Archive for emission line stars

ESO/ALMA imaging of planet formation in an Earth-like orbit

Posted in astronomy with tags , , , on April 2, 2016 by Tim Kendall
( ALMA‘s best image of a protoplanetary disc to date. This picture of the nearby young star TW Hydrae reveals the classic rings and gaps that signify planets are in formation in this system. Credit: S. Andrews (Harvard-Smithsonian CfA); B. Saxton (NRAO/AUI/NSF); ALMA (ESO/NAOJ/NRAO). The star TW Hydrae is a popular target of study for astronomers because of its proximity to Earth and its status as an infant (or T Tauri) star about 10 million years old. Its distance has been recently re-calculated to be as close as 38 pc. The star itself is slightly less massive than the Sun, spectral type K8IVe (as given in an excellent recent review of young stars in nearby stellar associations here). It also has a face-on orientation as seen from Earth, giving astronomers a rare view of the complete protoplanetary disc around the star.

ALMA TW Hya central regions

This is the inner region of the TW Hydrae protoplanetary disk as imaged by ALMA. The image has a resolution of 1 AU (Astronomical Unit, the distance from the Earth to the Sun in our own Solar System). This new ALMA image reveals a gap in the disk at 1 AU, suggesting that a planet with the same orbit as Earth is forming there. Credit: S. Andrews (Harvard-Smithsonian CfA); B. Saxton (NRAO/AUI/NSF); ALMA (ESO/NAOJ/NRAO). The paper “Ringed Substructure and a Gap at 1 AU in the Nearest Protoplanetary Disk”, by S.M. Andrews et al., appearing in the Astrophysical Journal Letters (pdf copy via ESO). These recent observations represent a huge breakthrough in direct imaging at the resolutions required and are very suggestive evidence for the existence of Earth-like planets in nearby interstellar space. From the abstract:
We present long-baseline Atacama Large Millimeter/submillimeter Array (ALMA) observations of the 870 μm continuum emission from the nearest gas-rich protoplanetary disk, around TW Hya, that trace millimeter-sized particles down to spatial scales as small as 1 AU (20 milliarcseconds). These data reveal a series of concentric ring-shaped substructures in the form of bright zones and narrow dark annuli (1-6 AU) with modest contrasts (5-30%). We associate these features with concentrations of solids that have had their inward radial drift slowed or stopped, presumably at local gas pressure maxima. No significant non-axisymmetric structures are detected. Some of the observed features occur near temperatures that may be associated with the condensation fronts of major volatile species, but the relatively small brightness contrasts may also be a consequence of magnetized disk evolution (the so-called zonal flows). Other features, particularly a narrow dark annulus located only 1 AU from the star, could indicate interactions between the disk and young planets. These data signal that ordered substructures on ~AU scales can be common, fundamental factors in disk evolution, and that high resolution microwave imaging can help characterize them during the epoch of planet formation.

Update on the ongoing search for the proposed “Planet Nine”, from Scientific American: The article highlights the research of Fienga et al., (2016) using the Cassini spacecraft data to pinpoint the planet. The planet is likely sub-Jovian, ten Earth masses, eccentric, e ~ 0.6, distant but not that distant, ~ 700 AU, and possibly located in the region of the sky in the direction of the southern constellation of Cetus, with true anomaly 117.8°±11°. I predict that it will be found soon, and there is as good a chance of finding it by its own internal heat, in millimeter data, as by reflected light in the visible part of the spectrum.

Field of the southern B[e] star HD 87643

Posted in astronomy with tags , on July 19, 2013 by Tim Kendall

Image: ESO/F. Millour et al.

This image, showing a very rich field of stars towards the Carina arm of the Milky Way, is centred on the star HD 87643, a member of the class of B[e] stars. The amazing image is set ablaze by a flurry of stars of all colours and brightnesses, some of which are seen against a backdrop of clouds of dust and gas. The red emission nebula is RCW47 and was catalogued in 1960. HD 87643 has been extensively studied with a full range of ESO telescopes, including the Very Large Telescope Interferometer (VLTI). Surrounded by a complex, extended nebula that is the result of previous violent ejections, the star is shown to have a companion. Interactions in this double system, surrounded by a dusty disc, may be the engine fuelling the star’s remarkable nebula. The image, taken with the Wide Field Imager on the MPG/ESO 2.2-metre telescope at La Silla, is based on data obtained through different filters: B, V and R. The field of view is around 30 x 30 arcminutes.

More fascinating particle physics from CERN as well: the story of “neutral currents“, which paved the way to the discovery of the W and Z boson intermediaries of the electroweak force.