Curious about curiosity

What do people think of the little film on Astronomy Picture of the Day today?   About the landing of the Curiosity rover... July 31 2012 APOD

H.E.S.S. II first light

http://www.mpi-hd.mpg.de/hfm/HESS/pages/press/2012/HESS_II_first_light/

Dark Matter WIMPS ...

... are still wimping out:

http://www.interactions.org/cms/?pid=1032039

as elusive as the "goddamn" particle...

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.