Posted on by David Dickinson

Seeing the Red of ‘La Superba,’ a Magnificent Springtime Carbon Star

Finder chart for La Superba. (Photo by Author).

The Universe can be a very gray place. But this week, we’ll look at a fine example of a class of objects that defies this trend.

Many first time stargazers are surprised when the Trifid or the Orion Nebula fails to exhibit the bright splashy colors seen in Hubble photos. The fault lies not with the Universe, but in our very own eyes.

This is because the light sensitive fovea of our eye has two different types of photoreceptor cells; rods and cones. These act like slow and fast speed film (for those of us old enough to remember actual film!) Under low light conditions, objects have a very black-and-white appearance. It’s only with an increase in brightness that the color receptors in the cone cells of our eye begin to kick in.

One class of stars can induce this effect. They’re known as carbon stars.

A fine example of just such an object rides high in the late spring sky for northern hemisphere observers. This is the variable star Y Canum Venaticorum, also abbreviated as Y CVn or “La Superba” (The magnificent). This name was given to the star by Father Angelo Secchi in the mid-19th century. It is one of the reddest stars in the sky.

Astronomers gauge the “redness” of a star by measuring its magnitude contrast through a blue and visible (green peaking) filters. This is what is known as its B-V index, and the higher the value, the redder the star.

La Superba has a B-V value of +2.5. For contrast, the familiar orange-red stars Antares and Betelgeuse have a B-V value of +1.83 & +1.85, respectively.

Some other classic carbon stars and their B-V values are;

TX Piscium: +2.5

Herschel’s Garnet Star: +2.35

V Hydrae: +4.5

R Leporis (Hind’s Crimson Star): +2.7

Many of these are also variable stars, and they can appear redder visually near their minimum brightness. In the case of La Superba, it ranges from magnitude +4.8 to +6.3 over a span of 160 days, with a longer super-imposed cycle of about 6 years. We’re just coming off of a peak cycle in late May 2013, and La Superba is easy to spot with binoculars about a third of the way between the brilliant double star Cor Caroli (visited by the Enterprise in the Star Trek: The Next Generation Episode “Allegiance”) and Delta Ursa Majoris.

I’ve shown off carbon stars such as La Superba and Hind’s Crimson Star at public star parties to great effect. They can be an excellent star party “secret weapon” when every other ‘scope down the line is aimed at the Orion nebula.

For a faint constellation, Canes Venatici has lots to offer. One of the best globular clusters in the sky M3 can be found within its borders, as can a handful of decent galaxies. La Superba lies in a rather empty region of the constellation high above the galactic plane. In fact, an area about 15° degrees north of location in the adjoining constellation Ursa Major was picked for the famous Hubble Deep Field image for this very reason.

Burnham’s Celestial Handbook describes La Superba as “one of the reddest of all the naked eye stars, (with) a truly odd and vivid tint in large telescopes.” Astronomer Agnes Clerke described its appearance in 1905 as an “extraordinary vivacity of prismatic rays, separated into dazzling zones of red, yellow, and green by broad spaces of profound obscurity.”  (Note: the “spaces” referred to gaps in its spectra).

Through the telescope at low power, we see La Superba as an orange-red ember with shades of white. It’s an easy catch with binoculars, and one of the very few carbon stars that is visible to the naked eye under dark skies. We’d judge that only TX Piscium rivals it in brightness, and only V Hydrae and Hinds appear ruddier. I always like to ask first time observers of colored stars what they see… human eye-brain perception can vary greatly!

The coordinates of La Superba are:

Right Ascension: 12 Hours 45’ 08”

Declination: +45 26’ 25”

La Superba is about 600-800 light years distant. Physically, it is a massive star at three times the mass of our Sun. It’s also a monster in terms of diameter, at four astronomical units in size.  If you placed it within our solar system, it would swallow up the orbits of the interior planets out to Mars!

