Photobombing stars lead to cosmic false identity

Photobombing stars lead to cosmic false identity , Published online: 15 November 2018; doi:10.1038/d41586-018-07413-x

Imposters pose as the source of a bright cloud of gas.

Astronomers have discovered a planet around one of the closest stars to our Sun.

ESA's Science Programme Committee (SPC) has confirmed the continued operations of ten scientific missions in the Agency's fleet up to 2022.

The nearest single star to the Sun hosts an exoplanet at least 3.2 times as massive as Earth — a so-called super-Earth. One of the largest observing campaigns to date using data from a world-wide array of telescopes, including ESO’s planet-hunting HARPS instrument, have revealed this frozen, dimly lit world. The newly discovered planet is the second-closest known exoplanet to the Earth. Barnard’s star is the fastest moving star in the night sky.

A key piece in the exoplanet puzzle

A key piece in the exoplanet puzzle, Published online: 14 November 2018; doi:10.1038/d41586-018-07328-7

The detection of a low-mass exoplanet on a relatively wide orbit has implications for models of planetary formation and evolution, and could open the door to a new era of exoplanet characterization.

Podcast: Barnard’s Star, and clinical trials

Podcast: Barnard’s Star, and clinical trials, Published online: 14 November 2018; doi:10.1038/d41586-018-07403-z

Hear the latest science news, presented by Noah Baker and Benjamin Thompson.

A candidate super-Earth planet orbiting near the snow line of Barnard’s star

A candidate super-Earth planet orbiting near the snow line of Barnard’s star, Published online: 14 November 2018; doi:10.1038/s41586-018-0677-y

Analysis of 20 years of observations of Barnard’s star from seven facilities reveals a signal with a period of 233 days that is indicative of a companion planet.

An international team of astronomers, including from the University of Cambridge, discovered the massive object when trawling through data from the European Space Agency’s Gaia satellite. The object, named Antlia 2 (or Ant 2), has avoided detection until now thanks to its extremely low density as well as a perfectly-chosen hiding place, behind the shroud of the Milky Way’s disc. The researchers have published their results online today.

Ant 2 is known as a dwarf galaxy. As structures emerged in the early Universe, dwarfs were the first galaxies to form, and so most of their stars are old, low-mass and metal-poor. But compared to the other known dwarf satellites of our Galaxy, Ant 2 is immense: it is as big as the Large Magellanic Cloud (LMC), and a third the size of the Milky Way itself.

What makes Ant 2 even more unusual is how little light it gives out. Compared to the LMC, another satellite of the Milky Way, Ant 2 is 10,000 times fainter. In other words, it is either far too large for its luminosity or far too dim for its size.

“This is a ghost of a galaxy,” said Gabriel Torrealba, the paper’s lead author. “Objects as diffuse as Ant 2 have simply not been seen before. Our discovery was only possible thanks to the quality of the Gaia data.”

The ESA’s Gaia mission has produced the richest star catalogue to date, including high-precision measurements of nearly 1.7 billion stars and revealing previously unseen details of our home Galaxy. Earlier this year, Gaia’s second data release made new details of stars in the Milky Way available to scientists worldwide.

The researchers behind the current study – from Taiwan, the UK, the US, Australia and Germany – searched the new Gaia data for Milky Way satellites by using RR Lyrae stars. These stars are old and metal-poor, typical of those found in a dwarf galaxy. RR Lyrae change their brightness with a period of half a day and can be located thanks to these well-defined pulses.

“RR Lyrae had been found in every known dwarf satellite, so when we found a group of them sitting above the Galactic disc, we weren’t totally surprised,” said co-author Vasily Belokurov from Cambridge’s Institute of Astronomy. “But when we looked closer at their location on the sky it turned out we found something new, as no previously identified object came up in any of the databases we searched through.”

The team contacted colleagues at the Anglo-Australian Telescope (AAT) in Australia, but when they checked the coordinates for Ant 2, they realised they had a limited window of opportunity to get follow-up data. They were able to measure the spectra of more than 100 red giant stars just before the Earth’s motion around the Sun rendered Ant 2 unobservable for months.

The spectra enabled the team to confirm that the ghostly object they spotted was real: all the stars were moving together. Ant 2 never comes too close to the Milky Way, always staying at least 40 kiloparsecs (about 130,000 light-years) away. The researchers were also able to obtain the galaxy’s mass, which was much lower than expected for an object of its size.

