Astronomy Archives

May 27, 2011December 24, 2015 by VirtualAstro

Beginner’s Guide to Astronomy – Refractor Telescopes

If you ask someone to describe or draw a telescope, nine times out of ten it will be a refractor.

The refractor telescope is quite possibly the most common or easily recognized telescope. It is a very simple design, which has been around for hundreds of years.

The history of the refractor is that it was first invented in the Netherlands in 1608, and is credited to 3 individuals; Hans Lippershey, Zacharias Janssen – spectacle-makers and Jacob Metius.

In 1609 Galileo Galilei heard about the refracting telescope and made his own design, publically announcing his invention and further developing it through extensive experimentation. Galileo’s friend Johannes Kepler further experimented with the design, introducing convex lenses at both ends, improving the operation of the telescope.

Many advances were made and the refracting telescope became the primary instrument for astronomical observations, but there was one problem; they were huge and some were many tens of feet long!

But now, after more than 400 years and — luckily — through advances in know-how and technology, the refractor has become much more powerful and compact than some of the behemoths in the early days.

Refractors or refracting telescopes employ a simple optical system comprising of a hollow tube with a large primary or “objective lens” at one end, which refracts light collected by the objective lens and bends light rays to make them converge at a focal point.

Light waves which enter at an angle converge on the focal plane. It is the combination of both which form an image that is further refracted and magnified by a secondary lens which is actually the eyepiece. Different eyepieces give different magnifications.

The larger the size of the objective or primary lens = more light gathered. So a 6 inch refractor gathers more light than a 2 inch one. This means more detail can be seen.

There are two main types of refractor telescopes: “Chromatic” – entry level and upwards with 2 lens elements and “Apochromatic” – premium, advanced and expert level telescopes with 3 or more very high quality lens elements with exotic mixes of materials.

Chromatic refractor telescopes are particularly good for observing bright objects such as the moon, planets and resolving things like double stars, but many astronomers who image deep sky and other objects use very high quality apochromatic refractors, due to their superior optics.

Refractor telescopes are very low maintenance due to being a sealed system and it is a simple case of setup and enjoy, without the fiddling lengthy setup times you may get with other telescopes.

Refractors give clean and crisp views due to the sealed nature, unlike other telescopes like Newtonians which are subject to cooling and air turbulence issues.

Due to their small size they are very portable and can also be used for terrestrial observations the same as binoculars, which are basically two refractors bolted together.

May 25, 2011December 24, 2015 by Tammy Plotner

The Lone SuperStar

Credit: ESO/M.-R. Cioni/VISTA Magellanic Cloud survey. Acknowledgment: Cambridge Astronomical Survey Unit

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It hangs out in space some 160,000 light years away. Its neighborhood is the Large Magellanic Cloud. It calls the Tarantula Nebula home. It’s 150 times more massive than our Sun and it shines an astounding three million times brighter. What is it? Try a lone super star…

Utilizing the power of ESO’s Very Large Telescope, a team of international astronomers have been checking out star VFTS 682 in the Large Magellanic Cloud. Using an instrument aptly named FLAMES, they also discovered the star to be very hot, with a surface temperature of about 50 000 degrees Celsius. While most of the initial findings were rather unremarkable, when researchers cleared away the dust clouds they discovered this super star stood alone.

“We were very surprised to find such a massive star on its own, and not in a rich star cluster,” notes Joachim Bestenlehner, the lead author of the new study and a student at Armagh Observatory in Northern Ireland. “Its origin is mysterious.”

Why an enigma? For the most part, stars like VFTS 682 are found in the crowded centers of galactic clusters. They are young, hot and bright – destined to live short and explosive lifetimes. Their high mass makes them a candidate for an even more dramatic end – a long-duration gamma-ray burst, the brightest explosion in the Universe. It could happen to other super stars in the nearby stellar nursery cluster, because it has a sibling.

“The new results show that VFTS 682 is a near identical twin of one of the brightest superstars at the heart of the R 136 star cluster,” adds Paco Najarro, another member of the team from CAB (INTA-CSIC, Spain).

So how did VFTS 682 end up being solitary sun? There is speculation that it could be a “runaway”… ejected from its nest. But such a scenario is unlikely since it is doubtful such a heavy star could be thrown from the cluster by gravitational interactions.

