Looking Into The Green Eye Of Planetary Nebula IC 1295

This intriguing picture from ESO’s Very Large Telescope shows the glowing green planetary nebula IC 1295 surrounding a dim and dying star. It is located about 3300 light-years away in the constellation of Scutum (The Shield). This is the most detailed picture of this object ever taken. Credit: ESO

Located on Cerro Paranal in the Atacama Desert of northern Chile, the ESO’s Very Large Telescope was busy using the FORS instrument (FOcal Reducer Spectrograph) to achieve one of the most detailed observations ever taken off a lonely, green planetary nebula – IC 1295. Exposures taken through three different filters which enhanced blue light, visible green light, and red light were melded together to make this 3300 light year distant object come alive.

Located in the constellation of Scutum, this jewel in the “Shield” is a miniscule star that’s at the end of its life. Much like our Sun will eventually become, this white dwarf star is softly shedding its outer layers, like an unfolding flower in space. It will continue this process for a few tens of thousands of years, before it ends, but until then IC 1295 will remain something of an enigma.

“The range of shapes observed up to today has been reproduced by many theoretical works using arguments such as density enhancements, magnetic fields, and binary central systems. Despite this, no complete agreement between models and properties of a given morphological group has been achieved. One of the main reasons for this is selection criteria and completeness of studied samples.” say researchers at Georgia State University. “The samples are usually limited by available images in few bands such as Ha, [NII] and [OIII]. Of course they are also limited by distance, since the further away the object is, the harder it is to resolve its structure. Even with the modern telescopes, obtaining a truly complete sample is far from being achieved.”

Why is this common deep space object like IC 1295 such a mystery? Blame it on its structure. It is comprised of multiple shells.- gaseous layers which once were the star’s atmosphere. As the star aged, its core became unstable and it erupted in unexpected releases of energy – like expansive blisters breaking open. These waves of gas are then illuminated by the ancient star’s ultraviolet radiation, causing it to glow. Each chemical acts as a pigment, resulting in different colors. In the case of IC 1295, the verdant shades are the product of ionised oxygen.

Loading player…

This video sequence starts with a broad panorama of the Milky Way and closes in on the small constellation of Scutum (The Shield), home to many star clusters. The final detailed view shows the strange green planetary nebula IC 1295 in a new image from ESO’s Very Large Telescope. This faint object lies close to the brighter globular star cluster NGC 6712. Credit: ESO/Nick Risinger (skysurvey.org)/Chuck Kimball. Music: movetwo

However, green isn’t the only color you see here. At the heart of this planetary nebula beats a bright, blue-white stellar core. Over the course of billions of years, it will gently cool – becoming a very faint, white dwarf. It’s just all part of the process. Stars similar to the Sun, and up to eight times as large, are all theorized to form planetary nebulae as they extinguish. How long does a planetary nebula last? According to astronomers, it’s a process that could be around 8 to 10 thousand years.

“Athough planetary nebulae (PNe) have been discovered for over 200 years, it was not until 30 years ago that we arrived at a basic understanding of their origin and evolution.” says Sun Kwok of the Institute of Astronomy and Astrophysics. “Even today, with observations covering the entire electromagnetic spectrum from radio to X-ray, there are still many unanswered questions on their structure and morphology.”

Original Story Source: ESO Photo Release.

Kepler Team Identifies Planet Impostors that are Binary Stars in Disguise

A new study describes how the Kepler team aims to remove pseudo-planets from its database. A pseudo-planet can be caused by the superposition of a foreground bright constant target star, and background fainter multiple star systems as shown in the above artist sketch (image credit: regulus36/devianart).

Observations by the Kepler satellite have advanced our knowledge of stars and their orbiting planets, yielding more than 100 confirmed planets and about 3,000 candidates.  However, orbiting planets may not be the source for a fraction of those detections.

“There are many things in the sky that can produce transit-like signals that are not planets, and thus we must be sure to identify what really is a planet detected by Kepler,” Stephen Bryson told Universe Today.  NASA Ames Research Center scientists Bryson and Jon Jenkins (also at the SETI Institute) are the lead authors on a new paper that aims to identify pseudo-planets detected by Kepler.

Small eclipses present in Kepler brightness measurements for a star (a lightcurve) may be indicative of an orbiting planet blocking light from its host star (see image below).  However, under certain circumstances binary stars can mimic that signature.

Consider a Kepler target that is actually a chance superposition of a bright star and a fainter eclipsing binary system, whereby the objects lie at different distances along the sight-line.  The figure below illustrates that their combined light can produce a lightcurve that is similar to a transiting planet.  The bright foreground star dilutes the typically large eclipses produced by the binary system.

