Posted on by Jon Voisey

Interstellar Scintilation

Barnard 68 (Credit: ESO)
Barnard 68 (Credit: ESO)

[/caption]

Anyone who has looked at stars in the night sky (especially ones low on the horizon) has undoubtedly seen the common effect of twinkling. This effect is caused by turbulence in the atmosphere as small over densities cause the path of the light to bend ever so slightly. Often, vivid color shifts occur since the effects are wavelength dependent. All of this happens in the short distance between the edge of the atmosphere and our eyes. Yet often times, giant molecular clouds lie between our detectors and a star. Could these clouds of gas and dust cause a twinkling effect as well?


In theory, there’s no reason they shouldn’t. As the giant molecular clouds intercepting the incoming starlight move and distort, so too should the path of the light. The difference is that, due to the extremely low density and extremely large size, the timescales over which this distortion would take place would be far longer. Should it be discovered, it would provide astronomers another method by which to discover previously hidden gas.

Doing this is precisely the goals of a team of astronomers working from the Paris University and Sharif University in Iran. To get and understanding of what to expect, the team first simulated the effect, taking into account the properties of the cloud (distribution, velocity, etc…) as well as refraction and reflection. They estimated that, for a star in the Large Magellanic Cloud with light passing through typical galactic H2 gas, this would produce twinkles with changes taking around 24 minutes.

Yet there are many other effects which can produce modulations on the same timescale such as variable stars. Additional constraints would be necessary to claim that a change would be due to a twinkling effect and not a product of the star itself. As stated before, the effect is different for different wavelengths which would produce a “variation of the characteristic time scale … between the red side of the optical spectrum and the blue side.”

With expectations in hand, the team began searching for this effect in areas of the sky in which they knew especially high densities of gas to exist. Thus, they pointed their telescopes towards dense nebulae known as Bok globules like Barnard 68 (pictured above). Observations were taken using the 3.6 meter ESO NTT-SOFI telescope since it had the capabilities to also take infrared images and better explore the potential effects on the red side of the spectrum.

From their observations over two nights, the team discovered one instance in which the modulation of brightness in the different wavelengths followed the predicted effects. However, they note that from a single observation of their effects, it does not conclusively demonstrate the principle. The team also observed stars in the direction of the Small Magellanic Cloud to attempt to observe this twinkling effect in that direction due to previously undetected clouds along the line of sight. In this attempt, they were unsuccessful. Further similar observations along these lines in the future could help to constrain the amount of cold gas within the galaxy.

Posted on by Jon Voisey

The Hunt for Young Exoplanets

While there is a great deal of excitement and effort in the hopes of finding small, terrestrial sized exoplanets, another realm of exoplanet discovery that is often overlooked is that of ones of differing ages to explore how planetary systems can evolve. The first discovered exoplanet orbited a pulsar, showing that planets can be hardy enough to survive the potential violent deaths of their parent stars. On the other end, young planets can help astronomers constrain how planets form and a potential new discovery may help in those regards.


Historically, astronomers have often avoided looking at stars younger than about 100 million years. Their young nature tends to make them unruly. They are prone to flares and other eccentric behaviors that often make observations messy. Additionally, many young stars often retain debris disks or are still embedded in the nebula in which they formed which also obscures observations.

Despite this, some astronomers have begun developing targeted searches for young exoplanets. The age of the exoplanet is not independently derived, but instead, taken from the age of the host star. This too can be difficult to determine. For isolated stars, there are precious few methods (such as gyrochronology) and they generally have large errors associated with them. Thus, instead of looking for isolated stars, astronomers searching for young exoplanets have tended to focus on clusters which can be dated more easily using the main sequence turn off method.

Through this methodology, astronomers have searched clusters and other groups, such as Beta Pictoris which turned up a planet earlier this year. The Beta Pic moving group boasts an age of ~12 million years making it one of the youngest associations currently known.

Trumpler 37 (also known as IC 1396 and the Elephant Trunk Nebula) is one of the few clusters with an even younger age of 1-5 million years. This was one of several young clusters observed by a team of German astronomers led by Gracjan Maciejewski of Jena University. The group utilized an array of telescopes across the world to continuously monitor Trumpler 37 for several weeks. During that time, they discovered numerous flares and variable stars, as well as a star with a dip in its brightness that could be a planet.

