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Gaia satellite and amateur astronomers spot one in a billion star

Astronomy News - 20 July 2015 - 3:28pm

An international team of researchers, with the assistance of amateur astronomers, have discovered a unique binary star system: the first known such system where one star completely eclipses the other. It is a type of two-star system known as a Cataclysmic Variable, where one super dense white dwarf star is stealing gas from its companion star, effectively ‘cannibalising’ it.

The system could also be an important laboratory for studying ultra-bright supernova explosions, which are a vital tool for measuring the expansion of the Universe. Details of the new research will be published in the journal Monthly Notices of the Royal Astronomical Society.

The system, named Gaia14aae, is located about 730 light years away in the Draco constellation. It was discovered by the European Space Agency’s Gaia satellite in August 2014 when it suddenly became five times brighter over the course of a single day.

Astronomers led by the University of Cambridge analysed the information from Gaia and determined that the sudden outburst was due to the fact that the white dwarf – which is so dense that a teaspoonful of material from it would weigh as much as an elephant – is devouring its larger companion.

Additional observations of the system made by the Center for Backyard Astrophysics (CBA), a collaboration of amateur and professional astronomers, found that the system is a rare eclipsing binary, where one star passes directly in front of the other, completely blocking it out when viewed from Earth. The two stars are tightly orbiting each other, so a total eclipse occurs roughly every 50 minutes.

“It’s rare to see a binary system so well-aligned” said Dr Heather Campbell of Cambridge’s Institute of Astronomy, who led the follow-up campaign for Gaia14aae. “Because of this, we can measure the system with great precision in order to figure out what these systems are made of and how they evolved. It’s a fascinating system – there’s a lot to be learned from it.”

Using spectroscopy from the William Herschel Telescope in the Canary Islands, Campbell and her colleagues found that Gaia14aae contains large amounts of helium, but no hydrogen, which is highly unusual as hydrogen is the most common element in the Universe. The lack of hydrogen allowed them to classify Gaia14aae as a very rare type of system known as an AM Canum Venaticorum (AM CVn), a type of Cataclysmic Variable system where both stars have lost all of their hydrogen. This is the first known AM CVn system where one star totally eclipses the other.

“It’s really cool that the first time that one of these systems was discovered to have one star completely eclipsing the other, that it was amateur astronomers who made the discovery and alerted us,” said Campbell. “This really highlights the vital contribution that amateur astronomers make to cutting edge scientific research.”

AM CVn systems consist of a small and hot white dwarf star which is devouring its larger companion. The gravitational effects from the hot and superdense white dwarf are so strong that it has forced the companion star to swell up like a massive balloon and move towards it.

The companion star is about 125 times the volume of our sun, and towers over the tiny white dwarf, which is about the size of the Earth – this is similar to comparing a hot air balloon and a marble. However, the companion star is lightweight, weighing in at only one percent of the white dwarf’s mass.

AM CVn systems are prized by astronomers, as they could hold the key to one of the greatest mysteries in modern astrophysics: what causes Ia supernova explosions? This type of supernova, which occurs in binary systems, is important in astrophysics as their extreme brightness makes them an important tool to measure the expansion of the Universe.

In the case of Gaia14aae, it’s not known whether the two stars will collide and cause a supernova explosion, or whether the white dwarf will completely devour its companion first.

“Every now and then, these sorts of binary systems may explode as supernovae, so studying Gaia14aae helps us understand the brightest explosions in the Universe,” said Dr Morgan Fraser of the Institute of Astronomy.

“This is an exquisite system: a very rare type of binary system in which the component stars complete orbits faster than the minute hand of a clock, oriented so that one eclipses the other,” said Professor Tom Marsh of the University of Warwick. “We will be able to measure their sizes and masses to a higher accuracy than any similar system; it whets the appetite for the many new discoveries I expect from the Gaia satellite.”

“This is an awesome first catch for Gaia, but we want it to be the first of many,” said the Institute of Astronomy’s Dr Simon Hodgkin, who is leading the search for more transients in Gaia data. “Gaia has already found hundreds of transients in its first few months of operation, and we know there are many more out there for us to find.”

Gaia’s mission, funded by the European Space Agency and involving scientists from across Europe, is to make the largest, most precise, three-dimensional map of the Milky Way ever attempted. During its five-year mission, which began in late 2013, Gaia’s billion-pixel camera will detect and very accurately measure the motion of stars in their orbit around the centre of the galaxy. It will observe each of the billion stars about a hundred times, helping us to understand the origin and evolution of the Milky Way.

The research was supported by ESA Gaia, DPAC, and the DPAC Photometric Science Alerts Team. The DPAC is funded by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement.

The follow-up campaign used several professional telescopes, including those located in the Canary Islands, where observing time was made available through the International Time Program.