La Superba is thus much less dense than our own Sun, and at a surface temperature of about 2,800K, relatively cool. It is also the brightest “J-type” carbon star in the sky, a rare sub-type characterized by the presence of the isotope carbon-13 in its atmosphere.  A carbon star is a sun near the end of its life, accumulating carbon compounds in its outer atmosphere as it fuses heavier elements in one last “hurrah” before shedding its outer layers and forming a white dwarf embedded inside a planetary nebula. Carbon stars are much brighter in the infrared, and we see the very tail end of this absorption in the visible red end of the spectrum. In fact, La Superba is a full 9 magnitudes (nearly 4,000 times) brighter in the near-infrared than in the ultraviolet!

All amazing facts to ponder as we view a star near the end of its career, seeding the cosmos with the very element that makes life possible. Next time you’re out observing, be sure to go “into the red” and check out the fine carbon star!

 

Posted on by Dan Majaess

Astronomers Hint that our Sun won’t Terminate as the Typical Planetary Nebula

An artist's illustration of a planetary nebula engulfing its orbiting planets (image credit: Regulus36/deviantart, adjusted by DM to mitigate compression effects).

Textbooks often cite that planetary nebulae (PNe, plural) represent an endstate for lower-mass single stars. But conversely, recent research suggests that most PNe stem from binary systems. The lowest mass star theorized to form the typical PN is near 1 solar mass, and thus without a companion the Sun may not surpass the mass limit required to generate the hot glowing (ionized) nebula typically tied to PNe.  New research continues to question our original understanding of how the Sun’s life may end.

A new study spearheaded by G. Jacoby aimed in part to test that binary hypothesis by searching for PNe in star clusters occupying M31.  The team remarked that, “while the binary interaction model explains some of the anomalies associated with the observed planetary nebula population, this theory awaits final confirmation.”

“The traditional theory states that the progenitors of PNe are low- to intermediate-mass single stars … However, this theory does not provide a natural explanation for the non-spherical morphologies observed for the great majority of PNe, nor their low rate of formation. For these and other inconsistencies, a new paradigm has been developed, wherein most PNe are shaped via the interaction … with a binary companion,” said Jacoby et al. 2013.
Continue reading “Astronomers Hint that our Sun won’t Terminate as the Typical Planetary Nebula”

Posted on by Tammy Plotner

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.

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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.

Posted on by David Dickinson

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.

Posted on by David Dickinson

Pulsar Jackpot Scours Old Data for New Discoveries

Space Shuttle Atlantis passes behind the Parkes radio telescope after final undocking from the International Space Station in July 2011. (Image Copyright: John Sarkissian; used with permission).

Chalk another one up for Citizen Science.  Earlier this month, researchers announced the discovery of 24 new pulsars. To date, thousands of pulsars have been discovered, but what’s truly fascinating about this month’s discovery is that came from culling through old data using a new method.

A pulsar is a dense, highly magnetized, swiftly rotating remnant of a supernova explosion. Pulsars where first discovered by Jocelyn Bell Burnell and Antony Hewish in 1967. The discovery of a precisely timed radio beacon initially suggested to some that they were the product of an artificial intelligence. In fact, for a very brief time, pulsars were known as LGM’s, for “Little Green Men.” Today, we know that pulsars are the product of the natural death of massive stars.

The data set used for the discovery comes from the Parkes 64-metre radio observatory based out of New South Wales, Australia. The installation was the first to receive telemetry from the Apollo 11 astronauts on the Moon and was made famous in the movie The Dish.  The Parkes Multi-Beam Pulsar Survey (PMPS) was conducted in the late 1990’s, making thousands of 35-minute recordings across the plane of the Milky Way galaxy. This survey turned up over 800 pulsars and generated 4 terabytes of data. (Just think of how large 4 terabytes was in the 90’s!)

Artist's conception of a pulsar. (Credit: NASA/GSFC).
Artist’s conception of a pulsar. (Credit: NASA/GSFC).

