Cosmic-ray acceleration in a superbubble

Cosmic-rays are very energetic particles that pervade the Universe. Discovered one century ago, their origin is still unclear. In the Galaxy, the most promising sources are the powerful magnetized shock waves triggered by supernovae, which mark the cataclysmic end of a star: the thermonuclear disruption of a white dwarf (as for SN 1006) or the core-collapse of a massive star (as for RX J1713-3946). Massive stars are born in groups, called OB associations. And as they live fast and die young, they are likely to spend their whole life into clusters. Their strong stellar winds, together with their subsequent explosions, profoundly alter their environment: they carve huge, hot and tenous cavities around them, called superbubbles. It is naturally expected that these objects play a key role in the acceleration of cosmic rays in the Galaxy. And measurements of the composition of the cosmic rays indeed point to OB associations and their superbubbles as the likely source of the material of a substantial fraction of them. But the particles that we collect on the Earth don't tell where they come from: being charged particles, they wandered a lot in the Galactic magnetic field before reaching us. We can spot freshly accelerated particles next to their sources thanks to the high-energy radiation they emit. But, until recently, observations of superbubbles were very scarce.

The situation changed dramatically in the past years with the rise of a new generation of instruments. The Fermi satellite is one of them. Launched by NASA in 2008, this international mission observes the gamma-ray sky between the energies of about 100 MeV to 100 GeV with unprecedented sensitivity. It monitors all the sky, and, of particular interest for us today, a massive star forming region in the direction of Cygnus. Analyzing the data from high-energy instruments is a difficult task, especially for extended sources. After modelling and carefully removing a number of backgound diffuse emissions, scientists found a significant excess of high-energy emission from this part of the sky. They were stricken to see that the emission is coincident with the cavities formed around the numerous clusters of massive stars: it nicely follows the ionization fronts eroding the surrounding molecular clouds, as if in a "cocoon". Various objects can produce gamma-ray radiation (individual stars, pulsars and their nebulae), but after checking all possibilities the collaborators concluded that such small sources don't make a good match to the extended emission. The most likely explanation is that the cocoon is filled with cosmic-rays, that slowly diffuse inside the superbubble, and radiate some of their energy in the process (they could be either electrons or protons). The energy distribution of the observed photons is notably hard, meaning that the fraction of particles with the highest energies is higher than usual. Because it's all the more easy for particles to escape their accelerator when they are energetic, this hardness points to freshly accelerated particles. So here we have it: the Fermi observation provides the first strong direct evidence for the long-advocated hypothesis that OB associations host cosmic-ray factories.

The two main clusters in the cocoon are so young (4 to 6 million years for Cygnus OB2, 6 million years for NGC6910) that they might or not have experienced supernovae yet. But the winds of massives stars themselves can produce similar shock waves. And they generate lots of magnetic turbulence in the bubble, which traps particles in the cocoon, where they can get re-accelerated by other shocks and/or by magnetic waves. Existing models of acceleration into superbubbles predict spectra with a shape similar to that infered, which gives credance to the scenario. However it is too early for a detailed comparison of models with the cocoon spectrum: more work is needed on both fronts. Theoreticians will refine their models, and observers will have a closer look a other regions. The Arches, Quintuplet, and Sgr B2 clusters are good targets towards the Galactic centre, as are Westerlund 1 and Westerlund 2. These objects have already been detected at even higher energies, by one of the other prominent new instruments, the H.E.S.S. telescope.

Brian Schmidt's wine isn't quite as good as his science, but it is a nice tipple.  There he is pressing grapes at the top of the page - the guy with the akubra hat. And there's a bunch of astronomers picking the grapes for him at his Canberra vineyard. May his universe keep accelerating towards more and more happiness.

And the Nobel Prize in Physics goes too...

Saul Perlmutter, Brian Schmidt and Adam Riess for the discovery of the accelerating expansion of the universe.  The expansion of the universe has been known for many years now.  However Perlmutter, Schmidt and Riess, along with their supporting cast took those measurements to the next level.

Perlmutter and Schmidt investigated the light from Type Ia Supernovae explosions by setting up two rival teams to search for these energetic explosions.  Riess, working for Schmidt, took the data and converted the amount of light we received from the explosion into what the Type Ia's intrinsic luminosity.  With that in hand he could calculate the distance to these objects and compare that against their redshift.  This allowed for an extremely precise measurement of the expansion of the universe and its evolution in time.

What they found was amazing.  Instead of a fixed expansion like was expected from a simple Hubble Law, they found that the expansion changed overtime.  It changed in such a way that as one got closer to the present time the universe was expanding faster and faster.  Thus the universe's expansion was accelerating.

This discovery set off a flurry of activity in the cosmological community to explain this expansion as well as figure out what will happen if it continues.  If the expansion continues to accelerate, and given the fact that the universe appears to have a flat geometry, it seems that the eventual fate of the universe is that we will expand forever to the point where we will no longer see any other stars in the sky.  Naturally this will take hundreds of billions of years.  This also assumes that the acceleration continues and does not reverse itself in the future.  Regardless of the future fate of the now incorrectly named Hubble constant, we know for sure that the expansion is variable and currently accelerating.