The team cautions that the detection may not be a planet. Several objects can mimic planetary transit lightcurves such as “the central transit of a low-mass star in front of a large main-sequence star or red giant, grazing eclipses in systems consisting of two main-sequence stars and a contamination of a fainter eclipsing binary along the same line of sight.” Due to the physics of small objects, the size of brown dwarfs and many Jovian type planets are similar leading difficulty in distinguishing from the light curve alone. Spectroscopic results will have to be undertaken to confirm the object truly is a planet.

However, assuming it is, based on the size of the dip in brightness, the team predicts the planet is about twice the radius of Jupiter, and about 15 times the mass. If so, this would be in good agreement with models of planetary formation for the expected age. Ultimately, planets of such age will help test our understanding of how planets form, whether it be from a single gravitational collapse early on, or slow accretion over time.

Posted on by Matt Williams

Last Day of Summer

Winter Solstice
Earth as viewed from the cabin of the Apollo 11 spacecraft. Credit: NASA

Summertime is a joyous time for so many reasons. There’s the sense of vacation, that feeling of freedom we remember so fondly from our childhoods. There’s the warmth weather, the sunshine, the early mornings and cool, late evenings. Seriously, there’s nothing wrong with summer, except the unfortunate fact that sooner or later, it has to end.

But when exactly is the very last day of summer? Well, it differs from place to place, depending on your location, whether you are north or south of the equator and by how much. But in the Northern Hemisphere, the change in seasons occurred on September 22nd for the year of 2010. In the Southern Hemisphere, it took place on February 28th.

In order to understand why this date was pegged as the end of the season, we need to understand exactly how the season itself is measured. These have to do with the equinoxes and solstices, seasonal markers that occur twice a year respectively. From an astronomical point of view, the equinoxes and solstices are in the middle of the respective seasons, but a variable seasonal lag means that the meteorological start of the season, which is based on average temperature patterns, occurs several weeks later than the start of the astronomical season.

According to meteorologists, summer extends for the whole months of June, July and August in the northern hemisphere and the whole months of December, January and February in the southern hemisphere. Interestingly enough, in this hemisphere, the end of the summer season is also dependent on whether or not it is a leap year (during leap years, an extra day is added).

In North America, summer is often fixed as the period from the summer solstice (June 20 or 21, depending on the year) to the fall equinox (September 22 or 23, again depending on the year). Therefore, Sept. 22 was the last day of summer and the beginning of the 2010 autumnal equinox, which officially began at 11:09 p.m. EST., the full moon having peaked the following morning at 5:17 a.m. EST which marked it as the first day of fall in the Northern Hemisphere.

The moon closest to the September equinox is considered the “Harvest Moon.” Its name stems from when farmers would rely on the light to work in the fields as the days grew shorter. For the first time since 1991, the full moon fell on the equinox, creating a “Super Harvest Moon.” In the Southern Hemisphere, the last day of summer was February 28th since 2010 was not a leap year.

We have written many articles about Summer for Universe Today. Here’s an article about the summer solstice, and here’s an article about the Earth seasons.

If you’d like more info on Earth, check out NASA’s Solar System Exploration Guide on Earth. And here’s a link to NASA’s Earth Observatory.

We’ve also recorded an episode of Astronomy Cast all about planet Earth. Listen here, Episode 51: Earth.

Sources:
http://en.wikipedia.org/wiki/Summer
http://www.tonic.com/article/last-day-of-summer-first-night-of-fall-super-harvest-moon/
http://en.wikipedia.org/wiki/Equinox
http://en.wikipedia.org/wiki/Solstice
http://wiki.answers.com/Q/What_is_the_last_day_of_summer_in_Southern_Hemisphere

Posted on by Matt Williams

What is Interstellar Space?

Glittering Metropolis of Stars
Glittering Metropolis of Stars

[/caption]

The boundary of what is known, that place known as the great frontier, has always intrigued and enticed us. The mystery of the unknown, the potential for discovery, the fear, the uncertainty; that place that exists just beyond the edge has got it all! At one time, planet Earth contained many such places for explorers, vagabonds and conquerors. But unfortunately, we’ve run out of spaces to label “here be dragons” here at home. Now, humanity must look to the stars to find such places again. These areas, the vast stretches of space that fall between the illuminated regions where stars sit, is what is known as Interstellar Space. It can be the space between stars but also can refer to the space between galaxies.

