Hubble Space Telescope discovers 11-billion-year-old galaxy.

Using the Hubble Space Telescope, a team of astronomers has used a tricky technique to discover an elusive 11-billion-year-old galaxy. Rather than observe the light this realm emits, they watched for the light it absorbs.

Just as we see a light bulb via the light it emits, astronomers usually observe galaxies using the light their stars emit. Galaxies put out light waves found across the entire electromagnetic spectrum, and  different telescopes are able to observe these cosmic objects in different wavelengths of light to form a full picture. 

But, when a galaxy is located along the same line of sight as another, more distant, source of bright light, there's another way to go about these galactic observations. As light passes through a background galaxy toward a foreground galaxy, for instance, gas and dust in the foreground galaxy will absorb some of the background one's wavelengths. And because chemical elements absorb light at specific wavelengths, looking for gaps in the light output  —  or spectra  —  from a background source can tell astronomers what that light had passed through on its way to our telescopes. In other words, light in those "gaps" would've been absorbed by a foreground object on the way to our vantage point. 

Source: www.space.com

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