Edwin Hubble made an amazing discovery: the universe is continually expanding. The gamma-ray bursts that are reaching us today actually occurred billions of years ago. Since light travels at a finite rate of speed, scientists can calculate how far away and how long ago the bursts we are observing today actually occurred.
On Earth, we measure distance in miles. But in space, miles don’t mean much considering the amount of distance to be covered, and the lack of stationary focal points. In space, there is a better way of measuring distance: light years. A light year is defined as the distance that light can travel in one year. One light year is equal to about 5.9 trillion miles. The closest star to our solar system is Alpha Centauri, which is 4 light years away (or about 23.6 trillion miles away). One way to explain this concept is the light from Alpha Centauri observed by a high school senior (today), left 4 years ago while the student was a freshman.
One of the reasons scientist hypothesize that gamma-ray bursts come from far away is the even distribution of them across the sky. There are no clumps of them, and no voids in space where they are absent. If they came from close by, such as the Oort cloud that surrounds the Sun, they would have to be generated from comets. However, comets are very cold, low-energy objects. Comets do not emit high-energy gamma-rays. Therefore, gamma-ray bursts must come from very, very far away.
Swift is a satellite designed by Penn State researchers and launched by NASA to study gamma-ray bursts. Launched in November of 2005, the satellite was named after the swift, a small, quickly moving bird. Catching a GRB is no easy task. The burst can appear from any direction without warning and can last for only a few milliseconds to just over a minute. So, the satellite has to move quickly and be in position to capture the data. According to NASA, no other satellite turns faster. In addition to GRBs, Swift searches and records other phenomena it observes in the sky.
The Swift satellite is comprised of three telescopes: the Burst Alert Telescope (BAT); the X-ray Telescope (XRT); and the Ultraviolet/Optical Telescope (UVOT). The BAT detects and locates the GRBs. Once one is identified, Swift repositions itself so that the other two telescopes can collect data on the afterglow of the burst. All the data is transmitted to earth and is available publicly within 30 minutes of the GRB detection.