ALMA First Light

The Atacama Large Millimeter/submillimeter Array (ALMA) has released it's first light images (seen above) and is now is open for business.  Located in the Atacama desert in Chile, it is in one of the driest regions in the world.  The plateau itself is 5 km above sea level and shielded by the Chilean Coastal Range.  This insures that the desert gets no water.  This is great for submillimeter astronomers, as water vapor is a significant foreground to their measurements.

ALMA itself has been about a decade in the making and is a collaboration between the National Radio Astronomy Observatory (NRAO), the European Southern Observatory (ESO), and the National Astronomical Observatory of Japan (NAOJ).  Currently made of nineteen 12 meter radio telescopes ALMA will continue to expand until it reaches completion in 2013 with 66 telescopes.  This will allow ALMA to reach resolutions 5 times smaller than the Hubble Space Telescope and 10 times better than the Very Large Array (VLA).  This will allow astronomers to get an unprecedented look at the submillimeter sky.  This view will allow us to better understand protostellar formation, planet formation, black hole physics, and starburst galaxies just to name a few.

Speaking of starburst galaxies, the first light image is of the Antennae galaxy which happens to be one.  The Antennae is the result of a major merger of two spiral galaxies of roughly the same size.  The image shows the famous Hubble image in blue with the ALMA image in yellow and orange.  The magatama shaped ALMA image shows where the protostars in this starburst galaxy are forming.  These stars are currently buried in their natal clouds and as such are invisible to Hubble due to extinction.  However, ALMA reveals these regions allowing us to probe the locations of star formation themselves, before the stars that form blow away all the surrounding gas and dust.

A Beginning and an End

China successfully launched the first piece of its upcoming space lab on Thursday.  Named Tiangong 1 (Heavenly Palace), it is intended to serve as a testing base for space technologies that China will need in the future.  This makes China the third country to successfully have launched their own space station, following Russia and the US.  The station module is currently unmanned but will see several visitors in the coming months including China's first female astronaut.

In other news, the Tevatron shuts down for the final time tomorrow.  After nearly 25 years of operation, it has seen its last ion particle beams.  Tevatron bridged the gap between the cancellation of the Superconducting Super Collider and the building of the Large Hadron Collider (LHC).  With the closure of the Tevatron the US will lack a high energy particle collider on the scale of the LHC, meaning that US particle physicists interested in high energy collisions will have to go to CERN to do their experiments.  The Tevatron itself may be recommissioned as a muon collider making it one of the first in the world to collide leptons at super high energy.

Particles faster than the speed of light???

This surprising and confusing possibility was brought up due to recent results from OPERA (Oscillation Project with Emulsion-tRacking Apparatus), a neutrino experiment at Gran Sasso Laboratory (the paper can be found here).  The experiment works by firing neutrinos from CERN at Gran Sasso through the ground.  The original intent of the experiment was to study neutrino oscillations, but they ended up with a curious result.

When the timed how long it took the neutrinos to reach the detector at Gran Sasso from CERN they clocked in at 987.8 ns (Gran Sasso is 730.085 km away from CERN).  When they checked how long light would have taken in a vacuum they got 1048.5 ns, a difference of 60.7+/-6.9(statistical)+/-7.4(systematic) ns.  In other words the neutrinos appear to be traveling 0.00248+/-0.00028(statistical)+/-0.00030(systematic) percent faster than the speed of light.  The statistical and systematics after the numbers are the calculated errors on the measurements.

This is a mind boggling result, contrary to all that we expect from physics as we know it.  Thus the physicists who work on OPERA have asked other neutrino experiments such as T2K and MINOS to confirm this result.  Naturally they are also searching for any errors in their calculations.  If it is not confirmed then the measurement by OPERA is suspect and there is likely an error in their analysis.  However if confirmed, things will get a little weird to say the least.

Like the OPERA physicists I will refrain from speculating about what this might entail for physics if true.  This result is too significant to speculate on.  We need to know for certain if this is true.  Odds are definitely on the side of it being flat out wrong. Too much of modern physics works too well, which casts significant doubt on this measurement.  Not to mention that a significant delay was not seen between the neutrinos arriving and us observing the explosion of Supernova 1987A.  This single event already ruled out this result, but only for electron neutrinos, the neutrinos in this case are muon and tau neutrinos.  Also there is history to consider, in 2007 a similar claim was made in Chicago but it had a huge margin of error that ruled out the measurement being significant.  This measurement though is way above the normal 3 sigma level of significance (basically 3 times the error bar size) usually needed for scientific data so it deserves close scrutiny.  Naturally the entire scientific community will be holding its collective breath until it is either confirmed or falsified.

Why is the Sun Yellow?

This classic childhood question actually has the same answer as, "Why the sky is blue?'', which is actually not the same answer as many teachers give when teaching introductory Astronomy courses, including myself.  This was pointed out in an article, written by Jonathan M. Marr and Francis P. Wilkin at Union College, which appeared on arXiv today.

The usual explanation for why the Sun is yellow is given by the use of Wien's Law which describes where the peak of a blackbody spectrum is given the temperature of the body.  Using Wien's Law and the surface temperature of the Sun, 5800 K, we end up with a wavelength of 500 nm, which we perceive as green.  However, the Sun isn't green by yellow.  Thus the explanation goes that the sky preferentially scatters blue light, via Rayleigh scattering, which shifts the color towards yellow.  Plus the way the human eye perceives the light and the shape of the blackbody curve naturally favor a yellow color rather than green.

