Hard X-ray astronomy gets a HERO

William Atkins
Sunday, 09 September 2007 19:37

Science - Space

X-ray astronomy is difficult for astronomers because high-energy X rays are so energetic that instead of bouncing off ordinary mirrors they pass right through them. Telescopes cannot use such mirrors but must rely on nearly parallel mirrors called grazing incidence mirrors. That’s where the HERO comes in to save the day.          

HERO, short for High Energy Replicated Optics, is a device that can guide high-energy X rays, or hard X rays, so that they are useful for astronomers who want to study such astronomical objects as black holes, exploding stars, and colliding galaxies. These objects are very energetic, which is why they are called “colliding” and “exploding”, and why inside such objects many X rays are found and are continually ejected for eventual journeys throughout the universe and, especially, to the Earth. To understand more about such energetic objects astronomers need high-energy X-ray telescopes to observe them.

The HERO contains 96 tube-like mirrors, built at the NASA Marshall Space Flight Center, Huntsville, Alabama, that are “nested like the layers of an onion” so that when X rays hit one of the mirrors they graze off of it like a rock skipping off of a pond when thrown nearly parallel to the water. These sideway, or grazing incidence, mirrors work together to guide these very energetic X-rays (hard X rays).

In other words, instead of the mirror being positioned perpendicular to the direction of, say, visible light, a glazing incidence mirror is nearly parallel to incoming X rays. The X rays do not go through the mirror, but because the mirrors are positioned nearly in the same direction as the X rays are traveling, the X rays skip off of the mirror (like a rock skipping off of water) and are guided down tubes to detectors where they form an image—and where they can be studied in more detail.

The HERO detector is being tested on board balloons launched from Fort Sumner in New Mexico (United States). (It is much less expensive to use balloons that rockets to test HERO.) The balloons are lofted up so they are above 99% of the Earth’s atmosphere (in the stratosphere) where it is easy to collect X rays.  The Fort Sumner location is ideal for launching of balloons because in certain months, such as around May and September ,the winds there are very calm.

The balloons used for HERO are about 500 feet (150 meters) wide and rise about 1,000 feet (300 meters) above HERO. The HERO scientists hope that their device will allow them to see new cosmic images never seen before.

NASA provides very good descriptions of HERO at their “Science at NASA” websites “HERO will provide new view of X-ray universe” and “The Universe Through the Looking Glass”.