Most Galaxies Drift Away With the Expansion of the Universe, but M90 Inches Closer
In our ever-expanding universe, light from distant galaxies takes longer to reach us and may someday escape our ability to see it entirely. After all, when we’re looking deep into space that’s millions of light years away, we’re seeing far into the past. What we observe today may have traveled beyond our ability to see it or no longer exist at all. That’s why it’s especially interesting when scientists discover parts of our distant universe that appear to be moving closer over time. That’s exactly what the astronomers who captured the latest image of the Messier 90 spiral galaxy (pictured above) uncovered through their observation.
Hubble representatives provided a statement, as reported by LiveScience, that explains how astronomers measure light to calculate the movement of an entire galaxy that’s approximately 60 million light years away from our own:
The galaxy is compressing the wavelength of its light as it moves towards us, like a slinky being squashed when you push on one end. On the visible light spectrum, shorter wavelengths appear blue. So, because its light is compressed from our perspective, Messier 90 exhibits a phenomenon called ‘blueshift,’ which indicates to scientists that Messier 90 is moving closer to us.
Scientists measure the expansion of our universe by looking for the opposite: redshift. Based on the same principles, redshift indicates movement away. Despite the names of these terms, neither actually indicates a color of light but rather refers to human perception of the visible light spectrum. We perceive the longest visible wavelengths as red. While violet technically represents the shortest end of the spectrum, blueshift (or, alternatively, negative redshift) is nevertheless how we describe the compression of light frequency that indicates closer proximity.
These terms represent our best approximation of color at such a great distance, but light frequencies change as they interact with various matter throughout the universe. Earth’s atmosphere, for example, acts as an opaque barrier to the vast majority of the electromagnetic spectrum while remains almost completely transparent to the sliver of that spectrum that we call visible light. The small amount of the visible spectrum Earth’s atmosphere absorbs gives us the appearance of a blue sky rather than a white one.
When we look at images of distant galaxies they tend to look flat—just like anything else we look at from a significant distance—but the colors in images like that of the Messier 90 give us more than an aesthetic. Powerful telescope like Hubble use filters to capture monotone images of only specific frequency ranges of electromagnetic wavelengths. This not only helps understand the distance of light but provide a means of using color to represent that distance in the published images. Not every image of space uses color for the same purposes, but in context, the color in a captured image can tell you more about what you’re looking at. In this case, it’s about distance.
The ability to capture multiple distance images can sometimes impose other restrictions, which is why the latest representation of Messier 90 looks like someone cut a staircase out of it. Powerful imaging systems can only capture so much with the desired amount of detail at a given time. Sometimes that results in some missing areas.
Even with the ability to calculate the approximate movement of distant galaxies, we’re still left wondering why Messier 90 seems to grow closer when most of the universe essentially runs away from our vision. Scientists hypothesize that relates to the composition of the Virgo Cluster—a grouping of over 1,200 galaxies that include Messier 90. Virgo’s enormous mass appears to accelerate the movement of its galaxies into unusual orbits that send them closer and farther away from our perspective on Earth over time.
Of course, with roughly 60 million light years between the Milky Way and Messier 90, we can only derive these conclusions from the visual data telescopes like Hubble can capture. We still require far more data to fully understand what’s actually happening so far beyond our reach. While we can capture beautiful images of far off galaxies and learn about their light, we’re only looking at the light that escapes and has changed throughout its travels.
The evolution of telescopes and other imaging technology will allow us more precise measurements in the future and we may learn we’ve been looking at a picture that’s far less complete than we once thought. Nevertheless, it’s amazing to live in an era where we can regularly take a peak into the parts of our universe that live millions of lightyears away.
Top image credit: ESA/Hubble & NASA, W. Sargent et al.