This explanation turns out to be partially correct.  While Wien's Law does give the peak emission for a blackbody curve, it only does so for the intensity, B_{\lambda}, and only when done in wavelength.  If one does the emission in frequency, which is inversely related to wavelength one ends up with the blackbody peak being at 880 nm, which is red.  One can't have two peaks so what is going on here?

This ends up being a pretty subtle, but power piece of radiative transfer (I apologize in advance this gets a little technical).  It turns out what matters is the units one looks at.  If one looks at the proper units for the emission, the peaks line up.  The proper units to look at are not intensity but what is termed the spectral energy distribution (SED).  Whereas intensity, B_{\nu} in this case, is in ergs/sec/cm^2/str/Hz, the SED is measured in \nu B_{\nu} which is ergs/sec/cm^2/str.  With the per frequency dependence gone, the peak now lines up properly with the peak gotten from doing the analogous thing with \lambda B_{\lambda}.  This is because the frequency and wavelength are inversely related.  This shifts the respective intensities in different ways.  The wavelength version shifts the intensity down to smaller wavelength, higher frequency.  The frequency version does the opposite by shifting the frequency down and increasing the wavelength.  The SED formulation removes this dependency, reconciling the two.

Using the SED version of the Planck function, another name for a blackbody distribution, the peak is now in between the two at around 633 nm, which is red.  The Sun isn't red though so what's the deal?  It turns out that astronomers have been abusing Wien's Law.  The Planck function isn't sharply peaked around its peak.  Rather it slowly falls off in the immediate region surrounding the peak wavelength.  Over the visual range, which is actually quite small in terms of wavelength space at 390-750 nm, the SED of light between the red and blue end only varies by about 1% which is less than the eye can discern.  Thus the eye would see the unmodified light of the Sun as white, and not any color.

Then why does the Sun look yellow?  Well the atmosphere preferentially scatters blue light via Rayleigh scattering as noted before.  This gives the sky its blue color.  All the blue light that comes from the sky has to be removed from the light coming directly coming from the Sun.  As a result this leaves only the red and green light, which our eyes perceive as yellow.

Thus from now on whenever I, or any other astronomer for that matter, are asked why the Sun is yellow or why the sky is blue, we can give the same answer from now on.

Planet found around Double Suns

This iconic scene from Star Wars may not be too far from reality.  It turns out that Kepler-16, has a planet orbiting around a binary star.  While the planet is much, much larger than the fictional Tatooine, about the size of Saturn, it illustrates that it is possible to have planets in stable orbits around a close binary star.

Why are orbits around binary stars thought to be unstable?  Much for the same reason that Jupiter acts like a giant scatterer in the outer Solar System.  Large bodies orbiting each other tend to push and pull orbits that come into their gravitational influence.  Actually NASA regularly uses this effect to change the orbits of satellites.  The larger the planet, or star, the larger the influence.  This can cause orbits to become unstable and if a close encounter occurs the body in question may be ejected in to interstellar space.  This is thought to be the cause of high velocity stars that we see flying through our galaxy.

However, in the case of Kepler-16 we have a close binary that also has a planet that is fairly close in, at only 0.7 AU.  Even more interesting is the fact that is has a low orbital inclination, meaning that the planet likely originally belonged to the star system when it formed.  Thus Kepler-16 likely shows that binary stars can have stable planets.

Not that this is entirely unexpected, theorists have been able to model stable orbits around binary stars for quite a while.  Observationally, though, this is the first time that a binary has been confirmed to have a planet.  Thus it should constrain the theoretical models of how planets form and orbit around binaries, giving us an even better chance of finding a planet in a similar situation to Tatooine.

SDO Views an Eclipse

One might think it weird to position a Sun observing telescope such that it would experience an eclipse of that celestial body.  However, that is what is happening now to the Solar Dynamics Observatory (SDO) as the Earth moves towards the Autumnal Equinox on September 23rd.  For the next 3 weeks around the equinox the Earth will block out the Sun for the SDO for up to 72 minutes.

So why did NASA decide to do that?  Well it was to put the SDO in a convenient position to be able to transmit data to Earth constantly to the same ground station.  This was deemed to be more important than the ability to monitor the Sun 24/7, especially since the eclipses are not very long.

Similar to many communications satellites, weather satellites and the GPS system, the SDO sits in geosynchronous orbit (GEO).  At that orbit you go around the Earth at the same speed as the Earth rotates which makes you appear stationary with respect to the Earth's surface.  The orbit is at a radius of 42,164 km from the center of the Earth, which is much closer than the Moon.  In order to be truly geosynchronous the orbit has to be inclined the same amount as the Earth's tilt (24.3 degrees) such that it hovers over the equator.

This is tilt means that for most of the year the Earth will not block out the Sun for the SDO. The Earth has only an apparent angular size of 17 degrees from the point of view of the satellite.  Since the inclination of the SDO's orbit follows the Earth's tilt, it is usually far enough away the ecliptic, the plane of the orbit of the Earth around the Sun, when it is behind the Earth not to have the Earth block its view.  This is due to the Earth's north pole tilting towards the Sun in the northern hemisphere's summer, which moves the orbit behind the Earth above the ecliptic, and away during the winter, which moves the orbit behind the Earth below the ecliptic.  This is the same reason why we don't get Lunar and Solar eclipses all the time, because the orbit Moon is inclined with respect to the ecliptic.

