What makes variable stars so important for understanding galaxies?

Variable stars are crucial tools for astronomers because they act as 'standard candles'. Their changing brightness allows for accurate distance measurements to galaxies, which is a key step in understanding these faint galaxies. Examples include RR Lyrae stars, excellent for older stellar populations, and Anomalous Cepheids, useful for intermediate-age populations. They provide a unique window into the universe, helping to map galactic structure.

What are Dwarf Cepheids, and how are they useful in astronomy?

Dwarf Cepheids, also known as 8 Scuti or SX Phe stars, are found in dwarf spheroidal galaxies. They pulsate, causing their brightness to vary. The pulsation period is related to their intrinsic luminosity. Finding these stars is challenging because they are faint and their brightness changes rapidly. Studying Dwarf Cepheids helps astronomers understand the composition and history of galaxies.

What are researchers doing to study Dwarf Cepheids?

Researchers are actively using instruments like the Dark Energy Camera (DECam) on the Blanco telescope in Chile to find Dwarf Cepheids in satellite galaxies, such as the Sextans dwarf spheroidal galaxy. Initial results show that Sextans has fewer Dwarf Cepheid stars than Carina, which may indicate differences in the stellar populations, like age or metallicity (the abundance of elements heavier than hydrogen and helium), between the two galaxies.

Why is the study of variable stars significant in the context of galactic evolution?

Studying variable stars in the Milky Way's satellite galaxies allows astronomers to measure accurate distances, determine physical properties, and study stellar populations. This provides valuable information for understanding galactic evolution and the role of dwarf galaxies in the broader cosmic picture. It helps to unlock the secrets of galactic structure and evolution.

What is the significance of the period-luminosity relationship for Dwarf Cepheids?

The period-luminosity relationship of Dwarf Cepheids means that their pulsation period is related to their absolute brightness. This property enables astronomers to use them as standard candles to measure distances to galaxies. Furthermore, Dwarf spheroidal galaxies are interesting because they offer a unique environment to study these stars, as they contain stars with different ages and metallicities than other regions.

Swirling galaxy with variable stars and orbiting dwarf galaxies.

Milky Way's Hidden Gems: Unlocking Secrets with Variable Stars

Elliot Brynn in Science & Nature December 2025 • 4 min read.

"How faint and bright variable stars are helping astronomers map the structure and history of our galaxy's satellites."

The last few years have dramatically changed our understanding of the Milky Way's neighborhood. The discovery of about 20 dwarf systems orbiting our galaxy has nearly doubled the number of known satellites since 2014. These new satellites, often extremely faint, are opening exciting new avenues for research into low-mass galaxies and the formation of galaxies like our own.

A key step in understanding these faint galaxies is accurately measuring their distance from us. Variable stars, which change in brightness over time, have long been valuable tools for astronomers. They act as 'standard candles,' allowing us to calculate distances. RR Lyrae stars, for example, are excellent for tracing older stellar populations, while Anomalous Cepheids indicate intermediate-age populations.

This article explores two ongoing projects that use variable stars to study the satellites of the Milky Way, shedding light on their composition, history, and role in the broader cosmic picture.

Dwarf Cepheids: Finding Faint Variable Stars in Sextans

Swirling galaxy with variable stars and orbiting dwarf galaxies.

Dwarf Cepheid stars, also known as 8 Scuti or SX Phe stars, can be found alongside other types of stars in dwarf spheroidal galaxies. These stars pulsate (expand and contract) which causes their brightness to vary. This pulsation is useful for astronomers as the period of pulsation is related to the star's intrinsic luminosity.

Finding these stars in other galaxies is challenging because they are faint, and their brightness changes rapidly. Also, dwarf galaxies cover a large area of the sky, making it difficult to conduct a complete survey. Overcoming these hurdles will be made easier by projects like the upcoming Vera C. Rubin Observatory (LSST).

Dwarf Cepheids follow a period-luminosity relationship, meaning their pulsation period is related to their absolute brightness.
This relationship could allow astronomers to use them as standard candles, similar to other variable stars, to measure distances to galaxies.
Dwarf spheroidal galaxies offer a unique environment to study these stars, as they contain stars with different ages and metallicities (the abundance of elements heavier than hydrogen and helium) than those found elsewhere in our galaxy.

Researchers have started looking for dwarf Cepheids in several satellite galaxies using the Dark Energy Camera (DECam) on the Blanco telescope in Chile. One target is the Sextans dwarf spheroidal galaxy, and the preliminary results show that Sextans has fewer dwarf Cepheid stars than Carina, another dwarf galaxy. This could be due to Sextans having fewer intermediate-age stars. The periods of the two dwarf Cepheid stars found in Sextans are shorter than those in Carina, possibly reflecting a difference in metallicity.

Why Variable Stars Matter: Unlocking Galactic History

Studying variable stars in the Milky Way's satellite galaxies provides valuable information for understanding galactic evolution. They allow astronomers to measure accurate distances, determine physical properties, and study the stellar populations within these systems.

By analyzing the distribution and properties of RR Lyrae stars, researchers can gain insights into the formation scenarios of the Milky Way. The ultra-faint galaxies may contribute to a specific segment of the halo RR Lyrae population, but mergers with larger galaxies likely play a more significant role in shaping the overall distribution.

Dwarf Cepheid stars are also important because they may serve as reliable standard candles for measuring distances within the Local Group, especially with the advent of advanced telescopes like the LSST. Understanding these stars will contribute significantly to our knowledge of the universe's structure and history.