Left, the lightcurve for a star featuring a transiting planet, whereby the planet blocks a minute fraction of the host star’s light (image credit: Institute for Astronomy, University of Hawaii at Manoa).  Right, the combined light from a foreground bright star and a fainter eclipsing binary system can mimic a transiting planet (image credit: chart and assembly, D. Majaess – cropped stellar graphics from Collier Cameron 2012, Nature).

“Most of the time these eclipsing binaries are not exactly aligned with our target star,” Bryson added, “and we can carefully examine the pixels to discover that the location of the transit signal is not the target star.”  The team developed algorithms to identify pseudo-planets when the stars are individually resolved.  Tagging spurious planet detections is important since there are numerous candidates, and yet limited observing time for follow-up efforts.

The team has been refining those algorithms as knowledge of the satellite’s in situ behavior increases.  “These algorithms have been developed and used over the last four years.  Some details of the techniques in the paper are new and will appear in future versions of the Kepler [software processing] pipeline,” said Bryson.

However, if multiple stars fall within the same pixel they are not individually resolved by Kepler, and a separate approach is required to infer their presence.  Consider the example highlighted in the image below, where several stars were unresolved by Kepler yet appear in higher resolution images.  The matter is exacerbated in part because Kepler’s spatial resolution is not optimal, and thus multiple stars may be confused as a single object.  By contrast, certain ground-based telescopes can achieve ~20 times Kepler’s spatial resolution when adaptive optics are implemented.

High-resolution images (right panel) can reveal stars that were unresolved in lower-resolution images (left panel, e.g., Kepler).   Unresolved stars dilute eclipses caused by transiting planets, and in certain cases can strongly bias the derived parameters (image credit: right panel from Adams et al. 2012, arXiv/AJ – left panel, image blurred to provide a lower-resolution glimpse of the target, assembly by D. Majaess).

Adams et al. 2012 obtained high-resolution images of 90 Kepler targets, one of which is highlighted above.  That team noted that, “Close companions … are of particular concern … Of the [90 Kepler targets surveyed] 20% have at least one companion within [half a Kepler pixel].”  The high-resolution images were acquired via the MMT observatory (shown below) and the Palomar Hale-200-inch telescope.

Obviously, the resolution problem becomes more acute when observing rich stellar fields (high densities), such as near the plane of our Galaxy.   

“Background eclipsing binaries account for as many as 35% of all planet-like transit signals when we are looking near the Milky Way, because there are many stars in the background,” Bryson told Universe Today. “When we look away from the Milky Way the fraction of background eclipsing binaries falls to about 10% of all planet-like transit signals because there are far fewer background stars of all types.”

However, regarding Kepler’s coarser resolution Bryson underscored that, “[it is] expected with such a large field telescope.” Kepler’s large field is certainly advantageous, as it permits the satellite to monitor 100,000+ stars over more than 100 square degrees of field.

The adaptive optics (AO) system at the MMT observatory provides astronomers with high-resolution images to search the vicinity of Kepler planet candidates for contaminating stars (image credit: Thomas Stalcup, SPIE).

Radial velocity measurements are an ideal means for evaluating planet candidates (and to help yield the mass).  The data are pertinent since velocity shifts occur in the spectrum of the host star owing to the planet’s gravity.  However, Adams et al. 2012 note that “Many of these objects do not have … radial velocity measurements because of the amount of observing time required, particularly for small planets around relatively faint stars. Another method is needed to confirm these types of planets … High-resolution images are thus a crucial component of any transit follow-up program.”

Identifying unresolved stars is crucial for yet another reason.  Note that the fundamental parameters determined for a transiting planet depend in part on the fraction of the host star’s light that is obscured (the eclipse depth).  However, if multiple unresolved stars exist they will contribute to the overall brightness, and hence the observed planet eclipse will be diluted and underestimated (see figure 2, above).  Indeed, Adams et al. 2012 note that, “Corrections to the planetary parameters based on nearby [contaminating] stars can range from a few to tens of percents, making high resolution images an important tool to understanding the true sizes of other discovered worlds.”

The case of K00098 is a prime example underscoring the importance of identifying unresolved contaminating stars.   K00098 features two rather bright stars that were unresolved and unknown prior to the acquisition of high-resolution images. Consequently, previously determined parameters for that star’s transiting planet were incorrect. Concerning K00098, Adams et al. 2012 remarked that, “for K00098, the dilution [of the eclipse depth] … were substantial: the [planet’s] radius increased by 10%, the mass by 60% … and the density changed by 25% [from that published]. Without high resolution images, we would have had a very inaccurate picture of this planet.”