However if one is at GEO there are two times of year when the Earth's axis is not tilted away or towards the Sun, the equinoxes.  At those points the orbital section behind the Earth is in the ecliptic and the shadow of the Earth falls on the satellites in that orbit.  Thus the SDO is eclipsed for a short period of time during these sections of the Earth's orbit.  Not that the SDO can't do interesting science during these times. It will have to opportunity to look at the Earth and its surroundings during this time, not to mention that eclipses give a great chance to study the corona of the Sun.

In other news the US Senate has proposed an appropriations bill for NASA which continues funding for JWST.  Thank you to all those who contacted their representatives and senators.  The bill is not final however and still needs to be reconciled with the House version as well as voted on.  So continued support is appreciated.

AREPO vs. Gadget-2

Remarkably the image posted here is not of actual galaxies but rather those simulated by two codes.  The top is from a code called AREPO while the bottom is from the code Gadget-2.  Even more remarkable is that this simulation was for a code test of AREPO to see how it compared to a well established code like Gadget-2.

Both codes were developed by Volker Springel at Heidelberg University.  Both codes solve hydrodynamics and gravitational collapse.  However, the two codes could not be more different in terms of how they solve the hydrodynamics. 

Gadget-2 solves hydrodynamics via smoothed particle hydrodynamics (SPH).  SPH codes solve hydrodynamics in a similar way to N-body simulations.  Fluids after all are just a collection of particles whose collective evolution can be explained by the Navier-Stokes equations.  SPH just assumes that the particles in question are very large.  Since fluid mechanics a scale free, so long as your particles are not too large they will act the same as a fluid with much smaller particles.

SPH codes are popular for cosmology simulations because they allow you to solve gravity in a similar way to normal N-body codes.  This is convenient because the most computationally expensive part is usually solving the gravity.  There are a number of tricks one can use with N-body simulations to reduce the expense which can be applied to SPH as well.

The downside is that SPH does a poor job of capturing shocks and other fluid discontinuities.  These are important to track as these control fluid mixing as well as heating of the gas.  Thus SPH usually gets the general structure correct but it looks clumpy, due to the particles, and shocks are much more diffusive than one would like.

In order to capture shocks and discontinuities properly one typically falls back on grid based codes.  These codes treat the fluid in its continuum limit rather than treating it as a collection of particles.  Having a grid allows one to solve the equations of fluid dynamics directly at each grid interface, leading to much sharper discontinuities.  The problem with these types of codes is that gravity is difficult to and the resolution does not adjust with the flow, unlike in SPH where the resolution naturally follows where the gas is.

One can alleviate this problem by doing adaptive mesh refinement (AMR), which adapts the structure of the grid to the flow pattern.  However, you still have a problem that the code is Eulerian rather than Lagrangian.  In an Eulerian calculation one fixes a frame with respect to the gas and then calculates the flow with respect to that frame.  This can lead to large errors if the flow is moving fast through the frame in question.  On the other hand Lagrangian calculations follow a gas element of a specified mass.  The fluid equations are solved in the frame of that gas, reducing errors due to its motion.  This is another advantage SPH has.

Ideally one would like to have both the advantages of SPH and grid based codes.  Well AREPO was developed to do just that.  AREPO has what is known as a unstructured mesh, which is common in engineering circles.  However, AREPO takes it one step further by allowing the mesh to move with the flow in a psuedo-Lagrangian way.  This allows the grid to resize and shape itself as the fluid evolves, putting higher resolution in denser areas and reducing the errors due to fluid motion.

This leads to the much sharper and better looking galaxies in the AREPO image.  One can see movies showing individual galaxies, here.  It's uncanny how realistic these simulations look compared to real observations.

All is not roses for AREPO though as it is an expensive code to run, taking 50% longer to execute than Gadget-2.  Plus the memory overhead is large for these type of codes.  Nonetheless, the pay off one gets in terms of resulting simulation is quite impressive.

One more thing to wrap up this ridiculously long post (congrats to making it this far).  Fermi released their 2 year all sky map.  It shows even more sources than the 1 year map and with greater detail.  Very cool stuff.

HH47 Puts on a Show

This amazing video was released recently by Hubble of a jet coming from a young star.  Taken over 14 years from 1994 to 2008, these images give us a rare look at the time evolution of an astrophysical system.  Normally it is impossible to see time variability in large astronomical objects as their shear size and distance give them evolution times that are much longer than any human could hope to see.  However, some objects are close enough, small enough or moving fast enough that we can make out their motion as shown in the above clip.

The above object is called HH47.  HH is the designation for a Herbig-Haro object.  HH objects are now known to be glowing portions of jets that are ejected by a young star when it forms.  These jets originate at the accretion disc of the star and then are collimated by magnetic fields and rotation.  The clumpiness and structure in the jet is currently a subject of much study in the astrophysical fluids community.  The nature of the clumps and their formation can tell us a lot about the formation of the jet and its propagation.

Type Ia in M101

Excitement is spreading through the Supernova community as a Type Ia supernova was detected in M101 (aka the Pinwheel Galaxy). This makes it one of the closest supernovae in recent years (21 Mpc), even closer than the recent one in M51 (aka the Whirlpool Galaxy). It was caught early in its evolution by the Palomar Transient Factory and has been designated as SN 2011fe (PTF11kly). It is expected to brighten to around 10th magnitude, which should be visible to anyone with a moderate sized telescope. M101 is just above of the handle of the Big Dipper and so should be visible for most of the night. Today's APOD shows a picture of the supernova in M101, which should make it easier to find (a smaller version in visible on this page).

