About 13 billion years ago, hydrogen gas went from neutral to ionized. Why did this happen? It’s a question astronomers continue to grapple with. And a galaxy 13 billion light years away could help astronomers answer it.
The 10-meter telescope at the W.M. Keck Observatory sitting atop Mauna Kea, Hawaii helped a team of scientists see the faint galaxy. That, and gravitational lensing. This is a phenomenon where a distant galaxy can be magnified thanks to the gravity from an object between the target galaxy and us.
The massive galaxy cluster MACS2129.4-0741 magnified the target galaxy enough for scientists to see it. Gravity from the cluster sliced the 13 billion light year away galaxy into three different images. By comparing the spectra from the three images, scientists were able to determine they showed the same galaxy.
Marc Kassis, a staff astronomer at the Keck Observatory, explained why this distant galaxy is an exciting find. “This galaxy is exciting because the team infers a very low stellar mass, or only 1 percent of 1 percent of the Milky Way galaxy.” Because of the low stellar mass and where it’s located, scientists believe it can give clues to the reionization of the early universe. “That’s when stars turned on and matter became more complex.”
The best telescope for the job
Without the Keck Observatory, this discovery would not have happened. “Keck Observatory’s telescopes are simply the best in the world for this work,” said co-team leader of the study Marusa Bradac. “Their power, paired with the gravitational force of a massive cluster of galaxies, allows us to truly see where no human has seen before.”
The Keck Observatory combines great equipment with an even better location. Sitting atop the 13,796 foot Mauna Kea summit, the twin Keck telescopes can observe the night skies with minimal atmospheric turbulence. And the atmospheric turbulence that is there is eliminated using adaptive optics. A deformable mirror changes shape to correct for the blurring caused by Earth’s atmosphere.
Keck II telescope was the first to adopt the technology in 1999. “The results provided a tenfold improvement in image clarity compared to what was previously possible with Keck and other large, ground-based telescopes,” reads the official Keck Observatory website. It also gave rise to the powerful laser we sometimes see in images of telescopes.
Credit: Ethan Tweedie/Keck Observatory.
Adaptive optics rely on bright stars to work. But there’s only so many bright stars that work – just 1% in the sky. That’s where the laser system comes in. It creates an artificial star to measure distortions in the atmosphere and correct them.
One instrument on the Keck telescope, in particular, played a vital role in finding the faint galaxy I talk about above. The DEIMOS (Deep Extragalactic Imaging Multi-Object Spectrograph) instrument. It’s described as the most advanced optical spectrograph in the world and can observe the spectra from more than 130 galaxies in a single exposure.
The W.M. Keck Observatory doesn’t just focus on the most distant galaxies in the universe. It also sheds light on bodies much closer to home. In 2013, data from the twin telescopes showed the strongest evidence yet for a vast, salty ocean beneath Europa’s surface.