8/12/2019 The Dark Energy Camera

1/2

The Dark

Energy

Camera(DEcam)

AKSHAY KUMAR S.R

GOVARDHANAN D

VIKAS V

nlike the human eye,digital cameras canstare at the sky for a

long time and store more andmore light. By replacing thehuman eye with cameras,astronomers can detect fainterand more distant objects. Oureyes cannot detect or cantolerate too much of light andso it is not able to see so manyobjects especially far away anddarker objects. Thus digitalcameras can be used for suchpurposes. But even a digitalcamera is applicable only forbrighter objects.

In 1998, two teams ofastronomers studying distantsupernovae made theremarkable discovery that theexpansion of the universe isspeeding up. Yet, according toEinstein's theory of GeneralRelativity, gravity should lead to

a slowing of the expansion. Toexplain cosmic acceleration,cosmologists are faced withtwo possibilities: Either 75% ofthe universe exists in an exoticform, now called dark energy,that exhibits a gravitationalforce opposite to the attractivegravity of ordinary matter, orGeneral Relativity must bereplaced by a new theory ofgravity on cosmic scales. Thisled to the Dark Energy Surveythat probes the origin of

accelerating universe and thenature of the mysterious darkenergy by measuring the 14

Billion years of cosmicexpansion in the universe andwith extremely high precision.The ultimate aim of the surveyis to build an extremelysensitive 572 megapixel digitalcamera. There came the idea

of a DEcam also known as TheDark Energy Camera. Thename portrays the camerascapability to detect objectswhich are of very lessbrightness through the faintenergy emitted from thoseobjects. It is to be mounted onthe Blanco 4-meter telescopeat Cerro Tolono Inter-AmericanObservatory high in the ChileanAndes. The entire setupconsists of 2 main parts. One isthe camera and the other is theabove mentioned telescope.

Camera:

Cameras used foroptical astronomyare usuallycomposed of an array of digitalchips called charge-coupleddevices (CCDs). CCDs convertlight into electrons. Each chip isdivided into millions of pixels.The electrons generated by thelight that hits each pixel areconverted to a digital value thata computer can store ordisplay. In concept, these arethe same devicesthat makeup the heart of any home digital

camera. However, unlike homecameras that are used torecord images of things that arevery bright, astronomical CCDsmust be souped up in order todetect the tiny amount of lightthat reaches us from faintand/or distant objects. Much ofthe light from extremely distantgalaxies and supernovae hasbeenred shifted into long-wavelength red and infraredlight, which conventional CCDsdo not detect very well.

Named DECam, thislarge, 570 Megapixel cameraswill hold 74 CCDs constructedspecifically to be sensitive tothered shifted light from distantgalaxies and stars. DECam willhave the widest field of view inthe NOAO ground-based

optical/infrared system ofimagers. Its 2.2 degree field ofview is so large that a singleimage will record data from anarea of the sky 20 times thesize of the moon as seen fromearth. This wide field of viewrequires that DECam use asystem of five lenses, each oneuniquely shaped to correct avariety of optical aberrations,with the biggest of these lensesbeing almost 1 meter indiameter.

U

https://www.darkenergysurvey.org/terms/redshift.shtmlhttps://www.darkenergysurvey.org/terms/reshift.shtmlhttps://www.darkenergysurvey.org/terms/reshift.shtmlhttps://www.darkenergysurvey.org/terms/redshift.shtml

8/12/2019 The Dark Energy Camera

2/2

Telescope:

The science of theDark Energy Survey requires

the construction of a uniqueastronomical instrument able tomeet demanding requirements.The idea of building an entirelynew system to answer aspecific scientific question is arelatively new but growing trendin the field of astronomy. In thepast, most telescopes wereconstructed as general-purposefacilities that might have smallpieces added or undergo slightmodifications to meet differentneeds. As told before DECamwill be mounted on the VictorM. Blanco Telescope, alsoknown as the Blanco 4m,located at the Cerro TolonoInter-American Observatory(CTIO) in Chile. CTIO islocated on top of twomountains in the ChileanAndes; Cerro Tolono, which is7,200 feet (2,200 meters) high,and Cerro Pachon, which is8,900 feet (2,700 meters)high. Given below is the abovementioned telescope.

To give a sense of theimmense scale of thetelescope, compare its size tothe human highlighted by thered circle. The green circleindicates the prime focus cagewhere the DES imagingdevice,DECam, will beinstalled. The Blanco is ideallysuited to receive this newdevice because it was originally

built to hold a heavy load at thistop end. When it was built,people rode in the prime focuscage and took astronomicalpictures using heavy glassphotographic plates. Now,DECam will be taking pictures

of roughly the same size withelectronic CCD's.

The Data managementSystem:

Each DECam image isa gigabyte in size. The DarkEnergy Survey will take about400 of these extremely largeimages per night. This presentsa very high data-collection ratefor an astronomy experiment.The data are sent via amicrowave link to La Serena.From there, an optical linkforwards them to the NationalCentre for SupercomputerApplications (NCSA) in Illinoisfor storage and reduction.Reduction consists of standardimage corrections of the rawCCD information to removeinstrumental signatures andartefacts and the joining ofthese images into 0.5 square

degrees combined images.Then galaxies and stars in theimages are identified,catalogued, and finally theirproperties measured andstored in a database.

Other Application:

In addition to its usefor the Dark Energy Survey,

DECam will be a facilityinstrument on the Blancotelescope. This means it will be

available for general use by theastronomical community,providing an order ofmagnitude increase in reachover the current Blanco imager,MOSAIC II. Apart from themain application of the DEcam,

it can be used for various otherastronomical applicationsmainly due to its use of CCDs.The DEcam can help inknowing various untouchedareas of the universe and theother parts of our own galaxy.

The DEcam is not inregular use and its still in thedevelopment stages. The DarkEnergy Mission was begun by

September 2012 andcontinuing for five years, DESwill survey a large swath of thesouthern sky out to vastdistances in order to providenew clues to this mostfundamental of questionsregarding the universe.

https://www.darkenergysurvey.org/DECam/camera.shtmlhttps://www.darkenergysurvey.org/DECam/camera.shtml