On the whole, this area of space is defined by its emptiness. That is, there are no stars or planetary bodies in these regions that we know of. That does not mean, however, that there is absolutely nothing there. In fact, interstellar areas do contain quantities of gas, dust, and radiation. In the first two cases, this is what is known as interstellar medium (or ISM), the matter that fills interstellar space and blends smoothly into the surrounding intergalactic space. The energy that occupies the same volume, in the form of electromagnetic radiation, is known as the interstellar radiation field. On the whole, the ISM is thought to be made up primarily of plasma (aka. ionized hydrogen gas) because its temperature appears to be high by terrestrial standards.

The nature of the interstellar medium has received the attention of astronomers and scientists over the centuries. The term first appeared in print in the 17th century in the works of Sir Francis Bacon and Robert Boyle, both of whom were referring to the spaces that fell between stars. Before the development of electromagnetic theory, early physicists believed that space must be filled with an invisible “aether” in order for light to pass through it. It was not until the 20th century though that deep photographic imaging and spectroscopy that scientists were able to postulate that matter and gas existed in these regions. The discovery of cosmic waves in 1912 was a further boon, leading to the theory that interstellar space was pervaded by them. With the advent of ultraviolet, x-ray, microwave, and gamma ray detectors, scientists have been able to “see” these kinds of energy at work in interstellar space and confirm their existence.

Many satellites have been launched with the intention of sending back information from interstellar space. These include the Voyager 1 and 2 spacecraft which have cleared the known boundaries of the Solar System and passed into the heliopause. They are expected to continue to operate for the next 25 to 30 years, sending back data on magnetic fields and interstellar particles.

We have written many articles about interstellar space for Universe Today. Here’s an article about deep space, and here’s an article about interstellar space travel.

If you’d like more information on the Interstellar Space, here’s a link to Voyager’s Interstellar Mission Page, and here’s the homepage for Interstellar Science.

We’ve recorded an episode of Astronomy Cast all about Interstellar Travel. Listen here, Episode 145: Interstellar Travel.

Sources:
http://en.wikipedia.org/wiki/Interstellar_space#Interstellar
http://en.wikipedia.org/wiki/Interstellar_medium
http://www.seasky.org/solar-system/interstellar-space.html
http://en.wikipedia.org/wiki/Electromagnetic_radiation
http://en.wikipedia.org/wiki/Heliopause#Heliopause

Posted on by Matt Williams

Cosmology

Planck Time
The Universe. So far, no duplicates found@

[/caption]

Ever wonder why we are here, how and why the universe that we inhabit came to be, and what our place is in it? If so, than in addition to philosophy, religion, and esotericism, you might be interested in the field of Cosmology. This is, in the strictest sense, the study of the universe in its totality, as it is today, and what humanity’s place is in it. Although a relatively recent invention from a purely scientific point of view, it has a long history which embraces several fields over the course of many thousand years and countless cultures.

In western science, the earliest recorded examples of cosmology are to be found in ancient Babylon (circa 1900 – 1200 BCE), and India (1500 -1200 BCE). In the former case, the creation myth recovered in the EnûmaEliš held that the world existed in a “plurality of heavens and earths” that were round in shape and revolved around the “cult place of the deity”. This account bears a strong resemblance to the Biblical account of creation as found in Genesis. In the latter case, Brahman priests espoused a theory in which the universe was timeless, cycling between expansion and total collapse, and coexisted with an infinite number of other universes, mirroring modern cosmology.

The next great contribution came from the Greeks and Arabs. The Greeks were the first to stumble onto the concept of a universe that was made up of two elements: tiny seeds (known as atoms) and void. They also suggested, and gravitated between, both a geocentric and heliocentric model. The Arabs further elaborated on this while in Europe, scholars stuck with a model that was a combination of classical theory and Biblical canon, reflecting the state of knowledge in medieval Europe. This remained in effect until Copernicus and Galileo came onto the scene, reintroducing the west to a heliocentric universe while scientists like Kepler and Sir Isaac Newton refined it with their discovery of elliptical orbits and gravity.