Low and high-resolution images of stars in the galaxy M33. The bright object detected in the low-resolution image is actually several stars, as indicated by the higher-resolution image. A similar effect occurs when comparing Kepler (lower-resolution) and AO images (higher-resolution). A single Kepler target can actually constitute multiple stars seen along the sight-line (image credit: Mochejska et al. 2001, arXiv).
Low and high-resolution images of stars in the galaxy M33. The bright object detected in the low-resolution image is actually several stars, as indicated by the higher-resolution image (right). A similar effect occurs when comparing Kepler (lower-resolution) and AO images (higher-resolution). A single Kepler target can actually constitute multiple stars seen along the sight-line (image credit: Mochejska et al. 2001, arXiv).

Incidentally, unaccounted for light from unresolved stars isn’t merely a problem for exoplanet studies.  The issue is rather pertinent when researching the cosmic distance scale and the Hubble constant (expansion rate of the Universe).  Consider the images above which feature the same field in M33.  The image exhibited on the left is from a ground-based facility, whereas the higher-resolution image displayed on the right is from the Hubble Space Telescope (HST).  The brightest star at the center of the image is a Cepheid variable star, which is a pulsating star that is used to establish distances to galaxies.  In turn those distances are subsequently employed to determine the Hubble constant.  The HST image reveals stars that are unresolved in the ground-based image, and thus the distance inferred from that observation is compromised since the Cepheid appears (spuriously) brighter than it should be.

“Blending [e.g., added light caused by unresolved stars] leads to systematically low distances to galaxies observed with the HST, and therefore to systematically high estimates of the Hubble constant,” remarked Mochejska et al. 2004.  However, there is an ongoing debate concerning the importance of such an effect (Ferrarese et al. 2000, Mochejska et al. 2001).

In sum, numerous groups are developing methods to identify pseudo-planets in the Kepler database.  Given the large sample and sizable investment of time required to confirm a planet candidate: such efforts are important (e.g., Bryson et al. 2013).  Data from the Kepler mission have helped advance our understanding of stars and their orbiting planets, and more is yet to come.  If you’d like to help the Kepler team identify planets around other stars: join the Planet Hunters citizen science project.

The Bryson et al. 2013 findings have been submitted to PASP for peer review, and a preprint is available on arXiv.  The coauthors on the study are J. Jenkins, R. Gilliland, J. Twicken, B. Clarke, J. Rowe, D. Caldwell, N. Batalha, F. Mullally, M. Haas, and P. Tenenbaum.  The interested reader desiring additional information will find the following pertinent:  Adams et al. 2012Collier Cameron 2012 (e.g., for other scenarios that can mimic the lightcurve of a transiting-planet), “Strange New Worlds: The Search for Alien Planets and Life beyond Our Solar System” by Ray Jayawardhana, “Distant Wanderers: The Search for Planets Beyond the Solar System” by Bruce Dorminey.  For discussion on how light from unresolved sources affects the cosmic distance scale see Mochejska et al. 2004 (and for the opposite point of view, and subsequent rebuttal: Ferrarese et al. 2000Mochejska et al. 2001).

WISE Nabs the Closest Brown Dwarfs Yet Discovered

WISE J104915.57-531906 from NASA's WISE survey (centered) and resolved to should its binary nature by the Gemini Observatory (inset). (Credit: NASA/JPL/Gemini Observatory/AURA/NSF).

We now know our stellar neighbors just a little better, and a new discovery may help tell us how common brown dwarfs are in our region of the galaxy. Early this week, researchers at Pennsylvania State University announced the discovery of a binary brown dwarf system. With a parallax measurement of just under 0.5”, this pair is only 6.5 light years distant making it the third closest system to our own and the closest example of the sub-stellar class of objects known as brown dwarfs yet discovered.

Named WISE J104915.57-531906, the system was identified by analysis of multi-epoch astrometry carried out by NASA’s Wide-field Infrared Survey Explorer (WISE). The discovery was made by associate professor of astronomy and astrophysics at Penn State’s Center for Exoplanets and Habitable Worlds Kevin Luhman. The system’s binary nature and follow up observations were confirmed by spectroscopic analysis carried out by the Gemini Observatory’s Multi-Object Spectrographs (GMOS).

Animation showing the motion of WISE 1049-5319 across the All-WISE, 2MASS & Sloan Digital Sky Survyies from 1978 to 2010. (Credit: NASA/STScI/JPL/IPAC/University of Massachusetts.)
Animation showing the motion of WISE 1049-5319 across the All-WISE, 2MASS & Sloan Digital Sky Surveys from 1978 to 2010. (Credit: NASA/STScI/JPL/IPAC/University of Massachusetts.)

