Using the Hubble Space Telescope, a team of astronomers has used a complicated technique to discover an elusive 11 billion-year-old galaxy. Instead of observing the light emitted by this realm, they observed the light it absorbs.
Just as we see a light bulb through the light it emits, astronomers typically observe galaxies using the light emitted by their stars. Galaxies emit the light waves present in the whole electromagnetic spectrumand different telescopes are able to observe these cosmic objects in different wavelengths of light to form a complete picture.
But when a galaxy is along the same line of sight as another, more distant source of intense light, there is another way to proceed with these galactic observations. When light passes through a background galaxy to a foreground galaxy, for example, gas and dust in the foreground galaxy will absorb some of the wavelengths of the background one. And because chemical elements absorb light at specific wavelengths, looking for gaps in light output – or spectra – from a background source can tell astronomers what that light passed through on its way to our telescopes. In other words, the light in those “empty spaces” would have been absorbed by a foreground object on its way to our vantage point.
A potentially useful background source for this technique is quasarswhich are extremely luminous galactic hearts powered by supermassive black holes that emit jets of radiation and matter as they feed on the surrounding material.
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“To find absorbing galaxies, we first look for quasars that are particularly red,” says Johan Fynbo, an astronomer at the Cosmic Dawn Center. said in a statement. “Because star dust tends to absorb blue light but not red light, if there is a dusty galaxy in the foreground, the quasar will be red.”
He and his team have identified several absorbing galaxies by analyzing the light from reddened quasars, but once they do so, they face a much more challenging task: searching for the light emitted by the absorbing galaxy itself.
A firefly on a cosmic beacon
When located directly behind a galaxy, quasars tend to disturb our view of foreground galaxies because they are immensely bright. So much so that they essentially overwhelm the combined light of every star in an entire galaxy.
This makes spotting an absorbing galaxy with its own light output similar to trying to spot a firefly perched on a lighthouse lamp while on the shore. While this may prove too intimidating a challenge for many, Fynbo and colleagues appreciate it.
Unfortunately, scientists have not yet identified the light coming from their recently discovered 11 billion-year-old absorbing galaxy, but the absorption patterns this object has revealed are remarkable. The galaxy, seen as it was when our 13.8 billion-year-old universe was only about 3 billion years old, absorbs more light than other similarly found galaxies, meaning it is likely a more mature galaxy like the Galaxy . Milky Way.
“The features we found in the missing light tell us something about the dust in the foreground galaxy,” Lise Christensen, a member of the discovery team and astronomer at the Cosmic Dawn Center, said in the statement. “Indeed, the dust appears to resemble the dust we see locally in the Milky Way and one of our nearby galaxies.”
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The team was also able to determine that the galaxy has a luminous counterpart. That galaxy, which seems to be born stars at an intense rate, it is so close to the absorbing galaxy that the team also believes the two are likely gravitationally bound. This means that, at some point after they were noticed, the two galaxies probably formed a group of galaxies similar to the local group in which the Milky Way is located.
Fynbo intends to revisit this region space with other instruments, including the Nordic Optical Telescope of La Palma, to search for other members of this galactic group in the hope of being able to see the absorbing galaxy emitting its own light.
“This makes galaxies even more interesting to study,” concluded the astronomer.
The team’s research has been accepted for publication in the journal Astronomy & Astrophysics. In the meantime, a pre-peer review version is available on the site arXiv research archive.