The Invasion of “Teapots From Space!”

With a combination of alien invasion and British invasion, a new video series provides an amusing way to learn about different aspects of astronomy and space. “Teapots from Space” was created by UK astronomers Edward Gomez, Jon Yardley and Olivia Gomez, and these vodcasts convey lots of science in a short and entertaining package.

“The aim of the series to make astronomy a bit more light hearted but still give a good representation of the science,” said Edward Gomez, from Cardiff University. “I took a lot of inspiration from Douglas Adams when I wrote the episodes, and so the Teapots are like a cross between a sci-fi B-movie and Douglas Adams’ ‘Hitchhikers Guide to the Galaxy.'”

The Teapots come to learn about Earth and the humans that inhabit it. They abduct human scientists who explain all the questions the Teapots have about astronomy, technology and space. But before sending them back to Earth, the scientists’ minds are wiped so they don’t remember the abduction. Sometimes, disembodied robot astronomers provide the answers. Don’t worry, though: no astronomers were harmed in the making of these “potcasts.”

“There are lots of vodcasts available in the world of science but I wanted to make some which were fun and accessible but did not turn down the volume on the science,” Gomez said. “The idea of the Teapots from Space came into being as a vehicle for telling different scientific stories. Nothing is taken too seriously, but the science is all correct.”

Currently there are four episodes available, and another should be released soon. The first episode is about space junk while #2 is about the Herschel and Planck spacecraft; episode 3 is about how to spot (and abduct) astronomers, and the newest episode is about supernovae.

So, settle in on a comfy chair for some afternoon tea and tasty biscuits to watch Teapots From Space.

New Results from the CDMS II Experiment

It’s no secret that astronomers claim that most of our universe is made of dark matter that cannot be readily detected. From Fritz Zwicky’s observations of the Coma clusters in the 1920’s which suggested that additional mass would be necessary to hold the cluster together, to the flat rotation curves of galaxies, to lensing in such places as the Bullet Cluster, all signs point to matter that neither emits nor absorbs any form of light we can detect. One possible solution was that this missing matter was ordinary, but cold matter floating around the universe. This form was called Massive astrophysical compact halo objects, or MACHOs, but studies to look for these came up relatively empty. The other option was that this dark matter was not so garden variety. It posed the idea of hypothetical particles which were very massive, but would only rarely interact. These particles were nicknamed WIMPs (for weakly interacting massive particles). But if these particles were so weakly interacting, detecting them would be a challenge.

An ambitious project, known as the Cryogenic Dark Matter Search, has been attempting to detect one of these particles since 2003. Today, they made a major announcement.

The experiment is located a half-mile underground in the Soudan mine in northern Minnesota. The detector is kept here to shield it from cosmic rays. The detectors are made from germanium and silicon which, if struck by a potential WIMP, will become ionized and resonate. The combination of these two features allow for the team to gain some insight as to what sort of particle it was that triggered the event. To further weed out false detections, the detectors are all cooled to just above absolute zero which prevents most of the “noise” caused by the random jittering of atoms thanks to their temperature.

Although the detector had not previously found signs for any dark matter they have provided understanding of the background levels to the degree that the team felt confident that they would be able to begin distinguishing true events. Despite this, false positives from neutron collisions have required the team to “throw out roughly 2/3 of the data that might contain WIMPs, because these data would contain too many background events.”

The most recent review of the data covered the 2007-2008 set. After carefully cleaning the data of as many false events and as much background noise as possible the team discovered that two detection events remained. The significance of these two detections was the result of today’s conference.

Although the presence of these two detections from 8/5 and 10/27 2007, could not be ruled out as genuine dark matter detections, the presence of only two detections was not statistically significant enough to be able to truly stand out from the background noise. As the summary of results from the team described it, “Typically there must be less than one chance in a thousand of the signal being due to background. In this case, a signal of about 5 events would have met those criteria.” As such, there is only a 1:4 probability that this was a true case of a detection of WIMPs.

Astronomer turned writer, Phil Plait put it slightly more succinctly in a tweet; “The CDMS dark matter talk indicates two signals, but they are not statistically strong enough to say “here be dark matter”. Damn.”

