̽��ֱ�� of Cambridge - Morgan Fraser

Gaia results revealed – first data release from the most detailed map ever made of the sky

sc604 — Wed, 14 Sep 2016 11:51:09 +0000

Detailed information about more than a billion stars in the Milky Way has been published in the first data release from the Gaia satellite, which is conducting the first-ever ‘galactic census.’ ̽��ֱ��release marks the first chance astronomers and the public have had to get their hands on the most detailed map ever made of the sky.

Gaia, which orbits the sun at a distance of 1.5 million kilometres from the earth, was launched by the European Space Agency in December 2013 with the aim of observing a billion stars and revolutionising our understanding of the Milky Way. During its expected five-year lifespan, Gaia will observe each of a billion stars about 70 times.

̽��ֱ��unique mission is reliant on the work of Cambridge researchers who collect the vast quantities of data transmitted by Gaia to a data processing centre at the ̽��ֱ��, overseen by a team at the Institute of Astronomy.

“Gaia’s first major data release is both a wonderful achievement in its own right, and a taster of the truly dramatic advances to come in future years,” said Professor Gerry Gilmore from the Institute of Astronomy, who is also the UK Principal Investigator for Gaia. “Several UK teams have leading roles in Gaia’s Data Processing and Analysis efforts, which convert the huge raw data streams from the satellite into the beautiful science-ready information now made available for the global scientific and public communities. UK industry made critical contributions to the Gaia spacecraft. ̽��ֱ��UK public, including school students, as well as scientists, are sharing the excitement of this first ever galactic census.”

In addition to the work taking place at Cambridge, teams from Edinburgh, the Mullard Space Science Laboratory (MSSL) at UCL London, Leicester, Bristol and the Science and Technology Facilities Council’s Rutherford Appleton Lab are all contributing to the processing of the vast amounts of data from Gaia, in collaboration with industrial and academic partners from across Europe.

̽��ֱ��team in Cambridge, led by Dr Floor van Leeuwen, Dr Dafydd Wyn Evans and Dr Francesca De Angeli, processed the flux information – the amount of energy that crosses a unit area per unit time – providing the calibrated magnitudes of around 1.6 billion stars, 1.1 billion of which are now published as part of the first data release.

̽��ֱ��Cambridge team also check the daily photometric data for unexpected large outliers, which led to the regular publication of photometric science alerts that were ready for immediate follow-up observations from the ground.

“ ̽��ֱ��sheer volume of data processed for this first release is beyond imagination: around 120 billion images were analysed, and most of these more than once, as all the processing is iterative,” said van Leeuwen, who is Gaia photometric data processing lead. “Many problems had to be overcome, and a few small ones still remain. Calibrations have not yet reached their full potential. Nevertheless, we are already reaching accuracies that are significantly better than expected before the mission, and which can challenge most ground-based photometric data in accuracy.”

“This first Gaia data release has been an important exercise for the Gaia data reduction teams, getting them to focus on deliverable products and their description,” said Evans. “But it is only the first small step towards much more substantial results.”

While today marks the first major data release from Gaia, in the two years since its launch, the satellite has been producing scientific results in the form of Gaia Alerts.

Dr Simon Hodgkin, lead of the Cambridge Alerts team said, “ ̽��ֱ��Gaia Alerts project takes advantage of the fact that the Gaia satellite scans each part of the sky repeatedly throughout the mission. By comparing successive observations of the same patch of sky, scientists can search for transients – astronomical objects which brighten, fade, change or move. These transients are then announced to the world each day as Gaia Alerts for both professional and amateur astronomers to observe with telescopes from the ground.”

̽��ֱ��range of Gaia’s discoveries from Science Alerts is large – supernovae of various types, cataclysmic variable stars, novae, flaring stars, gravitational microlensing events, active galactic nuclei and quasars, and many sources whose nature remains a mystery.

Gaia has discovered many supernovae, the brilliant explosions of stars at the end of their lives. Many of these have been ‘Type Ia’ supernovae, which can be used to measure the accelerating expansion of the Universe. But among these apparently typical supernovae there have been some rarer events. Gaia16ada was spotted by Gaia in the nearby galaxy NGC4559, and appears to be an eruption of a very massive, unstable star. ̽��ֱ��Hubble Space Telescope observed this galaxy some years ago, allowing astronomers to pinpoint the precise star which erupted.

Another lucky catch for Gaia was the discovery of Gaia16apd – a supernova which is nearly a hundred times brighter than normal. Astronomers still don't know what the missing ingredient in these ultra-bright supernovae is, and candidates include exotic rapidly spinning neutron stars, or jets from a black hole. Cambridge astronomer Dr Morgan Fraser is trying to understand these events, saying, “We have only found a handful of these exceptionally bright supernovae, compared to thousands of normal supernovae. For Gaia to spot one so nearby is a fantastic result.”

Many of the Gaia Alerts found so far are bright enough to be observable with a small telescope. Amateur astronomers have taken images of supernovae found by Gaia, while schoolchildren have used robotic telescopes including the Faulkes Telescopes in Australia and Hawaii to do real science with transients.

Dr Hodgkin said: “Since the announcement of the first transients discovered with Gaia in September 2014, over one thousand alerts have been released. With Gaia continually relaying new observations to ground, and our team working on finding transients continually improving their software, the discoveries look set to continue well into the future!”

