There are things happening all around us that we can't see.
If humans could see in wavelengths beyond visible light, the whole cosmos would look like a glowing, sparkling ball of light. Some of that extra light we can't see is made of X-rays that regularly crash into Earth's atmosphere. Now a new NASA study has returned some puzzling observations on those X-rays. Earth is getting peppered with X-rays, and scientists can't figure out where they're coming from.
NASA's DXL sounding rocket, which stands for Diffuse X-ray emission from the Local Galaxy, studied X-rays hitting Earth's atmosphere and discovered that some of the X-rays come from solar wind, and some come from a theoretical clump of hot material surrounding our solar system called the Local Hot Bubble. But the research also revealed there's a clump of really high-energy X-rays that can't be explained by solar wind or the Local Hot Bubble. So NASA solved one mystery, but stumbled upon another at the same time.
"The temperature of the Local Hot Bubble is not high enough to produce X-rays in this energy range," Youaraj Uprety, lead author on the new study, said in a statement. "So we're left with an open question on the source of these X-rays."
The X-rays we know about: We know the sun constantly ejects solar material out into space. That material is made of streams of charged particles that we call solar wind. When solar wind passes through neutral gas, it can generate X-rays, according to NASA. Some of those X-rays make their way to Earth.
The theoretical Local Hot Bubble is another source of X-rays. Scientists have long speculated this envelope of hot material exists, but they didn't have much evidence until the DXL sounding rocket mission.
"We show that the X-ray contribution from the solar wind charge exchange is about forty percent in the galactic plane, and even less elsewhere," Massimiliano Galeazzi, an author on the study, said in the statement. "So the rest of the X-rays must come from the Local Hot Bubble, proving that it exists."
The X-rays that are still a mystery: The DXL sounding rocket was able to distinguish X-rays that came from solar wind and X-rays from the Local Hot Bubble, but it also picked up X-rays that couldn't have come from either source.
For now, the source of these extra X-rays is completely unknown. We'll need more research to trace them back to their origin.