By Jonny Lupsha, Wondrium Staff Writer
Scientists build telescopes to focus on different parts of the electromagnetic spectrum. The Hubble Telescope specializes in visible light while the upcoming James Webb Space Telescope observes infrared. A new X-ray telescope launched Thursday.
“Exploded stars, black holes, and other violent high-energy events unfolding in the universe.” This is what NASA’s latest X-ray telescope has been sent to observe in space, according to AP News. The X-Ray Polarization Explorer, or IXPE for short, has gone into orbit in order to use X-ray technology to observe space phenomena not visible to the naked eye.
Space telescopes often accrue data from different wavelengths of light to perceive the universe. Hubble focuses mainly on the visible portion of the spectrum while the soon-to-launch James Webb Space Telescope utilizes infrared to look farther into the past. In his video series Introduction to Astrophysics, Dr. Joshua N. Winn, Professor of Astrophysical Sciences at Princeton University, explains the ins and outs of X-ray astronomy.
Not Just for Pinpointing Broken Bones
“For our purposes, we only need to divide the [electromagnetic] spectrum into three parts,” Dr. Winn said. “We’re going to lump together the infrared, visible, and ultraviolet and just call it ‘optical,’ for short. Everything with lower energies, longer wavelengths, we’ll call ‘radio.’ And everything to the other side, with higher energies and shorter wavelengths, we’ll call ‘X-rays.'”
To X-rays, Earth’s atmosphere is completely opaque. According to Dr. Winn, X-ray photons have enough energy to knock apart molecules and rip off electrons, so those photons collide with a molecule and get stopped. That may be good news for our bodies, but it’s bad news for X-ray astronomy outside Earth’s atmosphere. When scientists Bruno Rossi and Riccardo Giacconi convinced NASA to launch an X-ray telescope in 1962, many in the scientific community doubted there would be anything to see.
“Of course, the sky turned out to have a glittering display of X-ray sources, which are now understood to be related to black holes, neuron stars, supernovas, all kinds of fascinating phenomena,” Dr. Winn said.
Focusing X-rays is much more difficult than it may sound.
“You can’t just use a regular mirror,” Dr. Winn said. “The photons would penetrate through it instead of getting reflected. X-rays will reflect from metals as long as they strike the surface at a very grazing angle, like skipping a stone off the surface of a pond.”
According to Dr. Winn, X-ray mirrors look very much like polished metal cylinders, but they aren’t. The sides are sloped a small amount so X-rays can skip off that surface and land on a charge-coupled device for detection. A charge-coupled device, or CCD, is a light-sensitive integrated circuit containing an array of coupled capacitors, each of which can transfer its electrical charge to another capacitor. This way, it can capture images by converting photons to electrons.
“In 1999, NASA launched the Chandra X-ray Observatory, which makes the sharpest X-ray images of any facility,” Dr. Winn said. “The Chandra mirrors are glass, coated with iridium, and to boost the collecting area, Chandra uses multiple mirrors, nesting small ones inside the larger ones. And there’s a second set of hyperboloid mirrors, to reduce the image aberrations.”
IXPE’s use of polarimetry, which measures the angle of rotation of a plane of polarized light, sets it apart from its predecessors.