The nature of these discoveries presented theoretical astrophysicists with a dilemma. Namely, the number of short period and binary pulsars was lower than expected. Clearly, there were more pulsars in the data waiting to be found.

Enter Citizen Science. Using a program known as Einstein@Home, researchers were able to sift though the recordings using innovative modeling techniques to tease out 24 new pulsars from the data.

“The method… is only possible with the computing resources provided by Einstein@Home” Benjamin Knispel of the Max Planck Institute for Gravitational Physics told the MIT Technology Review in a recent interview. The study utilized over 17,000 CPU core years to complete.

Einstein@Home screenshot. (Credit: LIGO Consortium).
Einstein@Home screenshot. (Credit: LIGO Consortium).

Einstein@Home is a program uniquely adapted to accomplish this feat. Begun in 2005, Einstein@Home is a distributed computing project which utilizes computing power while machines are idling to search through downloaded data packets. Similar to the original distributed computing program SETI@Home which searches for extraterrestrial signals, Einstein@Home culls through data from the LIGO (Laser Interferometer Gravitational Wave Observatory) looking for gravity waves. In 2009, the Einstein@Home survey was expanded to include radio astronomy data from the Arecibo radio telescope and later the Parkes observatory.

Among the discoveries were some rare finds. For example, PSR J1748-3009 Has the highest known dispersion measure of any millisecond pulsar (The dispersion measure is the density of free electrons observed moving towards the viewer). Another find, J1750-2531 is thought to belong to a class of intermediate-mass binary pulsars. 6 of the 24 pulsars discovered were part of binary systems.

These discoveries also have implications for the ongoing hunt for gravity waves by such projects as LIGO. Specifically, a through census of binary pulsars in the galaxy will give scientists a model for the predicted rate of binary pulsar mergers. Unlike radio surveys, LIGO seeks to detect these events via the copious amount of gravity waves such mergers should generate. Begun in 2002, LIGO consists of two gravity wave observatories, one in Hanford Washington and one in Livingston Louisiana just outside of Baton Rouge. Each LIGO detector consists of two 2 kilometre Fabry-Pérot arms in an “L” configuration which allow for ultra-precise measurements of a 200 watt laser beam shot through them.  Two detectors are required to pin-point the direction of an incoming gravity wave on the celestial sphere. You can see the orientation of the “L’s” on the display on the Einstein@Home screensaver. Two geographically separate detectors are also required to rule out local interference. A gravity wave from a galactic source would ripple straight through the Earth.

Arial view of LIGO Livingston. (Image credit: The LIGO Scientific Collaboration).
Arial view of LIGO Livingston. (Image credit: The LIGO Scientific Collaboration).

Such a movement would be tiny, on the order of 1/1,000th the diameter of a proton, unnoticed by all except the LIGO detectors. To date, LIGO has yet to detect gravity waves, although there have been some false alarms. Scientists regularly interject test signals into the data to see if system catches them. The lack of detection of gravity waves by LIGO has put some constraints on certain events. For example, LIGO reported a non-detection of gravity waves during the February 2007 short gamma-ray burst event GRB 070201. The event arrived from the direction of the Andromeda Galaxy, and thus was thought to have been relatively nearby in the universe. Such bursts are thought to be caused by neutron star and/or black holes mergers. The lack of detection by LIGO suggests a more distant event. LIGO should be able to detect a gravitational wave event out to 70 million light years, and Advanced LIGO (AdLIGO) is set to go online in 2014 and will increase its sensitivity tenfold.

The control room at LIGO Livingston. (Photo by Author).
The control room at LIGO Livingston. (Photo by Author).

