Telescope takes photos of the past

Friday, January 8, 2010
by Nikki Staab and Diane Boudreau

The latest image from the Hubble Space Telescope gives us a glimpse of 12 billion years of cosmic history. It shows us what the universe looked like in the past.

How can a camera take pictures of the past? The answer has to do with the speed of light.

Light travels very fast. It travels 186,000 miles in a single second. When you turn on a light, you see the light right away because it takes much less than a second to travel from the bulb to your eyes.

A light-year is the distance that light can travel in one year. One light-year is almost 6 trillion miles. The Hubble Telescope takes pictures of stars and galaxies that are billions of light-years away. This means that their light has been traveling for billions of years. It is only reaching our eyes today after all that time.

What we see on the Hubble image is what that light looked like when it started its journey all those years ago. We can’t see what those galaxies look like today. Today’s light won’t reach Earth until billions of years in the future.

Hubble Telescope image 


The latest Hubble image combines pictures from two separate cameras. It captures a broad range of colors, from the ultraviolet, through visible light (the rainbow), into the infrared range. Scientists have never put together such a detailed multi-color view of the universe before.

“It’s like taking off rose-colored glasses and seeing the universe in a whole new light, and what we’re seeing is fantastic,” says Rogier Windhorst, an ASU astronomer who works with the newest Hubble camera. “We’re seeing stars on a galactic scale being born, we’re seeing galaxies in formation, galaxies replenished with new fuel for making stars. We’re seeing a messy universe, a universe in action, and we’re seeing it like astronomers have never seen it before.”

The Hubble image is helping astronomers figure out how galaxies form. They are looking at mature spiral and elliptical galaxies. They are also looking at older, smaller, irregularly shaped galaxies. These smaller galaxies are considered the building blocks of the larger galaxies that we see today.

The image shows a rich tapestry of 7,500 galaxies stretching back through most of cosmic history. The closest galaxies seen in the foreground emitted their light only 0.9 billion years ago. The farthest galaxies, a few of the very faint red specks, are seen as they appeared more than 13 billion years ago. This was roughly 650 million years after the Big Bang.

The new Hubble view highlights many stages in the galaxy-making process. The ultraviolet light shows the blue glow of hot, young stars in galaxies teeming with star-birth. The orange light reveals the nearly final assembly stages of massive galaxies about 8 billion to 10 billion years ago. The near infrared reveals the red glow of very distant galaxies – in a few cases as far as 12 billion to 13 billion light years away. Their light has been stretched, like a toy Slinky, from short ultraviolet light waves to longer infrared waves because the universe is expanding.

Read more about this research at ASU News.