Archive for April 21, 2013

Distant Blazar Is A High-Energy Astrophysics Puzzle

Blazars are the brightest of active galactic nuclei, and many emit very high-energy gamma rays. New observations of the blazar known as PKS 1424+240 show that it is the most distant known source of very high-energy gamma rays, but its emission spectrum now appears highly unusual in light of the new data.

A team led by physicists at the University of California, Santa Cruz, used data from the Hubble Space Telescope to set a lower limit for the blazar’s redshift (z ≥ 0.6035), which corresponds to a distance of at least 7.4 billion light-years. Over such a great distance, a substantial proportion of the gamma rays should be absorbed by the extragalactic background light, but calculations that account for the expected absorption yield an unexpected emission spectrum for the blazar.

“We’re seeing an extraordinarily bright source which does not display the characteristic emission expected from a very high-energy blazar,” said Amy Furniss, a graduate student at the Santa Cruz Institute for Particle Physics (SCIPP) at UCSC and first author of a paper describing the new findings. The paper has been accepted for publication in Astrophysical Journal Letters and is currently posted on

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New Earth-Like Planets Found

A team of scientists, including Carnegie’s Alan Boss, has discovered two Earth-like planets in the habitable orbit of a Sun-like star. Their work is published in Science Express.

Using observations gathered by NASA’s Kepler Mission, the team, led by William Borucki of the NASA Ames Research Center, found five planets orbiting a Sun-like star called Kepler-62. Four of these planets are so-called super-Earths, larger than our own planet, but smaller than even the smallest ice giant planet in our Solar System. These new super-Earths have radii of 1.3, 1.4, 1.6, and 1.9 times that of Earth. In addition, one of the five was a roughly Mars-sized planet, half the size of Earth.

The two super-Earths with radii of 1.4 and 1.6 Earth radii orbit their star at distances where they receive about 41% and 120%, respectively, of the warmth from their star that the Earth receives from the Sun. The planets are thus in the star’s habitable zone; they have the right temperatures to maintain liquid water on their surfaces and are theoretically hospitable to life.

“This appears to be the best example our team has found yet of Earth-like planets in the habitable zone of a Sun-like star,” Boss said.

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