This find is also the closest stellar system discovered to our own solar system since the discovery of Barnard’s star by astronomer E.E. Barnard in 1916. Incidentally, Barnard’s star was the center of many spurious and controversial claims of extrasolar planet discoveries in the mid-20th century. Barnard’s star is 6 light years distant, and the closest star system to our own is Alpha Centauri measured to be 4.4 light years distant in 1839. In 1915, the Alpha Centauri system was determined to have a faint companion now known as Proxima Centauri at 4.2 light years distant. The Alpha Centauri system also made headlines last year with the discovery of the closest known exoplanet to Earth. WISE 1506+7027 is the closest brown dwarf to our solar system yet discovered. This also breaks the extended the All-WISE survey’s own previous record of the closest brown dwarf released in 2011, WISE 1506+7027 at 11.1 light years distant.

When looking for nearby stellar suspects, astronomers search for stars displaying a high proper motion across the sky. The very first parallax measurement of 11 light years distant was obtained by Friedrich Bessel for the star 61 Cygni in 1838. 61 Cygni was known as “Piazzi’s Flying Star” for its high 4.2” proper motion across the sky. To giving you an idea of just how tiny an arc second is, a Full Moon is about 1800” in diameter. With a proper motion of just under 3” per year, it would take WISE 1049-5319 over 600 years to cross the same apparent distance in the sky as viewed from the Earth!

An artist's conception of looking back at Sol from the binary brown dwarf system WISE 1049-5319, 6.5 light years distant. (Credit: Janella Williams, Penn State University).
An artist’s conception of looking back at Sol from the binary brown dwarf system WISE 1049-5319, 6.5 light years distant. (Credit: Janella Williams, Penn State University).

“Based on how this star system was moving in images from the WISE survey, I was able to extrapolate back in time to predict where it should have been located in older surveys,” stated Luhman. And sure enough, the brown dwarf was there in the Deep Near-Infrared Survey of the Southern Sky (DENIS), the Two Micron All-Sky Survey (2MASS) and the Sloan Digitized Sky Survey (SDSS) spanning a period from 1978 to 1999. Interestingly, Luhman also points out in the original paper that the pair’s close proximity to the star rich region of galactic plane in the constellation Vela deep in the southern hemisphere sky is most likely the reason why they were missed in previous surveys.

The discovery of the binary nature of the pair was also “an unexpected bonus,” Luhman said. “The sharp images from Gemini also revealed that the object actually was not just one, but a pair of brown dwarfs orbiting each other.” This find of a second brown dwarf companion will go a long way towards pinning down the mass of the objects. With an apparent separation of 1.5”, the physical separation of the pair is 3 astronomical units (1 AU= the Earth-Sun distance) in a 25 year orbit.

Size comparison of stellar vs substellar objects. (Credit: NASA/JPL-Caltech/UCB).
Size comparison of stellar vs substellar objects. (Credit: NASA/JPL-Caltech/UCB).

Brown dwarfs are sub-stellar objects with masses too low (below ~75 Jupiter masses) to sustain the traditional fusion of hydrogen into helium via the full proton-proton chain process. Instead, objects over 13 Jupiter masses begin the first portion of the process by generating heat via deuterium fusion. Brown dwarfs are thus only visible in the infrared, and run a spectral class of M (hottest), L, T, and Y (coolest). Interestingly, WISE 1049-5319 is suspected to be on the transition line between an L and T-class brown dwarf. To date, over 600 L-type brown dwarfs have been identified, primarily by the aforementioned SDSS, 2MASS & DENIS infrared surveys.

General location of WISE 1049-5319 in the constellation Vela. Note its proximity to the galactic plane. (Created by the author using Starry Night).
General location of WISE 1049-5319 in the constellation Vela. Note its proximity to the galactic plane. (Created by the author using Starry Night).

This discovery and others like it may go a long ways towards telling us how common brown dwarfs are in our region of the galaxy. Faint and hard to detect, we’re just now getting a sampling thanks to surveys such as WISE and 2MASS. The James Webb Space Telescope will do work in the infrared as well, possibly extending these results. Interestingly, Luhman notes in an interview with Universe Today that the potential still exists for the  discovery of a brown dwarf closer to our solar system than Alpha Centauri. “No published study of the data from WISE or any other survey has ruled out this possibility… WISE is much more capable of doing this than any previous survey, but the necessary analysis would be fairly complex and time consuming. It’s easier to find something than to rule out its existence.” Said Luhman. Note that we’re talking a nearby brown dwarf that isn’t gravitationally bound to the Sun… this discussion is separate from such hypothetical solar companions as Nemesis and Tyche…and Nibiru conspiracy theorists need not apply!

The WISE 1049-5319 system is also a prime target in the search for nearby extra-solar planets.  “Because brown dwarfs have very low masses, they exhibit larger reflex motions due to orbiting planets than more massive stars, and those larger reflex motions will be easier to detect.” Luhman told Universe Today. Said radial surveys for exoplanets would also be carried out in the IR band, and brown dwarfs also have the added bonus of not swamping out unseen planetary companions in the visible spectrum.

