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NGC 3972 and NGC 1015
Hubble Helps Astronomers Measure Accurate Distances to Galaxies
These Hubble Space Telescope images showcase 2 of the 19 galaxies analyzed in a project to improve the precision of the universe's expansion rate, a value known as the Hubble constant.
The color-composite images show NGC 3972 (left) and NGC 1015 (right), located 65 million light-years and 118 million light-years, respectively, from Earth. The yellow circles in each galaxy represent the locations of pulsating stars called Cepheid variables. These stars blink at a rate matched closely by their intrinsic brightness, making them ideal cosmic lighthouses for measuring accurate distances to relatively nearby galaxies.
Another reliable milepost marker is a special class of exploding star called a Type Ia supernova. All of these supernovae peak at the same brightness and are brilliant enough to be seen over relatively longer distances. The small cross-shaped feature in each galaxy denotes the location of a Type Ia supernova.
Astronomers search for Cepheid variables in nearby galaxies containing a Type Ia supernova so they can compare the true brightness of both types of stars. That brightness information is used to calibrate the luminosity of Type Ia supernovae in far-flung galaxies so that astronomers can calculate the galaxies' distances from Earth. Once astronomers know accurate distances to galaxies near and far, they can determine and refine the universe's expansion rate.
The observations for NGC 3972 were taken in 2015; for NGC 1015 in 2013. Both galaxies were observed by Hubble's Wide Field Camera 3.
About the Data
- Data DescriptionData DescriptionProposal: A description of the observations, their scientific justification, and the links to the data available in the science archive.
Science Team: The astronomers who planned the observations and analyzed the data. "PI" refers to the Principal Investigator. - InstrumentInstrumentThe science instrument used to produce the data.WFC3/UVIS/IR
- Exposure DatesExposure DatesThe date(s) that the telescope made its observations and the total exposure time.NGC 3972 (April-July 2015), NGC 1015 (June-October 2013)
- FiltersFiltersThe camera filters that were used in the science observations.IR/F160W, UVIS/F814W, UVIS/F555W, UVIS/F350LP
- Object NameObject NameA name or catalog number that astronomers use to identify an astronomical object.NGC 3972, NGC 1015
- Object DescriptionObject DescriptionThe type of astronomical object.Galaxies with Cepheid Variable Stars and Supernovae
- Release DateFebruary 22, 2018
- Science ReleaseImproved Hubble Yardstick Gives Fresh Evidence for New Physics in the Universe
- Credit
These images are a composite of separate exposures acquired by the WFC3/UVIS/IR instrument on the Hubble Space Telescope. Several filters were used to sample narrow wavelength ranges. The color results from assigning different hues (colors) to each monochromatic (grayscale) image associated with an individual filter. In this case, the assigned colors are: Luminosity: F350LP Blue: F555W Green: F814W Red: F160W
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Claire Andreoli
NASA’s Goddard Space Flight Center
Greenbelt, Maryland
claire.andreoli@nasa.gov
