Hubble Finds Young White Dwarfs on the Fast Track

These images show young and old white dwarf stars – the burned-out relics of normal stars – in the ancient globular star cluster NGC 6397.

The image at left, taken by a ground-based telescope, shows the dense swarm of hundreds of thousands of stars that make up the globular cluster. The white box outlines the location of the observations made by NASA's Hubble Space Telescope.

The image at top, right, taken by Hubble's Advanced Camera for Surveys, reveals young white dwarfs less than 800 million years old and older white dwarfs between 1.4 and 3.5 billion years old. The photo shows 12 of the 84 white dwarfs in the Hubble study. The blue squares pinpoint the young white dwarfs; the red circles outline the older white dwarfs. The Hubble researchers distinguished the younger from the older white dwarfs based on their color and brightness. The younger white dwarfs are hotter and therefore bluer and brighter than the older ones.

The astronomers were surprised to find young white dwarfs far away from the cluster's core. They had assumed that the youngsters would reside at the center and migrate over time to the cluster's outskirts. The astronomers proposed that the cluster stars that burn out as white dwarfs are given a boost that propels them to the edge of the cluster.

Close-up images of the white dwarfs are shown at bottom, right. The blue boxes represent the young white dwarfs; the red boxes indicate the older white dwarfs.

The ground-based image was taken June 5, 2005. The Hubble images were taken in March and April 2005.

About the colours

The HST images are composites of many separate exposures made by the ACS instrument on the Hubble Space Telescope using several different filters. Three filters sample broad wavelength ranges, one isolates the light of hydrogen. The color results from assigning different hues (colors) to each monochromatic image. In this case, the assigned colors are: Orange: F814W (I) Cyan: F606W (V)

About the data

This image was created from HST data from proposal 10424 :

H. Richer (University of British Columbia), P. Guhathakurta (University of California, Santa Cruz), R.M. Rich (University of California, Los Angeles), J. Anderson (STScI), G. Fahlman (NRC Herzberg Institute of Astrophysics/National Research Council Canada, Saanich, British Columbia), B. Gibson (Swineburne University of Technology, Australia), B. Hansen (University of California, Los Angeles), J. Hurley (Swinburne University of Technology, Australia), J. Kalirai (University of California, Santa Cruz), I. King (University of Washington, Seattle), M. Shara (American Museum of Natural History), and P. Stetson (National Research Council/Herzberg Institute of Astrophysics, Canada).

The science team comprises: H. Richer (University of British Columbia), I. King (University of Washington, Seattle), J. Anderson (STScI), J. Coffey (University of British Columbia, Vancouver), G. Fahlman (Herzberg Institute of Astrophysics/National Research Institute of Canada, British Columbia), J. Hurley (Swinburne University of Technology, Australia), and J. Kalirai (University of California, Santa Cruz).