Congrats to Mr. Luhman and the Center for Exoplanets and Habitable Worlds on the discovery. You just never know what’s lying around in your own stellar backyard!

Read this original discovery paper here.

12 Star Party Secret Weapons

Awaiting sunset... (Photo by author).

We’ve all been there. Well OK, all public star party telescope operators have been there. You’re set up and you’ve got a stunning view of Saturn centered in the field of view. But then the first member of the viewing public takes a quick glance and steps back from the eyepiece, stating “yeah, I saw that through the last four ‘scopes…”

What do you do when every telescope down the row is aimed at the same object? Or worse yet, what do you aim at when there is no Moon or bright planets above the horizon? Every seasoned telescope operator has a quick repertoire of secret favorites, little known but sure-fire crowd pleasers.  Sure, Saturn is awesome and you should see it through a telescope… but it’s a big universe out there. 

I’ve even seen clubs assign objects to individual telescopes to avoid having everyone point at the same thing, but this method is, well, boring for the scope operators themselves.  Most backyard astronomers can simply look at a tube pointed at Orion and know the neighboring telescope is aimed at the Orion Nebula. What follows is our very own highly subjective (but tested in the field!) list of secret star party faves. Yes, it is mid-northern latitude-centric. It also covers a span of objects of all types, as well as a handy information chart of where in the sky to find ‘em and a few surprises. We also realize that many public star parties often take place downtown under light polluted skies, so a majority of these are brighter objects.  Don’t see your favorite? Drop us a line and let us know!

12. The Double Cluster:  Straddling the border of the constellations Perseus and Cassiopeia, this pair of clusters is a fine sight at low power. The technical designation of the pair is NGC 884 and NGC 869 respectively and the clusters sit about 7000 light years distant.  You can just see the pair with the naked eye under suburban skies.

The location of Herschel 3945 in Canis Major. (Created by Author in Starry Night).
The location of Herschel 3945 in Canis Major. (Created by Author in Starry Night).

11. Herschel 3945:  A popular summer-to-fall star party target is the colored double star Albireo is the constellation Cygnus. But did you know there’s a similar target visible early in the year as well? I call Herschel 3945 the “winter Albireo” for just this reason. This 27” split pair of sapphire and orange stars offers a great contrast sure to bring out the “ohs” and “ahs.” Continue reading “12 Star Party Secret Weapons”

Greek Observatory Probes Ancient Star

An image of the enclosure of the new 2.3-m Aristarchos telescope, sited at Helmos Observatory. Credit: P. Boumis, National Observatory of Athens.

Some 2,500 years ago, a Greek astronomer named Aristarchus certainly made some very correct assumptions when he postulated the Sun to be at the center of our known Universe and that the Earth revolved around it. Through this, he also knew that the stars were incredibly far away and now his namesake telescope, the new 2.3 meter Aristarchos, is taking that distant look from the Helmos Observatory, high atop the Peloponnese Mountains in Greece. Its purpose is to determine the distance and evolution of a mysterious star system – one which is encased in an ethereal nebula.

While looking at the demise of a possible binary star system, researchers Panos Boumis of the National Observatory of Athens and John Meaburn of the University of Manchester, set out to photograph this enigmatic study with the narrowband imaging camera onboard the Aristarchos telescope. Their target designation is planetary nebula KjPn8, and it was originally discovered during the 1950’s Palomar Sky Survey. What makes it out of the ordinary is two huge lobes, measuring a quarter of a degree across, which surround the system. This artifact was researched by Mexican astronomers at the San Pedro Martir Observatory some four decades after its revelation, but it wasn’t until the year 2000 that the Hubble Space Telescope uncovered its central star.

An image of the giant lobes of the planetary nebula KjPn 8 in the light of the emission lines of hydrogen and singly ionised nitrogen, obtained with the narrowband camera on the new 2.3-m Aristarchos telescope. Detailed measurements of the lobes have allowed the determination of their expansion velocity, distance and ages. The results indicate their origin in a remarkable eruptive binary system. Credit: P. Boumis / J. Meaburn
An image of the giant lobes of the planetary nebula KjPn 8 in the light of the emission lines of hydrogen and singly ionised nitrogen, obtained with the narrowband camera on the new 2.3-m Aristarchos telescope. Detailed measurements of the lobes have allowed the determination of their expansion velocity, distance and ages. The results indicate their origin in a remarkable eruptive binary system. Credit: P. Boumis / J. Meaburn

Dr. Boumis and Prof. Meaburn began to study this ancient cosmic artifact, concentrating on measuring the expansion with utmost accuracy. Through their work, they were unable to uncover the system’s distance and trace the history of the lobes through time. What they discovered was KjPn8 is roughly 6,000 light years away and the lobes of material have three epochs: 3200, 7200 and 50,000 years. According to the research team: “The inner lobe of material is expanding at 334 km per second, suggesting it originates in an Intermediate Luminosity Optical Transient (ILOT) event. ILOTs are caused by the transfer of material from a massive star to its less massive companion, in turn creating jets that flow in different directions. We believe that the core of KjPn8 is therefore a binary system, where every so often ILOT events lead to the ejection of material at high speed.”

