Sloan Digital Sky Survey
| Sloan Digital Sky Survey (SDSS | |
| Plats | Sunspot, Otero County, New Mexico, New Mexico  USA |
|---|---|
| Typ | Observatorium, forskningsprojekt |
| Användning | Astronomi, astrofysik |
| Färdigställd | 2000 |
| 32°46′49″N 105°49′13″V / 32.78028°N 105.82028°V | |
SSDS, eller The Sloan Digital Sky Survey, är ett kartläggningsprojekt av rödförskjutning som nyttjar det optiska teleskopet vid Apache Point-observatoriet vid Sunspot i New Mexico, USA. Projektet har uppkallats efter Alfred P. Sloan Foundation som stått för en väsentlig del av finansieringen.
Datainsamlingen inleddes 2000 och täckte i januari 2011 35 procent av stjärnhimlen med fotometriska observationer av drygt 500 miljoner objekt och spektroskopiska data för mer än 3 miljoner objekt.[1]
Resultat
Genomsnittsgalaxen i den insamlade datan har en genomsnittlig rödförskjutning av z = 0,1. Bland luminiösa röda galaxer finns rödförskjutning på upp till z = 0,7 och för kvasarer så pass höga värden som z = 5. Projektet har också upptäckt några kvasarer med en rödförskjutning överstigande z = 6.[3]
Se även
- Astronomiska upptäckter av SDSS
Referenser
Noter
- ^ ”SDSS Data Release 8” (på engelska). sdss3.org. http://www.sdss3.org/dr8/. Läst 18 december 2016.
- ^ ”Quasars Acting as Gravitational Lenses” (på engelska). ESA/Hubble Picture of the Week. http://www.spacetelescope.org/images/potw1212a/. Läst 18 december 2016.
- ^ ”SDSS Data Release 10” (på engelska). sdss3.org. http://www.sdss3.org/dr10/. Läst 18 december 2016.
Externa länkar
Media som används på denna webbplats
Författare/Upphovsman: NASA, ESA/Hubble and F. Courbin (Ecole Polytechnique Federale de Lausanne, Switzerland), Licens: CC BY 3.0
Astronomers using the NASA/ESA Hubble Space Telescope have made images of several galaxies containing quasars, which act as gravitational lenses to amplify and distort images of the galaxies aligned behind them.
Quasars are among the brightest objects in the Universe, far outshining the total output of their host galaxies. They are powered by supermassive black holes, which pull in surrounding material that then heats up as it falls towards the black hole. The path that the light from even more distant galaxies takes on its journey towards us is bent by the enormous masses at the centre of these galaxies. Gravitational lensing is a subtle effect which requires extremely high resolution observations, something for which Hubble is extremely well suited.
To find these rare cases of galaxy–quasar combinations acting as lenses, a team of astronomers led by Frederic Courbin at the Ecole Polytechnique Federale de Lausanne (EPFL, Switzerland) selected 23 000 quasar spectra in the Sloan Digital Sky Survey (SDSS). They looked for the spectral imprint of galaxies at much greater distances that happened to align with foreground galaxies. Once candidates were identified, Hubble’s sharp vision was used to look for the characteristic gravitational arcs and rings that would be produced by gravitational lensing.
In Hubble’s images, the quasars are the bright spots visible at the centre of the galaxies, while the lensed images of distant galaxies are visible as fainter arc-shaped forms that surround them. From left to right, the galaxies are: SDSS J0919+2720, with two bluish lensed images clearly visible above and below the galaxy’s centre; SDSS J1005+4016, with one yellowish arc visible to the right of the galaxy’s centre; and SDSS J0827+5224, with two lensed images very faintly visible, one above and to the right, and one below and to the left of the galaxy’s centre.
Quasar host galaxies are hard or sometimes even impossible to see because the central quasar far outshines the galaxy. Therefore, it is difficult to estimate the mass of a host galaxy based on the collective brightness of its stars. However, gravitational lensing candidates are invaluable for estimating the mass of a quasar’s host galaxy because the amount of distortion in the lens can be used to estimate a galaxy’s mass.