The 20th century was a boon for cosmology. Beginning with Einstein, scientists now believed in an infinitely expanding universe based on the rules of relativity. Edwin Hubble then demonstrated the scale of the universe by proving that “spiral nebulae” observed in the night sky were actually other galaxies. By showing how they were red-shifted, he also demonstrated that they were moving away, proving that the universe really was expanding. This in turn, led to the Big Bang theory which put a starting point to the universe and a possible end (echoes of the Braham expansion/collapse model).

Today, the field of cosmology is thriving thanks to ongoing research, debate and continuous discovery, thanks in no small part to ongoing efforts to explore the known universe.

We have written many articles about cosmology for Universe Today. Here’s an article about the galaxy, and here are some interesting facts about stars.

If you’d like more info on cosmology, the best place to look is NASA’s Official Website. I also recommend you check out the website for the Hubble Space Telescope.

We’ve recorded many episodes of Astronomy Cast, including one about Hubble. Check it out, Episode 88: The Hubble Space Telescope.

Sources:
http://en.wikipedia.org/wiki/Cosmology#cite_note-5
http://en.wikipedia.org/wiki/En%C3%BBma_Eli%C5%A1
http://en.wikipedia.org/wiki/Timeline_of_cosmology
http://www.newscientist.com/article/dn9988-instant-expert-cosmology.html
http://en.wikipedia.org/wiki/Geocentric_model
http://en.wikipedia.org/wiki/Heliocentrism
http://en.wikipedia.org/wiki/Red_shift

Posted on by Steve Nerlich

Astronomy Without A Telescope – Blazar Jets

A 5000 light year long jet observable in optical light from the giant elliptical galaxy M87 - which is not technically a blazar, but only because it's jet isn't more closely aligned with Earth. Credit: ESA/Hubble.

[/caption]

Polar jets are often found around objects with spinning accretion disks – anything from newly forming stars to ageing neutron stars. And some of the most powerful polar jets arise from accretion disks around black holes, be they of stellar or supermassive size. In the latter case, jets emerging from active galaxies such as quasars, with their jets roughly orientated towards Earth, are called blazars.

The physics underlying the production of polar jets at any scale is not completely understood. It is likely that twisting magnetic lines of force, generated within a spinning accretion disk, channel plasma from the compressed centre of the accretion disk into the narrow jets we observe. But exactly what energy transfer process gives the jet material the escape velocity required to be thrown clear is still subject to debate.

In the extreme cases of black hole accretion disks, jet material acquires escape velocities close to the speed of light – which is needed if the material is to escape from the vicinity of a black hole. Polar jets thrown out at such speeds are usually called relativistic jets.

Relativistic jets from blazars broadcast energetically across the electromagnetic spectrum – where ground based radio telescopes can pick up their low frequency radiation, while space-based telescopes, like Fermi or Chandra, can pick up high frequency radiation. As you can see from the lead image of this story, Hubble can pick up optical light from one of M87‘s jets – although ground-based optical observations of a ‘curious straight ray’ from M87 were recorded as early as 1918.

Polar jets are thought to be shaped (collimated) by twisting magnetic lines of force. The driving force that pushes the jets out may be magnetic and/or intense radiation pressure, but no-one is really sure at this stage. Credit: NASA.

A recent review of high resolution data obtained from Very Long Baseline Interferometry (VLBI) – involving integrating data inputs from geographically distant radio telescope dishes into a giant virtual telescope array – is providing a bit more insight (although only a bit) into the structure and dynamics of jets from active galaxies.

The radiation from such jets is largely non-thermal (i.e. not a direct result of the temperature of the jet material). Radio emission probably results from synchrotron effects – where electrons spun rapidly within a magnetic field emit radiation across the whole electromagnetic spectrum, but generally with a peak in radio wavelengths. The inverse Compton effect, where a photon collision with a rapidly moving particle imparts more energy and hence a higher frequency to that photon, may also contribute to the higher frequency radiation.

Anyhow, VLBI observations suggest that blazar jets form within a distance of between 10 or 100 times the radius of the supermassive black hole – and whatever forces work to accelerate them to relativistic velocities may only operate over the distance of 1000 times that radius. The jets may then beam out over light year distances, as a result of that initial momentum push.