“It seems to be easier to form the biggest and brightest stars in rich star clusters,” adds Jorick Vink, another member of the team. “And although it may be possible, it is harder to understand how these brilliant beacons could form on their own. This makes VFTS 682 a really fascinating object.”

Shine on, you crazy diamond!

May 25, 2011December 24, 2015 by Tammy Plotner

New Arm Embraces Milky Way

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Some sixteen decades ago, Lord Rosse was the first to point out spiral structure in distant “nebula”… and today astrophysicists Thomas Dame and Patrick Thaddeus are discovering it closer to home. Our Milky Way Galaxy was believed to only have six spiral arms, but their research has revealed an outer extension of the Scutum-Centaurus arm from the inner galaxy.

“We have identified a spiral arm lying beyond the Outer Arm in the first Galactic quadrant ~15 kpc from the Galactic center.” says Dame and Thaddeus. “One of the detections was fully mapped to reveal a large molecular cloud with a radius of 47 pc and a molecular mass of ~50,000 M. At a mean distance of 21 kpc, the molecular gas in this arm is the most distant yet detected in the Milky Way. The new arm appears to be the continuation of the Scutum–Centaurus Arm in the outer Galaxy, as a symmetric counterpart of the nearby Perseus Arm.”

Over the last 50 years, many models of our galaxy have been proposed – revealing a pleasing, duo-symmetry. However, finding evidence to prove these theories has been a bit more elusive. Since we cannot observe ourselves, seeing spiral structure on the far side of the galaxy is problematic – hidden by near-side emission at the same velocity. But these researchers didn’t stop. The new arm was found as a result of attempts to follow the Sct–Cen Arm past its tangent.

“The new arm was largely overlooked in existing 21 cm surveys probably because it lies mainly out of the Galactic plane, its Galactic latitude steadily increasing with longitude as it follows the warp in the distant outer Galaxy.” says Dame. “In the first quadrant the only prominent HI spiral feature in the outer Galaxy is the well-known Outer Arm, a feature also well traced by CO. However, at 3 degrees above the plane one sees instead the new arm as a prominent linear feature running roughly parallel to the locus of the Outer Arm but shifted to more negative velocities.”

Is our smoothly constructed galaxy indeed a mirror image of itself? This new evidence suggests the Scutum-Centaurus arm embraces the entire Milky Way – forming a symmetrical, star-forming counterpart to the galaxy’s other arm, Perseus. “Confirmation of the present feature as the ”Outer Sct-Cen Arm” will require a great deal of new data from several telescopes and much observing time over an extended period.” says Thaddeus. “Key steps toward confirming the proposal include, as mentioned, tracking Sct–Cen in the fourth quadrant and, even harder, tracking the Perseus Arm from the point where it passes inside the solar circle near longitude 50 degrees to its putative origin at the far end of the bar.”

Mapping the findings of galactic data on atomic hydrogen gas isn’t going to happen overnight… and even more discoveries and clarifications could be revealed in the future. “The Galactic symmetry suggested by the present work and clearly demonstrated by the identification of the Far 3-kpc Arm a few years ago, coupled with evidence for a global two-armed spiral pattern in the old stars, and, indeed, with the discovery of the bar itself, all hint at Galactic spiral structure that is both simpler and more amenable to study than had long been assumed. As emphasized here, much work remains, but aided by greatly improved distances from forthcoming astrometric surveys, a reasonably complete picture of our Galaxy’s spiral pattern may be achieved over the next decade.”

May 25, 2011December 24, 2015 by Tammy Plotner

Australian Student Uncovers the Universe’s Missing Mass

Comic Microwave Background Courtesy of NASA / WMAP Science Team

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Not since the work of Fritz Zwicky has the astronomy world been so excited about the missing mass of the Universe. His evidence came from the orbital velocities of galaxies in clusters, rotational speeds, and gravitational lensing of background objects. Now there’s even more evidence that Zwicky was right as Australian student – Amelia Fraser-McKelvie – made another breakthrough in the world of astrophysics.

