- 2907 - FAST RADIO BURSTS - what is the source? FRBs are powerful, millisecond-duration radio waves coming from deep space outside the Milky Way Galaxy. They have been among the most mysterious astronomical phenomena ever observed. These waves are only milliseconds in duration.
--------------------------- 2907 - FAST RADIO BURSTS - what is the source?
- FRBs are bursts of radio waves lasting only milliseconds in duration. A millisecond is only one thousandth of one second. On millisecond is the time of a camera flash, or the time for light to travel 300 kilometers, or 186 miles.
-
- Since FRBs were first discovered in 2007, astronomers from around the world have used radio telescopes to trace the bursts and look for clues on where they come from and how they're produced.
-
- What are the engines of FRBs and what is the mechanism to produce them.
-
- Two competing theories have been proposed to interpret the mechanism that produce FRBs. One theory is that they're similar to gamma-ray bursts (GRBs) which are the most powerful explosions in the universe.
-
- The other theory is tha they are more like radio pulsars, which are spinning neutron stars that emit bright, coherent radio pulses. The GRB-like models predict a non-varying polarization angle within each burst whereas the pulsar-like models predict variations of the polarization angle.
-
- FAST is a 500 meter aperture telescope in China used to observe one repeating FRB source and discovered 11 bursts from it. Surprisingly, seven of the 11 bright bursts showed diverse polarization angle swings during each burst. The polarization angles not only varied in each burst, the variation patterns were also diverse among bursts.
-
- These observations essentially rules out the GRB-like models and offers support to the pulsar-like models.
-
- Magnetars are incredibly dense, city-sized neutron stars that possess the most powerful magnetic fields in the universe. Magnetars occasionally make short X-ray or soft gamma-ray bursts through dissipation of magnetic fields, so they have been long speculated as plausible sources to power FRBs during high-energy bursts.
-
- The first conclusive evidence of this came on April 28, 2020, when an extremely bright radio burst was detected from a magnetar at a distance of about 30,000 light years from Earth in the Milky Way Galaxy. This FRB was associated with a bright X-ray burst.
-
- The event was detected by CHIME and STARE2, two telescope arrays with many small radio telescopes that are suitable for detecting bright events from a large area of the sky.
-
- During the FAST observations there were another 29 X-ray bursts emitted from the magnetar. However, none of these “X-ray bursts” were accompanied by a “radio burst“.
-
- Fast Radio Bursts were first discovered in 2007. Astronomers have been studying them for over a dozen years and we still cannot explain what they are?
-
- Astronomers have “seen” incredibly strong bursts of radio waves that last for one or two milliseconds. They believe the sources to be up to a billion lightyears distant. And, they can detect up to 1,000 of them each day coming from all directions in the sky.
-
- These signals are different than “pulsars”. Pulsars originate when supernovae leave behind a spinning core of neutrons, a neutron star. These cores spin several times a second and radiate beams exiting out their poles. These beams can be oriented to sweep by the Earth. The beam then appears as a repetitive pulse of radio or light energy.
-
- The FRB radio bursts are different. First the radio beam is broadband covering a wide range of frequencies. Secondly, the lower frequencies arrive slightly later than the higher frequencies.
-
- The beams must travel great distances and the lower frequencies interact with elements in space while the more energetic higher frequencies fly past. The greater the delay the greater distances the signal has traveled. Astronomers call this a “signal dispersion measurement“.
-
- Dispersion measurements on signals from a nearby galaxy are about 200. These FRB dispersion measurement are 790, meaning they are billions of lightyears away. For the signal to be so bright and that far away it must be extremely powerful.
-
- Astronomers have found one source for these repeating radio bursts. It appears to be a dwarf galaxy that is 3 billion lightyears away. Its size is only about 10% that of our Milky Way Galaxy. This is contrary to astronomer’s speculation that FRB’ should be large, super massive blackholes at the center of galaxies.
-
- The majority of the FRB’s disappear after one flash. Only ten are known to repeat. The causes are speculated to be powerful supernovae, supermassive blackholes, or explosions on neutron stars. Another speculation is that the source could be a “magnetar” , a fast spinning neutron star with an extraordinary magnetic field.
-
- Only a couple FRB’s sightings have been found an identifying source. Astronomers need to find several more so further study can fine tune the theories. It was 2012 that the first repeating FRB was discovered. In 2017 this FRB was tracked to a dwarf galaxy 2.5 billion lightyears away.
-
- In 2019 nine more repeating FRB’s were discovered. Were they neutron stars with high magnetic fields? Were they mergers between white dwarfs or blackholes?
-
- Astronomers need to find more FRB’s. They need to learn if they all from the same phenomena or some different creations all together? Do all FRB’s repeat? Is there any pattern if they do repeat? Are they the same phenomena or are there several ways radio bursts are creating these signals?
-
- Perhaps they are Neutron stars that exhibit some new physics that we need to learn? The wide dispersion of the radio signals may help us learn the composition of space between the galaxies? The dispersion may offer a method to study magnetic fields in space? What else will we learn?
-
- It was in 1973 that the U.S. military declassified the existence of gamma-ray bursts that had been detected by their military satellites. They were found by accident since the satellites were looking for nuclear weapon tests starting in the 1960’s. After years of study these gamma ray bursts were found to be super massive stars collapsing into supernovae. In 10% of the cases the sources were determined to be 2 neutron stars that were merging.
-
- Supernovae themselves have been found to have a multiple of origins. The most common is the large star that runs out of fuel and collapses in a giant explosion leaving behind a neutron star, or a blackhole.
-
- Smaller supernovae occur when white dwarf stars gain mass and reignites as a supernovae. Because these explosions have predictable mass and resulting explosions are used as “standard candles” to measure distances throughout the universe.
-
- Some call the mystery of “fast radio bursts” the greatest mystery in radio astronomy. A good science research project for some graduating student to become famous. A single burst lasting a millisecond has more energy that the Sun releases in 24 hours. That has got to be something incredible to learn about. The mystery of FRB’s is only deepening
-
--------------------------- Other reviews available upon request:
-
- 1879 - Fermi Bubbles and radio bursts. Another puzzle astronomers need to solve.
-
- 1473 - Fine Structure Constant, the math that makes the atom work.
-
- 1336 - The mystery of the Find Structure Constant.
-
- 2134 - The force Carriers, gluons, bosons, and photons.
-
- November 17, 2020 2264 2907
----------------------------------------------------------------------------------------
----- Comments appreciated and Pass it on to whomever is interested. ----
--- Some reviews are at: -------------- http://jdetrick.blogspot.com -----
-- email feedback, corrections, request for copies or Index of all reviews
--- to: ------ jamesdetrick@comcast.net ------ “Jim Detrick” -----------
--------------------- --- Thursday, November 19, 2020 ---------------------------
No comments:
Post a Comment