Knowledge of where these potential pulsar mergers are by such discoveries as the Parkes radio survey will also give LIGO researchers clues of targets to focus on. “The search for pulsars isn’t easy, especially for these “quiet” ones that aren’t doing the equivalent of “screaming” for our attention,” Says LIGO Livingston Data Analysis and EPO Scientist Amber Stuver. The LIGO consortium developed the data analysis technique used by Einstein@Home. The direct detection of gravitational waves by LIGO or AdLIGO would be an announcement perhaps on par with CERN’s discovery of the Higgs Boson last year. This would also open up a whole new field of gravitational wave astronomy and perhaps give new stimulus to the European Space Agencies’ proposed Laser Interferometer Space Antenna (LISA) space-based gravity wave detector. Congrats to the team at Parkes on their discovery… perhaps we’ll have the first gravity wave detection announcement out of LIGO as well in years to come!

-Read the original paper on the discovery of 24 new pulsars here.

-Amber Stuver blogs about Einstein@Home & the spin-off applications of gravity wave technology at Living LIGO.

-Parkes radio telescope image is copyrighted and used with the permission of CSIRO Operations Scientist John Sarkissian.

-For a fascinating read on the hunt for gravity waves, check out Gravity’s Ghost.

 

Posted on by Dan Majaess

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.

Posted on by Jason Major

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.

Posted on by Tammy Plotner

Portrait Of NGC 5189: New Light On An Old Planetary Nebula

Composite Image of NGC 5189 Courtesy of Robert Gendler

Stretching across three light years of space and located about 3,000 light years away in the direction of the constellation of Musca, an incredible and rather understudied planetary nebula awaits a new hand to bring out new light. While most planetary nebula have a rather normal, bloated star look, NGC 5189 shows an extraordinary amount of loops and curls not normally seen in objects of its type. Just what is going on here?

This incredibly detailed image comes from the one and only Robert Gendler and was assembled from three separate data sources. The detail for the nebula is from Hubble Space Telescope data, the background starfield from the Gemini Observatory/AURA and the color data from his own equipment. Here we see fanciful gas clouds with thick clumps decorating them. Intense radiation and gas streams from the central dying star in waves, fashioning out hollows and caves in the enveloping clouds. While these clumps in the clouds may appear as wispy details, each serves as a reminder of just how vast space can be… for each an every one of them is about the same size as our Solar System.

“The complex morphology of this PN is puzzling and has not been studied in detailed so far. Our investigation reveals the presence of a new dense and cold infrared torus (alongside the optical one) which probably generated one of the two optically seen bipolar outflows and which might be responsible for the twisted appearance of the optical torus via an interaction process.” says L. Sabin (et al). ” The high-resolution MES-AAT spectra clearly show the presence of filamentary and knotty structures as well as three expanding bubbles. Our findings therefore suggest that NGC 5189 is a quadrupolar nebula with multiple sets of symmetrical condensations in which the interaction of outflows has determined its complex morphology.”

And just as incredibly large as some things can be – others can be as small. At the heart of NGC 5189 shines the tiny light of its central star… no bigger than Earth. It wobbles its way through time, rotating rapidly and spewing material into space like a runaway fire hydrant. Astronomers speculate there might be a binary star hidden inside, since usually planetary nebulae of this type have them. However, only one star has been found at the nebula’s center and it might be one very big, very bad wolf.

“Around 15% are known or suspected binaries, while the remaining 18% are non-emission line nuclei which require further study. Selecting for LIS (low ionization structures) therefore will give a mix of mostly binary and emission line nuclei which will require further observations to separate.” explains B. Miszalski (et al). “Almost all the [WR] CSPN in the sample belong to the hot [WO] type that have more extreme and chaotic LIS covering their entire nebulae, presumably due to turbulence from the strong [WR] winds disrupting pre-existing LIS.”

Just why is this celestial tapestry so complicated and complex? The answer isn’t a simple one – it’s one that has many plausible theories. We know that when a star similar to the Sun expends its fuel, it will begin to shed its outer layers… layers which normally take on very basic shape. These “normal” shapes are usually a sphere, sometimes a double lobe and at times it can be a ring or helix. However, NGC 5189 just doesn’t follow rules. Over time, researchers have speculated it has given off different outlfows at different stages – one prominent as a very visible torus situated around mid-point in the structure – consistent with the theory of a binary star system with a precessing symmetry axis. Still, there is clearly more research needed.

