Guest blogger Ray Villard, STScI News Director
As the news director for STScI, I have Hubble pictures for breakfast, lunch, and dinner. And, after 28 years of having a ringside seat to Hubble’s eagle-eye views, one is always tempted to think we’ve seen it all with this prolific space observatory.
But that’s never the case with Hubble.
In fact, I was going through our press release archive and pulled up this news photo from November 2017, with the cute title “Hubble Sees Nearby Asteroids Photobombing Distant Galaxies.”
In the deep-sky exposure, arc-shaped streaks of foreground asteroids are etched over a portrait of a massive cluster of galaxies called Abell 370. When we released the image, we joked about the foreground asteroids photobombing the picture. It was a novelty.
At the time, I treated this photo as just another day, another awesome Hubble picture in my busy schedule. But in revisiting it, I was suddenly taken aback.
The picture is such a holistic snapshot of the cosmos. It underscores the realization that this is not your father’s universe from the pre-Hubble days. There is so much going on. The photo unveils a compulsive universe. The yin-yang interplay of matter and energy relentlessly drives a discordant and evolving cosmos.
A casual look at the photo is too easily lost on the average viewer -– aside from the notion that it looks, well, busy. The asteroids look like firefly trails on a summer’s night, mindlessly skipping along. They are the vagabonds of the solar system. The immense background galaxy cluster that is the central target, blazes with the opulence of at least 100 trillion stars among several hundred galaxies.
But when you try to wrap your mind around the not-so-obvious three-dimensionality embedded in this view, all comprehension stretches to unimaginable scales.
The asteroids are roughly 250 million miles away. The brilliant foreground star at lower right is inside our Milky Way and at least hundreds of millions of times farther than the asteroids. The background cluster of galaxies is hundreds of trillions of times farther still. The fragmentary galaxies beyond them, looking like confetti on black velvet, are vastly farther away.
Despite all the clutter, one simple force in nature shapes this view: gravity. The asteroids whirl around the sun as they have done for several billions of years. The arc shape of their trails is observational evidence that Hubble is following a racetrack-like orbit around Earth. (Nicholas Copernicus, who in the late 1500s proposed that Earth is not the unmoving center of the universe, would be delighted with this photo.)
The galaxies in the immense Abell cluster are all pulling on each other. A time-lapse movie taken over eons would show them zipping around each other like a swarm of bees. And, they are just the tip of the iceberg. What’s just as important is what’s not seen in the image. The powerful gravitational glue of unseen dark matter -– which makes up the bulk of the mass of the universe -– keeps the lid on galaxies from flying apart from each other.
The dark matter also makes the cluster a giant magnifying lens in space that warps and brightens the images of much farther background galaxies. Embedded in the cluster picture is an uncanny image of a snake-like feature. It’s the multiply stretched image of a background galaxy. When we photographed this cluster in 2009 with Hubble’s newly installed Wide Field Camera 3, we were all left scratching our heads at first. We finally nicknamed it “the dragon.”
As mere mortals, with lifetimes that are far shorter than a blink of an eye on cosmic timescales, this view is just a frozen snapshot of a dynamically obsessive universe. It presents an overwhelming and humbling reality where just about anything is imaginable within a few simple and elegant laws of physics.
This would likewise be a jaw-dropping photo for both Newton and Einstein, who formulated the physical underpinnings of the universe, but could not have imagined such an awesome view.