Tracing Dark Matter in Faint Draco Dwarf Galaxy using Stellar Motions | Hubble
A three-paneled image shows different perspectives of the Draco dwarf spheroidal galaxy. At left is the Digitized Sky Survey view of the Draco dwarf galaxy. Many yellow, blue-white, and white stars are dispersed across the black background of space. They vary in shape and size, though most resemble small, circular points of light. Larger stars, some with four diffraction spikes, are scattered infrequently across the field of view. A thin, light brown oval highlights the area of interest, which contains two small white squares in its center. The area of each square is magnified at right, showing views captured by the Hubble Space Telescope. The top right square reveals a black patch of space with many small points of light and a large, four-point diffraction spike toward the left. The bottom right square shows a black patch of space filled with small points of light, some with diffraction spikes.
Digitized Sky Survey wide-field image of region around Draco dwarf galaxy
Close-up of area around Draco dwarf galaxy. It is one of the faintest galaxies known.
When theory and observations favor different results, how can astronomers determine which one is more feasible? Increasing confidence in one theory over another oftentimes requires building a richer dataset to improve current models and lower uncertainties. A team of astronomers has turned toward NASA's Hubble Space Telescope to try and clarify this debate by measuring the dynamic motions of stars within the Draco dwarf galaxy, a system located roughly 250,000 light-years from Earth. It is one of the faintest galaxies known. Using observations that spanned 18 years, they succeeded in building the most accurate three-dimensional understanding of stars' movements within the diminutive galaxy.
Since dwarf galaxies are known to have a higher proportion of dark matter content than other types of galaxies, the team honed in on the Draco dwarf galaxy. It is a relatively small and spheroidal nearby satellite of the Milky Way galaxy.
The team analyzed a series of epochs spanning from 2004 to 2022, an extensive baseline that only Hubble could offer, due to the combination of its sharp stable vision and record time in operation. The telescope's rich data archive helped decrease the level of uncertainty in the measurement of the stars' proper motions. The precision is equivalent to measuring an annual shift a little less than the width of a golf ball as seen on the Moon from Earth.
With three dimensions of data, the team reduced the amount of assumptions applied in previous studies and considered characteristics specific to the galaxy—such as its rotation, and distribution of its stars and dark matter—in their own modeling efforts.
To learn about dark matter within a galaxy, scientists can look to its stars and their movements that are dominated by the pull of dark matter. A common approach to measure the speed of objects moving in space is by the Doppler Effect—an observed change of the wavelength of light if a star is approaching or receding from Earth. Although this line-of-sight velocity can provide valuable insight, only so much can be gleaned from this one-dimensional source of information.
These results are accepted for publication in The Astrophysical Journal:
Image Credits: NASA, ESA, Eduardo Vitral (STScI), Roeland van der Marel (STScI), Sangmo Tony Sohn (STScI), DSS
Image Processing: Joseph DePasquale (STScI)
Release Date: July 11, 2024
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