Campbell, HC et al, Total eclipse of the heart: The AM CVn Gaia14aae / ASSASN-14cn, Monthly Notices of the Royal Astronomical Society (2015). 

The Gaia satellite has discovered a unique binary system where one star is ‘eating’ the other, but neither star has any hydrogen, the most common element in the Universe. The system could be an important tool for understanding how binary stars might explode at the end of their lives.

It’s a fascinating system – there’s a lot to be learned from itHeather CampbellMarisa Grove/Institute of AstronomyArtist’s impression of Gaia14aae

The text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.


Cambridge scientists receive Royal Society awards

Astronomy News - 20 July 2015 - 3:26pm

The Royal Society, the UK’s independent academy for science, has announced the recipients of its 2015 Awards, Medals and Prize Lectures. The scientists receive the awards in recognition of their achievements in a wide variety of fields of research. The recipients from the University of Cambridge are:

Professor George Efstathiou FRS (Institute of Astronomy) receives the Hughes Medal for many outstanding contributions to our understanding of the early Universe, in particular his pioneering computer simulations, observations of galaxy clustering and studies of the fluctuations in the cosmic microwave background.

Professor Benjamin Simons (Wellcome Trust/Cancer Research UK Gurdon Institute, Cavendish Laboratory) receives the Gabor Medal for his work analysing stem cell lineages in development, tissue homeostasis and cancer, revolutionising our understanding of stem cell behaviour in vivo.

Professor Russell Cowburn FRS (Department of Physics) receives the Clifford Paterson Medal and Lecture for his remarkable academic, technical and commercial achievements in nano-magnetics.

Dr Madan Babu Mohan (MRC Laboratory of Molecular Biology) receives the Francis Crick Medal and Lecture for his major and widespread contributions to computational biology.

View the full list of recipients.

Four Cambridge scientists have been recognised by the Royal Society for their achievements in research.

The text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.


Vibrating stars could reveal elusive ripples in space-time

Astronomy News - 20 July 2015 - 3:25pm
Stars vibrate like musical instruments, a property that tells us about their insides – and that could reveal gigantic gravitational waves

New Horizons team baffled by discovery of icy plains on Pluto

Astronomy News - 20 July 2015 - 3:25pm
Data downloaded from NASA's New Horizons spacecraft in the past few days has revealed strange terrain, a large atmosphere and yet more mysteries on Pluto

Probe zooms into Pluto's plains

Astronomy News - 20 July 2015 - 3:07pm

The American space agency's New Horizons probe returns further images of Pluto that include a view of the dwarf planet's strange icy plains.

Hawking backs new search for aliens

Astronomy News - 20 July 2015 - 3:06pm

Prof Stephen Hawking launches a new effort to answer the question of whether there is life elsewhere in space.

Rosetta preparing for perihelion

Astronomy News - 16 July 2015 - 9:23am

Rosetta's investigations of its comet are continuing as the mission teams count down the last month to perihelion – the closest point to the Sun along the comet's orbit – when the comet's activity is expected to be at its highest.

Jupiter Twin Discovered Around Solar Twin

Astronomy News - 16 July 2015 - 9:21am
An international group of astronomers has used the ESO 3.6-metre telescope to identify a planet just like Jupiter orbiting at the same distance from a Sun-like star, HIP 11915. According to current theories, the formation of Jupiter-mass planets plays an important role in shaping the architecture of planetary systems. The existence of a Jupiter-mass planet in a Jupiter-like orbit around a Sun-like star opens the possibility that the system of planets around this star may be similar to our own Solar System. HIP 11915 is about the same age as the Sun and, furthermore, its Sun-like composition suggests that there may also be rocky planets orbiting closer to the star.

From Mountains to Moons: Multiple Discoveries from NASA’s New Horizons Pluto Mission

Astronomy News - 16 July 2015 - 9:21am
Icy mountains on Pluto and a new, crisp view of its largest moon, Charon, are among the several discoveries announced Wednesday by the NASA's New Horizons team, just one day after the spacecraft’s first ever Pluto flyby.

Laboratory confirmation of C60+ as the carrier of two diffuse interstellar bands

Astronomy News - 16 July 2015 - 9:20am

Laboratory confirmation of C60+ as the carrier of two diffuse interstellar bands

Nature 523, 7560 (2015). doi:10.1038/nature14566

Authors: E. K. Campbell, M. Holz, D. Gerlich & J. P. Maier

The diffuse interstellar bands are absorption lines seen towards reddened stars. None of the molecules responsible for these bands have been conclusively identified. Two bands at 9,632 ångströms and 9,577 ångströms were reported in 1994, and were suggested to arise from C60+ molecules (ref. 3), on the basis of the proximity of these wavelengths to the absorption bands of C60+ measured in a neon matrix. Confirmation of this assignment requires the gas-phase spectrum of C60+. Here we report laboratory spectroscopy of C60+ in the gas phase, cooled to 5.8 kelvin. The absorption spectrum has maxima at 9,632.7 ± 0.1 ångströms and 9,577.5 ± 0.1 ångströms, and the full widths at half-maximum of these bands are 2.2 ± 0.2 ångströms and 2.5 ± 0.2 ångströms, respectively. We conclude that we have positively identified the diffuse interstellar bands at 9,632 ångströms and 9,577 ångströms as arising from C60+ in the interstellar medium.