Working with a team at the Monash School of Physics, the 22-year-old undergraduate Aerospace Engineering/Science student conducted a targeted X-ray search for the hidden matter and within just three months made a very exciting discovery. Astrophysicists predicted the mass would be low in density, but high in temperature – approximately one million degrees Celsius. According to theory, the matter should have been observable at X-ray wavelengths and Amelia Fraser-McKelvie’s discovery has proved the prediction to be correct.

Dr Kevin Pimbblet from the School of Astrophysics explains: “It was thought from a theoretical viewpoint that there should be about double the amount of matter in the local Universe compared to what was observed. It was predicted that the majority of this missing mass should be located in large-scale cosmic structures called filaments – a bit like thick shoelaces.”

Up until this point in time, theories were based solely on numerical models, so Fraser-McKelvie’s observations represent a true break-through in determining just how much of this mass is caught in filamentary structure. “Most of the baryons in the Universe are thought to be contained within filaments of galaxies, but as yet, no single study has published the observed properties of a large sample of known filaments to determine typical physical characteristics such as temperature and electron density.” says Amelia. “We examine if a filament’s membership to a supercluster leads to an enhanced electron density as reported by Kull & Bohringer (1999). We suggest it remains unclear if supercluster membership causes such an enhancement.”

Still a year away from undertaking her Honors year (which she will complete under the supervision of Dr Pimbblet), Ms Fraser-McKelvie is being hailed as one of Australia’s most exciting young students… and we can see why!

May 24, 2011December 24, 2015 by Tammy Plotner

Carina Nebula: Pumping More Than Just Iron

Carina Nebula - Credit: NASA/CXC/PSU/L.Townsley et al.

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We are all just star stuff… But when it comes to the elements produced by a star, it just doesn’t get any heavier than iron. So how do more exotic elements come into existence? Try the Great Cosmic Recycler – supernova. Its energy disperses newly synthesized materials right into the interstellar neighborhood where an enriched generation of stars begin life again.

The beautiful Carina Nebula may very well be a literal supernova factory. Encompassing a large field of 1.4 square degrees, Chandra made of a mosaic of 22 individual pointings. In total, the image represents 1.2 million seconds – or nearly two weeks – of Chandra observing time. In addition, multi-wavelength data, such as infrared observations from the Spitzer Space Telescope and the Very Large Telescope (VLT), were then added to the mix to reveal that the supernova process has already begun. Clues, such as the lack of bright x-ray sources from Trumpler 15, suggest its massive stars have already been destroyed. In addition, six candidate neutron stars – instead of just one – provide additional evidence that supernova activity is gearing up in Carina.

But stellar destruction isn’t the only evidence Chandra has found. A new population of young massive stars has also been detected… potentially doubling the number of known young, massive stars which are usually destined to be destroyed later in supernova explosions. In the composite image, they appear as bright X-ray sources scattered across the x-ray emission like freckles on a child’s face. But what really holds our interest is the infamous Eta Carinae – a massive, unstable star on the brink of extinction.

Thanks to this latest research, we now know it’s not alone…

May 24, 2011December 24, 2015 by Tammy Plotner

A New “Spin” On Stellar Age

Artist's Conception of Hypothetical Planet courtesy of David A. Aguilar (CfA)

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It might not be polite to ask a lady her true age, but when it comes to stars it’s not as easy as checking a driver’s license. From our point of view, all stars can look pretty much the same – so how do we tell one that’s one billion years old from one that ten billion? The answer could be stellar spin rate.

In Monday’s 218th meeting of the American Astronomical Society, astronomer Soren Meibom of the Harvard-Smithsonian Center for Astrophysics presented his findings. “A star’s rotation slows down steadily with time, like a top spinning on a table and can be used as a clock to determine its age.” says Meibom. “Ultimately, we need to know the ages of the stars and their planets to assess whether alien life might have evolved on these distant worlds. The older the planet, the more time life has had to get started. Since stars and planets form together at the same time, if we know a star’s age, we know the age of its planets too.”

By determining a star’s age in advance, it assists astronomer’s working with projects like Kepler. Knowing where to begin in a galaxy filled with stars helps us to understand how planetary systems form and evolve and why they are so different from each other. In some circumstances, like galactic star clusters, we’re pretty much on the mark at knowing a star’s age because we believe they all formed about the same time. However, for a lone star that harbors planets, determining age is much more difficult. Measuring the rotation of stars in clusters with different ages reveals exactly how spin and age are related. Then by extension, astronomers can measure the spin of a single isolated star and calculate its age.