Even more exciting for astronomers is it's type as a Ia supernova. Type Ia supernovae are a special type of supernovae that lack hydrogen and show a singly ionized silicon line in their spectra. The leading theory to explain these observations is that a Type Ia supernovae is really a white dwarf that exceeded the Chandrashekar limit for mass of 1.4 solar masses and detonated like a massive thermonuclear bomb. White dwarves don't have any surrounding hydrogen and are rich in silicon, explaining the spectra.

White dwarves when they form typically aren't close to the Chandrashekar limit so they must accrete the mass some how. Currently it is thought that this is done either by the white dwarf pulling mass off of a companion star that is in a close orbit or it merges with another white dwarf. It is thought that when the white dwarf has accumulated enough mass, it undergoes a thermonuclear fusion runaway which starts as a deflagration but then converts to a detonation completely obliterating the white dwarf. This releases a ridiculous amount of energy to the tune of 10^{51} ergs (one FOE), which interestingly is equal to the gravitational binding energy of the white dwarf.

The fact that the white dwarf explodes at a preset mass and has a predetermined energy output based on that mass makes Type Ia's useful as standard candles. Since Type Ia's are super-bright they can be seen for a very long distance, even out to cosmologically relevant distances. In fact Type Ia's are so useful as standard candles in cosmology there is an entire subsection of astronomy devoted to their detection. With that data cosmologists have been able to show that the universe is not only expanding but that the expansion is accelerating.

However, there is still quite a bit that is unknown about Type Ia's as astrophysical objects which puts limits on the precision of distance measurements. In order to learn more, astronomers investigate Type Ia's that are closer by or that have already exploded. This is why the Type Ia in M101 is so exciting, it is closer than any Type Ia in recent history and we can use all our current instruments to take a very close look at it.

Of course what would be even more exciting would be to have a Type Ia go off in our own galaxy. We expect one to go off roughly every 100 years in our own Milky Way and since the last one was spotted by Kepler back in 1604, we are long past due for one. In fact we are due for a supernova of any type as the last one that we know of to go off in our galaxy was in the 1860's.

arXiv at 20

Happy belated birthday to arXiv.org, which turned 20 on Sunday! Since its inception in 1991, arXiv has become the premier location for posting preprints of scientific articles. Originally just for high energy physics, arXiv quickly expanded to include the rest of physics (including astrophysics), math, nonlinear sciences, computer science, quantitative biology, quantitative finance, and statistics.

A fascinating and humorous article posted by the founder of arXiv, Paul Ginsparg, commemorating the anniversary can be found here. What is the future of arXiv? No one can really say, as the fabric that makes up the internet has shifted drastically over the now 50 years since its inception. What can be said though is that the world of scientific research and publishing has benefited greatly from the creation of arXiv and sister sites such as ADS.

Juno On It's Way

Juno was launched on it's way to Jupiter last week on Friday, the latest in a long line of probes to visit the gas giant. Today's APOD shows the launch of Juno on top of an Atlas V rocket. Astrophysicists and space scientists are excited about Juno as it will be the first time since Galileo that a space craft has orbited the planet. Even more valuable it will do so in a polar orbit getting a good look at the north and south poles of the planet.

This is of particular interest to plasma physicists as Jupiter has the most powerful magnetic field in the Solar System (outside the Sun of course) which creates many interesting plasma effects. One of the most notable are the aurorae which can be seen from Earth. Even more fascinating is the auroral footprint of the moon Io, whose atmosphere is highly ionized. This ionized atmosphere means that Io creates many interesting plasma effects which Juno will be able to investigate.

Juno has another distinction as the furthest satellite we have sent which is powered solely by solar power. Since the solar flux at Jupiter is 25 times weaker than at Earth, Juno employs massive solar arrays to collect enough power. Juno will arrive at Jupiter in 2016 and will be deorbited into Jupiter upon completion of its one year mission.

Salt water on Mars

We already knew that there was frozen water on Mars and that it was highly likely there was liquid water that occasionally streamed down the sides of craters. However, the recent discovery by Lujendra Ojha and Alfred McEwen at the University of Arizona seems to indicate that Mars is far wetter than we thought.

Using observations taken by the Mars Reconnaissance Orbiter and differencing software, they looked for changes in the geography over 3 years. What they found was that there were features at the edges of craters and slopes that changed seasonally on Mars. These streaks grew in the summer and faded in the winter. The hypothesis is that these streaks are made by water seeping out of the ground. Since the surface of Mars is below freezing the only way this could be liquid water is if the water was actually salt water, which lowers the freezing point of pure water.

The abundance of water on Mars is good new for those who hope to find life there. This recent finding provides new places to look for life as it is thought that it is more likely to exist in regions with liquid water. It is also good new for those who wish to bring Earth life to Mars as they won't have to haul along their own water.