“Our preliminary results of a comparative spectroscopic study of these two objects shows that the chemical composition of the two nebulae is completely different, even though their morphology is most probably quite similar.” says VF Polcaro (et al). ” In addition, the PN appears much more chemically homogeneous. These features are clearly associated with the evolutionary paths of the stars.”

“The striking broad emission line spectroscopic appearance of Wolf-Rayet (WR) stars has long defied analysis, due to the extreme physical conditions within their line and continuum forming regions.” explains Paul Crowther. “Theoretical and observational evidence that WR winds depend on metallicity is presented, with implications for evolutionary models, ionizing fluxes, and the role of WR stars within the context of core-collapse supernovae and long-duration gamma ray bursts.”

Is NGC 5189 the handiwork of a binary star? Or is it the product of an intensely hot Wolf-Rayet? Like the proverbial Tootsie Pop equation… the world may never know.

Many thanks to Robert Gendler for sharing this incredible image with us.

Posted on by Jason Major

Galactic Gas Cloud Could Help Spot Hidden Black Holes

Illustration of gas cloud G2 approaching Sgr A* . Our central supermassive black hole periodically snacks on clouds and other material like this. That gives off X-rays and other emissions. (ESO/MPE/M.Schartmann/J.Major)
Illustration of gas cloud G2 approaching Sgr A* . Our central supermassive black hole periodically snacks on clouds and other material like this. That gives off X-rays and other emissions. (ESO/MPE/M.Schartmann/J.Major)

The heart of our Milky Way galaxy is an exotic place. It’s swarming with gigantic stars, showered by lethal blasts of high-energy radiation and a veritable cul-de-sac for the most enigmatic stellar corpses known to science: black holes. And at the center of the whole mélange is the granddaddy of all the black holes in the galaxy — Sagittarius A*,  a supermassive monster with 4 million times more mass than the Sun packed into an area smaller than the orbit of Mercury.

Sgr A* dominates the core of the Milky Way with its powerful gravity, trapping giant stars into breakneck orbits and actively feeding on anything that comes close enough. Recently astronomers have been watching the movement of a large cloud of gas that’s caught in the pull of Sgr A* — they’re eager to see what exactly will happen once the cloud (designated G2) enters the black hole’s dining room… it will, in essence, be the first time anyone watches a black hole eat.

But before the dinner bell rings — estimated to be sometime this September — the cloud still has to cover a lot of space. Some scientists are now suggesting that G2’s trip through the crowded galactic nucleus could highlight the locations of other smaller black holes in the area, revealing their hiding places as it passes.

In a new paper titled “G2 can Illuminate the Black Hole Population near the Galactic Center” researchers from Columbia University in New York City and the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Massachusetts propose that G2, a cloud of cool ionized gas over three times more massive than Earth, will likely encounter both neutron stars and other black holes on its way around (and/or into) SMBH Sgr A*.

Estimated number of stellar-mass black holes to be encountered by G2 along its trajectory (Bartos et al.)
Estimated number of stellar-mass black holes to be encountered by G2 along its trajectory (Bartos et al.)

The team notes that there are estimated to be around 20,000 stellar-mass black holes and about as many neutron stars in the central parsec of the galaxy. (A parsec is equal to 3.26 light-years, or 30.9 trillion km. In astronomical scale it’s just over 3/4 the way to the nearest star from the Sun.) In addition there may also be an unknown number of intermediate-mass black holes lurking within the same area.

These ultra-dense stellar remains are drawn to the center region of the galaxy due to the effects of dynamical friction — drag, if you will — as they move through the interstellar material.

Of course, unless black holes are feeding and actively throwing out excess gobs of hot energy and matter due to their sloppy eating habits, they are very nearly impossible to find. But as G2 is observed moving along its elliptical path toward Sgr A*, it could very well encounter a small number of stellar- and intermediate-mass black holes and neutron stars. According to the research team, such interactions may be visible with X-ray spotting spacecraft like NASA’s Chandra and NuSTAR.

