Extrasolar planets: Window on a watery world
Nature 513, 7519 (2014). doi:10.1038/513493a
Authors: Eliza M. R. Kempton
The first definitive signs of water have been seen in the atmosphere of a Neptune-sized exoplanet, paving the way towards the search for water on smaller Earth-like planets. See Letter p.526
While scanning the sky to measure the positions and movements of stars in our Galaxy, Gaia has discovered its first stellar explosion in another galaxy far, far away.
This powerful event, now named Gaia14aaa, took place in a distant galaxy some 500 million light-years away, and was revealed via a sudden rise in the galaxy’s brightness between two Gaia observations separated by one month.
Gaia, which began its scientific work on 25 July, repeatedly scans the entire sky, so that each of the roughly one billion stars in the final catalogue will be examined an average of 70 times over the next five years.
“This kind of repeated survey comes in handy for studying the changeable nature of the sky,” comments Simon Hodgkin from the Institute of Astronomy in Cambridge, UK.
Many astronomical sources are variable: some exhibit a regular pattern, with a periodically rising and declining brightness, while others may undergo sudden and dramatic changes.
“As Gaia goes back to each patch of the sky over and over, we have a chance to spot thousands of ‘guest stars’ on the celestial tapestry,” notes Dr Hodgkin. “These transient sources can be signposts to some of the most powerful phenomena in the Universe, like this supernova.”
Dr Hodgkin is part of Gaia’s Science Alert Team, which includes astronomers from the Universities of Cambridge, UK, and Warsaw, Poland, who are combing through the scans in search of unexpected changes.
It did not take long until they found the first ‘anomaly’ in the form of a sudden spike in the light coming from a distant galaxy, detected on 30 August. The same galaxy appeared much dimmer when Gaia first looked at it just a month before.
“We immediately thought it might be a supernova, but needed more clues to back up our claim,” explains Łukasz Wyrzykowski from the Warsaw University Astronomical Observatory, Poland.
Other powerful cosmic events may resemble a supernova in a distant galaxy, such as outbursts caused by the mass-devouring supermassive black hole at the galaxy centre.
Supernova Gaia14aaa and its host galaxy
However, in Gaia14aaa, the position of the bright spot of light was slightly offset from the galaxy’s core, suggesting that it was unlikely to be related to a central black hole.
So, the astronomers looked for more information in the light of this new source. Besides recording the position and brightness of stars and galaxies, Gaia also splits their light to create a spectrum. In fact, Gaia uses two prisms spanning red and blue wavelength regions to produce a low-resolution spectrum that allows astronomers to seek signatures of the various chemical elements present in the source of that light.
Read the full story on Gaia's first supernova discovery on the ESA Portal.
Astronomers have found an unlikely object in an improbable place: a monster black hole lurking inside one of the tiniest galaxies known. The dwarf galaxy containing the black hole is the densest galaxy ever seen, cramming 140 million stars within a diameter of about 300 light-years (just 1/500th of our Milky Way galaxy's diameter). However, the black hole inside the galaxy is five times the mass of the black hole at the center of our Milky Way. This suggests that the dwarf galaxy may actually be the stripped remnant of a larger galaxy that was torn apart during a close encounter with a more massive galaxy. The finding implies that there are many other compact galaxies in the universe that contain supermassive black holes.
Highlights in the study of exoplanet atmospheres
Nature 513, 7518 (2014). doi:10.1038/nature13782
Author: Adam S. Burrows
Exoplanets are now being discovered in profusion. To understand their character, however, we require spectral models and data. These elements of remote sensing can yield temperatures, compositions and even weather patterns, but only if significant improvements in both the parameter retrieval process and measurements are
Advances in exoplanet science from Kepler
Nature 513, 7518 (2014). doi:10.1038/nature13781
Authors: Jack J. Lissauer, Rebekah I. Dawson & Scott Tremaine
Numerous telescopes and techniques have been used to find and study extrasolar planets, but none has been more successful than NASA's Kepler space telescope. Kepler has discovered most of the known exoplanets, the smallest planets to orbit normal stars and the planets most likely to
A supermassive black hole in an ultra-compact dwarf galaxy
Nature 513, 7518 (2014). doi:10.1038/nature13762
Authors: Anil C. Seth, Remco van den Bosch, Steffen Mieske, Holger Baumgardt, Mark den Brok, Jay Strader, Nadine Neumayer, Igor Chilingarian, Michael Hilker, Richard McDermid, Lee Spitler, Jean Brodie, Matthias J. Frank & Jonelle L. Walsh
Ultra-compact dwarf galaxies are among the densest stellar systems in the Universe. These systems have masses of up to 2 × 108 solar masses, but half-light radii of just 3–50 parsecs. Dynamical mass estimates show that many such dwarfs are more massive than expected from their luminosity. It remains unclear whether these high dynamical mass estimates arise because of the presence of supermassive black holes or result from a non-standard stellar initial mass function that causes the average stellar mass to be higher than expected. Here we report adaptive optics kinematic data of the ultra-compact dwarf galaxy M60-UCD1 that show a central velocity dispersion peak exceeding 100 kilometres per second and modest rotation. Dynamical modelling of these data reveals the presence of a supermassive black hole with a mass of 2.1 × 107 solar masses. This is 15 per cent of the object’s total mass. The high black hole mass and mass fraction suggest that M60-UCD1 is the stripped nucleus of a galaxy. Our analysis also shows that M60-UCD1’s stellar mass is consistent with its luminosity, implying a large population of previously unrecognized supermassive black holes in other ultra-compact dwarf galaxies.
Nature 513, 7518 (2014). doi:10.1038/513327a
Author: Leslie Sage
It is hard to imagine now, and the younger people in the field will not remember this, but there was a period when the search for exoplanets had rather a bad reputation, based on a number of high-profile claims that were subsequently disproved. Although there