For more information:

Collaboration’s Website

Liveblogging of Conference by Cosmic Variance

Spirals, Tides, and M51

Spiral galaxies are undoubtedly one of the most beautiful structures in the universe. Yet, their simple elegance belies a complex nature. How do such structures not “wind up” and what causes them in the first place? The answers to these questions is a long standing challenge. Under one model, spiral structure is created by spiral density waves. In another, they are induced by tidal interactions. It is this approach that is explored in a new paper by Dobbs et al., accepted for publication in the Monthly Notices of the Royal Astronomical Society. Specifically, the authors attempted to use modeling of tidal forces to recreate the structure of the spiral arms on the grand design spiral, M51.

M51sim1To model the interaction, they began with a model of a simple galaxy with a mass distribution (broken into a disc, bulge, and halo) similar to that for M51. Their initial galaxy was initially free of spiral structure, but “gravitational instabilities in the stars [Note: as opposed to the galactic gas. Not in individual stars.] produce a multi-armed” and patchy spiral structure (known as a flocculent spiral). This flocculent nature was first predicted in a 1964 paper by Toomre and has been simulated numerous times since then. Dobbs’ team then introduced a point source to represent the smaller galaxy (NGC 5195) along the orbital parameters derived by previous simulations of Theis and Spinneker in 2003.

For the first 60 million years, significant new structure was not evidence. The disc showed some perturbation due to the approaching companion, but no new spiral structure arose. However, by 120 million years from the start of the simulation, hints of a spiral arm on the side of the galaxy closest to the companion begin forming and by 180 million years, two pronounced “grand design” spiral arms dominate the face of the galaxy, spanning over 15,000 light years.

But the arms were too good to last. By 240 million years, the arms only stretch to a mere 6,500 light years as the gravitational forces from the companion seem to shepherd the galaxy’s gas as it is pulled around in its orbit. By 300 million years, the spiral arms have grown again and the pair looks remarkably similar to the present state of the M51/NGC 5195 system.

Comparison of simulation at 300 million years to HST image.
Comparison of simulation at 300 million years to HST image.

The authors note several features their simulation has in common with the observed galaxy. On the side where the companion first approached the galaxy, they note a “kink” in one arm (labeled as A in image to left). Another similarity is a splitting of one of the spiral arms although, again, the exact positioning is different (labeled B).

Another comparison the authors made was to the strengths (or amplitude) of various arm patterns (1 arm, 2 arm, 3 arm, etc…) over time. They found that the two armed pattern was the most predominant, but from the mechanics, they determined there were underlying higher armed structures that never fully took hold. However, these higher armed patterns did come close to the strength of the 2 arm spiral. The authors note that this is consistent with the observational findings of another group studying M51 in a work that has yet to be prepared for publication.

However, there are also some differences. A plume of gas extended from the simulated M51 which has no counterpart in actual observations (labeled C). Actual observations show large amounts of gas in front of the companion galaxy which are not present to the same degree in the simulation (labeled D). Lastly, real observations show a noticeable flattening of M51’s arms closest to the companion. Again, these do not appear in the simulation. The authors suggest discrepancies may be due to the over simplistic modeling of NGC 5195 as a point source instead of an extended body, or slight differences in initial parameters when compared to the actual system.

Even with these differences, the authors suggest that their modeling of the interaction shows that spiral structure, at least in this case, is most likely the result of the tidal interaction on M51 by NGC 5195. They also note that spiral density waves are likely not the culprit since other studies have not been able to determine a consistent “pattern speed” for the galaxy (the pattern speed is the angular speed at which the arms would rotate if viewed as a coherent structure). Instead, observations showed that the arms should have different pattern speeds at different radii.

Although their work does not suggest that all spiral structure is formed by tidal interactions with companions, this work makes a strong case for the possibility in many galaxies which would have such companions and M51 in specific. Furthermore, the simulations also reveal that these tidally induced arms are a temporary phenomenon. Since they do not have a fixed speed, they will slowly wind up and as the interaction progresses, the galaxies will be further distorted and eventually merge.

(Thanks to Claire Dobbs for permission to reproduce images from the paper as well as clarification on a few points.)