Read more: Chandra Stares Deep Into the Heart of Sagittarius A*

NuSTAR X-ray image of a flare emitted by Sgr A* in July 2012 (NASA/JPL-Caltech)
NuSTAR X-ray image of a flare emitted by Sgr A* in July 2012 (NASA/JPL-Caltech)

The chances of G2 encountering black holes and interacting with them in such a way as to produce bright enough x-ray flares that can be detected depends upon a lot of variables, like the angles of interaction, the relative velocities of the gas cloud and black holes, the resulting accretion rates of in-falling cloud matter, and the temperature of the accretion material. In addition, any observations must be made at the right time and for long enough a duration to capture an interaction (or possibly multiple interactions simultaneously) yet also be able to discern them from any background X-ray sources.

Still, according to the researchers such observations would be important as they could provide valuable information on galactic evolution, and shed further insight into the behavior of black holes.

Read the full report here, and watch an ESO news video about the anticipated behavior of the G2 gas cloud around the SMBH Sgr A* below:

This research was conducted by Imre Bartos, Zoltán Haiman, and Bence Kocsis of Columbia University and Szabolcs Márka of the Harvard-Smithsonian Center for Astrophysics. 

Posted on by Jason Major

One of the Largest Astronomical Images Ever Made

The northern portion of the Cygnus Loop, as seen in an enormous new panorama from the National Optical Astronomy Observatory (NOAO) and WIYN partners

Looking for a stunning new desktop image to wrap up the year? Try this: it’s an amazing panorama of the Cygnus Loop, a supernova remnant located 1,500 light-years away in the constellation (you guessed it) Cygnus. The full-size image, acquired with the wide-field Mosaic camera on the WIYN 0.9-meter telescope at Kitt Peak, Arizona, is a staggering 600 million pixels in size — over 1.68 gigabytes — making it one of the largest astronomical images ever made!

See the full image (and links to download larger versions) below:

2000-pixel-wide version of the full Cygnus Loop panorama

The entire structure of the Cygnus Loop, the gaseous remains of a supernova that occurred 5,000 – 10,000 years ago, covers an area nearly 45 times the size of the full Moon in the sky.

In the image, hydrogen alpha, sulphur, and oxygen ions correspond to the red, green, and blue color values, respectively.

“Images like this are amazing because they can remind you of the big picture and beauty that surrounds us.”

–  Dr. Richard Cool, MMT Observatory

From the NOAO press release:

Astronomers estimate the supernova explosion that produced the nebula occurred between 5,000 to 10,000 years ago. First noted in 1784 by William Herschel, it is so large that its many parts have been catalogued as separate objects, including NGC 6992, NGC 6995 and IC 1340 along the eastern (left) side of the image, NGC 6974 and NGC 6979 near the top-center, and the Veil Nebula (NGC 6960) and Pickering’s Triangle along the western (right) edge. The bright star near the western edge of the image, known as 52 Cygnus, is not associated with the supernova.

“Often, astronomical research reduces images to dry tables of numerical information that we analyze in order to more deeply understand our universe,” said Dr. Richard Cool, astronomer at the MMT Observatory in Arizona, who originally obtained the images in 2003 while still a graduate student. “Images like this are amazing because they can remind you of the big picture and beauty that surrounds us.”

This incredible image demonstrates that even relatively small telescopes are capable of producing cutting-edge research, when equipped with modern cameras.

Got bandwidth to spare? Download the full-size 1686.5 MB TIFF image here, or find other versions on the NOAO page here.

Image Credit: T.A. Rector (University of Alaska Anchorage), Richard Cool (University of Arizona) and WIYN/NOAO/AURA/NSF. Inset image: original dome of the Kitt Peak 0.9-meter telescope. (NOAO/AURA/NSF)