a wall of energy—it could be the end of spacetime itself,” Polchinski says. “Anything hitting it would break up into its fundamental bits and effectively dissolve.” At first, many physicists strenuously objected to the bizarre idea of firewalls. “I tried very hard to get rid of them, but I don’t think it’s likely that will happen,” Bousso says. “I’ve decided that the most promising thing for me is to assume there are firewalls, and look into why they form.” Even the main authors of the idea aren’t completely onboard. “There is a group of people, including me half the time, that thinks there must be some subtle assumption that we’ve made that’s not valid,” Polchinski says. Yet he and everyone else admit they haven’t identified a flaw in the reasoning so far.

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Formed in the Albian Cretaceous, F8 Class Star HD 166191 is Having Collisions in its Habitable Zone

THE NEARBY, YOUNG, ISOLATED, DUSTY STAR HD 166191

Authors:

Schneider et al.

Abstract:

We report an in-depth study of the F8-type star HD 166191, identified in an ongoing survey for stars exhibiting infrared emission above their expected photospheres in the Wide-field Infrared Survey Explorer all-sky catalog. The fractional IR luminosity measured from 3.5 to 70 μm is exceptionally high (L IR/L bol ~ 10%). Near-diffraction-limited imaging observations with the T-ReCS Si filter set on the Gemini South telescope and adaptive optics imaging with the NIRC2 Lp filter on the Keck II telescope confirmed that the excess emission coincides with the star. Si-band images show a strong solid-state emission feature at ~10 μm. Theoretical evolutionary isochrones and optical spectroscopic observations indicate a stellar age in the range 10-100 Myr. The large dust mass seen in HD 166191's terrestrial planet zone is indicative of a recent collision between planetary embryos or massive ongoing collisional grinding associated with planet building.

GD 61: A White Dwarf 170 Light Years Away, Formed at the Triassic-Jurassic Boundary and Tore Apart a Minor Planet with Water

Astrophysicists have found the first evidence of a water-rich rocky planetary body outside our solar system in its shattered remains orbiting a white dwarf.

A new study by scientists at the Universities of Warwick and Cambridge published in the journal Science analysed the dust and debris surrounding the white dwarf star GD61 170 light years away.

Using observations obtained with the Hubble Space Telescope and the large Keck telescope on Hawaii, they found an excess of oxygen – a chemical signature that indicates that the debris had once been part of a bigger body originally composed of 26 per cent water by mass. By contrast, only approximately 0.023 per cent of the Earth's mass is water.

Evidence for water outside our solar system has previously been found in the atmosphere of gas giants, but this study marks the first time it has been pinpointed in a rocky body, making it of significant interest in our understanding of the formation and evolution of habitable planets and life.

We know from our own solar system that the dwarf planet Ceres contains ice buried beneath an outer crust, and the researchers draw a parallel between the two bodies. Scientists believe that bodies like Ceres were the source of the bulk of our own water on Earth.

The researchers suggest it is most likely that the water detected around the white dwarf GD 61 came from a minor planet at least 90 km in diameter but potentially much bigger, that once orbited the parent star before it became a white dwarf.

Like Ceres, the water was most likely in the form of ice below the planet's surface. From the amount of rocks and water detected in the outer envelope of the white dwarf, the researchers estimate that the disrupted planetary body had a diameter of at least 90km.

However, because their observations can only detect what is being accreted in recent history, the estimate of its mass is on the conservative side.

It is likely that the object was as large as Vesta, the largest minor planet in the solar system. In its former life, GD 61 was a star somewhat bigger than our Sun, and host to a planetary system.

About 200 million years ago, GD 61 entered its death throes and became a white dwarf, yet, parts of its planetary system survived. The water-rich minor planet was knocked out of its regular orbit and plunged into a very close orbit, where it was shredded by the star's gravitational force. The researchers believe that destabilising the orbit of the minor planet requires a so far unseen, much larger planet going around the white dwarf.

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Detecing Exoplanet's Magnetic Fields

Astronomers may soon be able to observe the shockwaves between the magnetic fields of exoplanets and the flow of particles from the stars they orbit.

Magnetic fields are crucial to a planet’s (and as it turns out a moon’s) habitability. They act as protective bubbles, preventing harmful space radiation from stripping away the object’s atmosphere entirely and even reaching the surface.

An extended magnetic field – known as a planetary magnetosphere – is created by the shock between the stellar wind and the intrinsic magnetic field of the planet. It has the potential to be huge. Within our own Solar System, Jupiter’s magnetosphere extends to distances up to 50 times the size of the planet itself, nearly reaching Saturn’s orbit.

When the wind of high-energy particles from the star hits the planetary magnetosphere, it interacts in a bow shock that diverts the wind and compresses the magnetosphere.

Recently a team of astronomers, led by PhD student Joe Llama of the University of St. Andrews, Scotland, have worked out how we might observe planetary magnetospheres and stellar winds via their bow shocks.

Llama took a careful look at the planet HD 189733b, located 63 light years away toward the constellation Vulpecula. From the Earth, the planet is seen to transit its host star every 2.2 days, causing a dip in the overall light from the system.

As a bright star, HD 189733b has been studied extensively by astronomers. Data collected in July 2008 by the Canada-France-Hawaii telescope mapped the star’s magnetic field. While the magnetic field varied, it was on average 30 times greater than that of our Sun – meaning that the stellar wind is much higher than the solar wind.

This allowed the team to carry out extensive simulations of the stellar wind around HD 189733b – characterizing the bow shock created as the planet’s magnetosphere passes through the stellar wind. With this information they were able to simulate the light curves that would result from the planet and the bow shock orbiting the star.

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Coldest Brown Dwarfs Hint at Continuum from Planet to Star, not Separate Formation Types

Astronomers are constantly on the hunt for ever-colder star-like bodies, and two years ago a new class of such objects was discovered by researchers using NASA's WISE space telescope. However, until now no one has known exactly how cool their surfaces really are - some evidence suggested they could be room temperature.

A new study shows that while these brown dwarfs, sometimes called failed stars, are indeed the coldest known free-floating celestial bodies, they are warmer than previously thought with temperatures about 250-350 degrees Fahrenheit.

To reach such low surface temperatures after cooling for billions of years means that these objects can only have about 5 to 20 times the mass of Jupiter. Unlike the Sun, these objects' only source of energy is from their gravitational contraction, which depends directly on their mass.

"If one of these objects was found orbiting a star, there is a good chance that it would be called a planet," says Trent Dupuy, a Hubble Fellow at the Harvard-Smithsonian Center for Astrophysics. But because they probably formed on their own and not in a proto-planetary disk, astronomers still call these objects brown dwarfs even if they are "planetary mass."

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