Just how is calculating stellar spin rate done? Try exactly how we know our own Sol’s rotation – sunspots. Each time a “star spot” rotates across the visible surface, it dims ever so slightly. By measuring how long these changes take place gives us substantial clues to just how fast a star rotates. Although these changes are minute and decrease as a star ages, the sensitivity of the Kepler spacecraft was designed specifically to measure stellar brightnesses very precisely in order to detect planets (which block a star’s light ever so slightly if they cross the star’s face from our point of view).

But this task was far from easy. In a four year preparatory study conducted with specially designed instrument (Hectochelle) mounted on the MMT telescope on Mt. Hopkins in southern Arizona, Meibom and his colleagues sorted out information in nearly 7000 individual stars and used Kepler data to determine how fast those stars were spinning. Their findings included stars with rotation periods between 1 and 11 days, confirming that gyrochronology is an exciting new method to learn the ages of isolated stars.

“This work is a leap in our understanding of how stars like our Sun work. It also may have an important impact on our understanding of planets found outside our solar system,” said Meibom.

May 24, 2011December 24, 2015 by Jon Voisey

Want to Make Planets? Better Hurry.

Artist's impression of planetary formation. Image credit: NASA

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Currently, astronomers have two competing models for planetary formation. In one, the planets form in a single, monolithic collapse. In the second, the core forms first and then slowly accretes gas and dust. However, in both situations, the process must be complete before the radiation pressure from the star blows away the gas and dust. While this much is certain, the exact time frames have remained another matter of debate. It is expected that this amount should be somewhere in the millions of years, but low end estimates place it at only a few million, whereas upper limits have been around 10 million. A new paper explores IC 348, a 2-3 million year old cluster with many protostars with dense disks to determine just how much mass is left to be made into planets.

The presence of dusty disks is frequently not directly observed in the visible portion of the spectra. Instead, astronomers detect these disks from their infrared signatures. However, the dust is often very opaque at these wavelengths and astronomers are unable to see through it to get a good understanding of many of the features in which they’re interested. As such, astronomers turn to radio observations, to which disks are partially transparent to build a full understanding. Unfortunately, the disks glow very little in this regime, forcing astronomers to use large arrays to study their features. The new study uses data from the Submillimeter Array located atop Mauna Kea in Hawaii.

To understand how the disks evolved over time, the new study aimed to compare the amount of gas and dust left in IC 348’s disc to younger ones in star forming regions in Taurus, Ophiuchus, and Orion which all had ages of roughly 1 million years. For IC 348, the team found 9 protoplanetary disks with masses from 2-6 times the mass of Jupiter. This is significantly lower than the range of masses in the Taurus and Ophiuchus star forming regions which had protoplanetary clouds ranging to over 100 Jupiter masses.

If planets are forming in IC 348 at the same frequency in which they form in systems astronomers have observed elsewhere, this would seem to suggest that the gravitational collapse model is more likely to be correct since it doesn’t leave a large window in which forming planets could accrete. If the core accretion model is correct, then planetary formation must have begun very quickly.

While this case don’t set any firm pronouncements on which model of planetary formation is dominant, such 2-3 million year old systems could provide an important test bed to explore the rate of depletion of these reservoirs.

May 15, 2011December 24, 2015 by Jon Voisey

Cyanoacetylene in IC 342

IC 342 - Ken and Emilie Siarkiewicz/Adam Block/NOAO/AURA/NSF

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Star formation is an incredible process, but also notoriously difficult to trace. The reason is that the main constituent of stars, hydrogen, looks about the same well before a gravitational collapse begins, as it does in the dense clouds where star formation happens. Sure, the temperature changes and the hydrogen glows in a different part of the spectrum, but it’s still hydrogen. It’s everywhere!

So when astronomers want to search for denser regions of gas, they often turn to other atoms and molecules that can only form or be stimulated to emit under these relatively dense conditions. Common examples of this include carbon monoxide and hydrogen cyanide. However, a study published in 2005, led by David Meier at the University of Illinois at Urbana-Champaign, studied inner regions of the nearby face-on spiral by tracing eight molecules and determined that the full extent of the dense regions is not well mapped by these two common molecules. In particular, cyanoacetylene, an organic molecule with a chemical formula of HC₃N, was demonstrated to correlate with the most active star forming regions, promising astronomers a peek into the heart of star forming regions and prompting a follow-up study.

