Wednesday, December 19, 2018

Supernova Remnants: Secret Seeds of the Galaxy

A massive star that has reached the end of its life explodes and becomes a supernova. The force of the explosion causes matter to be expelled into the interstellar medium. The celestial object that forms as this explosion is called a supernova remnant.

Supernova remnants determine the structure of the interstellar medium by providing kinetic and thermal energy. Particles accelerate to relativistic speeds as the matter heats up and produce very high-energy gamma radiation when they interact with light and gas. According to an article in the Open Physics Journal published online by Bentham Science Publishers, supernova remnants can trigger the formation of new stars.

Different Means of Detection

A number of different variables must be measured in order to determine the effect of supernova remnants, include the energy of the explosion, the density of the interstellar medium in the location of the explosion, and the rate at which SNRs occur.

However, in order to measure any of these phenomena, it is first necessary to locate the supernova remnants, and that can be a difficult task. Despite their size, as large as the full moon according to one researcher, they are invisible to the naked eye, and conventional optical telescopes are useless for detecting them as well. SNRs can only be located and measured based on what they put out into the universe, specifically gamma radiation and other emissions.

Special Telescopes Detect Previously Unknown Objects

Used for studying the galaxy for the last 15 years, H.E.S.S. telescopes detect gamma radiation with very high energy, specifically in the range of 1,012 electron volts, also known as the TeV energy range, using the radiation emissions to detect celestial objects inside as well as outside of the galaxy. Researchers often correlate the data to objects studied with conventional telescopes to discover the source of the radiation. If there was no visible object with which to correlate the object, the data relating to TeV gamma radiation was not enough to determine the type of object from which the radiation originated.

Identifying Objects With High Probability

Recent advances delivering detailed data have now allowed researchers to identify three of the unidentified sources of gamma rays as supernova remnants on the basis of TeV data alone. They have not made the identification with absolute certainty, but the probability is high.

These are not the first supernova remnants that scientists have discovered with the H.E.S.S. telescopes, and researchers are now asking why these three went undetected until now. One theory that has scientists particularly excited is that there may be a substantial difference of some kind between the SRNs that the H.E.S.S. telescope has investigated in the past, and that the difference complicated detection and identification. Other possibilities are that gas in the foreground partially obscured them, or that they were indistinguishable from many other objects in the galaxy because of their large extension and position in the Milky Way galaxy.

Determining Distance

Once supernova remnants have been identified, another important step in determining their ages, sizes, evolutionary states and explosion energy is to measure their distance from Earth. In another study, this was accomplished using astronomical spectroscopy, which analyzes electromagnetic radiation emitted and absorbed by different objects in order to determine their distances, yielding new distances for objects that previously had none and laying the groundwork for further study of the SNRs origins, according to an article published online by The Bentham Science Publishers.

The Significance of Supernova Remnants

According to NASA, in addition to triggering the formation of stars, supernova remnants also distribute heavy elements throughout the galaxy. These elements are formed by the explosion of the star, also known as a supernova. SNRs contain these elements and then introduce them into the interstellar medium, altering its chemical makeup, and thereby altering the chemical make-up of any planets or stars that form out of the interstellar medium.