What two kinds of space signals were identified by early radio astronomy and space-based detectors?

• A. Radio emissions from the sky and X-rays in space
• B. Infrared radiation and gamma rays
• C. Optical light and ultraviolet
• D. Neutrinos and gravitational waves

Answer: (A)

The main idea is that the universe reveals itself in different ways across the electromagnetic spectrum, and different detectors are needed to see those signals. Early radio astronomy showed that space is full of radio waves produced by energetic processes in many objects—nebulas, supernova remnants, and galaxies all emit in the radio. But some of the most revealing signals come at much higher energies, in the X-ray portion of the spectrum. X-rays don’t reach Earth’s surface because the atmosphere absorbs them, so detecting them required instruments placed in space. Once space-based X-ray detectors came online, astronomers identified a rich population of X-ray sources, pointing to extreme environments like matter spiraling into black holes, neutron stars, and very hot gas near stellar explosions. So the two kinds of space signals identified were radio emissions from space and X-ray radiation in space.