Forming Planets Around Binary Stars

Young binarys stars: Image credit: NASA

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Fanciful science fiction and space art frequently depict the lovely visage of a twin sunset where a pair of binary stars dips below the horizon (think Star Wars). While it has been established that planets could exist in such a system by orbiting in resonances, that only holds true for fully formed planets. Can forming star systems even support an accretion disk from which to form planets? This is the question a new paper by M. G. Petr-Gotzens and S. Daemgen of the European Southern Observatory with S Correia from the Astronomiches Institut Potsdam attempts to answer.

Observations of single young stars with disks have revealed that the main force causing the dispersion of the disk is the star itself. The stellar wind and radiation pressure blow the disk away within 6 to 10 million years. Predictably, more massive and hotter stars will disperse their disks more quickly. However, “many stars are members of a binary or multiple system, and for nearby solar-like stars the binary fraction is even as high as ~60%.” Could gravitational perturbations or the added intensity from two stars strip disks before planets could form?

To explore this, the team observed 22 young and forming binary star systems in the Orion Nebula to look for signs of disks. They used two primary methods: The first was to look for excess emission in the near infrared. This would trace accretion disks as they radiate away absorbed energy as heat. The second was to look spectroscopically for specific bromine emission that is excited as the magnetic field of the young star pulls this (and other) elements from the disk onto the stars surface.

When the results were analyzed they found that as much as 80% of the binary systems had an active accretion disk. Many only contained a disk around the primary star although nearly as many contained disks around both stars. Only one system had evidence of an accretion disk around only the secondary (lower mass) star. They authors note, “[t]he under-representation of active accretion
disks among secondaries hints at disk dissipation working faster on (potentially) lower mass secondaries, leading us to speculate that secondaries are possibly less likely to form planets.”

However, the average age of the stars observed was only ~1 million years. This means that, even though disks may be able to form, the study was not comprehensive enough to determine whether or not they would last. Yet a survey of the currently known extra-solar planets reveal that they must. The authors comment, “[a]lmost 40 of all the extra-solar planets discovered to date reside in wide binary systems where the component separation is larger than 100AU (large enough that planet formation around one star should not strongly be inuenced [sic] by the companion star).”

Strangely, this seems to stand at odds with a 2007 paper by Trilling et al. which studied other binary systems for the same IR excess indicative of debris disks. In their study, they determined “[a] very large fraction (nearly 60%) of observed binary systems
with small (<3 AU) separations have excess thermal emission.” This suggests that such close systems may indeed be able to retain disks for some time. It is unclear on whether or not it can be retained long enough to form planets although it seems unlikely since no exoplanets are known around close binaries.

Megaparsec

velocity vs distance, from Hubble's 1929 paper

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A megaparsec is a million parsecs (mega- is a prefix meaning million; think of megabyte, or megapixel), and as there are about 3.3 light-years to a parsec, a megaparsec is rather a long way. The standard abbreviation is Mpc.

Why do astronomers need to have such a large unit? When discussing distances like the size of a galaxy cluster, or a supercluster, or a void, the megaparsec is handy … just as it’s handy to use the astronomical unit (au) for solar system distances (for single galaxies, 1,000 parsecs – a kiloparsec, kpc – is a more natural scale; for cosmological distances, a gigaparsec (Gpc) is sometimes used).

Reminder: a parsec (a parallax of one arc-second, or arcsec) is a natural distance unit (for astronomers at least) because the astronomical unit (the length of the semi-major axis of the Earth’s orbit around the Sun, sorta) and arcsec are everyday units (again, for astronomers at least). Fun fact: even though the first stellar parallax distance was published in 1838, it wasn’t until 1913 that the word ‘parsec’ appeared in print!

As a parsec is approximately 3.09 x 1016 meters, a megaparsec is about 3.09 x 1022 meters.

You’ll most likely come across megaparsec first, and most often, in regard to the Hubble constant, which is the value of the slope of the straight line in a graph of the Hubble relationship (or Hubble’s Law) – redshift vs distance. As redshift is in units of kilometers per second (km/s), and as distance is in units of megaparsecs (for the sorts of distances used in the Hubble relationship), the Hubble constant is nearly always stated in units of km/s/Mpc (e.g. 72 +/- 8 km/s/Mpc, or 72 +/- 8 km s-1 Mpc-1 – that’s its estimated value from the Hubble Key Project).