The new study was conducted from the Very Large Array in late 2005. Specifically, it studied the emissions due to 5-4, 10-9, and 16-15 transitions which each correspond to different levels of heating and excitation. The dense regions uncovered by this study were consistent with the ones reported in 2005. One, discovered by the previous survey from another tracer molecule, was not found by this most recent study, but the new study also discovered a previously unnoticed giant molecular cloud (GMC) through the presence of HC₃N.

Another technique that can be applied is examining the ratios of various levels of excitation. From this, astronomers can determine the temperature and density necessary to produce such emission. This can be performed with any type of gas, but using additional species of molecules provides independent checks on this value. For the area with the strongest emission, the team reported that the gas appeared to be a cool 40 K (-387°F) with a density of 1-10 thousand molecules per cubic centimeter. This is relatively dense for the interstellar medium, but for comparison, the air we breathe has approximately 10²⁵ molecules per cubic centimeter. These findings are consistent with those reported from carbon monoxide.

The team also examined several of the star forming cores independently. By comparing the varying strengths of tracer molecules, the team was able to report that one GMC was well progressed in making stars while another was less evolved, likely still containing hot cores which had not yet ignited fusion. In the former, the HC₃N is weaker than in the other cores explored, which the team attributes to the destruction of the molecules or dispersal of the cloud as fusion begins in the newly formed stars.

While using HC₃N as a tracer is a relatively new approach (these studies of IC 342 are the first conduced in another galaxy), the results of this study have demonstrated that it can trace various features in dense clouds in similar fashions to other molecules.

May 11, 2011December 24, 2015 by Jon Voisey

Energizing the Filaments of NGC 1275

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When examining clusters of galaxies, astronomers often find massive elliptical galaxies lurking at the centers. In some of these, long filaments of gas and dust extend outwards from the core. One of the best examples of this is the relatively nearby galaxy NGC 1275 which lies in the constellation of Perseus. In this galaxy these tendrils are exceptionally narrow, only about 200 light years across, but as long as 20,000 light years in length. While many groups have studied them, their nature is a topic of much debate. The structures tend to be far removed from star forming regions which can cause the gas to glow. So what energy source powers these gaseous ribbons?

Answering this question is the goal of a recent paper by a team of astronomers led by Andrew Fabian at Cambridge University. Previous studies have explored the spectra of these filaments. Although the filaments have strong Hα emission, created by warm hydrogen gas, the spectra of these tendrils are unlike any nebulae within our own galaxy. The closest resemblance to galactic objects was the Crab Nebula, the remnant of a supernova that was witnessed in 1054 AD. Additionally, the spectra also reveal the presence of molecules such as carbon monoxide and H₂.

Another, previous challenge astronomers faced with these tendrils was explaining their formation. Since molecules were present, it meant the gas was cooler than the surrounding gas. In this case, the clouds should collapse due to their self gravity to form more stars than are actually present. But surrounding these tendrils is ionized plasma which should interact with the cold gas, heating it and causing it to disperse. While these two forces would counteract one another, it is impossible to consider that they would balance each other perfectly in one case, let alone for the numerous tendrils in numerous central galaxies.

This problem was apparently solved in 2008, when Fabian published a paper in Nature suggesting that these filaments were being columnated by extremely weak magnetic fields (only 0.01% the strength of Earth’s). These field lines could prevent the warmer plasma from directly entering the cold filaments since, upon interaction with the magnetic field, they would be redirected. But could this property help to explain the lesser degree of heating that still causes the emission spectra? Fabian’s team thinks so.

In the new paper, they suggests that some of the particles of the surrounding plasma do eventually penetrate the cold tendrils which explains some of the heating. However, this flow of charged particles also affects the field lines themselves inducing turbulence which also heats the gas. These effects make up the main bulk of the observed spectra. But the tendrils also exhibit an anomalous amount of X-ray flux. The team proposes that some of this is due to charge exchange in which the ionized gas entering the filaments steals electrons from the cold gas. Unfortunately, the interactions are expected to be too infrequent to explain all of the observed X-rays leaving this portion of the spectrum not fully explained by the new model.