For the UK teams the future means providing improvements in the pre-processing of the data and extending the processing to cover the photometric Blue and Red prism data. Also data from the Radial Velocity Spectrometer, with major involvement from MSSL, will be included in future releases. ̽��ֱ��photometric science alerts will continue to operate throughout the mission, and summaries of the results will be included in future releases. “Despite the considerable amount of data, the first Gaia data release provides just a taste of the accuracy and completeness of the final catalogue,” said De Angeli.

̽��ֱ��Cambridge Gaia team has also released a dedicated smartphone app, which will allow anyone worldwide to follow the Gaia Alerts discoveries as they happen. Real spacecraft data will be available to the world as soon as it is processed, with users able to follow the discoveries and see what they are. Information to access the app is available at https://gaia.ac.uk.

̽��ֱ��Gaia data processing teams in the UK have been and are being supported by the UK Space Agency and the STFC. STFC helped the set-up of the data applications centre and STFC’s current support involves the UK exploitation of the scientific data to be yielded from the mission. Industrial partners include Airbus, MSSL and e2v Technologies.

̽��ֱ��first results from the Gaia satellite, which is completing an unprecedented census of more than one billion stars in the Milky Way, are being released today to astronomers and the public.

Gaia’s first major data release is both a wonderful achievement in its own right, and a taster of the truly dramatic advances to come in future years.

Gerry Gilmore

ESA/Gaia/DPAC

Gaia’s first sky map

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

Yes

How to escape a black hole

sc604 — Thu, 26 Nov 2015 19:00:00 +0000

̽��ֱ��results, published in the journal Science, are based on new radio observations tracking a star as it gets torn apart by a black hole. Such violent events yield a burst of light which is produced as the bits and pieces of the star fall into the black hole. For the first time, the researchers were able to show that this burst of light is followed by a radio signal from the matter that was able to escape the black hole by travelling away in a jetted outflow at nearly the speed of light.

̽��ֱ��discovery of the jet was made possible by a rapid observational response after the stellar disruption (known as ASAS-SN-14li) was announced in December 2014. ̽��ֱ��radio data was taken by the by the 4 PI SKY team at Oxford, using the Arcminute Microkelvin Imager Large Array located in Cambridge.

“Previous efforts to find evidence for these jets, including my own, were late to the game,” said Sjoert van Velzen of Johns Hopkins ̽��ֱ��, the study’s lead author. Co-author Nicholas Stone added that “even after they got to the game, these earlier attempts were observing from the bleachers, while we were the first to get front row seats.”

In this branch of astronomy, the ‘front row’ means a distance of 300 million light years, while previous observations were based on events at occurring least three times as far away.

Jets are often observed in association with black holes, but their launch mechanism remains a major unsolved problem in astrophysics. Most supermassive black hole are fed a steady diet of gas, leading to jets that live for millions of years and change little on a human timescale. However, the newly discovered jet behaved very differently: the observations show that following a brief injection of energy, it produced short but spectacular radio fireworks.

̽��ֱ��observed jet was anticipated by the so-called scale-invariant model of accretion, also known as the Matryoshka-doll theory of astrophysics. It predicts that all compact astrophysical objects (white dwarfs, neutron stars, or black holes) that accrete matter behave and look the same after a simple correction based on solely the mass of the object. In other words, the larger Matryoshka doll (a supermassive black hole) is just a scaled-up version of the smaller doll (a neutron star). Since neutron stars consistently produce radio-emitting jets when they are supplied with a large amount of gas, the theory predicts that supermassive black holes should do the same when they swallow a star.

“I always liked the elegant nature of the scale-invariant theory, but previous observations never found evidence for the new type of jet it predicted,” said van Velzen. “Our new findings suggest that this new type of jet could indeed be common and previous observations were simply not sensitive enough to detect them.”

“These jets are a unique tool for probing supermassive black holes,” said co-author Dr Morgan Fraser of Cambridge’s Institute of Astronomy. “While black holes themselves do not emit light, by observing how a star is torn apart as it falls in we can indirectly study the sleeping monster at the heart of a galaxy.”

̽��ֱ��study hypothesises that every stellar disruption leads to a radio flare similar to the one just discovered. Ongoing surveys such as the Gaia Alerts project, led by the ̽��ֱ�� of Cambridge will find many more of these rare events.

“Gaia has exceptionally sharp eyes, and is ideally suited to find events like this, which occur in the very centres of galaxies,” said co-author Dr Heather Campbell, also from Cambridge’s Institute of Astronomy. “Finding more of these rare events may further our understanding of the processes that allow black holes to launch such spectacular outflows.”

Reference:
Van Velzen, S. et. al. ‘A radio jet from the optical and X-ray bright stellar tidal disruption flare ASASSN-14li.’ Science (2015). DOI: 10.1126/science.aad1182

Adapted from a Johns Hopkins press release.

An international team of astrophysicists, including researchers from the ̽��ֱ�� of Cambridge, has observed a new way for gas to escape the gravitational pull of a supermassive black hole.

These jets are a unique tool for probing supermassive black holes

Morgan Fraser

NASA/Goddard Space Flight Center/CI Lab

Detail from animation of a black hole devouring a star

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

Yes

Gaia satellite and amateur astronomers spot one in a billion star

sc604 — Thu, 16 Jul 2015 23:12:32 +0000

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.

̽��ֱ��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.

̽��ֱ��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 ̽��ֱ�� 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. ̽��ֱ��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. ̽��ֱ��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. ̽��ֱ��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.

̽��ֱ��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 ̽��ֱ�� 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.

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

̽��ֱ��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.

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

̽��ֱ��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. ̽��ֱ��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 it

Heather Campbell

Marisa Grove/Institute of Astronomy

Artist’s impression of Gaia14aae

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

Yes