Rhythms in the Stars

In these early frames of what will be the greatest cosmic movie ever made, we see NSF–DOE Vera C. Rubin Observatory's unparalleled ability to detect celestial objects that change in brightness. This capability will reveal the flickers, pulses, and explosions of light across the Universe that only repeated observations can capture. During its 10-year survey, Rubin will record an unprecedented number of cosmic light shows, revealing patterns and one-time wonders, and unlocking clues about the Universe’s behavior over time.

In this video, Rubin showcases 46 subtly pulsating stars — classified as RR Lyrae variable stars — detected in this first set of observations. Three individual stars are shown varying in brightness over time using a technique called difference imaging (link). Then we zoom out to a view of the southern region of the Virgo Cluster where other RR Lyrae variable stars visible to Rubin are highlighted. Although the stars are observed in the direction of the Virgo Cluster, they are much closer to Earth in our home galaxy, the Milky Way. Over the next 10 years, Rubin will detect up to about 100,000 of these stars extending out to more than a million light-years away, allowing scientists to map the outer reaches of our Galaxy and explore the structure of the Galactic halo that surrounds the Milky Way and extends nearly halfway to our closest neighbor, the Andromeda galaxy. The structures of galaxies like the Milky Way are fascinating  environments — Vera Rubin herself produced the first convincing evidence for dark matter by studying spiral galaxies. While RR Lyrae stars might not look flashy at first glance, they play a quiet but critical role in helping us understand the scale and shape of our own galaxy. 

RR Lyrae variables are a type of star that acts like a cosmic metronome, pulsing steadily and predictably over time. These stars are old, low-mass, and typically found in ancient parts of galaxies like globular clusters and stellar halos. They brighten and dim in a regular cycle, usually over the course of less than a day. RR Lyrae stars were selected as a target for Rubin’s First Look observations because their quick variations in brightness can be detected by Rubin over just a few nights. Their rhythmic variability isn’t just a curiosity — it’s a powerful tool for scientists. Because the relationship between an RR Lyrae star’s brightness and its pulsation period is well understood, these stars can be used as “standard candles” to measure distances across the Milky Way and nearby galaxies. RR Lyrae stars are like signposts in space! 

Other telescopes can detect changes in a star’s brightness, but Rubin is the only one that can simultaneously catch multiple faint, steady pulses of RR Lyrae stars across huge swaths of the sky and also detect them very far away from Earth. Rubin's sensitive camera captures variations so subtle that our eyes can barely detect them when looking at the images. Rubin will collect nearly a thousand measurements for each variable star, ensuring that scientists who focus on variable stars can amass huge samples to study. Rubin’s wide view and fast survey speed will give us data on far more of these stars than ever before — even those way out in the outskirts of the Milky Way — giving us a much clearer picture of what our Galaxy really looks like. 

This video features data collected by Rubin Observatory using the 3200-megapixel LSST Camera — the largest digital camera in the world.