It is certainly a triumph for the Aristachos Telescope and the new Greek facility. Dr. Bournis is quite proud of the conclusive results gathered by telescope – especially when the object in question cries out for more research. He comments: “Greece is one of the global birthplaces of astronomy, so it is fitting that research into the wider universe continues in the 21st century. With the new telescope we expect to contribute to that global effort for many years to come.”

Original Story Source: Royal Astronomical Society News Release.

Nearby Ancient Star is Almost as Old as the Universe

A billion years after the big bang, hydrogen atoms were mysteriously torn apart into a soup of ions. Credit: NASA/ESA/A. Felid (STScI)).

A metal-poor star located merely 190 light-years from the Sun is 14.46+-0.80 billion years old, which implies that the star is nearly as old as the Universe!  Those results emerged from a new study led by Howard Bond.  Such metal-poor stars are (super) important to astronomers because they set an independent lower limit for the age of the Universe, which can be used to corroborate age estimates inferred by other means.

In the past, analyses of globular clusters and the Hubble constant (expansion rate of the Universe) yielded vastly different ages for the Universe, and were offset by billions of years! Hence the importance of the star (designated HD 140283) studied by Bond and his coauthors.

“Within the errors, the age of HD 140283 does not conflict with the age of the Universe, 13.77 ± 0.06 billion years, based on the microwave background and Hubble constant, but it must have formed soon after the big bang.” the team noted.

Metal-poor stars can be used to constrain the age of the Universe because metal-content is typically a proxy for age. Heavier metals are generally formed in supernova explosions, which pollute the surrounding interstellar medium. Stars subsequently born from that medium are more enriched with metals than their predecessors, with each successive generation becoming increasingly enriched.  Indeed, HD 140283 exhibits less than 1% the iron content of the Sun, which provides an indication of its sizable age.

HD 140283 had been used previously to constrain the age of the Universe, but uncertainties tied to its estimated distance (at that time) made the age determination somewhat imprecise.  The team therefore decided to obtain a new and improved distance for HD 140283 using the Hubble Space Telescope (HST), namely via the trigonometric parallax approach. The distance uncertainty for HD 140283 was significantly reduced by comparison to existing estimates, thus resulting in a more precise age estimate for the star.

Age estimate for HD 140283 is 14.46+-0.80 Gyr.  On the y-axis is the star's pseudo-luminosity, on the x-axis its temperature.  An evolutionary track was applied to infer the age (credit: adapted by D. Majaess from Fig 1 in Bond et al. 2013, arXiv).
HD 140283 is estimated to be 14.46+-0.80 billion years old. On the y-axis is the star’s pseudo-luminosity, on the x-axis its temperature. Computed evolutionary tracks (solid lines ranging from 13.4 to 14.4 billion years) were applied to infer the age (image credit: adapted from Fig 1 in Bond et al. 2013 by D. Majaess, arXiv).

The team applied the latest evolutionary tracks (basically, computer models that trace a star’s luminosity and temperature evolution as a function of time) to HD 140283 and derived an age of 14.46+-0.80 billion years (see figure above).  Yet the associated uncertainty could be further mitigated by increasing the sample size of (very) metal-poor stars with precise distances, in concert with the unending task of improving computer models employed to delineate a star’s evolutionary track.  An average computed from that sample would provide a firm lower-limit for the age of the Universe.  The reliability of the age determined is likewise contingent on accurately determining the sample’s metal content.  However, we may not have to wait long, as Don VandenBerg (UVic) kindly relayed to Universe Today to expect, “an expanded article on HD 140283, and the other [similar] targets for which we have improved parallaxes [distances].”

As noted at the outset, analyses of globular clusters and the Hubble constant yielded vastly different ages for the Universe.  Hence the motivation for the Bond et al. 2013 study, which aimed to determine an age for the metal-poor star HD 140283 that could be compared with existing age estimates for the Universe.  The discrepant ages stemmed partly from uncertainties in the cosmic distance scale, as the determination of the Hubble constant relied on establishing (accurate) distances to galaxies.  Historical estimates for the Hubble constant ranged from 50-100 km/s/Mpc, which defines an age spread for the Universe of ~10 billion years.