Rapidly rotating second-generation progenitors for the ‘blue hook’ stars of ω Centauri

Astronomy News - 16 July 2015 - 9:20am

Rapidly rotating second-generation progenitors for the ‘blue hook’ stars of ω Centauri

Nature 523, 7560 (2015). doi:10.1038/nature14516

Authors: Marco Tailo, Francesca D’Antona, Enrico Vesperini, Marcella Di Criscienzo, Paolo Ventura, Antonino P. Milone, Andrea Bellini, Aaron Dotter, Thibaut Decressin, Annibale D’Ercole, Vittoria Caloi & Roberto Capuzzo-Dolcetta

Horizontal branch stars belong to an advanced stage in the evolution of the oldest stellar galactic population, occurring either as field halo stars or grouped in globular clusters. The discovery of multiple populations in clusters that were previously believed to have single populations gave rise to the currently accepted theory that the hottest horizontal branch members (the ‘blue hook’ stars, which had late helium-core flash ignition, followed by deep mixing) are the progeny of a helium-rich ‘second generation’ of stars. It is not known why such a supposedly rare event (a late flash followed by mixing) is so common that the blue hook of ω Centauri contains approximately 30 per cent of the horizontal branch stars in the cluster, or why the blue hook luminosity range in this massive cluster cannot be reproduced by models. Here we report that the presence of helium core masses up to about 0.04 solar masses larger than the core mass resulting from evolution is required to solve the luminosity range problem. We model this by taking into account the dispersion in rotation rates achieved by the progenitors, whose pre-main-sequence accretion disk suffered an early disruption in the dense environment of the cluster’s central regions, where second-generation stars form. Rotation may also account for frequent late-flash–mixing events in massive globular clusters.

Astrochemistry: Fullerene solves an interstellar puzzle

Astronomy News - 16 July 2015 - 9:19am

Astrochemistry: Fullerene solves an interstellar puzzle

Nature 523, 7560 (2015). doi:10.1038/523296a

Authors: Pascale Ehrenfreund & Bernard Foing

Laboratory measurements confirm that a 'buckyball' ion is responsible for two near-infrared absorption features found in spectra of the interstellar medium, casting light on a century-old astrochemical mystery. See Letter p.322

VIDEO: Stephen Hawking on Pluto mission

Astronomy News - 16 July 2015 - 9:16am

Stephen Hawking has congratulated the New Horizons team and NASA for their successful mission to the dwarf planet Pluto.

Nasa releases historic Pluto images

Astronomy News - 16 July 2015 - 9:15am

Nasa has presented the first images acquired by the New Horizons probe during its historic flyby of Pluto.

VIDEO: What do new Pluto images reveal?

Astronomy News - 16 July 2015 - 9:14am

Pluto has mountains made of ice that are as high as those in the Rockies, images from the New Horizons probe have revealed.

VIDEO: Pluto revelations 'not what we expected'

Astronomy News - 16 July 2015 - 9:14am

Pluto has mountains made of ice that are as high as those in the Rockies, images from the New Horizons probe have revealed.

Cluster solves the mystery of equatorial noise

Astronomy News - 15 July 2015 - 10:10am

ESA's Cluster mission has solved a mystery which puzzled scientists for almost half a century. Data sent back by two of the spacecraft have revealed for the first time the physical mechanism behind the generation of "noisy" waves in near-Earth space.

NASA's Three-Billion-Mile Journey to Pluto Reaches Historic Encounter

Astronomy News - 15 July 2015 - 10:07am
NASA’s New Horizons spacecraft is at Pluto. After a decade-long journey through our solar system, New Horizons made its closest approach to Pluto Tuesday, about 7,750 miles above the surface -- roughly the same distance from New York to Mumbai, India – making it the first-ever space mission to explore a world so far from Earth.

NASA's New Horizons ‘Phones Home’ Safe after Pluto Flyby

Astronomy News - 15 July 2015 - 10:04am
The call everyone was waiting for is in. NASA’s New Horizons spacecraft phoned home just before 9 p.m. EDT Tuesday to tell the mission team and the world it had accomplished the historic first-ever flyby of Pluto.

Hadron Collider discovers new particle

Astronomy News - 15 July 2015 - 9:28am

Scientists at the Large Hadron Collider have announced the discovery of a new particle called the pentaquark.