John Huchra’s page on the Hubble constant is great for seeing megaparsecs in action.

Given the ubiquity of megaparsecs in extragalactic astronomy, hardly any Universe Today article on this topic is without its mention! Some examples: Chandra Confirms the Hubble Constant, Radio Astronomy Will Get a Boost With the Square Kilometer Array, and Astronomers Find New Way to Measure Cosmic Distances.

Questions Show #7, an Astronomy Cast episode, has megaparsecs in action, as does this other Questions Show.

How Galaxies Lose Their Gas

Galaxy mergers, such as the Mice Galaxies will be part of Galaxy Zoo's newest project. Credit: Hubble Space Telescope
The Mice galaxies, merging. Credit: Hubble Space Telescope

As galaxies evolve, many lose their gas. But how they do this is a point of contention. One possibility is that it is used to form stars when the galaxies undergo intense periods of star formation known as starburst. Another is that when large galaxies collide, the stars pass through one another but the gas gets left behind. It’s also possible that the gas is pulled out in close passes to other galaxies through tidal forces. Yet another possibility involves a wind blowing the gas out as galaxies plunge through the thin intergalactic medium in clusters through a process known as ram pressure.

A new paper lends fresh evidence to one of these hypotheses. In this paper, astronomers from the University of Arizona were interested in galaxies that displayed long gas tails, much like a comet. Earlier studies had found such galaxies, but it was unclear whether or not this gas tail was pulled out from tidal forces, or pushed out from ram pressure.

To help determine the cause of this the team used new observations from Spitzer to look for subtle differences in the causes of a tail following the galaxy ESO 137-001. In cases where tails are known to be pulled out tidally (such as in the M81/M82 system), there “is no physical reason why the gas would be preferentially stripped over stars.” Stars from the galaxy are pulled out as well and often large amounts of new star formation are induced. Meanwhile, ram pressure tails should be largely free of stars although some new star formation may be expected if there is turbulence in the tail which causes regions of higher density (think like the wake of a boat).

Examining the tail spectroscopically, the team was unable to detect the presence of large numbers of stars suggesting tidal processes were not responsible. Furthermore, the disk of the galaxy seemed relatively undisturbed by gravitational interactions. To support this, the team calculated the relative strengths of the forces acting on the galaxy. They found that, between the tidal forces acting on the galaxy from its parent cluster, and its own centripetal forces, the internal forces where greater, which reaffirmed that tidal forces were an unlikely cause for the tail.

But to confirm that ram pressure was truly responsible, the astronomers looked at other parameters. First they estimated the gravitational force for the galaxy. In order to strip the gas, the force generated by the ram pressure would have to exceed the gravitational one. The energy imparted on the gas would then be measurable as a temperature in the gas tail which could be compared to the expected values. When this was observed, they found that the temperature was consistent with what would be necessary for ram stripping.

From this, they also set limits on how long gas could last in such a galaxy. They determined that in such circumstances, the gas would be entirely stripped from a galaxy in ~500 million to 1 billion years. However, because the density of the gas through which the galaxy would slowly become denser as it passed through the more central regions of the cluster, they suggest the timescale would be much simpler. While this timescale say seem long, it is still shorter than the time it takes such galaxies to make a full orbit in their cluster. As such, it is possible that even in one pass, a galaxy may lose its gas.

If the gas loss occurs on such short timescales, this would further predict that tails like the one observed for ESO 137-001 should be rare. The authors note that an “X-ray survey of 25 nearby hot clusters only discovered 2 galaxies with X-ray tails.”

Although this new study in no way rules out other methods of removing a galaxy’s gas, this is one of the first galaxies for which the ram stripping method is conclusively demonstrated.

