On my walk this morning, I was musing about the ongoing AAS meeting in Long Beach when I found myself having one of those epiphanies that seem to open a window into the heart of things. The day was unusually warm but gusts of wind tossed the trees and low clouds laced with rain scudded past. And suddenly I was no longer walking along a quiet street but became aware that I walking a planet within a star system, within a cloud of stars, and that by being made up of elements from those stars, I was in some sense an expression of that universe as it observed itself.
It’s hardly an original notion, but the sense of it was palpable, an almost physical awareness that translated something known factually into something experienced. It was spurred by the recent news that the Milky Way is fifty percent more massive than we thought, maybe the twin of the Andromeda Galaxy. Increasing our sense of scale adds to the grandeur. The punch of the Fermi Paradox comes from the sheer size of galaxies — we wonder about other civilizations because we understand that there are hundreds of billions of stars around us in this celestial city, surely many of them not all that different from our own.
I felt awash in immensity as I walked the windy streets. For if it’s breathtaking to think that the Milky Way may hold hundred of billions of stars — 400 billion is a figure often cited — how much more so to consider it as massive as three trillion suns?
Image: The Andromeda Galaxy, perhaps a twin of our own. We can see Andromeda from without, but determining the structure of the galaxy we move through ourselves is a continuing challenge. Credit: NASA.
A mass of three trillion suns is what the work of Mark Reid (Harvard-Smithsonian Center for Astrophysics) and colleagues suggests. The team of astronomers used the Very Long Baseline Array to look at star-forming regions across the galaxy, zeroing in on natural radio emissions that are amplified by gas molecules in certain areas. These ‘cosmic masers’ are markers that can be studied by the VLBA through parallax, measuring the apparent shift of the objects against the cosmic background. The work is particularly telling because it relies on few assumptions:
“The new VLBA observations of the Milky Way are producing highly-accurate direct measurements of distances and motions,” said Karl Menten of the Max Planck Institute for Radio Astronomy in Germany, a member of the team. “These measurements use the traditional surveyor’s method of triangulation and do not depend on any assumptions based on other properties, such as brightness, unlike earlier studies.”
Using these direct measurements, the astronomers could determine that most of the star-forming regions move around the galactic center not in a circular but an elliptical orbit. They were also able to determine that the Milky Way probably has four spiral arms of gas and dust that are continually producing stars, with young stars dominating two of these. But most striking was the team’s finding that our Solar System is rotating much faster around the galactic core than previously believed, in the neighborhood of 965,000 kilometers per hour.
The higher speed of our movement around the center demonstrates the need to up our estimates of the galaxy’s mass by the fifty percent mentioned earlier. And it brings home a crucial fact: Although we live within it, we still must contend with our limited knowledge of the Milky Way’s size and structure. And if we are going to start talking about a serious upgrade to the mass of the Milky Way, as the evidence that Reid reported at the AAS session on Monday suggests, we have to remember that we still cannot see ourselves whole, the way we can examine, say, Andromeda.
Walking in the early morning winds, I reflected on all this, and on the fact that seeing something complete from within is notoriously tricky, whether that something be as vast as a swarm of stars or as miniature as a human relationship. Identifying the markers, like Reid’s cosmic masers, is crucial, but even then, the sample of markers has to be extended to broaden the picture. As we work out the science, the sense of awe inspired by our newly massive galaxy creates a freshening humility that enriches everyday experience.