Hubble Deep Field

The Hubble Deep Field (HDF) is an image of a tiny part of the sky in the constellation Ursa Major. It was taken by the Hubble Space Telescope. The picture shows an area about 2.6 arcminutes across. This is so small that it is like looking at a tennis ball from 100 metres away. The image was made by combining 342 pictures taken over ten days in December 1995.

Because the area is so small, most of the objects in the picture are faraway galaxies. Some of these are some of the youngest galaxies ever seen. The Hubble Deep Field is very important for scientists who study the early universe.

Later, similar pictures were taken in other parts of the sky, like the Hubble Deep Field South and the even deeper Hubble Ultra-Deep Field. These images helped scientists learn that the universe looks mostly the same in all directions. This supports the idea that Earth is in a typical place.

Conception

One of the main goals of the Hubble Space Telescope was to study distant galaxies. Because Hubble orbits above Earth’s atmosphere, it can take clearer pictures of light and ultraviolet light. Even when it had an early problem, Hubble could still see faraway galaxies. This showed us how galaxies looked billions of years ago.

After repairs in 1993 made Hubble’s vision better, scientists used it to look at very distant and faint galaxies. They saw big differences between galaxies today and those from long ago. In 1995, the director of the Space Telescope Science Institute decided to use special time to study a typical patch of sky. This helped us learn more about the early universe.

Target selection

The Hubble Deep Field image was taken of a small area in the constellation Ursa Major. Scientists chose this spot because it had to meet some important rules. The area needed to be far from bright stars and other objects that could block the view.

Scientists also wanted the area to be in a part of the sky that Hubble could watch all the time without the Earth or the moon getting in the way. They picked a spot that was about 2.6 arcminutes wide, which is very small compared to the whole sky. This helped scientists see very faraway galaxies clearly.

Observations

The Hubble Deep Field used special tools called filters to take pictures of a very small part of the sky. Scientists chose four filters to capture different colors of light, including blue, red, and near-ultraviolet light.

Between December 18 and 28, 1995, the Hubble Space Telescope took 342 pictures of this area. It went around Earth about 150 times during this time. The telescope spent many hours taking pictures of each color of light, creating a detailed view of faraway stars and galaxies.

Data processing

The Hubble Deep Field image was made using a careful process to clean up the data. Bright spots caused by cosmic rays were removed by comparing pictures taken one after another. Scientists also removed streaks from space debris and satellites, and scattered light from the Earth.

The cleaned pictures were combined using a special method called "drizzling." This involved pointing the telescope slightly differently between each exposure. This made the final image sharper. The result was a colorful picture made by combining images taken at different wavelengths. The colors shown are an approximation and not the true colors seen by the human eye.

Contents

The final images from the Hubble Deep Field were released in January 1996. They showed about 3,000 distant, faint galaxies, including both irregular and spiral galaxies. Most objects in the image are faraway galaxies, with only a few nearby stars.

The image also includes about fifty blue points of light. Some of these are likely areas where new stars are forming, while others might be distant quasars. Early ideas suggested these points were not white dwarfs, but newer studies show that some white dwarfs can appear blue.

Scientific results

The Hubble Deep Field image helped scientists learn amazing things about space. It showed many distant galaxies that were much farther away than we knew before. Some were so far that their light had traveled about 12 billion years to reach us. These discoveries helped us understand how galaxies change over time.

Scientists also learned that in the early universe, galaxies bumped into each other more often, forming bigger galaxies. The image helped us see how the rate of new stars being born has changed over the universe’s history. It also showed there weren’t many faint stars in our galaxy’s outer parts, which helped scientists think about what dark matter might be.

Multifrequency followup

Scientists used many telescopes to study the Hubble Deep Field in different kinds of light. They discovered that some galaxies, which look faint in ordinary light, shine brightly in infrared light. This happens because of lots of dust and new stars being born.

They also used X-ray telescopes and found six X-ray sources. These came from different kinds of galaxies, including some very active ones.

Radio telescopes found many radio sources in the same area. These matched up with galaxies seen in ordinary light. These observations help us learn more about the distant universe and the many different objects within it.

Subsequent HST observations

The Hubble Deep Field South looks very much like the original Hubble Deep Field. This supports the cosmological principle that the universe appears mostly the same in every direction.

After that, an even deeper view called the Hubble Ultra-Deep Field was made. It showed galaxies that may have formed very early in the universe’s history.

This was followed by the Hubble eXtreme Deep Field, finished in 2012. It revealed galaxies that might have formed within the first 500 million years after the Big Bang.