Hubble Traces Dark Matter in Draco Dwarf Galaxy Using Stellar Motions

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By Lydia Amazouz Published on July 11, 2024 13:45
Hubble Traces Dark Matter In Draco Dwarf Galaxy Using Stellar Motions

Recent observations by NASA's Hubble Space Telescope have revealed a significant clump of dark matter at the center of the Draco Dwarf Galaxy.

This discovery sheds new light on the elusive nature of dark matter and its distribution within galaxies.

Understanding Dark Matter Distribution

Dark matter, often referred to as the invisible "glue" that binds the universe together, remains one of the most mysterious substances in the cosmos. Despite its pervasive presence, understanding how dark matter is distributed within galaxies has been a challenging endeavor for astronomers.

Computer simulations have long suggested that dark matter should accumulate at the centers of galaxies, forming a density cusp. However, many telescopic observations have indicated that dark matter is more evenly spread throughout galaxies.

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To address this discrepancy, a team of astronomers turned to the Hubble Space Telescope to analyze the dynamic motions of stars within the Draco Dwarf Galaxy, a system located about 250,000 light-years from Earth. "Our models tend to agree more with a cusp-like structure, which aligns with cosmological models," said Eduardo Vitral of the Space Telescope Science Institute (STScI) in Baltimore and lead author of the study. "While we cannot definitively say all galaxies contain a cusp-like dark matter distribution, it's exciting to have such well-measured data that surpasses anything we've had before."

Draco Dwarf Spheroidal

Charting Stellar Movements

The astronomers employed a meticulous approach to understand the dark matter distribution by studying the stars and their movements within the Draco Dwarf Galaxy. By observing the stars' movements, both towards and away from Earth, as well as their lateral movements (proper motion), the team created an unprecedented three-dimensional analysis of the stars' dynamics. This comprehensive data set allowed the researchers to build a more accurate model of dark matter distribution within the galaxy.

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Roeland van der Marel of STScI, a co-author of the paper who initiated the study more than a decade ago, emphasized the importance of this detailed analysis. "Improvements in data and improvements in modeling usually go hand in hand," van der Marel explained. "If you don't have very sophisticated data or only one-dimensional data, then relatively straightforward models can often fit. The more dimensions and complexity of data you gather, the more complex your models need to be to truly capture all the subtleties of the data."

Focusing on the Draco Dwarf Galaxy

The Draco Dwarf Galaxy, with its relatively small size and spheroidal shape, became the perfect candidate for this study. Dwarf galaxies, known for having a higher proportion of dark matter content than other types of galaxies, offer an ideal environment for researching dark matter. The team meticulously measured the shifting positions of stars over an 18-year period, reducing uncertainties and providing precise measurements.

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Sangmo Tony Sohn of STScI, another co-author of the paper and the principal investigator of the latest observational program, explained, "When measuring proper motions, you note the position of a star at one epoch and then many years later measure the position of that same star. You measure the displacement to determine how much it moved. For this kind of observation, the longer you wait, the better you can measure the stars shifting."

The extensive baseline of Hubble's observations, spanning from 2004 to 2022, allowed the researchers to decrease the level of uncertainty in measuring the stars' proper motions. This 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.

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Implications for Future Dark Matter Studies

The methodologies and models developed for the Draco Dwarf Galaxy will serve as a blueprint for future studies on other galaxies. The team is already analyzing Hubble observations of the Sculptor and Ursa Minor dwarf galaxies. Moreover, NASA's upcoming Nancy Grace Roman Space Telescope will reveal new details of dark matter's properties among different galaxies, thanks to its ability to survey large swaths of the sky.

"This kind of study is a long-term investment and requires a lot of patience," reflected Vitral. "We're able to do this science because of all the planning that was done throughout the years to actually gather these data. The insights this brilliant team has collected are the result of a larger group of researchers that has been working on these things for many years."

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An editor specializing in astronomy and space industry, passionate about uncovering the mysteries of the universe and the technological advances that propel space exploration.

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