Age estimates for globular clusters were previously larger than that inferred for the Age of the Universe from the Hubble constant (NASA, R. Gilliland (STScI), D. Malin (AAO))
Age estimates for the Universe as inferred from globular clusters and the Hubble constant were previously in significant disagreement (image credit: NASA, R. Gilliland (STScI), D. Malin (AAO)).

The aforementioned spread in Hubble constant estimates was certainly unsatisfactory, and astronomers recognized that reliable results were needed.  One of the key objectives envisioned for HST was to reduce uncertainties associated with the Hubble constant to <10%, thus providing an improved estimate for the age of the Universe. Present estimates for the Hubble constant, as tied to HST data, appear to span a smaller range (64-75 km/s/Mpc), with the mean implying an age near ~14 billion years.

Determining a reliable age for stars in globular clusters is likewise contingent on the availability of a reliable distance, and the team notes that “it is still unclear whether or not globular cluster ages are compatible with the age of the Universe [predicted from the Hubble constant and other means].” Globular clusters set a lower limit to the age of the Universe, and their age should be smaller than that inferred from the Hubble constant (& cosmological parameters).

In sum, the study reaffirms that there are old stars roaming the solar neighborhood which can be used to constrain the age of the Universe (~14 billion years). The Sun, by comparison, is ~4.5 billion years old.

The team’s findings will appear in the Astrophysical Journal Letters, and a preprint is available on arXiv.  The coauthors on the study are E. Nelan, D. VandenBerg, G. Schaefer, and D. Harmer.  The interested reader desiring complete information will find the following works pertinent: Pont et al. 1998, VandenBerg 2000, Freedman & Madore (2010), Tammann & Reindl 2012.

Bright Jets Blast Out from a Newborn Star

A young star is spotted firing jets of material out into space (ESA/Hubble & NASA. Acknowledgement: Gilles Chapdelaine)

Like very young humans, very young stars also tend to make a big mess out of the stuff around them — except in the case of stars it’s not crayon on the walls and Legos on the floor (ouch!) but rather huge blasts of superheated material that are launched from their poles far out into space.

The image above, acquired by the Hubble Space Telescope, shows one of these young stars caught in the act.

HL Tau is a relatively newborn star, formed “only” within the past several hundred thousand years. During that time it has scooped up vast amounts of gas and dust from the area around itself, forming a disc of hot, accelerated material that surrounds it. While most of this material eventually falls into the star, increasing its mass, some of it gets caught up in the star’s complex, rotating magnetic fields and is thrown out into space as high-speed jets.

As these jets plow thorough surrounding interstellar space they ram into nearby clouds of molecular gas, ionizing the material within them and causing them to glow brightly. These “shocks” are known as Herbig-Haro objects, after researchers George Herbig and Guillermo Haro who each discovered them independently in the early 1950s.

Detail of HH 151's jet
Detail of HH 151’s jet

In this Hubble image HH 151 is visible as a multiple-lobed cone of material fired away from HL Tau, with the leftover glows from previous outbursts dimly illuminating the rest of the scene.

The material within these jets can reach speeds of several hundred to a thousand kilometers a second. They can last anywhere from a few years to a few thousand years.

HH 151 is embedded within the larger star-forming region LDN 1551, located about 450 light-years away in the constellation Taurus. LDN 1551 is a stellar nursery full of dust, dark nebulae, newborn stars… and Herbig-Haro objects like HH 151.

(Hey, if baby stars are going to make a mess at least they can do it in the nursery.)

Read more on the ESA/Hubble news release here.

A Cosmic Snake for Chinese New Year

Barnard 72 - the "Snake Nebula" (Wikisky.org)

Gong Hey Fat Choy! Today marks the beginning of the Chinese New Year and what better way to celebrate the Year of the Black Snake than with a look at an enormous shadowy cosmic serpent, the Snake Nebula!

Also known as Barnard 72, the Snake Nebula is a meandering lane of dark dust located about 650 light-years away in the constellation Ophiuchus. Several light-years long, its opaque dust blocks our view of stars within the central bulge of the galaxy… but also reveals its presence since that region of the sky is literally filled with stars.

The Snake Nebula is part of the larger Dark Horse Nebula.

The bright star seen in the image just below the snake’s middle (looks like it may have just had dinner!) is HD 157398, a giant orange star 538 light-years from Earth. Here it shines brightly, but in the sky its visible magnitude is 6.67 — just a bit dimmer than what can be seen with the naked eye under the darkest skies.

Image via Wikisky.org.