Saturn, STS-135 and JWST

If you like fluid dynamics, or just love looking at awesome pictures of fluid instabilities then you will love today's APOD. Featuring the aptly named Serpent Storm, this gigantic storm on Saturn resembles the classic fluid dynamics problem of a flow past a cylinder. The head of the storm acts like a barrier which deflects the ambient flow of Saturn's atmosphere. This in turn causes a wake of turbulence and shear instabilities (Kelvin-Helmholtz). The Serpent storm originally appeared Dec. 5, 2010 and has been raging ever since. In fact the storm is so violent it is a huge source of radio emission, due to lightning activity. Nobody is quite sure why the storm appeared or what is powering it. However, it seems to be related to the changing of the Saturnian seasons as the northern hemisphere moves towards spring.

In other news, STS-135 launched successfully after some worry about the weather. Atlantis is now en route to the International Space Station to deliver supplies for the last time. It is scheduled to return on July 20th, formally ending the space shuttle program.

Finally, stunning news rocked the astronomy world yesterday as a proposal was made by the US House Appropriations Committee to scrap the James Webb Space Telescope (JWST). More complete information can be found in various locations. JWST is the successor to Hubble and will provide unrivaled views of the universe in the near infrared. The project is currently 75% complete with most of the hardware already built or in the process of being built. Unfortunately the project is also $1 billion dollars over budget and 3 years late due to organizational mismanagement. However, JWST has gone through a major organizational review and the management problems have been resolved.

In spite of its flawed history (Hubble had a flawed history as well and it produced amazing science), the hopes of many future US and international astronomers are pinned to the success of the JWST mission which promises to have a huge scientific pay off. Plus JWST is the only large scale telescope mission NASA has planned, and its older major space based observatories are nearing the end of their useful life span. The American Astronomical Society has released a statement regarding JWST asking Congress to continue funding it, the statement can be read here. Naturally if you are a US citizen voicing your support for astronomy, NASA, NSF, and general science and technology research money to your local member of Congress would be greatly appreciated.

The JWST is in trouble in the current budget recommendations!

Check TG Daily and Aviation Week.

The JWST is in trouble in the current budget recommendations!

Last Shuttle Launch Reminder plus Other News

The final launch of NASA's Space Shuttle program is tomorrow, July 8th at 11:26 am EDT (10:26 am Winnipeg time), providing that weather cooperates and nothing goes wrong during the countdown. This will be the last chance to see a shuttle launch live as the final shuttle Atlantis will be retired when it returns to Earth from the International Space Station. After which in order to see a shuttle you will have either watch classic videos or make a trip to one of the 4 locations that houses one in the US.

A few other notes. There is a cool news story on SOFIA (Stratospheric Observatory for Infrared Astronomy) here. SOFIA is pretty awesome as it has a 2.5 meter infrared telescope mounted in the side of a modified Boeing 747SP widebody. As one might imagine it is pretty tricky to put a hole in an aircraft that large and still have it be able to fly well.

Another article came out recently about Saturn and the storm that has been raging there. Apparently its been going for a year now and is larger that the Earth. Also the highest redshift galaxy ever detected has changed hands recently. That distinction now belongs to ULAS J1120+0641 at z=7.1. This means the light left the galaxy almost 13 billion years ago, very far away.

Last Shuttle Roll Out

Today's APOD highlights a historic event in human space flight. After 30 years NASA's successful space shuttle program is coming to a close. With the shuttle fleet aging, it was decided to retire the remaining fleet with STS-135 being the last one. Atlantis will carry her four person crew to the ISS on July 8th, barring any delays.

So what is next for human spaceflight after the shuttle? Well Russia has been using its Soyuz capsules for now on 50 years. This will be the primary vehicle to get into orbit until a new system is developed to replace the shuttles. With the Constellation Program canceled, NASA has moved to a program which will be reliant in the future on commercially developed launch vehicles. However, until these vehicles are ready the only way to get to the ISS is via the Soyuz rocket. Unfortunately, no clear plan has been put forward as to what to do with human spaceflight beyond the ISS. Proposals have included going back to the Moon, landing on an asteroid and landing on Mars.

Photos of Lunar eclipse 15 June 2011

Here are some pictures of today's (June 15, 2011) total lunar eclipse which was visible to observers in Europe, Africa, southern Asia, and Australia. This is one of the darkest and longest eclipses of this century lasting around 100 minutes and second only to the total lunar eclipse on July 16, 2000. 


These pictures were taken from Toledo, Spain between 11 pm and 12 am by my husband, who is attending a conference there! Below is the link to the photos (lots of Moon photos though -- taken with Nikon D3100 300mm lens in manual mode). If possible, enlarge (zoom in) and view the photos...you can see the craters as well..its awesome! Just a caution that the time set in Camera was for Saskatoon timing, so the photos carry a different time.


https://picasaweb.google.com/sanjeev.research/Moon?authkey=Gv1sRgCJOMqcSguqPDwgE#

New Maunder Minimum?

At the annual meeting of the Solar Physics division of the American Astronomical Society, Frank Hill, Matt Penn, William Livingston, Richard Altrock and collaborators presented data indicating that the Sun may be heading that direction after Solar Cycle 24 is complete. So what does this mean?

Well first lets go over what the Maunder Minimum was. Humans have been observing sunspots regularly since Galileo first turned his telescope towards the Sun. (WARNING: DO NOT DO THIS UNLESS YOU HAVE A SOLAR FILTER FOR YOUR TELESCOPE!!!) Since that time a record has been kept of the number of sunspots on the Sun. This one of the longest scientific observing records to date, with over 400 years of data. It was discovered that the number of sunspots rises and falls over a period of 11 years. However, something strange happened to this pattern between 1645 and 1715, known as the Maunder Minimum. During this time the Sun showed few if any sunspots.

