There is on average at least one planet orbiting every star in the Milky Way. This remarkable conclusion comes from an international team of astronomers, including leading scientists from the Zentrum für Astronomie der Universität Heidelberg (ZAH), who used a method known as gravitational microlensing. After a six-year search that surveyed millions of stars, the researchers conclude from their comprehensive statistical analysis that planets orbiting stars, or “exoplanets”, are the rule rather than the exception. The results will appear in the journal “Nature“ on 12 January 2012.
This artists’s cartoon view gives an impression of how common planets are around the stars in the Milky Way. The planets, their orbits and their host stars are all vastly magnified compared to their real separations. A six-year search that surveyed millions of stars using the microlensing technique concluded that planets around stars are the rule rather than the exception. The average number of planets per star is greater than one.
Over the past 16 years, astronomers have detected more than 700 exoplanets and have started to probe the spectra and atmospheres of several of these remote worlds. One basic question remains: How commonplace are planets in our Milky Way? Most currently known exoplanets were found either by detecting the effect of the gravitational pull of the planet on its host star or by catching the planet as it passes in front of its star and slightly dims it. Both of these techniques, i.e., the radial velocity and transit methods, are most sensitive to planets that are either very massive or close to their stars, or both. Until now many exoplanets were simply overlooked because they were beyond the limits of detection of these techniques.
Prof. Dr. Joachim Wambsganss, Director of the Centre for Astronomy of Heidelberg University, and his collaborators use another method to search for exoplanets. Gravitational microlensing reveals them by measuring the effect of their gravitational fields on the light of background stars. In this method, the star and its planet act like a lens, focussing the light rays of the background star to the observer and hence making this star appear brighter for several days. The change in brightness over time, the light curve, has a very characteristic shape. The planet’s influence is often measurable for only a few hours. This technique makes it possible to detect planets located further away from their stars and over a broader range of masses, and it is well suited for statistical analyses. Yet the probability for detection is extremely low. “In order to detect a single stellar gravitational microlensing event, the brightnesses of several million stars need to be measured several times a week. And even if all the lensing stars have a planet, this planet reveals itself in less than one percent of cases,” explains Prof. Wambsganss.
“We combed through six years of microlensing observations. Remarkably, these data show that planets are more common than stars in our Galaxy”, says the lead author of the Nature paper, Dr. Arnaud Cassan, a former postdoc of Prof. Wambsganss at the ZAH, now with the Institut d'Astrophysique de Paris (France). The results of the study are largely based on work that Dr. Cassan did during his time in Heidelberg. For the investigations, the scientists from Australia, Austria, Chile, Croatia, Denmark, France, Germany, Great Britain, Japan, New Zealand, Poland, South Africa and the US – among them researchers from the European Southern Observatory (ESO) – used data from the PLANET (Probing Lensing Anomalies NETwork) and OGLE (Optical Gravitational Lensing Experiment) observational teams.
Between 2002 and 2007, the scientists repeatedly measured the brightnesses of several million stars. They observed a total of 3,247 gravitational microlensing events generated by stars. Three of these light curves were clearly planets: one “super-Earth”, one Neptune-like planet and another with a mass similar to Jupiter. The international research team combined the data of these three discoveries with that of seven other exoplanets that had likewise been found through gravitational microlensing. Also included were a large number of stars observed over the six years where no planets were detected. According to Dr. Cassan, the non-detections were just as important for the statistical analysis as the detected planets.
By comparing the data with intensive computer simulations, the astronomers concluded that approximately one in six stars is being orbited by a Jupiter-like planet. The analysis also indicated that roughly half of all stars have planets with the mass of Neptune, and two-thirds host a “super-Earth”. The survey was sensitive to planets between 75 million to 1.5 billion kilometres from their stars and with masses ranging from five times the mass of the Earth up to ten Jupiter masses.
Contact:Prof. Dr. Joachim Wambsganss
Marietta Fuhrmann-Koch | idw
X-ray photoelectron spectroscopy under real ambient pressure conditions
28.06.2017 | National Institutes of Natural Sciences
New photoacoustic technique detects gases at parts-per-quadrillion level
28.06.2017 | Brown University
An international team of scientists has proposed a new multi-disciplinary approach in which an array of new technologies will allow us to map biodiversity and the risks that wildlife is facing at the scale of whole landscapes. The findings are published in Nature Ecology and Evolution. This international research is led by the Kunming Institute of Zoology from China, University of East Anglia, University of Leicester and the Leibniz Institute for Zoo and Wildlife Research.
Using a combination of satellite and ground data, the team proposes that it is now possible to map biodiversity with an accuracy that has not been previously...
Heatwaves in the Arctic, longer periods of vegetation in Europe, severe floods in West Africa – starting in 2021, scientists want to explore the emissions of the greenhouse gas methane with the German-French satellite MERLIN. This is made possible by a new robust laser system of the Fraunhofer Institute for Laser Technology ILT in Aachen, which achieves unprecedented measurement accuracy.
Methane is primarily the result of the decomposition of organic matter. The gas has a 25 times greater warming potential than carbon dioxide, but is not as...
Hydrogen is regarded as the energy source of the future: It is produced with solar power and can be used to generate heat and electricity in fuel cells. Empa researchers have now succeeded in decoding the movement of hydrogen ions in crystals – a key step towards more efficient energy conversion in the hydrogen industry of tomorrow.
As charge carriers, electrons and ions play the leading role in electrochemical energy storage devices and converters such as batteries and fuel cells. Proton...
Scientists from the Excellence Cluster Universe at the Ludwig-Maximilians-Universität Munich have establised "Cosmowebportal", a unique data centre for cosmological simulations located at the Leibniz Supercomputing Centre (LRZ) of the Bavarian Academy of Sciences. The complete results of a series of large hydrodynamical cosmological simulations are available, with data volumes typically exceeding several hundred terabytes. Scientists worldwide can interactively explore these complex simulations via a web interface and directly access the results.
With current telescopes, scientists can observe our Universe’s galaxies and galaxy clusters and their distribution along an invisible cosmic web. From the...
Temperature measurements possible even on the smallest scale / Molecular ruby for use in material sciences, biology, and medicine
Chemists at Johannes Gutenberg University Mainz (JGU) in cooperation with researchers of the German Federal Institute for Materials Research and Testing (BAM)...
19.06.2017 | Event News
13.06.2017 | Event News
13.06.2017 | Event News
28.06.2017 | Physics and Astronomy
28.06.2017 | Physics and Astronomy
28.06.2017 | Health and Medicine