X-ray Astrophysics at Goddard's LHEA

Scientific research in the X-ray group involves a lot of gathering evidence or observations and then "putting the pieces together" into a coherent whole that makes sense and agrees with the observations. Science is about asking questions, or, more precisely, asking the right kind of questions, questions that can be answered, in some form or another, by making observations. The observations needed to answer the questions may be difficult to make, as in the case of very high energy cosmic rays, and the conclusions that follow from the observations are not always obvious. It is part of the excitement and challenge of astrophysics to understand things like black holes, neutron stars and supernova remnants, as well as ideas like general relativity, without actually directly touching or experimenting on the objects in the lab.

There are many different research groups at the Laboratory for High Energy Astrophysics. Some groups study only the results from a specific instrument, such as Astro-D ( or ASCA) or the X-Ray Timing Experiment (XTE); others use many different instruments to study one class of objects. Below are highlights of research of current working groups in the X-ray Astrophysics Branch at Goddard. Notice how in each case the scientists are putting together facts and observations like the pieces of a puzzle, and how an understanding of our universe comes from putting these pieces together.

Scientists are not always "right". Sometimes it takes many years before a phenomenon is well understood. The best understood object in our universe is the Earth, and there are still many things about the Earth that we do not yet understand, such as how exactly does an increase in carbon-dioxide in the atmosphere affect long term weather and climate patterns? We also know much about the planets of our solar system, and the moon. Some of these we have even visited. However, there are multitudes of objects in the universe that we cannot observe at such close range, such as supernovae, black holes, quasars, other galaxies. We would like to understand how those objects behave and evolve, and how they may affect the evolution of space around us. The scientific method of testing hypotheses with experiments leads to a more accurate and more complete understanding of the things that surround us. Each observation contributes in this process. Some objects have been well studied and are well understood. Some have been well studied and are as yet not as well understood. And some things we have only begun to study.

A Bit of Philosophy: Science and the Spherical Cow

Supernova Remnant Group

The

SNR General Areas of Research:

• Acceleration of Cosmic Rays: These particles found throughout space have energies a billion times greater than those created in our most powerful particle accelerators. Where do they come from? Scientists have long thought that Supernova Remnants may be responsible; X-ray astrophysicists at LHEA are figuring out how and why .
  
  
• X-ray Spectroscopy of young SNR: You can't very well study a star that exploded hundreds or thousands of years ago... Or can you? Scientists use spectroscopy as clues to what the star was like before it blew up and became a spectacular supernova remnant.



• Interaction between SNR and the ISM: Since the forward shock of the remnant heats and compresses the gas it encounters, making it radiate strongly in the X-ray, studying the X-ray emission from SNR as they sweep up interstellar gas is a good way to learn about the mysteries of the ISM.



• Thermal Conduction: This process could be responsible for a new class of SNR that do not look like SNR theories predict. What is happening in the middle of these remnants to make them X-ray bright? Examining how thermal conduction works in SNR can reveal how it works in the ISM in general.



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