Peering nearly 11 billion years back, scientists uncover a galaxy not by its light emission, but its absorption.
In the vastness of space, light is the beacon that guides astronomers. Whether it’s the warm glow of a distant sun or the sharp flash from an exploding star, these radiations guide our search for galaxies. But what happens when a galaxy hides not by emitting light but by absorbing it?
When we observe space, we’re essentially looking for sources of light. Be it the blazing brilliance of a sun or the subtle reflection from a planet, it’s all about the light. Similarly, galaxies, the grand celestial cities of stars, primarily become visible through the light they emit across the electromagnetic spectrum.
However, an intriguing alternate method focuses on the ability of a galaxy to swallow light, giving researchers a unique perspective.
The Absorption Phenomenon
Picture a galaxy positioned perfectly in the sightline of a distant, luminous object. This galaxy, with its interstellar gas and dust, can absorb certain wavelengths of that background light. When astronomers map out the light spectrum, these absorptions present themselves as distinct “holes,” signifying a galaxy’s stealthy presence.
By analyzing where these gaps occur, scientists can deduce physical characteristics of the hiding galaxy. The radiant backdrop, often a quasar with its hungry supermassive black hole, highlights the obstructing galaxy like a stadium projector would a firefly.
Chasing the Universe’s Ghosts
Johan Fynbo, an astronomy professor at Copenhagen’s Cosmic Dawn Center, finds these elusive galaxies fascinating. He identifies potential galaxies of interest by searching for unusually red quasars, hinting at the presence of a foreground galaxy absorbing the blue light.
This method has led to several discoveries. The primary challenge then becomes finding emitted light from the galaxy responsible for the absorption.
A Galactic Twin in the Making?
A recent endeavor had Fynbo’s team pursuing light from a distinctive absorber, notable for causing significant reddening of a background quasar. This absorber stood out, swallowing more light than usual, suggesting it could be similar to our Milky Way.
Lise Christensen, an associate professor at the Cosmic Dawn Center and a contributor to the study, noted that the absorber’s features resemble the dust in our Milky Way and neighboring galaxies. However, while the primary absorbing galaxy remained elusive, they found another neighboring star-forming galaxy.
Interestingly, these galaxies’ proximity ensures they remain gravitationally bound, unaffected by the universe’s expansion. This indicates they’ll eventually form a galaxy group, reminiscent of our Local Group, which includes the Milky Way and Andromeda among others.
Fynbo is eager to dive back into this field, using more advanced telescopes in hopes of unveiling more hidden galaxies.
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