“The simplest explanation of why Ant 2 appears to have so little mass today is that it is being taken apart by the Galactic tides of the Milky Way,” said co-author Sergey Koposov from Carnegie Mellon University. “What remains unexplained, however, is the object’s giant size. Normally, as galaxies lose mass to the Milky Way’s tides, they shrink, not grow.”

If it is impossible to puff the dwarf up by removing matter from it, then Ant 2 had to have been born huge. The team has yet to figure out the exact process that made Ant 2 so extended. While objects of this size and luminosity have not been predicted by current models of galaxy formation, recently it has been speculated that some dwarfs could be inflated by vigorous star formation. Stellar winds and supernova explosions would push away the unused gas, weakening the gravity that binds the galaxy and allowing the dark matter to drift outward as well.

“Even if star formation could re-shape the dark matter distribution in Ant 2 as it was put together, it must have acted with unprecedented efficiency,” said co-author Jason Sanders, also from Cambridge.

Alternatively, Ant 2’s low density could mean that a modification to the dark matter properties is needed. The currently favoured theory predicts dark matter to pack tightly in the centres of galaxies. Given how fluffy the new dwarf appears to be, a dark matter particle which is less keen to cluster may be required.

“Compared to the rest of the 60 or so Milky Way satellites, Ant 2 is an oddball,” said co-author Matthew Walker, also from Carnegie Mellon University. “We are wondering whether this galaxy is just the tip of an iceberg, and the Milky Way is surrounded by a large population of nearly invisible dwarfs similar to this one.”

The gap between Ant 2 and the rest of the Galactic dwarfs is so wide that this may well be an indication that some important physics is missing in the models of dwarf galaxy formation. Solving the Ant 2 puzzle may help researchers understand how the first structures in the early Universe emerged. Finding more objects like Ant 2 will show just how common such ghostly galaxies are, and the team is busy looking for other similar galaxies in the Gaia data.

Reference:
G. Torrealba et al. ‘The hidden giant: discovery of an enormous Galactic dwarf satellite in Gaia DR2.’ arXiv: 1811.04082

The Gaia satellite has spotted an enormous ‘ghost’ galaxy lurking on the outskirts of the Milky Way. 

When we looked closer, it turned out we found something newVasily BelokurovV. Belokurov based on the images by Marcus and Gail Davies and Robert GendlerL-R: Large Magellanic Cloud, the Milky Way, Antlia 2

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A copy of the physicist's signed PhD thesis sells for £584,750, nearly four times the guide price.

A population of luminous accreting black holes with hidden mergers

A population of luminous accreting black holes with hidden mergers, Published online: 07 November 2018; doi:10.1038/s41586-018-0652-7

High-resolution infrared observations of hard-X-ray-selected black holes show an excess of late-stage mergers in obscured luminous black holes compared with inactive galaxies of similar stellar masses and star formation rates.

Observations by ALMA and data from the MUSE spectrograph on ESO’s VLT have revealed a colossal fountain of molecular gas powered by a black hole in the brightest galaxy of the Abell 2597 cluster — the full galactic cycle of inflow and outflow powering this vast cosmic fountain has never before been observed in one system.

Holy Cow! Astronomers agog at mysterious new supernova

Holy Cow! Astronomers agog at mysterious new supernova, Published online: 02 November 2018; doi:10.1038/d41586-018-07260-w

An event known as ‘Cow’ that has rocked astronomy since June likely offers a close look at the birth of a neutron star or black hole.

Dark space cloud caught donning halo of hydrogen molecules

Dark space cloud caught donning halo of hydrogen molecules, Published online: 02 November 2018; doi:10.1038/d41586-018-07280-6

For the first time, a Galactic cloud is seen producing an ingredient that is fundamental in star formation.

Construction had halted in 2015 amid protests from native Hawaiians who consider the land sacred.

Nasa's Kepler telescope, which has been looking for inhabitable worlds, has run out of fuel and will look no more.

The NASA/ESA Hubble Space Telescope has captured part of the wondrous Serpens Nebula, lit up by the star HBC 672. This young star casts a striking shadow – nicknamed the Bat Shadow – on the nebula behind it, revealing telltale signs of its otherwise invisible protoplanetary disc.

