Web edition: August 29, 2012
Print edition: October 6, 2012; Vol.182 #7 (p. 13)
Super neutrinos spotted
Two super-high-energy particles have been detected by IceCube, the massive neutrino telescope buried in Antarctic ice. IceCube is looking for neutrinos that point toward the still-unknown astrophysical objects responsible for slinging ultra-high-energy cosmic rays toward Earth. These two neutrinos, one seen in August 2011 and the other in January 2012, have enough energy to be from an ultra-high-energy cosmic ray source, such as a gamma-ray burst. “They are at least 10 times the energy of any neutrino we’ve seen before,” says Francis Halzen, an IceCube team member from the University of Wisconsin–Madison, who discussed the find on August 22. But these particles are electron neutrinos — flavors that, instead of streaking through the detector and neatly pointing toward home, leave a more bulbous footprint. The shape means that even though IceCube scientists can find the general direction from which the particles came, they won’t be able to pinpoint a direct source in the sky.
More Milky Ways
The Milky Way and its satellite galaxies, the Magellanic Clouds, are not one-of-a-kind: There are at least two distant galaxies that very closely resemble the local assemblage, Aaron Robotham of Australia’s International Centre for Radio Astronomy Research and the University of St. Andrews in Scotland reported on August 23. Like our own spiral galaxy, these two galaxies also have relatively large and nearby companions. Astronomers spotted the Milky Way’s twins in data returned by the Galaxy and Mass Assembly survey. The survey, which is tasked with mapping the local universe, studies the nearest 340,000 galaxies. So far only 14 of those resemble the Milky Way and Magellanic Clouds — and only two are very close matches. Robotham and colleagues suggest that just 0.4 percent of Milky Way-mass galaxies host observable Magellanic Cloud-type satellites, meaning that while our Milky Way isn’t one of a kind, it also isn’t a dime a dozen.
Hot planet keeps its water
A small planet whizzing around its star in 17 hours, 41 minutes must surely be a lava world, a scorched pile of rock with nary a water molecule in sight, right? Wrong. New observations of the planet called 55 Cancri e, which is just two times larger than Earth, suggest that although the world is super-heated, the planet is most likely made of a rocky core and shrouded in an atmosphere containing as much as 20 percent water, said Diana Dragomir of the University of British Columbia on August 27. “This planet is so close to its star we don’t expect it to have an atmosphere, but there it is,” she said. Dragomir observed the planet as it passed between its star and Earth, which — when combined with previous data — allowed her to determine what the planet is probably made of. The results suggest that while the surface temperature is smoldering at thousands of degrees, 55 Cancri e has somehow managed to hold on to an atmosphere.
Seven Sisters distance
Though the Pleiades star cluster sparkles clearly in the night sky, astronomers still don’t really know how far away it is. Determining the distance to the young, bright cluster is important because astronomers base several principles on it, such as how young stars behave and how far away nearby galaxies are. Early estimates placed the cluster at an average of about 434 light-years away; then along came the Hipparcos satellite, which found a distance of roughly 398 light-years. “If Hipparcos is correct, then we have an incomplete understanding of young stars,” said Carl Melis of the University of California, San Diego. Melis is attempting to determine the distance to the stars using a super-sensitive array of radio telescopes, an ongoing project he described on August 27. So far, Melis has one measurement: 473 light-years. Another method, described by Siegfried Röser of Germany’s University of Heidelberg, determined a distance of 410 light-years. Some of the discrepancy, Röser suggests, could be a consequence of measuring stars at different edges in the cluster, which is spherical and expanding.
IceCube: F. Halzen. IceCube: Particle astrophysics with high energy neutrinos. International Astronomical Union General Assembly, August 22, 2012, Beijing. [Go to]
Milky Ways: A. Robotham et al. In search of local group analogues. International Astronomical Union General Assembly, August 23, 2012, Beijing. [Go to]
Milky Ways: A. Robotham et al. Galaxy and Mass Assembly (GAMA): In search of Milky Way Magellanic Cloud analogues. Monthly Notices of the Royal Astronomical Society. Vol. 424, August 2012, p. 1448.
Hot planet: D. Dragomir and J. Matthews. 2012 MOST photometry of the 55 Cancri system. International Astronomical Union General Assembly, August 27, 2012, Beijing.
Pleiades: C. Melis et al. Toward a VLBI resolution of the Pleiades distance controversy. International Astronomical Union General Assembly, August 27, 2012, Beijing.
Pleiades: S. Röser and E. Schilbach. A new assessment of the kinematic distance to the Pleiades — from radial velocities and proper motions only. International Astronomical Union General Assembly, August 27, 2012, Beijing.