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Astronomy Space

Daily Dose of Astronomy

Estimating the Milky Way’s Mass with Star Escape Speeds

Discover how astronomers have developed a novel method to measure the mass of the Milky Way Galaxy by analyzing the escape velocity of stars. This approach, leveraging data from the Gaia spacecraft, provides insights into the galaxy’s gravitational pull and offers a new perspective on the amount of dark matter present. Understand the significance of these findings and how they contribute to our comprehension of the galaxy’s structure and composition.

Ever wondered about your mass, or even the mass of the Milky Way? Let’s simplify these complex ideas into something you can grasp easily, without the need for a PhD in astrophysics!

How to Measure Your Mass

Determining your mass is as simple as stepping on a scale. The number you see reflects the gravitational pull of Earth on you. So if the number seems high, remember, it’s just Earth saying it finds you attractive! Interestingly, this principle also applies when we talk about measuring the Earth’s mass using a scale, albeit with a twist involving the gravitational interaction between Earth and the object being weighed.

The Challenge with Measuring the Milky Way

Moving onto a grander scale, measuring the mass of the Milky Way is a Herculean task. Unlike measuring mass on Earth with a scale, astronomers use the orbital speed of stars around the galactic center to estimate the galaxy’s mass. This method, based on the rotation curve of the galaxy, suggests the Milky Way’s mass is between 600 billion to a trillion solar masses. However, this wide range indicates the complexity and challenges in obtaining an accurate measure.

Estimated escape velocities at different galactic radii. Credit: Roche, et al

A New Method for Galactic Measurement

A groundbreaking study has introduced a novel approach by examining the escape velocity of stars. This method calculates the minimum speed needed for a star to break free from the Milky Way’s gravitational pull, offering insights into the galaxy’s total mass. The recent use of data from the Gaia spacecraft, which tracked the speed and position of a billion stars, has provided a more precise estimate of 640 billion solar masses. This figure, on the lower end of previous estimates, suggests less dark matter in our galaxy than thought.

Simplifying the Complex

Think of the Milky Way as a giant gravitational field, with stars acting like dust motes caught in its influence. By analyzing the movement and speed of these ‘dust motes,’ scientists can estimate the galaxy’s mass, similar to how one might gauge the Moon’s mass by observing the behavior of thrown dust particles.


The quest to understand the mass of celestial bodies, from ourselves to entire galaxies, is a fascinating journey that blends simple principles with complex astronomical techniques. The latest methods provide not just a clearer picture of the Milky Way’s mass but also a glimpse into the intricate dance of cosmic forces shaping our universe.

Reference: Roche, Cian, et al. “The Escape Velocity Profile of the Milky Way from Gaia DR3.” arXiv preprint arXiv:2402.00108 (2024).