In this article I’ve used the words “magnetic field”, “charge”, and “plasma” throughout, so of course the Electric Universe crowd is going to come flocking, declaring this validates everything they’ve ever said, just as they did when magnetic fields were first implicated in 2008. So before closing completely, I want to take a bit to consider how this new study conforms to their predictions. In general, the study agrees with their claims. However, that doesn’t mean their claims are correct. Rather, it implies they’re worthlessly vague and can be made to fit any circumstance that even briefly mentions such words as I listed above.

The EU supporters consistently refuse to provide any quantitative models which could provide true discriminating tests for their propositions. Instead, they leave the claims suspiciously vague and insist that complex physics is completely understandable with no more understanding than high school level E&M. As a result, the mere scale of their claims is horrifically inconsistent wherein they propose things like the paltry field in this article, or the slight charge on lunar craters are indicative of overwhelming currents powering stars and entire galaxies.

So while articles like this one do reinforce the EU position that electromagnetics does play a role in astronomy, it does not support the grandiose claims on entirely different scales. In the meantime, astronomers don’t argue that electromagnetic effects don’t exist (like EU supporters frequently claim). Rather, we analyze them and appreciate them for what they are: Generally weak effects that are important here and there, but they’re not some all powerful energy field pervading the universe.

May 10, 2011December 24, 2015 by Jon Voisey

Examining the Great Wall

Several superclusters revealed by the 2dF Galaxy Redshift Survey. This contains the structure known as the "Sloan Great Wall". Courtesy 2dF Galaxy Redshift Survey.

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Structure exists on nearly all scales in the universe. Matter clumps under its own gravity into planets, stars, galaxies, clusters, and superclusters. Beyond even these in scale are the filaments and voids. The largest of these filaments is known as the Sloan Great Wall. This giant string of galaxies is 1.4 billion light years across making it the largest known structure in the universe. Yet surprisingly, the Great Wall has never been studied in detail. Superclusters within it have been examined, but the wall as a whole has only come into consideration in a new paper from a team led by astronomers at Tartu Observatory in Estonia.

The Sloan Great Wall was first discovered in 2003 from the Sloan Digital Sky Survey (SDSS). The survey mapped the position of hundreds of millions of galaxies revealing the large scale structure of the universe and uncovering the Great Wall.

Within it, the wall contains several interesting superclusters. The largest of these SCl 126 has been shown previously to be unusual compared to superclusters within other large scale structures. SCl 126 is described as having an exceptionally rich core of galaxies with tendrils of galaxies trailing away from it like an enormous “spider”. Typical superclusters have many smaller clusters connected by these threads. This pattern is exemplified by one of the other rich superclusters in the wall, SCl 111. If the wall is examined in only its densest portions, the tendrils extending away from these cores are quite simple, but as the team explored lower densities, sub filaments became apparent.

Another way the team examined the Great Wall was by looking at the arrangement of different types of galaxies. In particular, the team looked for Bright Red Galaxies (BRGs) and found that these galaxies are often found together in groups with at least five BRGs present. These galaxies were often the brightest of the galaxies within their own groups. As a whole, the groups with BRGs tended to have more galaxies which were more luminous, and have a greater variety of velocities. The team suggests that this increased velocity dispersion is a result of a higher rate of interactions among galaxies than in other clusters. This is especially true for SCl 126 where many galaxies are actively merging. Within SCl 126, these BRG groups were evenly distributed between the core and the outskirts while in SCl 111, these groups tended to congregate towards the high density regions. In both of these superclusters, spiral galaxies comprised about 1/3 of the BRGs.

The study of such properties will help astronomers to test cosmological models that predict galactic structure formation. The authors note that models have generally done a good job of being able to account for structures similar to SCl 111 and most other superclusters we have observed in the universe. However, they fall short in creating superclusters with the size, morphology and distribution of SCl 126. These formations arise from density fluctuations initially present during the Big Bang. As such, understanding the structures they formed will help astronomers to understand these perturbations in greater detail and, in turn, what physics would be necessary to achieve them. To help achieve this, the authors intend to continue mapping the morphology of the Sloan Great Wall as well as other superclusters to compare their features.