A team of astronomers using the Hubble Space Telescope used a clever technique to discover an elusive galaxy that is 11 billion years old. Instead of observing the light emitted by this realm, they observed the light it absorbed.

Just as we see a light bulb through the light it emits, astronomers often observe galaxies using the light emitted by their stars. Galaxies emit light waves across the electromagnetic spectrum, and different telescopes can create a complete picture by observing these cosmic objects in different wavelengths of light.

But there is another way to make these galactic observations when a galaxy is in the same line of sight as another, more distant, bright light source. When light passes from a background galaxy to a foreground galaxy, for example, gas and dust in the foreground galaxy will absorb some of the background galaxy’s wavelengths. Because chemical elements absorb light at specific wavelengths, looking for gaps in the light emission (or spectrum) from the background source can tell astronomers what paths that light took on its way to our telescopes. In other words, light in these “slits” will be absorbed by the foreground object on its way to our line of sight.

A potentially useful background source for this technique are quasars, extremely bright galactic hearts fueled by supermassive black holes that spit out jets of radiation and matter as they feast on the material around them.

“To find absorber galaxies, we first look for quasars that are particularly red,” said astronomer Johan Finbo of the Cosmic Dawn Center. “Because stardust tends to absorb blue light, not red, if there is a dusty galaxy in the foreground, the quasar will be red.”

By sorting out the light from reddened quasars, he and his team detected many absorbing galaxies; But once this is done, they will face a much more difficult task: searching for the light emitted by the absorbing galaxy itself.

firefly in space lantern

When quasars are directly behind a galaxy, they tend to distort our view of the foreground galaxies because they are extremely bright. So much so that they actually block the combined light of every star in the entire galaxy.

This makes detecting an absorbing galaxy with its own light emission similar to detecting a firefly sitting on a lighthouse lamp while standing on shore. While this may be a daunting task for many, Fynbo and his colleagues love it.

Unfortunately, scientists have not yet been able to identify the light coming from the newly discovered 11 billion-year-old absorbing galaxy, but the absorption patterns revealed by this object are remarkable. The galaxy, when our 13.8 billion-year-old universe was only 3 billion years old, absorbs more light than other similarly discovered galaxies, meaning it is likely a more mature galaxy like the Milky Way.

“The features we find in the missing light tell us about dust in the foreground galaxy,” said Lisa Christensen, a member of the discovery team and an astronomer at the Cosmic Dawn Center. “In fact, the dust is similar to the dust we see locally in the Milky Way and one of our neighboring galaxies.”

The team was also able to detect that the galaxy has a bright counterpart. This galaxy, which appears to be producing stars at an intense rate, is so close to its host galaxy that the team also believes they are gravitationally bound. This means that at some point after they were observed, the two galaxies probably formed a group of galaxies similar to the Local Group, which includes the Milky Way.

Finbo plans to revisit this region of space with other instruments, including the Scandinavian Optical Telescope at La Palma, to look for other members of this galaxy group in the hope of seeing the absorbing galaxy emitting its own light.

“This makes studying galaxies even more interesting,” the astronomer said. Source