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News Release Archive:

News Release 241 of 966

May 7, 2009 09:00 AM (EDT)

News Release Number: STScI-2009-08

Refined Hubble Constant Narrows Possible Explanations for Dark Energy

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Image: Cepheid Variable Stars in Spiral Galaxy NGC 3021

Cepheid Variable Stars in Spiral Galaxy NGC 3021STScI-PRC2009-08a

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ABOUT THIS IMAGE:

This is a Hubble Space Telescope photo of the spiral galaxy NGC 3021. This was one of several hosts of recent Type Ia supernovae observed by astronomers to refine the measure of the universe's expansion rate, called the Hubble constant. Hubble made precise measurements of Cepheid variable stars in the galaxy, highlighted by green circles in the four inset boxes. These stars pulsate at a rate that is matched closely to their intrinsic brightness. This makes them ideal for measuring intergalactic distances. The Cepheids are used to calibrate an even brighter milepost marker that can be used over greater distances, a Type Ia supernova. The supernova was observed in the galaxy in 1995. The images in the boxes were taken with the Near Infrared Camera and Multi-Object Spectrometer (NICMOS).

Image Type: Astronomical/Illustration

Credit: NASA, ESA, and A. Riess (STScI/JHU)

NEWS RELEASE IMAGES

The above montage includes these images:

HST ACS/WFC Image of NGC 3021 Image Type: Astronomical HST ACS/WFC Image of NGC 3021 NGC 3021 NICMOS/ACS Detail 1 Image Type: Astronomical NGC 3021 NICMOS/ACS Detail 1 NGC 3021 NICMOS/ACS Detail 2 Image Type: Astronomical NGC 3021 NICMOS/ACS Detail 2 NGC 3021 NICMOS/ACS Detail 3 Image Type: Astronomical NGC 3021 NICMOS/ACS Detail 3 NGC 3021 NICMOS/ACS Detail 4 Image Type: Astronomical NGC 3021 NICMOS/ACS Detail 4

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