Since that time heliophysicists have discovered the cause of sunspots and the sunspot cycle. Sunspots are caused by regions of intense magnetic field on the Sun. This magnetic field keeps the region of the sunspot cooler than the surrounding plasma, thus the sunspot looks dark. The cycle of the sunspots is related to the cycle over which the magnetic field on the Sun reconfigures. Every 11 years, the magnetic field of the Sun flips its direction so that the North pole becomes the South and visa versa. During a minimum in Solar activity the magnetic field is stable in its orientation. However, as solar activity increases, indicated via the proxy of an increasing sunspot number, the magnetic field becomes chaotic as it flips direction. This chaotic field is the seed for the solar activity. Thus the Sun flips its magnetic field every 11 years, leading to the 11 year sunspot cycle.

Helioseismologists have recently uncovered more detail about this process. It all relates to the different flows with in the Sun's convection zone. In this region, particularly the region known as the tachocline, the magnetic field for the Sun is thought to be generated. Scientists have discovered large scale flows which control the motion of sunspots on the Sun. They have also discovered jet streams, similar to the ones found on Earth, which can be used to predict when new sunspot cycles begin. This was used to predict the late onset of the current sunspot cycle labelled Cycle 24.

Current data from Frank Hill's group shows that the jet streams for Cycle 25, the next cycle, have not formed yet which is unusual. If they don't form at all Cycle 25 probably won't happen. Penn and Livingston presented data that indicated that the sunspots have been weakening over the past 2 cycles. Altrock presented data showing that the field accumulation at the poles of the Sun has slowed as well. The combined data indicates that Cycle 25 will either be weak or not occur at all. If Cycle 25 doesn't happen it may be the start of another Maunder Minimum (aka grand minimum).

So what would be the implications for us here on Earth if another Maunder Minimum were to occur? Well there would be less activity from the Sun. A lower number of solar flares and Coronal Mass Ejections. This would lead to lower auroral activity. It would also make it safer for people out in space as the chances of being exposed to harmful radiation from the Sun would decrease. It would also lower the danger activity from the Sun poses to electronics in space and on Earth. The Sun would also put out less radiation making it slightly cooler here on Earth. In fact the Maunder Minimum coincided with the middle Little Ice Age in the 17th century. While the minimum certainly contributed to the Little Ice Age, the main cause was vulcanism here on Earth, so don't expect the cooler Sun from a minimum to counter act global warming. In fact the Sun would have to get 10 times cooler than it would become during a grand minimum to make up for the net effect of greenhouse emissions, so no worries of a new Ice Age yet.

A grand minimum would also be extremely interesting to heliophysicists. This is because we don't know what caused the original Maunder Minimum. Also while we have a pretty good idea about how the magnetic field on the Sun works, we still know very little about its generation. Observing another grand minimum would help us to understand both of these topics.

So will the Sun go into another grand minimum or not? Only time will tell if the predictions from the recent data hold true. As more data is accumulated better models will be generated and we will get a better idea of how Cycle 25 will likely play out. Ultimately, as with weather forecasting, you will never know for sure until you get to the actual date of the event to see if it happens.

Cool Solar Flare

This has been making the rounds and its pretty cool so I figure I would mention it as well. On June 7th the Sun let off a rather impressive solar flare which was observed by the satellites which observe the Sun, the Solar Dynamics Observatory (SDO), Solar and Heliospheric Observatory (SOHO), and Solar Terrestrial Relations Observatory (STEREO) to name a few. While this explosion wasn't out of the ordinary in terms of size or power, it was interesting because a lot of the material that was originally ejected fell back onto the surface of the Sun. This made for a rather spectacular movie by the SDO of material being shot up by the flare and then falling back to burn up on the surface.

So what is going on in the movie? Well a solar flare occurs because of magnetic fields on the Sun. Normally the magnetic fields on the Sun allow for material to flow off the Sun and form the Solar Wind. However if the fields get tangled that can stop that material from leaving the Sun and pressure begins to build up. Think of the Sun as a pot of boiling water and the Solar Wind as the steam rising off of the water to release energy. Tangled magnetic fields act like a very tight lid, which turns the Sun into a pressure cooker. The pressure builds and builds and builds until something gives way. In the case of the Sun, the magnetic field lines end up breaking in an event called reconnection. The reconnection event triggers the release of energy and material. This release is seen as a solar flare

In the case of this particular case the flare material didn't have enough energy to escape the Sun's gravity so it fell back on to the Sun. The material looks dark because it is cooler than the surface of the Sun. You will also notices that the material doesn't fall the way one expects. Rather it falls more slowly and is twisted around as it goes. This is the magnetic fields of the Sun at work again. The fields a strong enough to counter the force of gravity and channel the flow of material on the Sun.

The material from the flare that escaped was directed towards the Earth but only delivered a glancing blow to the Earth's magnetosphere. This caused a boost in auroral displays. We will be seeing more of these types of events from the Sun in the years to come as solar activity increases to its projected peak in 2013.

Supernova in M51

A new Type II Supernova was detected on June 2nd in M51 by French amateur's (Stephane Lamotte and Marc Deldem). It has been confirmed by the Palomar Transient Factory, also the possible progenitor has been found. This makes it the second supernova detected in M51 in 6 years.