ESA's Gaia mission has made a major breakthrough in unravelling the formation history of the Milky Way. Instead of forming alone, our Galaxy merged with another large galaxy early in its life, around 10 billion years ago. The evidence is littered across the sky all around us, but it has taken Gaia and its extraordinary precision to show us what has been hiding in plain sight all along.

Evidence of ancient Milky Way merger

Evidence of ancient Milky Way merger, Published online: 31 October 2018; doi:10.1038/d41586-018-07193-4

An analysis of data from the Gaia space observatory suggests that stars in the inner halo of the Milky Way originated in another galaxy. This galaxy is thought to have collided with the Milky Way about ten billion years ago.

The merger that led to the formation of the Milky Way’s inner stellar halo and thick disk

The merger that led to the formation of the Milky Way’s inner stellar halo and thick disk, Published online: 31 October 2018; doi:10.1038/s41586-018-0625-x

A galaxy slightly larger than the Small Magellanic Cloud merged with the Milky Way about 10 billion years ago, thickening the ancient disk and forging the Galaxy’s inner halo.

This blog post originated in the 2017 Science Mission Directorate Technology Highlights Report (33 MB PDF).

Technology Development

Relic radiation from the Big Bang—the Cosmic Microwave Background (CMB)—provides a Rosetta stone for deciphering the content, structure, and evolution of the early universe. Current theoretical understanding suggests that the universe underwent a rapid exponential expansion, called “inflation,” in the first fraction of a second. Such an event would result in an observable stochastic background of gravitational waves that impresses a faint polarized signature on the CMB. The National Research Council’s decadal survey recommended characterization of the CMB as a high-priority science objective, but measurement of the polarization signature is very difficult because it is so faint—about 10-8 of the 2.725 K isotropic component of the CMB.

The 40 GHz focal plane during assembly (top) and a completed 90 GHz focal plane (bottom). Both have been deployed to Chile for observations of the cosmic microwave background.

Not only would a detector need to be highly sensitive to detect these signals, it would also have to distinguish the minute polarized signal from both instrumental effects and other astrophysical sources.

NASA is sponsoring a team led by researchers at GSFC in collaboration with Johns Hopkins University (JHU) to develop detector technologies that will enable these important observations. This capability requires a highly sensitive and stable instrument, measurements in multiple spectral bands for astrophysical foreground removal, control over potential systematic measurement and calibration errors, and the ability to operate in the unique environmental conditions of space. To address these needs, the development team is implementing polarization-sensitive focal-plane arrays that are compatible with the space environment. The detector architecture combines the excellent beam-forming properties of feedhorns with the sensitivity of transition edge sensor (TES) devices. Focal-plane arrays operating at 40 GHz, 90 GHz, and 150/220 GHz are in development. The team’s objective is to advance these detectors to a Technology Readiness Level of 6 (model or prototype demonstration in a relevant environment).

In 2017, the team developed and validated critical details of the fabrication processes for 90-GHz detector wafers, and implemented these into production runs of dichroic 150/220-GHz detectors. The TES membrane thermal design was improved in both detector types, decreasing the thermalization time scales, and leading to improved noise performance at low frequencies. Finally, a cryogenic thermal calibration source was developed and validated from ~30-300 GHz for optical-efficiency polarimetric sensors.

Impact

The feedhorn-coupled TES-based detectors developed via this project are an important step toward implementing an instrument that can successfully characterize the CMB with unprecedented sensitivity. In addition to the performance improvements achieved on individual devices, these research efforts are driving the maturation of the processes required to realize large focal planes with improved reliability and yield.

The 40 GHz CLASS telescope, shown at the site in Chile, has been taking science data since September 2016. A 90 GHz telescope is currently being deployed and prepared for commissioning. Future Plans

Representative focal-plane arrays will be integrated by JHU into the Cosmology Large Angular Scale Surveyor (CLASS)—an array of microwave telescopes located at a high-altitude site in the Atacama Desert of Chile—to achieve and demonstrate the TRL objectives for this technology. Targeted test structures are planned to investigate the sensors’ coupling properties in detail, with an eye toward improved device performance and achieving greater control over key fabrication parameters.

Sponsoring Organization

The development of these feedhorn-coupled TES-based detectors is supported by the NASA SAT program through a grant to Dr. Edward Wollack at GSFC.

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