RESUMEN
Little is known about the portion of the Milky Way lying beyond the Galactic center at distances of more than 9 kiloparsec from the Sun. These regions are opaque at optical wavelengths because of absorption by interstellar dust, and distances are very large and hard to measure. We report a direct trigonometric parallax distance of [Formula: see text] kiloparsec obtained with the Very Long Baseline Array to a water maser source in a region of active star formation. These measurements allow us to shed light on Galactic spiral structure by locating the Scutum-Centaurus spiral arm as it passes through the far side of the Milky Way and to validate a kinematic method for determining distances in this region on the basis of transverse motions.
RESUMEN
It is thought that Galactic cosmic-ray nuclei are gradually accelerated to high energies (up to about 300 TeV per nucleon, where 1 TeV is 10(12) eV) in the expanding shock waves connected with the remnants of powerful supernova explosions. However, this conjecture has eluded direct observational confirmation since it was first proposed in 1953 (ref. 3). Enomoto et al. claim to have finally found definitive evidence that corroborates this model, proposing that very-high-energy, TeV-range, gamma-rays from the supernova remnant (SNR) RX J1713.7-3946 are due to the interactions of energetic nuclei in this region. Here we argue that their claim is not supported by the existing multiwavelength spectrum of this source. The search for the origin(s) of Galactic cosmic-ray nuclei may be closing in on the long-suspected supernova-remnant sources, but it is not yet over.