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.
Credits
NASA, ESA, A. Riess (STScI/JHU)| About The Object | |
|---|---|
| Object Name | NGC 3972, NGC 1015 |
| Object Description | Galaxies with Cepheid Variable Stars and Supernovae |
| About The Data | |
| Data Description | The HST observations include those from programs (R. Foley) and (A. Riess) |
| Instrument | WFC3/UVIS/IR |
| Exposure Dates | NGC 3972 (April-July 2015), NGC 1015 (June-October 2013) |
| Filters | IR/F160W, UVIS/F814W, UVIS/F555W, UVIS/F350LP |
| About The Image | |
| Color Info | 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 |
| About The Object | |
|---|---|
| Object Name | A name or catalog number that astronomers use to identify an astronomical object. |
| Object Description | The type of astronomical object. |
| R.A. Position | Right ascension – analogous to longitude – is one component of an object's position. |
| Dec. Position | Declination – analogous to latitude – is one component of an object's position. |
| Constellation | One of 88 recognized regions of the celestial sphere in which the object appears. |
| Distance | The physical distance from Earth to the astronomical object. Distances within our solar system are usually measured in Astronomical Units (AU). Distances between stars are usually measured in light-years. Interstellar distances can also be measured in parsecs. |
| Dimensions | The physical size of the object or the apparent angle it subtends on the sky. |
| About The Data | |
| Data Description |
|
| Instrument | The science instrument used to produce the data. |
| Exposure Dates | The date(s) that the telescope made its observations and the total exposure time. |
| Filters | The camera filters that were used in the science observations. |
| About The Image | |
| Image Credit | The primary individuals and institutions responsible for the content. |
| Publication Date | The date and time the release content became public. |
| Color Info | A brief description of the methods used to convert telescope data into the color image being presented. |
| Orientation | The rotation of the image on the sky with respect to the north pole of the celestial sphere. |