Type II Supernovae occur when a massive star ends it's life. When the core runs out of fusionable material the reduction in energy production removes pressure support from the interior of the star. The interior then collapses either into a neutron star or a black hole. In response to the collapse the rest of the star is ejected in a massive explosion of energy called a supernova.

Supernovae are detected all the time from the broader universe. However, one so close to us (about 7 Mpc) is uncommon. This gives astronomers an excellent opportunity to study these massive explosions in more detail than is available for a more distant supernovae. Even better would be a supernovae in our own Galaxy which is due to occur, (about 1-3 supernovae happen in our Galaxy every 100 years). The most recent Galactic supernovae was G1.9+0.3 whose light reached us 140 years ago.

Given the early nature of these observations, more details on this event will be forth coming as more instruments are brought to bear to observe the event.

Time-lapse with a Rotating Earth

It used to be thought that the Earth was stationary and the sky rotated around the Earth. However, with the advent of the heliocentric model and many proofs of the Earth's rotation we now follow the Copernican view of the universe in science. In this view the Earth is no longer the center of the universe but rather just a normal component of it, occupying no special physical place. Thus physics that occurs here is the same as it occurring in any other location, and there is no proper center to the universe. Einstein's theory of relativity then can be just thought of as a natural extension of the Copernican principle.

All that aside, we here on Earth continue to perceive the sky rotating around us rather than the other way around. This is especially evident in time-lapse photography of the sky. Well today's APOD takes us into a different frame than we are used to for time-lapse movies. Instead of using the ground as stationary, the movie has been edited such that the sky is stationary and the Earth moves instead. One can see the ground tumble and move all over the place as it rotates relative to the broader universe. You can also see in this movie the telescope array for the Very Large Telescope in Chile as well as laser guide stars shooting up from the telescopes. Definitely gives one a different perspective on our place in the universe.

The Crab's Gamma-Ray Flare

As noted on this blog last month, the Crab Nebula was seen by the Fermi telescope to flare in the gamma ray band. The flare itself is pictured to the right and was the subject of yesterday's APOD. The flare itself lasted for 3 days and saw a 30 fold increase in emission from the Crab.

Immediately after this occurred astronomers from all over the world looked with different instruments to see if there was increased emission from the Crab Nebula in other bands. No increase was detected though.

This is not the first time the Crab has done this, but it is confusing to astronomers trying to explain the flare. Since the flare lasts for only 3 days we know that the region of emission can't be that large. Since it was seen only in the gamma-rays seen by Fermi, we know that it is probably due to fluctuations in the synchrotron spectrum of the nebula. At these high energies the synchrotron light that is being seen is coming from the highest energy electrons, so fluctuations at these energies indicates fluctuations either in the magnetic field or the population of the highest energy electrons. No one is quite sure which, and while several theories have been tossed about, there is no favored model.

The variability in the gamma-ray is also a little concerning for observers in those bands as the Crab Nebula is used as a standard calibration source since it's emission is thought to be relatively steady. This is still likely true in the normal state, so astronomers just have to be aware if they are observing during a flaring state or not. Also most of the experiments using the Crab as a standard work in the TeV gamma-ray which is much higher energy than Fermi and do not see any fluctuations in the Crab's emission.

GOES Captures Last Month's Tornado Activity in the US Southeast

Well not exactly. GOES (Geostationary Operational Environmental Satellite) captured the storm systems which generated the series of tornadoes which ravaged the deep south of the US. The movie, linked here, shows a time-lapse of the weather systems that occurred in April along with red points indicating where tornadoes were detected by ground stations and observers. One can see that some of the storm systems stall over the midwest generating a series of tornadoes there, where as other systems sweep across the country spawning tornadoes on their way.

So what is GOES anyways? GOES is a series of satellites run by NOAA's National Weather Service (National Oceanic and Atmospheric Administration). There are 3 active GOES satellites. Each of them sit in geosynchronous orbit. These type of orbits are special, originally proposed by Arthur C. Clarke, in that the amount of time it takes to complete the orbit is the same as the amount of time it takes the Earth to rotate. Thus a satellite in this orbit, at a radius of about 42,000 km, appear to hover over the same region on the Earth. This makes it an ideal location for communications and weather satellites. The 3 active satellites in GOES watch three different regions of the western hemisphere. The three active satellites are dubbed GOES-West, which watches the western US and Pacific Ocean, GOES-East which watches the eastern US and Atlantic and GOES-South which covers South America.

The GOES satellites have a variety of instruments to measure weather phenomenon on Earth. They have visible light camera's to measure the reflected sunlight from the Earth, infrared cameras to see the heat emitting from the Earth, and sounding sensors which provide information about the atmospheric temperature, moisture and ozone levels. In addition GOES monitors the magnetic field and energetic particle environment in its orbit as well as monitoring the Sun.

With it's ability to provide a global images of current weather, GOES is an indispensable part of weather forecasting in both the US and Canada. Given how important GOES is for this there are always backup GOES satellites in orbit to take over in case one fails. Thus far, since 1975 there has been 15 GOES launched into orbit. Currently GOES 11-13 are active with 1-10 having been decommissioned or turned to alternate uses (GOES 3 serves as a communications relay for the research station at the South Pole) . GOES 14 and 15 are the two backup satellites with newer models set to be launched in 2015. Thus GOES will be the premier general purpose weather satellites for years to come.