Capturing black hole spin could further understanding of galaxy growth

July 29, 2013 — Astronomers have found a new way of measuring the spin in supermassive black holes, which could lead to better understanding about how they drive the growth of galaxies. The scientists at Durham University in the UK publish their work in a paper in the Oxford University Press journal Monthly Notices of the Royal Astronomical Society.The team of astronomers observed a black hole — with a mass 10 million times that of our Sun — at the centre of a spiral galaxy 500 million light years from Earth while it was feeding on the surrounding disc of material that fuels its growth and powers its activity.By viewing optical, ultra-violet and soft x-rays generated by heat as the black hole fed, they were able to measure how far the disc was from the black hole.This distance depends on black hole spin as a fast spinning black hole pulls the disc in closer to itself, the researchers said. Using the distance between the black hole and the disc, the scientists were able to estimate the spin of the black hole.The scientists said that understanding spin could lead to greater understanding of galaxy growth over billions of years.Black holes lie at the centres of almost all galaxies, and can spit out incredibly hot particles at high energies that prevent intergalactic gases from cooling and forming new stars in the outer galaxy. Scientists don’t yet understand why the jets are ejected into space, but the Durham experts believe that their power could be linked to the spin of the black hole. This spin is difficult to measure as it only affects the behaviour of material really close to the black hole.Lead researcher Professor Chris Done, in the Department of Physics, at Durham University, said: “We know the black hole in the centre of each galaxy is linked to the galaxy as a whole, which is strange because black holes are tiny in relation to the size of a galaxy. This would be like something the size of a large boulder (10m), influencing something the size of Earth.”Understanding this connection between stars in a galaxy and the growth of a black hole, and vice-versa, is the key to understanding how galaxies form throughout cosmic time.”If a black hole is spinning it drags space and time with it and that drags the accretion disc, containing the black hole’s food, closer towards it. This makes the black hole spin faster, a bit like an ice skater doing a pirouette.”By being able to measure the distance between the black hole and the accretion disc, we believe we can more effectively measure the spin of black holes.”Because of this, we hope to be able to understand more about the link between black holes and their galaxies.”The Durham scientists were able to measure the spin of the black hole using soft x-ray, optical and ultra-violet images captured by the European Space Agency’s XMM-Newton satellite.

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Snow in an infant solar system: A frosty landmark for planet and comet formation

July 18, 2013 — A snow line has been imaged in a far-off infant solar system for the very first time. The snow line, located in the disc around the Sun-like star TW Hydrae, promises to tell us more about the formation of planets and comets, the factors that decide their composition, and the history of the Solar System.The results are published today in Science Express.Astronomers using the Atacama Large Millimeter/submillimeter Array have taken the first ever image of the snow line in an infant solar system. On Earth, snow lines form at high altitudes where falling temperatures turn the moisture in the air into snow. This line is clearly visible on a mountain, where the snow-capped summit ends and the rocky face begins.The snow lines around young stars form in a similar way, in the distant, colder reaches of the dusty discs from which solar systems form. Starting from the star and moving outwards, water (H2O) is the first to freeze, forming the first snow line. Further out from the star, as temperatures drop, more exotic molecules can freeze and turn to snow, such as carbon dioxide (CO2), methane (CH4), and carbon monoxide (CO). These different snows give the dust grains a sticky outer coating and play an essential role in helping the grains to overcome their usual tendency to break up in collisions, allowing them to become the crucial building blocks of planets and comets. The snow also increases how much solid matter is available and may dramatically speed up the planetary formation process.Each of these different snow lines — for water, carbon dioxide, methane and carbon monoxide — may be linked to the formation of particular kinds of planets [1]. Around a Sun-like star in a solar system like our own, the water snow line would correspond to a distance between the orbits of Mars and Jupiter, and the carbon monoxide snow line would correspond to the orbit of Neptune.The snow line spotted by ALMA is the first glimpse of the carbon monoxide snow line, around TW Hydrae, a young star 175 light-years away from Earth. Astronomers believe this budding solar system shares many of the same characteristics of the Solar System when it was just a few million years old.”ALMA has given us the first real picture of a snow line around a young star, which is extremely exciting because of what it tells us about the very early period in the history of the Solar System,” said Chunhua “Charlie” Qi (Harvard-Smithsonian Center for Astrophysics, Cambridge, USA) one of the two lead authors of the paper. …

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