Comet C/2013 A1 Siding Spring and NGC 1316

NASA's NEOWISE mission detected comet C/2013 A1 Siding Spring on July 28, 2014, less than three months before this comet's close flyby of Mars on Oct. 19.

NEOWISE took multiple images of the comet, combined here so that the comet is seen in four different positions relative to the background stars. The image also includes, near the upper right corner, a view of radio galaxy Fornax A (NGC 1316).

NEOWISE previously observed comet Siding Spring on January 16, 2014 (see http://www.jpl.nasa.gov/spaceimages/details.php?id=PIA17833). NEOWISE is part of a team of observation resources to characterize the comet for the encounter with our neighboring planet. At the time of the July 28 observations, the comet was 144 million miles (1.55 astronomical units) from NEOWISE and 175 million miles (1.88 astronomical units) from the Sun. The observations help constrain estimates of dust and gas production as this comet from the outer solar system approaches Mars.

NGC 1316 is a famous radio galaxy, the fourth-brightest radio source in the sky at 1400 megahertz. It is in the Fornax galaxy cluster, which also includes two other galaxies visible in the image. NGC 1316 has an active nucleus, as evidenced by a radio jet and a compact nuclear gas disk. It is thought to be the remnant of a merger between a large elliptical galaxy and a smaller spiral galaxy about 100 million years ago.

Image credit: NASA/JPL-Caltech

Note: For more information, see NASA Mars Spacecraft Prepare for Close Comet Flyby and Orbiter Completes Maneuver to Prepare for Comet Flyby.

Centaurus A by ALMA

This new image of Centaurus A combines ALMA and near-infrared observations of the massive elliptical radio galaxy. The new ALMA observations, shown in a range of green, yellow and orange colors, reveal the position and motion of the clouds of gas in the galaxy. They are the sharpest and most sensitive such observations ever made.

ALMA was tuned to detect signals with a wavelength around 1.3 millimeters, emitted by molecules of carbon monoxide gas. The motion of the gas in the galaxy causes slight changes to this wavelength, due to the Doppler effect. The motion is shown in this image as changes in color. Greener features trace gas coming towards us while more orange features depict gas moving away. We can see that the gas to the left of the center is moving towards us, while the gas to the right of the center is moving away from us, indicating that the gas is orbiting around the galaxy.

The ALMA observations are overlaid on a near-infrared image of Centaurus A obtained with the SOFI instrument attached to the ESO New Technology Telescope (NTT).

Photo credit: ALMA (ESO/NAOJ/NRAO); ESO/Y. Beletsky

Astrophysical Shock Waves

This composition shows a number of diverse astronomical sources where shocks have been detected. Shock waves arise when supersonic flows of plasma are faced with an obstacle, such as a planet or a star with a magnetic field, or when they encounter a slower moving flow.

Depicted in the composition are: a bow shock around the very young star, LL Ori, in the Great Orion Nebula (upper row, left image); shock waves around the Red Spider Nebula, a warm planetary nebula (upper row, central image); very thin shocks on the edge of the expanding supernova remnant SN 1006 (central row, left image); artist's impressions of the bow shock created by the Solar System as it moves through the interstellar medium of the Milky Way (upper row, right image) and of Earth's bow shock, formed by the solar wind as it encounters our planet's magnetic field (central row, right image); shock-heated shells of hot gas on the edge of the lobes of the radio galaxy Cygnus A (lower row, left image); a bow shock in the hot gas in the merging galaxy cluster 1E 0657-56, also known as the 'Bullet Cluster'.

The image of a galaxy (NGC 6744) in the center of the composition serves to give a rough idea of the relative scales, sub- and super-galactic alike, of the shock waves present across the Universe.

Illustration credit: NASA/ESA and The Hubble Heritage Team STScI/AURA (LL Ori); ESA & Garrelt Mellema, Leiden University, the Netherlands (Red Spider Nebula); CEA/DSM/DAPNIA/SAp and ESA/XMM-Newton (SN 1006); ESA & Lotfi Ben Jaffel, Institut d'Astrophysique de Paris-CNRS-INSU, Martin Kornmesser & Lars Lindberg Christensen (Solar System); ESA/AOES Medialab (Earth's bow shock); ESO (NGC 6744); NRAO/AUI (Cygnus A); NASA/CXC/CfA/M.Markevitch et al. (Bullet Cluster).