Earthlike Exoplanets Are All Around Us

Artist's impression of a Jupiter-sized exoplanet orbiting an M-dwarf star

Artist’s impression of a rocky planet orbiting a red dwarf. Credit: David A. Aguilar (CfA)

We may literally be surrounded by potentially habitable exoplanets, according to new research by a team from the Harvard-Smithsonian Center for Astrophysics.

Using data gathered by NASA’s exoplanet-hunting Kepler spacecraft, the CfA researchers discovered that many red dwarf stars harbor planets, and some of those planets are rocky, Earth-sized worlds. Considering that red dwarfs, albeit optically dim, are the most abundant type of stars in our galaxy, this means that even a small percentage of them being host to Earthlike exoplanets puts the total number of potentially habitable worlds very high — and some of them could be right next door.

“We thought we would have to search vast distances to find an Earth-like planet,” said CfA astronomer and the paper’s lead author Courtney Dressing. “Now we realize another Earth is probably in our own backyard, waiting to be spotted.”

And our own backyard, in cosmic terms, could mean a mere 13 light-years away.

Our solar system is surrounded by red dwarfs. You can’t see them in the night sky because they are much too dim — less than a thousandth the brightness of the Sun. But they make up 75% of the stars in the local neighborhood, and based on the Kepler data the CfA team estimates that 6% of those red dwarfs likely have an Earth-sized planet in orbit around them.

And with at least 75 billion red dwarfs scattered across the galaxy… well, you do the math.*

“We now know the rate of occurrence of habitable planets around the most common stars in our galaxy,” said co-author David Charbonneau (CfA). “That rate implies that it will be significantly easier to search for life beyond the solar system than we previously thought.”

Red-Dwarfs

A visualization of the “unseen” red dwarfs in the night sky. Credit: D. Aguilar & C. Pulliam (CfA) See original here.

The conditions on a planet orbiting a red dwarf wouldn’t be exactly like Earth, of course. The planet would have to orbit rather closely to its star to be within its habitable zone, and would have to have a reasonably thick atmosphere to regulate heat and protect it from stellar outbursts. But one benefit to orbiting a red dwarf is that they have very long life spans — potentially longer than the current age of the Universe! So a habitable world around a red dwarf would literally have billions of years for life to evolve, thrive and develop on it.

“We might find an Earth that’s 10 billion years old,” Charbonneau said.

The team’s findings were presented today, Feb. 6, by Dressing during a press conference at the Harvard-Smithsonian Center for Astrophysics in Cambridge, MA. The results will be published in The Astrophysical Journal. (Added 2/7/13: here’s the video of the press conference.)

press_conference_d+c2013.pptxCfA astronomers identified 95 planetary candidates circling red dwarf stars. Of those, three orbit within the habitable zone (marked in green) – the distance at which they should be warm enough to host liquid water on the surface. Those three planetary candidates (marked with blue dots) are 0.9, 1.4, and 1.7 times the size of Earth. Credit: C. Dressing (CfA)

Read more on the CfA news release here.

*Ok, I did the math. That’s 4,500,000,000 Earth-like exoplanets around red dwarfs alone!

We Are Made of Stardust

This brief quote by the late Carl Sagan is wonderfully illustrated in the beautiful and poignant short film “Stardust,” directed by Mischa Rozema of Amsterdam-based media company PostPanic. Using actual images from space exploration as well as CGI modeling, Stardust reminds us that everything we and the world around us are made of was created inside stars… and that, one day, our home star will once again free all that “stuff” back out into the Universe.

The film was made in memory of talented Dutch designer Arjan Groot, who died of cancer in July 2011 at the age of 39.

“I wanted to show the universe as a beautiful but also destructive place. It’s somewhere we all have to find our place within. As a director, making Stardust was a very personal experience but it’s not intended to be a personal film and I would want people to attach their own meanings to the film so that they can also find comfort based on their own histories and lives.”
– Mischa Rozema, director

A truly stunning tribute.

See more about this on PostPanic’s Vimeo page. (Credits after the jump.)

Credits:
A PostPanic Production
Written & directed by Mischa Rozema
Produced by Jules Tervoort
VFX Supervisor: Ivor Goldberg
Associate VFX Supervisor: Chris Staves
Senior digital artists: Matthijs Joor, Jeroen Aerts
Digital artists: Marti Pujol, Silke Finger, Mariusz Kolodziejczak, Dieuwer Feldbrugge, Cara To, Jurriën Boogert
Camera & edit: Mischa Rozema
Production: Ania Markham, Annejes van Liempd
Audio by Pivot Audio , Guy Amitai
Featuring “Helio” by Ruben Samama
Copyright 2013 Post Panic BV, All rights reserved

In the grand scheme of the universe, nothing is ever wasted and it finds comfort in us all essentially being Stardust ourselves. Voyager represents the memories of our loved ones and lives that will never disappear.