An international team of astronomers has recently made an exciting discovery using the Hubble Space Telescope. Led by researchers at the Cosmic Dawn Center in Copenhagen, the team has found and investigated a galaxy from almost 11 billion years ago.
What’s also special about the discovery is that the team didn’t discover it by the light it emits, which would be typical. Nope, this one was discovered by the light it absorbs.
Reflecting vs. emitting vs. absorbing the light
“When we see things, we see them because they either emit light — such as the Sun or a flashlight — or because they reflect light emitted by someone else — such as the Moon or a bicycle,” scientists of Niels Bohr Institute explain in a statement. Although it sounds so simple, this explanation stretches to the way that we also find galaxies near and far. “Galaxies emit light across the full electromagnetic spectrum, and different telescopes can then detect different kinds of light,” the statement continues. This is why it’s so interesting that this galaxy was found by its ability to absorb light, rather than emit it.
“If a galaxy happens to be located along the line of sight to a more distant, bright light source, the galaxy will absorb some of the background source’s light. This absorption is caused by the gas and dust particles that lies in between the galaxy’s stars. The particles don’t absorb equally well at all wavelengths, however, but tend to absorb light at specific wavelengths.”
The challenges in observation
As NBI explains, we can learn a few physical characteristics about a galaxy only from the light it absorbs. But if we want to know more about it, we need light emission. The scientists can try and search for light emitted from the same region in the sky and bring the data together for conclusions.
The biggest problem when detecting the recently discovered galaxy was its placement. It’s located almost exactly in front of the bright quasar. “It is virtually like trying to observe a firefly in front of a stadium projector,” NBI explains.
Thankfully, Johan Fynbo of the Cosmic Dawn Center in Copenhagen enjoys a challenge:
“To find absorbing galaxies, we first look for quasars that are particularly red. Because star dust tends to absorb the blue light but not the red, if there is a dusty galaxy in the foreground the quasar will be reddened.”
Discovering the 11-billion-year-old galaxy
Recently, the research group focused their efforts on a specific light-absorbing galaxy we mentioned at the beginning. It appears to date back nearly 11 billion years. This galaxy was chosen for its notable effect of significantly reddening the light from a background quasar. The unusually high light absorption suggests that this galaxy is quite old, potentially resembling the Milky Way in some aspects.
“The features that we found in the missing light tell us something about the dust in the foreground galaxy,” says Lise Christensen of the Cosmic Dawn Center and the study participant. “In fact, the dust seems to resemble the dust that we see locally in the Milky Way and one of our neighboring galaxies.”
Despite their best efforts, the researchers still need to work on discovering more about this galaxy. They couldn’t identify any emitted light, so they still lack some data for learning more about it. However, they did uncover another nearby galaxy with a high star formation rate, suggesting that more discoveries could be ahead of us.
[via Space.com; lead image: “Stephan’s Quintet,” credits: NASA, ESA, and the Hubble SM4 ERO Team]