NASA | JPL-Caltech | 2017 Jan 05
[img3="This graphic shows all the cosmic light sources in the sky that are included in the NASA/IPAC Extragalactic Database (NED), an online repository containing information on over 100 million galaxies. Credit: NASA/JPL-Caltech"]http://www.jpl.nasa.gov/spaceimages/ima ... _hires.jpg[/img3][hr][/hr]A team of researchers has compiled a special catalog to help astronomers figure out the true distances to tens of thousands of galaxies beyond our own Milky Way.
The catalog, called NED-D, is a critical resource, not only for studying these galaxies, but also for determining the distances to billions of other galaxies strewn throughout the universe. As the catalog continues to grow, astronomers can increasingly rely on it for ever-greater precision in calculating both how big the universe is and how fast it is expanding. NED-D is part of the NASA/IPAC Extragalactic Database (NED), an online repository containing information on more than 100 million galaxies. ...
Since other galaxies are extremely far away, there's no tape measure long enough to measure their distances from us. Instead, astronomers rely on extremely bright objects, such as Type Ia supernovae and pulsating stars called Cepheids variables, as indicators of distance. To calculate how far away a distant galaxy is, scientists use known mathematical relationships between distance and other properties of objects, such as their total emitted energy. More objects useful for these calculations have emerged in recent years. NED-D has revealed that there are now more than six dozen different indicators used to estimate such distances. ...
Redshift-Independent Distances in the NASA/IPAC Extragalactic Database: Methodology, Content and Use of NED-D - Ian Steer et al
- Astronomical Journal 153(1):37 (Jan 2017) DOI: 10.3847/1538-3881/153/1/37
arXiv.org > astro-ph > arXiv:1612.09263 > 29 Dec 2016