Source:

A Warm Molecular Hydrogen Tail Due to Ram Pressure Stripping of a Cluster Galaxy

dotAstronomy Conference

I’m attending the .Astronomy (dotAstronomy) Conference this week Leiden, The Netherlands, where we are discussing novel concepts of thinking and working in astronomy today. We’ll be discussing the data deluge that will be produced by upcoming surveys and instruments, how citizen science is making a real impact, and the new ways of communicating science to the public with web 2.0, blogs, podcasts and social networking. All week, you can watch the morning sessions of .Astronomy online at UStream, (or watch the stream below) and check out the .Astronomy website here to see what talks you are interested in. You can ask questions via the UStream chat, or follow along with the .Astronomy Twitter feed. I’ll be giving a talk on the 365 Days of Astronomy on Friday morning.

Live video by Ustream

Solo Sailor Spots Pacific Bolide

Jessica Watson and Ellas Pink Lady
Jessica Watson and Ella's Pink Lady

A 16-year-old high school girl who is attempting to sail solo around the world spotted a bright bolide over the Pacific Ocean during the peak of last week’s Leonid meteor shower. The International Meteor organization relies on reports just like this from observers in the field….or in this case “all at sea”.

Jessica Watson a student from Queensland, Australia, has set off on the adventure of a lifetime, attempting to become the youngest woman to sail solo and unassisted around the world.

Continue reading “Solo Sailor Spots Pacific Bolide”

High School Students Get Published in Astrophysics Journal

From the left: Klaus Beuermann (group leader), Jens Diese (back,teacher), and the high-school students Joshua Zachmann (front), Alexander-Maria Ploch (back), Sang Paik (front). JD, JZ, and AMP are from the Max-Planck-Gymnasium, SP is from the Felix-Klein-Gymnasium.

High school students from Germany have now done what many scientists strive for: had their research work published by a science journal. The Astronomy & Astrophysics science journal published a paper co-authored by three students who observed the light variations of the faint (19th magnitude) cataclysmic variable EK Ursae Majoris (EK UMa) over two months. Led by astronomer Klaus Beuermann from the University of Göttingen, and the students’ high school physics teacher, the team made use of a remotely-controlled 1.2-meter telescope in Texas. Astronomy & Astrophysics says the team “presents an accurate, long-term ephemeris,” and that “they participated in all the steps of a real research program, from initial observations to the publication process, and the result they obtained bears scientific significance.”

The students, Joshua Zachmann, Alexander-Maria Ploch, Sang Paik and their teacher, Jens Diese, made observations, analyzed the CCD images, produced and interpreted light curves, and looked at archival satellite data. Beuermann, the astronomer they worked with said, “Although it is fun to perform one’s own remote observations with a professional telescope from the comfort of a normal school classroom, it is even more satisfying to be involved in a project that provides new and publishable results rather than to perform experiments with predictable outcomes.”

Cataclysmic variable research is a field where the contributions of small telescopes has a long tradition. Cataclysmic variables are extremely close binary systems containing a low-mass star whose material is being stripped off by the gravitational pull of a white dwarf companion. Due to the transfer of matter between the stars, these systems vary dramatically in brightness on timescales in the whole range between seconds and years. This largely unpredictable variability makes them ideal targets for school projects, particularly since professional observatories are generally unable to provide enough observation time for regular monitoring.

An accurate ephemeris is needed to keep track of the orbital motions of the two stars, but none was available because EK UMa is faint in the optical range and requires a long-term observation of the light variations. The strong magnetic field of the white dwarf turns the light of the hot matter striking the surface of the white dwarf into two “lighthouse” beams. By measuring the times of the minimum between the beams, the group was able to determine an orbital period accurate enough to keep track of the eclipse that took place in 1985, over 100 000 cycles earlier. By combining their own measurements with those made by the Einstein, ROSAT, and EUVE satellites, they estimated the orbital period over 137 000 cycles to an accuracy of a tenth of a millisecond. Surprisingly, the orbital period is extremely stable, although the period of such very close binaries is expected to vary due to the presence of third bodies and magnetic activity cycles on the companion star.

The team’s paper: (not yet available) A long-term optical and X-ray ephemeris of the polar EK Ursae Majoris, by K. Beuermann, J. Diese, S. Paik, A. Ploch, J. Zachmann, A.D. Schwope, and F.V. Hessman.

Source: Astronomy & Astrophysics