Shock fronts can be found near the base of the jets, which may represent points at which magnetically driven flow (Poynting flux) fades to kinetic mass flow – although magnetohydrodynamic forces continue operating to keep the jet collimated (i.e. contained within a narrow beam) over light year distances.

Left: A Xray/radio/optical composite photo of Centaurus A - also not technically a blazar because its jets don't align with the Earth. Credit: X-ray: NASA/CXC/CfA/R.Kraft et al.; Submillimeter: MPIfR/ESO/APEX/A.Weiss et al.; Optical: ESO/WFI. Right: A composite image showing the radio glow from Centaurus A compared with that of the full Moon. The foreground antennas are CSIRO's Australia Telescope Compact Array, which gathered the data for this image.

That was about as much as I managed to glean from this interesting, though at times jargon-dense, paper.

Further reading: Lobanov, A. Physical properties of blazar jets from VLBI observations.

Posted on by Jon Voisey

Breaking News: The Sun Worked 175 Years Ago!

The sunspot butterfly diagram. This modern version is constructed (and regularly updated) by the solar group at NASA Marshall Space Flight Center.
The sunspot butterfly diagram. This modern version is constructed (and regularly updated) by the solar group at NASA Marshall Space Flight Center.

[/caption]

You’ll have to forgive my title. After writing so many articles as moderately as I could, I couldn’t help but engage in a bit of sensationalism of my own, especially in the interest of sarcasm. Although it’s not especially exciting that the sun has indeed been working for nearly two centuries (indeed, much longer than that), what is interesting is how using historical data, scientists have confirmed that process we see today have been relatively consistent since 1825.


The observations revolve around a familiar diagram known as the Butterfly diagram (pictured above). This diagram depicts the position of sunspots at various latitudes on the sun’s surface as time progresses. At the beginning of a cycle, sunspots start of at high latitudes and as the cycle progresses, appear at lower and lower latitudes until they disappear and the cycle repeats. The pattern formed resembles the wings of a butterfly, thereby giving the diagram its name.

Although sunspots have been observed as far back as 364 BC by Chinese astronomers, telescopic observations of them did not start until the early 1600’s. Continuous observation of the sun and its spots started in 1876 at the Royal Greenwich Observatory. There Edward Maunder recognized the pattern of sunspots and published them in the format that is the now famous Butterfly diagram in 1904. The diagram, as its usually shown only comprises data starting from around 1876 and continuing until present day. But the use of new records have extended the diagram back an additional 51 years, covering four new solar cycles. Although many observations exist with total sunspot counts, this new set of data includes detailed documentation of the position of the spots on the solar disc.

The observations were created by German astronomer Heinrich Schwabe. Originally an apothecary, he won a telescope in a lottery in 1825 and was fascinated, selling his family business four years later. Schwabe observed the Sun compulsively attempting to discover a new planet with an orbit interior to Mercury by witnessing it transiting the Sun. Although this effort was doomed to failure, Schwabe maintained detailed records of the sunspots. He even recognized the pattern of spots occurred in an 11 year cycle and published the discovery in 1843. It was met with little attention for several years until it was included in Alexander von Humboldt’s Kosmos. Due to this discovery, the 11 year solar cycle is also referred to as the Schwabe cycle.

From 1825 until 1867, Schwabe compiled at least 8468 observations of the Sun’s disc, drawn on 5cm circles. On his death, these documents, as well as the rest of his scientific works, were donated to the Royal Astronomical Society of London, and in 2009, were provided to a team of researchers for digitization. From the 8468 drawings, 7299 “have a coordinate system which is found to be aligned with the celestial equator” making them suitable for translation into scientific data.

Thus far, the team has converted 11% of the images into usable data and already, it has created a detailed butterfly diagram preceding those produced elsewhere. From it, the astronomers undertaking the conversion have made some interesting observations. The cycle beginning around 1834 was weaker than others around that time. The following one, starting around 1845, displayed a notable asymmetry where sunspots in the southern hemisphere were conspicuously lacking for the first 1-2 years of the cycle, whereas most cycles are fairly well mirrored. Although unusual, such phase shifts are not unprecedented. In fact, another study using historical records has demonstrated that, for the last 300 years, one hemisphere has always led (although not usually so greatly) for several cycles before trading off.

As with the recently discussed historical project on weather trends this reanalysis of historical data is one of many such projects giving us a broader picture of the trends we see today and how they have changed over time. While undoubtedly, many will be demonstrated to be mundane and familiar, undeserving of the exaggerated significance of my title, this is how science works: by expanding our knowledge to test our expectations.

NOTE: I’d Emailed the team asking for permission to show their image of the historical butterfly diagram, but since I haven’t gotten permission, I didn’t reproduce it here. But you can still view it in the paper. Go do so. It’s awesomely familiar.

Posted on by Nancy Atkinson

Carnival of Space #174

Carnival of Space. Image by Jason Major.

[/caption]

A little late posting this one, but here’s this week’s Carnival of Space, hosted by David Portree over at Beyond Apollo.

Click here to read the Carnival of Space #174.

And if you’re interested in looking back, here’s an archive to all the past Carnivals of Space. If you’ve got a space-related blog, you should really join the carnival. Just email an entry to [email protected], and the next host will link to it. It will help get awareness out there about your writing, help you meet others in the space community – and community is what blogging is all about. And if you really want to help out, let Fraser know if you can be a host, and he’ll schedule you into the calendar

Posted on by Jon Voisey

Virtual Observatory Discovers New Cataclysmic Variable

Simulation of Intermediate Polar CV star
Simulation of Intermediate Polar CV star (Dr Andy Beardmore, Keele University)

[/caption]

In my article two weeks ago, I discussed how data mining large surveys through online observatories would lead to new discoveries. Sure enough, a pair of astronomers, Ivan Zolotukhin and Igor Chilingarian using data from the Virtual Observatory, has announced the discovery of a cataclysmic variable (CV).


Cataclysmic variables are often called “novae”. However, they’re not a single star. These stars are actually binary systems in which their interactions cause large increases in brightness as matter is accreted from a secondary (usually post main-sequence) star, onto a white dwarf. The accretion of matter piles up on the surface until the it reaches a critical density and undergoes a brief but intense phase of fusion increasing the brightness of the star considerably. Unlike type Ia supernovae, this explosion doesn’t meet the critical density required to cause a core collapse.

The team began by considering a list of 107 objects from the Galactic Plane Survey conducted by the Advanced Satellite for Cosmology and Astrophysics (ASCA, a Japanese satellite operating in the x-ray regime). These objects were exceptional x-ray emitters that had not yet been classified. While other astronomers have done targeted investigations of individual objects requiring new telescope time, this team attempted to determine whether any of the odd objects were CVs using readily available data from the Virtual Observatory.

Since the objects were all strong x-ray sources, they all met at least one criteria of being a CV. Another was that CV stars often are strong emitters for Hα since the eruptions often eject hot hydrogen gas. To analyze whether or not any of the objects were emitters in this regime, the astronomers cross referenced the list of objects with data from the Isaac Newton Telescope Photometric Hα Survey of the northern Galactic plane (IPHAS) using a color-color diagram. In the field of view of the IPHAS survey that overlapped with the region from the ASCA image for one of the objects, the team found an object that emitted strongly in the Hα. But in such a dense field and with such different wavelength regimes, it was difficult to identify the objects as the same one.

To assist in determining if the two interesting objects were indeed the same, or whether they just happened to lie nearby, the pair turned to data from Chandra. Since Chandra has much smaller uncertainty in the positioning (0.6 arcsecs), the pair was able to identify the object and determine that the interesting object from IPHAS was indeed the same one from the ASCA survey.

Thus, the object passed the two tests the team had devised for finding cataclysmic variables. At this point, followup observation was warranted. The astronomers used the 3.5-m Calar Alto telescope to conduct spectroscopic observations and confirmed that the star was indeed a CV. In particular, it looked to be a subclass in which the primary white dwarf star had a strong enough magnetic field to disrupt the accretion disk and the point of contact is actually over the poles of the star (this is known as a intermediate polar CV).

This discovery is an example of how discoveries are just waiting to happen with data that’s already available and sitting in archives, waiting to be explored. Much of this data is even available to the public and can be mined by anyone with the proper computer programs and know-how. Undoubtedly, as organization of these storehouses of data becomes organized in more user friendly manners, additional discoveries will be made in such a manner.